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HANDBOOK    OF    PHYSIOLOGY 


WORKS    BY   THE    SAME    AUTHOR 


The  Physiology  of  Man ;  designed  to  represent  the  Existing 
State  of  Physiological  Science  as  applied  to  the  Func- 
tions of  the  Human  Body.  Volume  I.,  Introduction; 
Blood;   Circulation;    Respiration.      I  vol.,  8vo,  pp.  500. 

The  same,  Volume  II ,  Alimentation;  Digestion;  Absorption; 
Lymph  and  Chyle,     i  vol.,  8vo,  pp.  550. 

The  same.  Volume  III.,  Secretion;  Excretion;  Ductless 
Glands;  Nutrition;  Animal  Heat;  Movements;  Voice 
and  Speech.     I  vol.,  8vo,  pp.  520. 

The  same,  Volume  IV.,  The  Nervous  System,  i  vol.,  8vo, 
pp.  470. 

The  same.  Volume  V.,  Special  Senses;  Generation,  i  vol., 
8vo,  pp.  517. 

Recherches  experimentales  sur  une  nouvelle  fonction  du  foie, 

consistant  dans  la  separation  de  la  choK-sterine  du  sang 
et  son  elimination  sous  forme  de  stercorine.  Paris,  Ger- 
mer  Bailliere;  and  New  York,  D,  Appleton  &  Company, 
1868.     I  vol.,  8vo,  pp.  121.     S0.75. 

This  work  received  an  "  Honorable  Mention  "  with  a 
"Recompense"  of  1500  francs  from  the  Institute  of 
France  (^Academic  des  Sciences)  in  1869,  Concours  Mottt- 
yon  (^Medecine  et  Chirurgie). 

On  the  Physiological  Effects  of  Severe  and  Protracted  Mus- 
cular Exercise  ;  with  special  reference  to  its  Influence 
upon  the  Excretion  of  Nitrogen.  1871.  i  vol.,  8vo, 
cloth,  pp.  91.     Si.oo. 

Manual  of  Chemical  Examination  of  the  Urine  in  Disease ; 

with  brief  Directions  for  the  Examination  of  the  most 
common  Varieties  of  Urinary  Calculi.  Fifth  edition, 
1877.     I  vol.,  i6mo,  cloth,  pp.  76.     $1.00. 

Collected  Essays  and  Articles  on  Physiology  and  Medicine. 

2  vols.,  8vo,  pp.  465  and  51S.     Set,  Sio.oo. 


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Upper  Fig.  Anterior  Vie«_Lowcr  Fig.  Posterior  View 


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Digitized  by  the  Internet  Archive 

in  2010  with  funding  from 

Open  Knowledge  Commons  (for  the  Medical  Heritage  Library  project) 


http://www.archive.org/details/handbookofphysioOOflin 


Handbook  of  Physiology 


FOR   STUDENTS  AND  PRACTITIONERS 
OF   MEDICINE 


BY 

AUSTIN    FLINT,    M.D.,    LL.D. 

PROFESSOR   OF   PHYSIOLOGY   IN"    THE    CORNELL    UNIVERSITY   MEDICAL   COLLEGE;    CONSULTING    PHYSICIAN   TO 
BELLEVUE  HOSPITAL;    PRESIDENT  OF  THE  CONSULTING  BOARD  OF  THE  MANHATTAN  STATE  HOSPITAL 
FOR    THE    insane;     MEMBER    OF    THE    NEW   YORK    COL'NTY    MEDICAL   ASSOCIATION;    FELLOW 
OF  THE  NEW  YORK   STATE   MEDICAL  ASSOCIATION;    MEMBER  OF  THE  AMERICAN  MEDI- 
CAL ASSOCIATION;    HONORARY  MEMBER  OF  THE   AMERICAN  ACADEMY  OF  MEDI- 
CINE;    MEMBER    OF    THE    AMERICAN    MEDICO-PSYCHOLOGICAL    ASSOCIA- 
TION;    MEMBER    OF    THE    AMERICAN     PHILOSOPHICAL     SOCTETV; 
CORRESPONDENT    OF    THE    ACADEMY     OF     NATURAL     SCI- 
ENCES,   PHILADELPHIA;     FELLOW   OF    THE    AMERI- 
CAN ASSOCIATION    FOR  THE   ADVANCEMENT 
OF    SCIENCE;      ETTC.     ETC. 


WITH  TWO  HU.VDRED  AND  FORTY-SEVEN  ILLUSTRA- 
TIONS IN  THE  TEXT  —  INCLUDING  FOUR  IN  COLORS  — 
AND  AN  ATLAS  OF  SIXTEEN  COLOR-PLATES,  INCLUD- 
ING FORTY-EIGHT  ORIGINAL  FIGURES  TAKEN  FROM 
ACTUAL    STAINED     MICROSCOPICAL    PREPARATIONS 


THE    MACMILLAN    COiVIPANY 

LONDON:    MACMILLAN    &    CO.,   Ltd. 

1905 

All  rights   reseried 


I'  /.ifri'jr;. 


QT34 
F643 


Copyright,  1905, 
By  the   MACMILLAN   COMPANY. 

Set  up  and  electrotyped.     Published  September,  1905. 


NortoooU  43rtB3 

J.  S.  Cusliing  &  Co. —  Berwick  &  Smith  Co. 

Norwood,  Mass.,  U.S.A. 


PREFACE 

This  Handbook  is  the  outcome  of  a  desire  to  present  to  students 
a  work  that  may  serve  to  connect  pure  physiology  with  the  physiology 
specially  useful  to  physicians ;  and  I  have  endeavored  to  adapt  it  to  the 
curricula  of  medical  schools  where  the  subject  is  taught  in  the  English 
language.  With  this  end  in  view,  I  undertook  the  now  difficult  task  of 
selecting  from  the  vast  store  of  knowledge  what  I  trust  may  be  taken 
as  a  fairly  symmetrical  and  comprehensive  presentation  of  human  physi- 
ology, not  too  voluminous  for  students  or  for  ready  reference  by  active 
practitioners.  The  subject  has  been  treated  from  a  medical  standpoint; 
not  unduly  neglecting,  it  is  hoped,  pure  physiology  and  biology. 

In  1875  I  published  a  Text-book  of  Hwnati  Physiology,  which  was 
a  condensation  of  a  work  in  five  volumes  (i 866-1 874),  entitled  Physi- 
ology of  Man.  The  second  and  third  editions  of  that  work  con- 
tained such  corrections  and  additions  as  it  was  possible  to  make  in 
the  electrotype  plates.  The  book  was  rewritten  for  a  fourth  edition 
in  1888.  During  the  twenty-five  years  from  1875  to  1900,  about  twenty- 
one  thousand  copies  of  the  Text-book  were  distributed  by  sale.  The 
advances  in  physiology  since  1888  need  not  be  indicated  here.  Since 
1858  I  have  been  actively  engaged  in  teaching  physiology  to  medical 
students,  and  since  1875  have  used  my  own  text-book.  About  five 
years  ago,  however,  the  book  represented  my  teaching  so  imperfectly 
that  I  felt  obliged  to  use  more  modern  works  for  class  recitations. 

This  volume  represents  the  instruction  in  physiology  now  given  at 
the  Cornell  University  Medical  College,  somewhat  expanded  for  more 
extended  study  and  reference.  It  contains  little  of  the  text  of  former 
works,  except  parts  relating  to  descriptive  anatomy  and  established 
views  that  have  become  classic.  Few  unsettled  questions,  now  under 
discussion,  are  considered  at  length ;  but  I  have  attempted  to  present 
what  properly  belongs  to  human  physiology  in  a  manner  as  plain  and 
concise  as  possible. 

Long  experience  as  a  teacher  of  undergraduates  has  convinced  me 
that  students  can  not  be  assumed  to  be  sufficiently  familiar  with  the 
descriptive  anatomy  and  the  histology  of  parts  and  organs  to  acquire 


vi  PREFACE 

easily  a  knowledge  of  their  physiology ;  and  physiological  chemistry  is 
too  closely  connected  with  physiology  to  be  neglected  in  a  text-book. 
Again,  the  ordinary  text-books  on  chemistry  and  physics  contain  little 
information  in  regard  to  the  modern  physical  chemistry,  ionization,  dis- 
sociation, osmotic  pressure,  etc.,  all  of  which  have  important  bearings 
on  modern  views  in  regard  to  physiological  processes.  While  these 
subjects  are  by  no  means  exhaustively  considered,  they  are  discussed  at 
some  length.  Embryology  might  logically  precede  the  study  of  physi- 
ology proper;  but  the  difficulties  of  this  subject  are  more  easily  sur- 
mounted by  advanced  than  by  first-year  students,  and  for  that  reason 
it  is  considered  last.  Demonstrations,  recitations,  and  laboratory  work 
go  hand  in  hand;  but  laboratory  technique  is  a  subject  for  practical 
instruction  with  the  aid  of  special  manuals.  Descriptions  of  laboratory 
manipulations  and  illustrations  of  instruments  and  apparatus,  therefore, 
are  omitted. 

I  have  not  thought  it  desirable  to  give  in  extetiso  minute  details  of 
what  is  called  nerve-physiology,  and  only  the  general  results  of  such 
work  are  presented.  Full  descriptions  of  electrical  phenomena  in  nerve 
and  muscle  are  to  be  found  in  laboratory  manuals.  Xo  considerable 
account  has  been  taken  of  mathematical  formulae  and  calculations 
involved  in  certain  special  studies,  such  as  physiological  optics  and 
acoustics.  This  would  assume  a  knowledge  of  mathematics  on  the 
part  of  the  student  which  usually  does  not  exist.  Still,  the  special  senses 
are  considered  quite  as  fully  as  seems  necessary,  except  for  ophthal- 
mologists and  otologists.  The  same  may  be  said  of  embryologv,  a 
subject  too  large  to  be  fully  presented,  except  in  special  treatises.  The 
plan  of  teaching  and  the  arrangement  of  subjects  do  not  involve  a  study 
of  the  nervous  system  in  its  relations  to  circulation,  respiration,  diges- 
tion and  metabolism  until  the  second  year.  Consideration  of  these 
relations  is  given  mainly  in  the  chapters  on  the  nervous  system,  and 
they  are  briefly  mentioned  in  the  first  part  of  the  work. 

For  valuable  aid  in  the  important  matter  of  illustration,  I  am  under 
great  obligations  to  professional  friends ;  but  I  alone  must  be  held 
responsible  for  the  text  and  for  the  arrangement  of  subjects. 

In  the  matter  of  illustration  a  new  departure  is  made  which  bids 
fair  to  revolutionize  this  important  aid  to  the  study  of  histology.  After 
more  than  a  year  of  experimentation,  it  has  been  found  possible  to 
reproduce,  by  what  is  known  as  the  three-color  process,  stained  histo- 
logical objects,  at  all  magnifications  used  in  such  work,  as  they  actually 
appear  under  the  microscope.  This  had  already  been  done  in  1895- 
1896  by  Dr.  Edward  Leaming,  who  photographed  the  objects,  and  Mr. 
Edward  Bierstadt,  who  made  gelatin-prints  by  the  three-color  process 


PREFACE  VU 

of  M.  Ducos  du  Hauron ;  but  the  cost  of  reproduction  in  this  way  is 
prohibitory  as  regards  use  in  ordinary  text-books.  For  several  years 
before  1895,  the  printing,  from  ordinary  process-plates,  of  reproductions 
of  colored  drawings  or  lithographs  had  been  accomplished  commer- 
cially. So  far  as  I  know,  however,  this  has  not  been  done  before  in 
photomicrography.  The  difficulties  encountered  in  these  efforts  were 
considerable  ;  but  they  were  at  last  overcome  by  the  skilful  and  patient 
cooperation  of  Dr.  Learning  and  of  the  American  Colortype  Company. 
Forty-eight  illustrations  of  this  kind  are  in  the  Atlas  at  the  end  of  the 
book.  With  almost  perfect  fidelity  as  regards  definition  and  color,  they 
reproduce  the  objects  used,  and  they  may  be  studied  as  one  would  study 
with  the  microscope  actual  preparations.  Of  necessity,  however,  each 
picture  represents  a  single  field  focussed  for  but  one  plane.  The  pic- 
tures taken  from  actual  objects  are  supplemented  in  the  Atlas  with 
reproductions,  by  the  same  process,  of  plates  selected  from  the  histo- 
logical atlas  of  Sobotta.  These,  though  somewhat  idealized,  are  intro- 
duced for  the  reason  that  they  represent  difficult  objects,  and  some 
illustrate  in  a  single  page  groups  of  objects  that  would  require  many 
more  figures  if  made  from  actual  specimens.  Four  figures,  showing 
the  first  stages  of  cleavage  of  the  ovum,  have  been  reproduced,  without 
reduction  in  size,  from  the  original  negatives  taken  by  Dr.  Learning  for 
Professor  Wilson's  Atlas.  These  are  printed  in  blue,  although  the 
original  prints  were  in  black  and  white. 

It  seemed  to  me  very  important  to  solve  the  problem  of  reproducing, 
at  a  moderate  cost,  stained  objects  in  colors,  for  the  reason  that  photo- 
micrographs in  black  and  white  are  nearly  always  inadequate  and  some- 
times misleading.  Compare,  for  example.  Fig.  102,  p.  464,  in  the  text, 
with  Fig.  4,  Plate  V,  in  the  Atlas,  both  showing  sections  of  the  pancreas. 
For  useful  illustration,  indeed,  color-figures  must  be  used,  in  the  absence 
of  study  of  actual  objects,  if  for  no  other  reason  than  that  histological 
elements  are  so  often  differentiated  by  their  affinities  for  various  dyes 
and  can  be  recognized  only  in  stained  preparations.  Again,  the  student 
seldom  sees  in  his  laboratory  work  the  appearances  represented  in  books, 
even  by  the  best  and  most  costly  colored  drawings. 

The  technique  employed  in  the  photographic  work  is  given  by  Dr. 
Leaming,  in  a  note  introductory  to  the  Atlas.  The  negatives,  taken 
through  color-filters,  were  given,  with  the  objects,  to  the  Colortype  Com- 
pany, and  put  into  the  hands  of  their  most  intelligent  workman,  who 
was  instructed  first  in  the  use  of  the  microscope.  The  color-plates  were 
made  through  a  transparent  screen  with  a  ruling  of  one  hundred  and 
seventy-five  lines  to  the  inch.  The  etching  was  done  in  comparison 
with  the  actual  objects,  which  were  used  as  color-guides.     This  was  the 


Viii  PREFACE 

most  difficult  part  of  the  process.  The  printing  was  done  in  the  same 
way  as  in  ordinary  three-color  work.  Without  the  perfect  negatives 
made  by  Dr.  Learning  through  absolutely  correct  color-filters  and  the 
very  intelligent  and  skilful  work  of  the  Colortype  Company,  the  results 
obtained  would  not  have  been  possible,  —  a  fact  emphasized  by  repeated 
failures  during  many  months  of  experimentation.  The  cost  of  the 
three-color  work  has  made  but  an  insignificant  addition  to  the  price  of 
the  book,  w^hile,  it  is  believed,  the  color-illustrations  have  added  greatly 
to  its  practical  value. 

Through  the  generous  interest  of  the  publishers  in  the  manufacture 
of  the  book,  unusual  care  was  bestowed  on  the  two  hundred  and  forty- 
seven  illustrations  in  the  text.  Of  this  number,  one  hundred  and  sixty- 
five  were  selected  from  three  hundred  and  sixteen  that  appeared  in  a 
previous  work.  All,  however,  have  been  newly  reproduced  from  the 
originals.  Ninety  of  the  one  hundred  and  sixty-five  are  from  Sappey, 
Bonamy  and  Beau,  and  Hirschfeld.  These  were  imported  from  Paris 
in  1874.  They  are  not  only  highly  illustrative,  but  are  fine  examples 
of  engraving  on  wood,  now  practically  a  lost  art.  Eighty-two  figures, 
including  four  in  colors,  are  either  original  or  are  taken  from  modern 
works.     The  latter  could  hardly  be  improved  on  by  new  drawings. 

Special  mention  should  be  made  of  four  figures  reduced  from  photo- 
graphs in  Dalton's  Topographical  Anatomy  of  tJie  Brain,  and  six  figures 
reduced  from  photographs  in  the  Atlas  of  the  Karyokincsis  and  Fertili- 
zation of  the  Ovmn,  by  Professor  Edmund  B.  Wilson,  with  the  coopera- 
tion of  Dr.  Edward  Leaming.  A  small  edition  of  the  late  Professor 
Dalton's  work  was  printed  in  1885.  It  is  now  a  rare  book  and  little 
known ;  but  the  prints  represent  the  specimens  with  absolute  fidelity, 
and  are  quite  as  useful  for  purposes  of  study  as  actual  sections.  The 
prints  in  Professor  Wilson's  Atlas  are  superb  and  unique.  The  figures 
from  these  works  have  not  before  been  reproduced. 

It  may  fairly  be  presumed  that  a  considerable  majority  of  English- 
speaking  medical  practitioners  and  students  —  for  whom  this  work  is 
intended  —  have  been  accustomed,  by  early  education  and  common 
usage,  to  English  weights  and  measures.  To  such  readers,  the  metric 
system,  now  commonly  used  in  scientific  literature,  frequently  fails  to 
convey  a  definite  idea  without  a  mental  reduction  to  the  familiar  stand- 
ards. For  this  reason,  English  weights  and  measures  and  the  Fahren- 
heit scale  are  retained,  and  metric  equivalents  are  given  in  parentheses. 
The  micron  (yoVo  °^  ^  millimeter,  or  2  s-^fo  °^  ^^  inch),  indicated  by  ^t, 
is  frequently  employed. 

I  am  much  indebted  to  colleagues  and  others  for  aid  in  prepar- 
ing illustrations,  and  extend   to  them   my  grateful  acknowledgments : 


PREFACE  IX 

Dr.  James  Ewing,  Professor  of  Pathology,  and  Dr.  Jeremiah  S.  Ferguson, 
Instructor  in  Histology,  of  the  Cornell  University  Medical  College, 
assisted  me  greatly  in  the  preparation  and  selection  of  histological 
objects.  Professor  Gage,  of  Cornell  University,  furnished  the  photo- 
graph of  a  human  embryo,  reproduced  in  Fig.  226.  Dr.  Israel  Strauss, 
Instructor  in  Embryology  in  the  Cornell  University  Medical  College, 
furnished  the  sections  of  chick,  reproduced  in  color  in  the  Atlas.  With- 
out such  valuable  assistance,  the  illustration  would  have  been  more 
difficult  and  much  less  satisfactory. 

AUSTIN    FLINT. 
New  York, 
July,  1905. 


CONTENTS 


INTRODUCTION 

PAGE 

The  ameba  proteus  —  Protoplasm  —  The  typical  animal  cell  —  Karyokinesis  (Mitosis)  — 
Prophases  —  Metaphase  —  Telophases  —  Amitosis  —  Ehrlich's  side-chain  hypothesis 

—  Immunity —  Receptors  —  Passive  and  active  immunity —  Cytolysis  —  Alexins  (Com- 
plements) —  Amboceptors  (Immune  bodies)  —  Antibodies  —  Precipitins  —  Agglutins         i 

CHAPTER   I 
The  Blood 

Importance  of  the  blood  —  Quantity  of  blood  —  Opacity  —  Taste  —  Reaction  —  Specific 
gravit}'  —  Temperature  —  Color  —  Laking  of  blood  — •  Blood-corpuscles  —  Red  cor- 
puscles—  Hemoglobin  —  Precipitin-test  for  blood  —  Development  of  red  corpuscles 

—  Leucocytes  —  Lymphocytes  —  Blood-platelets  —  Plasma  and  serum  —  Fibrinogen 

—  Serum-globulin  —  Serum-albumin  —  Extractives  and  salts  —  Coagulation  of  the 
blood — Prothrombin  and  thrombin  —  Uses  of  coagulation  .....       14 

CHAPTER    II 

ClRCULATIOX   OF   THE    BLOOD   THROUGH   THE   HEART 

Discovery  of  the  circulation — Physiological  anatomy  of  the  heart  —  Tricuspid  valve  — 
Pulmonic  valves  —  Mitral  valve  —  Aortic  valves  —  Movements  of  the  heart  —  Cardiac 
cycle  —  Sounds  of  the  heart — Frequency  of  the  heart's  action  —  Cause  of  the  rhyth- 
mical contractions  of  the  heart  —  Accelerator  nerves  —  Direct  inhibition  of  the  heart 

—  Work  of  the  heart  .............       30 

CHAPTER    III 

Circulation  of  Blood  in  the  Vessels 

Circulation  of  blood  in  the  arteries  —  Physiological  anatomy  of  the  arteries  —  Locomotion 
of  the  arteries  and  production  of  the  pulse  —  Form  of  the  pulse  —  Pressure  of  blood 
in  the  arteries  —  Pressure  in  different  arteries  —  Influence  of  respiration — Influence 
of  muscular  action,  etc.  —  Influence  of  hemorrhage,  etc.  —  Rapidity  of  the  current 
of  blood  in  the  arteries  —  Circulation  of  blood  in  the  capillaries — Physiological  anat- 
omy of  the  capillaries  —  Pressure  of  blood  in  the  capillaries  —  Rapidity  of  the  capil- 
lary circulation  —  Relations  of  the  capillary  circulation  to  respiration  —  Causes  of  the 
capillary  circulation  —  Influence  of  temperature  on  the  capillary  circulation  —  Circu- 
lation of  blood  in  the  veins — Structure  and  properties  of  the  veins  —  Valves  of  the 
veins  —  Pressure  of  blood  in  the  veins  —  Rapidity  of  the  current  of  blood  in  the 
veins  —  Causes  of  the  venous  circulation  —  Influence  of  muscular  contraction  —  In- 
fluence of  aspiration  from  the  thorax  —  Uses  of  the  valves  of  the  veins  —  Conditions 
that  impede  the  venous  circulation  —  Circulation  in  the  cranial  cavity  —  Circulation 


xii  CONTENTS 


PAGE 


in  erectile  tissues  —  Derivative  circulation  —  Pulmonary  circulation  —  Circulation  in 
the  walls  of  the  heart  —  Migration  and  diapedesis — Rapidity  of  the  circulation  — 
Phenomena  in  the  circulatory  system  after  death  .......       50 

CHAPTER    IV 
Respiratory  Movements 

Physiological  anatomy  of  the  respiratory  organs  —  Movements  of  respiration  —  Action  of 
the  diaphragm  —  Action  of  the  muscles  which  raise  the  ribs  —  Scalene  muscles  — 
Intercostal  muscles  —  Levatores  costarum  —  Auxiliary  muscles  of  inspiration — Expi- 
ration—  Influence  of  the  elasticity  of  the  pulmonary  structure  and  walls  of  the  chest 

—  Action  of  muscles  in  expiration  —  Internal  intercostals  —  Infracostales  —  Triangu- 
laris sterni  —  Obliquus  externus  —  Obliquus  internus — Types  of  respiration  —  Fre- 
quency of  the  respiratory  movements  —  Respiratory  sounds  —  Coughing,  sneezing, 
sighing,  yawning,  laughing,  sobbing  and  hiccough  —  Quantity  of  air  changed  in  the 
respiratory  acts  —  Diffusion  of  air  in  the  lungs     ........       89 

CHAPTER   V 
Changes  which  the  Air  and  the  Blood  undergo  in  Respiration 

Composition  of  the  air  —  Consumption  of  oxygen  —  Exhalation  of  carbon  dioxide  —  Influ- 
ence of  age  —  Influence  of  sex  —  Influence  of  digestion  —  Influence  of  diet  —  In- 
fluence of  muscular  activity  —  Influence  of  moisture  and  temperature  —  Influence  of 
the  season  of  the  year  —  Relations  between  the  oxygen  consumed  and  the  carbon 
dioxide  exhaled  —  Sources  of  carbon  dioxide  in  the  expired  air  —  Respiratory  quotient 

—  Exhalation  of  watery  vapor  —  Exhalation  of  ammonia,  organic  matter  etc.  —  Ex- 
halation of  nitrogen  —  Changes  of  the  blood  in  respiration  —  Analysis  of  the  blood 
for  gases  —  Nitrogen  of  the  blood  —  Oxygen  of  the  blood  —  Carbon  dioxide  of  the 
blood  —  Respiration  by  the  tissues —  Respiratory  efforts  before  birth  —  Asphyxia       .     116 

CHAPTER   VI 
Alimentation 

Hunger  and  thirst  —  Nitrogenous  alimentary  substances  —  Non-nitrogenous  alimentary 
substances  —  Carbohydrates  —  Dextrose  —  Levulose  —  Galactose  —  Saccharose  — 
Lactose  —  Maltose  —  Starch  —  Glycogen  —  Cellulose,  inosite  and  gums  —  The  fats : 
triolein;  tripalmitin;  tristearin  —  Saponification  —  Emulsification  —  Inorganic  ali- 
mentary substances  —  Water  —  Sodium  chloride  —  Calcium  phosophate  —  Iron  — 
Alcohol  —  Coffee  —  Tea  —  Chocolate  —  Condiments  and  flavoring  articles  —  The 
daily  ration  —  Necessity  of  a  varied  diet  —  Meats  —  Bread  —  Potatoes  —  Milk  —  Eggs     1 38 

CHAPTER    VII 
Mastication,  Insalivation  and  Deglutition 

Physiological  anatomy  of  the  organs  of  mastication  —  The  teeth  —  Enamel  of  the  teeth  — 

—  Dentin  —  Cement  —  Pulp-cavity — Superior  maxillary  bones  —  Inferior  maxilla  — 
Temporo-maxillary  articulation  —  Muscles  of  mastication  —  Saliva  —  Parotid  saliva 

—  Submaxillary  saliva — Sublingual  saliva — Secretions  from  the  smaller  glands  of 
the  mouth,  tongue  and  pharynx  —  Mixed  saliva  —  General  properties  and  composi- 
tion of  the  saliva  —  Uses  of  the  saliva  —  Deglutition  —  Mechanism  of  deglutition  — 
Protection  of  the  posterior  nares  during  the  second  period  of  deglutition  —  Protection 

of  the  opening  of  the  larynx  and  uses  of  the  epiglottis  in  deglutition  .         .         .         .163 


CONTEXTS  xiii 

CHAPTER   VIII 
Gastric  Digestiox 

PAGE 

Physiological  anatomy  of  the  stomach  —  Peritoneal  coat  —  Muscular  coat — Mucous  coat 

—  Glands  of  the  stomach  —  Closed  follicles  —  Gastric   juice  —  Secretion  of  gastric 
•    juice  —  Quantity  of  gastric  juice  —  Properties  and  composition  of  gastric  juice  — 

Saline  constituents  of  the  gastric  juice  —  Pawlow's  experiments  on  the  gastric  juice 

—  Action  of  the  gastric  juice  on  meats  —  Action  on  albumin,  fibrin,  casein  and  gelatin 

—  Action  on  vegetable  nitrogenous  substances  —  Peptones — Action  on  fats,  sugars 
and  amylaceous  substances  —  Duration  of  stomach  digestion  —  Conditions  that  influ- 
ence stomach  digestion —  Movements  of  the  stomach  .,.,,,     185 

CHAPTER    IX 

Intestinal  Digestion 

Physiological  anatomy  of  the  small  intestine  —  Mucous  membrane  —  Intestinal  juice  — 
Action  of  the  intestinal  juice  in  digestion  —  Pancreatic  juice  —  Internal  secretion  by 
the  pancreas  —  Composition  and  properties  of  the  pancreatic  juice  —  Action  of  the 
pancreatic  juice  on  carbohydrates — Action  of  the  pancreatic  juice  on  proteids  — 
Action  of  the  pancreatic  juice  on  fats  —  Action  of  bile  in  digestion  —  Movements  of 
the  small  intestine  —  Physiological  anatomy  of  the  large  intestine  —  Ileo-csecal  valve 

—  Peritoneal  coat  —  Muscular  coat  —  Mucous  coat  —  Processes  of  fermentation  in 
the  intestinal  canal  —  Contents  of  the  large  intestine  —  Stercorin  —  Indol,  scatol, 
phenol,  cresol  etc.  —  Movements  of  the  large  intestine  — Defecation  —  Gases  found 

in  the  alimentary  canal        ............     206 

CHAPTER   X 

Absorption  —  Lymph  and  Chyle 

Absorption  by  bloodvessels  —  Absorption  by  lymphatic  and  lacteal  vessels  —  Physiological 
anatomy  of  the  lymphatic  and  lacteal  vessels  —  Structure  of  the  lymphatic  and  lacteal 
vessels  —  Lymphatic  glands — Absorption  of  proteids  by  the  lacteals — Absorption 
of  sugar  and  salts  by  the  lacteals  —  Absorption  of  water  by  the  lacteals  —  Absorption 
by  the  skin — Absorption  by  the  respiratory  surface — Absorption  from  closed  cavi- 
ties, reservoirs  of  glands,  etc.  —  Absorption  of  fats  and  insoluble  substances  —  Influ- 
ence of  the  condition  of  the  blood  and  of  the  vessels  on  absorption  —  Influence  of 
the  nervous  system  on  absorption  —  Osmosis  —  Mechanism  of  the  passage  of  liquids 
through  membranes  —  Osmotic  pressure  —  Lymph  and  chyle  —  Properties  and  com- 
position of  lymph  —  Corpuscular  elements  of  the  lymph  —  Origin  and  uses  of  the 
lymph  —  Properties  and  composition  of  chyle  —  Composition  of  chyle  ^Microscopical 
characters  of  the  chyle — Movements  of  the  lymph  and  chyle     .....     240 

CHAPTER   XI 
Secretion 

Classification  of  the  secretions — Mechanism  of  the  production  of  the  true  secretions  — 
Mechanism  of  the  production  of  the  excretions  —  Influence  of  the  composition  and 
pressure  of  the  blood  on  secretion  —  Influence  of  the  ner\'ous  system  on  secretion  — 
Paralytic  secretion  by  glands —  Anatomical  classification  of  glandular  organs  —  Secret- 
ing membranes  —  Follicular  glands  —  Tubular  glands —  Racemose  glands,  simple 
and  compound  —  Ductless,  or  blood-glands  —  Secretions  and  excretions  —  Synovial 
membranes  and  synovia  —  Mucous  membranes  and  mucus  —  Mechanism  of  the  secre- 


xiv  CONTENTS 


tion  of  mucus  —  Composition  and  varieties  of  mucus  —  General  uses  of  mucus  — 
Physiological  anatomy  of  the  sebaceous,  ceruminous  and  Meibomian  glands  —  Ordi- 
nary sebaceous  matter  —  Smegma  of  the  prepuce  and  labia  minora  —  Vernix  caseosa 

—  Cerumen  —  Mammary  secretion  —  Mechanism  of  the  secretion  of  milk  —  General 
conditions  which  modify  the  lacteal  secretion  —  Properties  and  composition  of  milk 

—  Microscopical  characters  of  milk  —  Composition  of  the  milk  —  Colostrum  —  Lacteal 
secretion  in  the  newly-born  ...........     268 

CHAPTER   XII 
Excretion  by  the  Skin 

Physiological  anatomy  of  the  skin  —  Layers  of  the  skin — The  corium,  or  true  skin  —  The 
epidermis — Physiological  anatomy  of  the  nails  —  Physiological  anatomy  of  the  hairs 

—  Roots  of  the  hairs,  and  hair-follicles — Growth  of  the  hairs  —  Sudden  blanching 
of  the  hair  —  Uses  of  the  hairs  —  Perspiration  —  Quantity  of  cutaneous  exhalation  — 
Properties  and  composition  of  the  sweat      .........     3°5 

CHAPTER   XIII 
Excretion  by  the  Kidneys 

Physiological  anatomy  of  the  kidneys  —  Pyramidal  substance  —  Cortical  substance  —  Tubes 
of  the  cortical  substance  —  Narrow  tubes  of  Henle  —  Distribution  of  bloodvessels  in 
the  kidney  —  Mechanism  of  the  production  and  discharge  of  urine  —  Influence  of 
blood-pressure,  the  nervous  system  etc.,  on  the  secretion  of  urine  —  Physiological 
anatomy  of  the  urinary  passages  —  Mechanism  of  the  discharge  of  urine  —  Properties 
and  composition  of  the  urine  —  Urea  —  Origin  of  urea  —  Influence  of  the  ingesta  on 
the  composition  of  the  urine  and  on  the  discharge  of  nitrogen  —  Influence  of  muscu- 
lar exercise  on  the  discharge  of  nitrogen  —  Uric  acid  and  its  compounds —  Hippuric 
acid,  hippurates  and  lactates  —  Calcium  oxalate  —  Xanthin,  hypoxanthin,  leucin, 
tyrosin  and  taurin  —  Fatty  matters  —  Inorganic  constituents  of  the  urine  —  Chlorides 

—  Sulphates — Phosphates  —  Water  as  a  product  of  excretion  —  Variations  in  the 
composition  of  the  urine  —  Variations  with  age  and  sex  —  Influence  of  mental  exer- 
tion—  Internal  secretion  —  Work  of  the  kidneys 322 

CHAPTER   XIV 

Uses  of  the  Liver  —  Ductless  Glands 

Physiological  anatomy  of  the  liver  —  Branches  of  the  portal  vein,  the  hepatic  artery  and 
the  hepatic  duct  —  Interlobular  vessels  —  Structure  of  a  lobule  —  Arrangement  of  the 
bile-ducts  in  the  lobules  —  Anatomy  of  the  excretory  passages  —  Gall-bladder,  cystic 
and  common  ducts  —  Chemistry  of  the  liver  —  Nerves  and  lymphatics  of  the  liver  — . 
Mechanism  of  the  secretion  of  bile  —  Quantity  of  bile  —  Uses  of  the  bile  —  Properties 
and  composition  of  the  bile  —  Biliary  salts  —  Cholesterin  and  stercorin  —  Bilirubin  — 
Tests  for  bile  —  Excretory  action  of  the  liver  —  Origin  of  cholesterin  —  Formation  of 
glycogen  in  the  liver  —  Conditions  that  influence  the  quantity  of  sugar  in  the  blood 

—  Ductless  glands  and  internal  secretion  —  Suprarenal  capsules  —  Cortical  substance 

—  Medullary  substance  —  Vessels  and  nerves  —  Chemistry  of  the  suprarenal  capsules 

—  Addison's  disease — The  spleen  —  Fibrous  structure  —  Malpighian  bodies  —  Spleen- 
pulp —  Bloodvessels,  nerves  and  lymphatics  —  Chemical  constitution  —  Variations  in 
volume  —  Extirpation  —  Thyroid  gland  —  Structure  —  Vessels  and  nerves — Myxoe- 
dema  — Thymus  gland  —  Pituitary  body  and  pineal  gland  —  Acromegaly  and  giantism 

—  Internal  secretion  by  the  testes  and  ovaries 355 


CONTENTS  XV 

CHAPTER   XV 
Metabolism  —  Nutrition  —  Animal  Heat  and  Force 

PAGE 

Action  of  glandular  cells  —  Metabolism,  anabolism  and  katabolism  —  General  nutrition  — 
Luxus-consumption  —  Isodynamic  values  of  foods  —  Animal  heat  and  force  —  Limits 
of  variations  in  the  normal  temperature  in  man — Variations  in  different  parts  of  the 
body  —  Variations  at  different  periods  of  life  —  Variations  at  different  times  of  the 
day  —  Influence  of  exercise  etc.,  on  the  heat  of  the  body  —  Influence  of  the  nervous 
system  on  the  production  of  animal  heat  (heat-centres)  —  Mechanism  of  the  produc- 
tion of  animal  heat  —  Equalization  of  the  animal  temperature  —  Relations  of  heat  to 
force 392 

CHAPTER    XVI 

Muscular  Movements 

Amorphous  contractile  substance  and  ameboid  movements  —  Ciliary  movements  —  Move- 
ments due  to  elasticity  —  Elastic  tissue' — Muscular  movements  —  Contraction  of 
involuntary  muscular  tissue  —  Physiological  anatomy  of  the  voluntary  muscular  tissue 

—  Connective  tissue  —  Bloodvessels  and  lymphatics —  Connection  of  the  muscles  with 
the  tendons  —  Chemical  composition  of  the  muscles  —  Physiological  properties  of 
the  muscles — Elasticity  of  muscles  —  Muscular  tonicity — Sensibility  of  the  muscles 

—  Muscular  contractility  and  excitability  —  Muscular  contraction  —  Changes  in  the 
form  of  fibres  during  contraction  —  Rigor  mortis  —  Passive  organs  of  locomotion  — 
Physiological  anatomy  of  the  bones  —  Lacunae  —  Canaliculi  —  Bone-cells  or  cor- 
puscles—  Marrow  of  the  bones  —  Periosteum — Physiological  anatomy  of  cartilage 

—  Cartilage-cavities — Cartilage-cells  —  Elastic  cartilage  and  fibro-cartilage       .         .412 

CHAPTER    XVII 

Voice  and  Speech 

Physiological  anatomy  of  the  vocal  organs — Muscles  of  the  larynx — -  Crico-thyroid  mus- 
cles— Arytenoid  muscle  —  Lateral  crico-arytenoid  muscles  —  Thyro-arytenoid  muscles 

—  Mechanism  of  the  production  of  the  voice  —  Movements  of  the  glottis  during  pho- 
nation  —  Action  of  the  intrinsic  muscles  of  the  larynx  in  phonation  —  Action  of  acces- 
sory vocal  organs  —  Laryngeal  mechanism  of  the  vocal  registers  —  Vocal  registers  in 
the  male  —  Vocal  registers  in  the  female  —  Mechanism  of  speech  —  Vowels  —  Con- 
sonants—  The  phonograph  and  telephone  .........     435 

CHAPTER   XVIII 
Structure  and  Properties  of  the  Nervous  System 

Divisions  and  structure  of  the  nervous  tissue —  Medullated  nerve-fibres  —  Xon-medullated 
nerve-fibres —  Gelatinous  nerve-fibres  (fibres  of  Remak)  —  Accessory  anatomical  ele- 
ments of  the  nerves  —  Branching  and  course  of  the  nerves  —  Termination  of  nerves 
in  voluntary  muscles  —  Termination  of  nerves  in  glands  —  Modes  of  termination  of 
sensory  nerves  —  Corpuscles  of  Vater,  or  of  Pacini  —  Tactile  corpuscles  —  End-bulbs 

—  General  mode  of  termination  of  the  sensory  nerves — -Structure  of  the  ner\'e-centres 

—  Nerve-cells  —  Nissl's  granules — The  neuron  —  Accessory  anatomical  elements  of 
the  nerve-centres  —  Degeneration  and  regeneration  of  nerves  —  Motor  and  sensory 
nerves  —  Mode  of  action  of  the  motor  nerves  —  Associated  movements — Mode  of 
action  of  the  sensory  nerves  —  Physiological  differences  between  motor  and  sensory 


xvi  '  CONTENTS 

PAGE 

nerves  —  Nervous  excitability  and  conductivity — Rapidity  of  nervous  conduction  — 
Personal  equation  —  Action  of  electricity  on  the  nerves  —  Law  of  contraction  — 
Electric  current  from  the  exterior  to  the  cut  surface  of  a  nerve  —  Electrotonus, 
anelectrotonus  and  catelectrotonus      ..........     455 

CHAPTER    XIX 

Spinal  Nerves  —  Motor  Cranial  Nerves 

Spinal  nerves  —  Cranial  nerves  —  Motor  oculi  communis  (third  nerve) — Physiological 
anatomy  —  Properties  and  uses  of  the  motor  oculi  communis  —  Patheticus,  or  troch- 
Icaris  (fourth  nerve)  —  Physiological  anatomy  —  Properties  and  uses  of  the  patheticus 

—  Motor  oculi  externus,  or  abducens  (sixth  nerve)  —  Physiological  anatomy  —  Prop- 
erties and  uses  of  the  motor  oculi  communis  —  Nerve  of  mastication  (the  small,  or 
motor  root  of  the  fifth  nerve)  —  Physiological  anatomy  —  Properties  and  uses  of  the 
nerve  of  mastication  —  Facial,  or  nerve  of  expression  (seventh  nerve)  —  Physiological 
anatomy  —  General  properties  of  the  facial  —  Uses  of  branches  of  the  facial  given  off 
within  the  aqueduct  of  Fallopius  —  Uses  of  the  chorda  tympani  —  Influence  of  certain 
branches  of  the  facial  on  the  movements  of  the  palate  and  uvula  —  Uses  of  the  ex- 
ternal branches  of  the  facial  —  Spinal  accessory  (eleventh  nerve)  —  Physiological 
anatomy  —  Properties  and  uses  of  the  spinal  accessory  —  Uses  of  the  internal  branch 
from  the  spinal  accessory  to  the  pneumogastric  —  Influence  of  the  internal  branch  of 
the  spinal  accessory  on  deglutition  —  Influence  of  the  spinal  accessory  on  the  heart 

—  Uses  of  the  external,  or  muscular  branches  of  the  spinal  accessory  —  Sublingual 
(twelfth  nerve)  —  Physiological  anatomy  —  Properties  and  uses  of  the  sublingual       .     492 

CHAPTER   XX 

Trifacial  Nerve  —  Pneumogastric  Nerve 

Trifacial  (large  root  of  the  fifth  nerve)  —  Physiological  anatomy  —  Properties  and  uses  of 
the  trifacial  —  Immediate  effects  of  division  of  the  trifacial  —  Remote  effects  of  divi- 
sion of  the  trifacial — Pneumogastric  (tenth  nerve)  —  Physiological  anatomy  —  Prop- 
erties and  uses  of  the  auricular  nerves  —  Properties  and  uses  of  the  pharyngeal  nerves 

—  Properties  and  uses  of  the  superior  laryngeal  nerves —  Properties  and  uses  of  the 
inferior,  or  recurrent  laryngeal  nerves  —  Properties  and  uses  of  the  cardiac  nerves  — 
Depressor  nerve  —  Properties  and  uses  of  the  pulmonary  nerves  —  Effects  of  division 
of  the  pneumogastrics  on  respiration  —  Effects  of  faradization  of  the  pncumogastrics 
on  respiration  —  Properties  and  uses  of  the  oesophageal  nerves  —  Properties  and  uses 
of  the  abdominal  nerves  —  Influence  of  the  pneumogastrics  on  the  liver  —  Influence 
of  the  pneumogastrics  on  the  stomach  and  intestines  —  Effects  of  faradization — In- 
fluence of  section  of  the  pneumogastrics  on  the  movements  of  the  stomach  —  Influence 

of  the  pneumogastrics  on  the  small  intestine        ........     521 

CHAPTER    XXI 

The  Spinal  Cord 

Membranes  of  the  encephalon  and  spinal  cord  —  Cephalo-rachidian  liquid  —  Physiological 
anatomy  of  the  spinal  cord  —  Columns  of  Tiirck  —  Crossed  pyramidal  tracts  —  An- 
terior ground  columns  —  Lateral  bundles  —  Ascending  and  descending  cerebellar 
fasciculi  —  Direct  cerebellar  fasciculi  —  Columns  of  Burdach  —  Columns  of  Goll  — 
Directions  of  nerve-fibres  in  the  cord  —  General  properties  of  the  spinal  cord  —  Re- 
lations of  the  posterior  white  columns  of  the  cord  to  muscular  coordination  — • 
Nerve-centres  in  the  spinal  cord  —  Reflex  action  of  the  spinal  cord  —  Reflexes  in  man     545 


CONTENTS  xvii 


CHAPTER   XXII 
The  Cerebrum  and  the  Basal  Ganglia 

PAGE 

Weights  of  the  encephalon  and  of  certain  of  its  parts  —  The  cerebral  hemispheres  —  Cere- 
bral convolutions  —  Basal  ganglia  —  Corpora  striata,  optic  thajami  and  internal  cap- 
sule —  Tubercula  quadrigemina  —  Crura  cerebri  —  Pons  Varolii  —  Directions  of  fibres 
in  the  cerebrum  —  Fibres  connecting  the  cerebrum  with  the  cerebellum  —  Fibres 
connecting  the  two  sides  of  the  brain —  Fibres  connecting  different  cerebral  convolu- 
tions on  the  same  side  (association  fibres) — Fibres  connecting  the  brain  with  the 
spinal  cord  —  Cerebral  localization  —  Motor  cortical  zone  (Rolandic  area)  — General 
uses  of  the  cerebrum — Extirpation  of  the  cerebrum  —  Comparative  development  of 
the  cerebrum  in  the  lower  animals  —  Development  of  the  cerebrum  in  different  races 
of  men  and  in  different  individuals  —  Facial  angle  —  Pathological  observations  — 
Reaction-time  —  Centre  for  the  expressions  of  ideas  in  language         ....     565 

CHAPTER    XXIII 

The  Cerebellum  and  the  Bulb 

The  cerebellum  —  Physiological  anatomy  —  Extirpation  of  the  cerebellum  —  Pathological 
observations — The  bulb  —  Physiological  anatomy  —  Uses  of  the  bulb  —  Nerve-centres 
in  the  bulb — Respiratory  centre — Vital  point  (so  called)  —  Rolling  and  turning 
movements  following  injury  of  certain  parts  of  the  encephalon  (forced  movements)    .     592 

CHAPTER   XXIV 
Sympathetic  System  —  Sleep 

Cranial  ganglia  —  Cervical  ganglia — Thoracic  ganglia  —  Ganglia  in  the  abdominal  and 
the  pelvic  cavities  —  General  properties  of  the  sympathetic  ganglia  and  nerves  — 
Direct  experiments  on  the  sympathetic  —  Vasomotor  centres  and  nerves  —  Reflex 
vasomotor  phenomena  —  Vaso-inhibitory  nerves — -Trophic  centres  and  nerves  — 
Sleep  —  Dreams  —  Condition  of  the  brain  and  nervous  system  during  sleep         .         .     606 

CHAPTER   XXV 
Sense  of  Touch  —  Olfaction  —  Gustation 

Muscular  sense  —  Sense  of  touch  —  Appreciation  of  temperature  —  Olfaction  —  Olfactory 
(first  nerve) — Properties  and  uses  of  the  olfactorj'  nerves  —  Mechanism  of  olfaction 
—  Relations  of  olfaction  to  the  sense  of  taste  —  Gustation  —  Nerves  of  taste  —  Chorda 
tympani  —  Glosso-pharyngeal  (ninth  nerve)  —  General  properties  of  the  glosso- 
pharyngeal —  Relations  of  the  glosso-pharyngeal  to  gustation —  Mechanism  of  gusta- 
tion—  Physiological  anatomy  of  the  organs  of  taste — Taste-beakers  .         .         .     625 

CHAPTER   XXVI 
The  Organ  of  Vision 

Optic  (second  nerve)  — General  properties  of  the  optic  nerves  —  Physiological  anatomy  of 
the  eyeball  —  Sclerotic  coat  —  Cornea  —  Choroid  coat — Ciliary  processes — Iris  — 
Pupillary  membrane  —  Retina  —  Layer  of  rods  and  cones  (Jacob's  membrane,  or 
bacillar  membrane) — Crystalline  lens  —  Suspensory  ligament  of  the  lens  (zone  of 
Zinn)  —  Aqueous  humor  —  Vitreous  humor  —  Summary  of  the  anatomy  of  the  globe 
of  the  eye  ...............     646 


xviii  CONTENTS 


CHAPTER  XXVII 
Refraction  in  the  Eye  —  Accommodation 

PAGE 

Refraction  in  the  eye  —  Certain  laws  of  refraction,  dispersion  etc.,  bearing  on  the  physiology 
of  vision — Refraction  by  lenses — Spherical  monochromatic  aberration  —  Chromatic 
aberration  —  Formation  of  images  in  the  eye  —  Visual  purple  and  visual  yellow  and 
accommodation  of  the  eye  for  different  degrees  of  illumination  —  Mechanism  of  re- 
fraction in  the  eye  —  Astigmatism — Movements  of  the  iris — Direct  action  of  light 
on  the  iris  —  Accommodation  of  the  eye  for  vision  at  different  distances  —  Changes  in 
the  crystalline  lens  in  accommodation  —  Changes  in  the  iris  in  accommodation  — 
Erect  impressions  produced  by  images  inverted  upon  the  retina  —  Field  of  indirect 
vision — Binocular  vision  —  Corresponding  points — The  horopter  —  Duration  of 
luminous  impressions  (after-images)  —  Irradiation 667 

CHAPTER   XXVIII 
Movements  of  the  Eyeball  —  Parts  for  Protection  of  the  Eye 

Action  of  the  recti  muscles  —  Action  of  the  oblique  muscles  —  Associated  action  of  the 
muscles  of  the  eyeball  —  Centres  for  vision  —  Perception  of  colors  —  Parts  for  the 
protection  of  the  eyeball  —  Muscles  that  open  and  close  the  eyelids  —  Conjunctival 
mucous  membrane  —  The  lachrymal  apparatus  —  The  tears         .         •         »         .         .     698 

CHAPTER   XXIX 
Audition 

Auditory  (eighth  nerve)  —  General  properties  of  the  auditory  nerves  —  Topographical 
■  anatomy  of  the  parts  essential  to  the  appreciation  of  sound  —  The  external  ear  — 
General  arrangement  of  parts  composing  the  middle  ear  —  General  arrangement  of 
the  bony  labyrinth  —  Physics  of  sound  —  Pitch  of  musical  sounds — Musical  scale  — 
Quality  of  musical  sounds  —  Harmonics,  or  overtones  —  Harmony  —  Discords  and 
dissonance  —  Tones  by  influence  —  Uses  of  different  parts  of  the  middle  ear  —  Struc- 
ture of  the  menibrana  tympani  —  Uses  of  the  membrana  tympani  —  Mechanism  of 
the  ossicles  of  the  ear  —  Physiological  anatomy  of  the  internal  ear —  General  arrange- 
ment of  the  membranous  labyrinth  —  Liquids  of  the  labyrinth  —  Distribution  of  the 
nerves  in  the  labyrinth  —  Organ  of  Corti  —  Uses  of  different  parts  of  the  internal  ear 

—  Uses  of  the  semicircular  canals  —  Uses  of  the  parts  contained  in  the  cochlea  — 
Centres  for  audition     .         .         .         .         .         .         .         .         •         •         •         •         -7'^ 

CHAPTER   XXX 

EmBR\''OLOGY' 

Female  organs  of  generation  —  The  ovaries  —  Graafian  follicles  —  The  parovarium  —  The 
uterus  —  The  Fallopian  tubes — Structure  of  the  ovum — Discharge  of  the  ovum  — 
Passage  of  ova  into  the  Fallopian  tubes  —  Puberty  and  menstruation  —  Changes  in 
the  Graafian  follicles  after  their  rupture  (corpus  luteum)  —  Corpus  luteum  of  preg- 
nancy—  Male  organs  of  generation  —  Interstitial  gland  of  the  testis  —  Vas  deferens 

—  Vesiculae  seminales  —  Prostate  —  Glands  of  the  urethra  —  Male  element  of  genera- 
tion—  Spermatozoids  .........•••     753 


CONTEXTS  xix 


CHAPTER   XXXI 
Fertilization  and  Karyokixesis  of  the  0\xm 

PAGE 

Fecundation — Maturation  of  the  ovum — Fertilization  of  the  ovum  —  Mendel's  laws  of 
heredity —  Superfecundation  —  Segmentation  of  the  ovum  —  Gastrulation  —  Primitive 
streak  —  Formation  of  the  membranes  —  Formation  of  the  amnion  —  Amniotic  liquid 

—  Formation  of  the  umbilical  vesicle  (yolk-sac)  —  Formation  of  the  allantois  and 
permanent  chorion  —  Membranse  deciduse  —  Formation  of  the  placenta  —  Uses  of 

the  placenta 787 

CHAPTER   XXXII 

Development  of  the  Ovum 

Development  of  the  cavities  and  layers  of  the  trunk  in  the  chick  —  Development  of  the 
skeleton,  muscular  system  and  skin  —  Notochord  —  Vertebral  column  etc.  —  Develop- 
ment of  the  nervous  system — Development  of  the  digestive  system  ^  Development 
of  the  respiratory  system  —  Development  of  the  face  —  Development  of  the  teeth  — 
Development  of  the  genito-urinary  apparatus  —  Development  of  the  urinary  system 

—  Development  of  the  external  organs  of  generation — Development  of  the  circula- 
tory system  —  The  first,  or  vitelline  circulation  —  The  second,  or  placental  circulation 

—  Development  of  the  heart —  Peculiarities  of  the  fcetal  circulation  —  The  third,  or 
adult  circulation  .............     816 

CHAPTER  XXXIII 

Fcetal  Life  —  Development  after  Birth  —  Death 

Duration  of  pregnancy  —  Size,  weight  and  position  of  the  foetus  —  Multiple  pregnancy  — 
Cause  of  the  first  contractions  of  the  uterus  in  normal  parturition  —  Involution  of  the 
uterus  —  Meconium  —  Dextral  preeminence  —  Development  after  birth  —  Ages  — 
Death 850 

IXDEX 869 


LIST    OF   TEXT-ILLUSTRATIONS 

(For  list  of  color-plates,  see  page  865.) 

FIG.  PAGE 

1.  Ameba  proteus  {Sedgmick  atid  IFi/son)       .........  i 

2.  Diagram  of  a  cell  (^IVilsott)          ...........  3 

3.  Diagram  showing  the  prophases  of  karyokinesis  (  ^z'/fo«)          .....  4 

4.  Diagram  of  the  later  phases  of  karyokinesis  (  IVi/son)         ......  6 

5.  Six  stages  of  karyokinesis  of  the  sea-urchin  (  Wilson)         ......  7 

6.  Groups  of  cells  with  amitotically  dividing  nuclei  (  Wilson,  after  Wheeler')  ...  8 

7.  Diagram  of  a  cell  with  receptors           ..........  9 

8.  Diagram  of  a  toxic  molecule        ...........  10 

9.  Diagram  showing  free  receptors  .         .  .         .         .         .         .         .         .         .         .11 

10.  Diagram  showing  the  alexin  combined  with  the  receptor     .         .         .         .         ,         .II 

11.  Diagram  showing  the  anticomplement         .         .         .         .         .         .         .         .         .12 

12.  Diagram  showing  the  anti-immune  body     .........  12 

13.  Blood-corpuscles  of  the  Guinea  pig  (6'/^r«i5^;'^)  ........  17 

14.  Blood-corpuscles  of  certain  of  the  inferior  animals      .......  18 

15.  Human  blood-corpuscles  in  rouleaux  (^Stratford)        .......  19 

16.  Heart  in  situ  {Dalton)         ...........         ^  33 

17.  Muscular  fibres  of  the  auricles  {^Bonamy  and  Beau)  .......  34 

18.  Heart,  anterior  view  (^owrtwzy  flMf/^iff??^)  .         ........  35 

19.  'i\&2iXi,\&it  c'SMxWt.i  (^Bonamy  and  Beau)      .........  36 

20.  Heart,  right  cavities  (^Bonamy  and  Beau)  .........  36 

21.  Muscular  fibres  of  the  ventricles  (^owrtwj  rf«(/ ^fa?<)         ......  37 

22.  Valves  of  the  heart  (^Bonamy  and  Beau)    .........  38 

23.  Trace  of  Vierordt         .............  54 

24.  Trace  of  Marey   ..............  55 

25.  Small  artery  and  capillaries  from  the  muscular  coat  of  the  urinary  bladder  of  a  frog 

(^fro7n  a  photograph  taken  at  the  United  States  Army  Medical  Aluseum)      .         .  65 

26.  Venous  radicles  uniting  to  form  a  small  vein,  from  the  muscular  coat  of  the  urinary 

bladder  of  a  frog  {from  a  photograph  taken  at  the  Utiited  States  Army  Medical 

Museum)      ..............  69 

27.  Migration  of  leucocytes  and  diapedesis  of  red  corpuscles  (^Councilman)     ...  84 

28.  Trachea  and  bronchial  tubes  (^Sappey)         .........  90 

29.  Lungs,  anterior  view  (^Sappey)     ...........  92 

30.  Bronchia  and  lungs,  posterior  view  {Sappey)       ........  93 

31.  Thorax,  anterior  view  {Sappey)   ...........  96 

32.  Thorax,  posterior  view  {Sappey)  .         ..........  96 

33.  Diaphragm  {Sappey) 98 

34.  Section  of  a  molar  tooth  of  man  {Sobotta)  .........  164 

35.  Muscles  of  the  pharynx  (Sappey)         ..........  177 

36.  Longitudinal  fibres  of  the  stomach  {Sappey)        .         .         .         .         .         .  .         .186 

37.  Fibres  seen  with  the  stomach  everted  {Sappey)  .         .         .         .         .         .         .         .187 

38.  Pits  in  the  mucous  membrane  of  the  stomach  and  openings  of  the  glands  {Sappey)   .  188 

XX  i 


xxii  LIST    OF    TEXT-ILLUSTRATIONS 

FIG.  PAGE 

39.  Glands  in  the  greater  pouch  of  the  stomach  (^Heidenhaitt)           .....  189 

40.  Pyloric  glands  (^Ebsteitt)      .         .         .         .         .         .         .         .         .         .         .         .189 

41.  Gastric  fistula  in  the  case  of  St.  Martin  (^Beaumoni)   .......  191 

42.  Stomach,  liver  and  small  intestine  (^Sappey)         ........  207 

43.  Intestinal  tubules  {Sappey)          ...........  210 

44.  Axial  section  of  a  villus  of  a  dog  (A'z<//.fc/iiV3/^/)  .  .  .         .         .         .         .211 

45.  Patch  of  Peyer  {Sappey) 213 

46.  Patch  of  Peyer  seen  from  its  attached  surface  (^Sappey)       ......  213 

47.  The  pancreas;    its  direction,  relations  and  two  excretory  ducts  (^Sappey)     .         .         .  217 

48.  Stomach,  pancreas  and  large  intestine  (^Sappey')  ........  226 

49.  Crystals  of  stercorin     .............  234 

50.  Origin  of  lymphatics  {Latidois)  .         .         .         .         .         .         .         .         .         .         .241 

51.  Lymphatic  plexus,  showing  the  endothelium  {Belaieff)       ......  243 

52.  Superficial  lymphatics  of  the  skin  of  the  palmar  surface  of  the  linger  (^Sappey')  .         .  244 

53.  Deep  lymphatics  of  the  skin  of  the  finger  (^Sappey)    .......  244 

54.  Same  finger,  lateral  view,  showing  lymphatic  trunks  connected  with  the  superficial 

network  {Sappey)         ............  244 

55.  Superficial  lymphatics  of  the  arm  {Sappey)          ........  245 

56.  Superficial  lymphatics  of  the  leg  {Sappey)  .........  245 

57.  Stomach,   intestine   and   mesentery,   with    the   mesenteric   bloodvessels    and   lacteals 

{Asellius) ,         .          .          .  247 

58.  Thoracic  duct  {Mascagni)  ............  248 

59.  Valves  of  the  lymphatics  {Sappey)      ..........  249 

60.  Lymphatics  and  lymphatic  glands  {Mascagni)    .  .  .         .  .         .         .         '251 

61.  Sebaceous  glands  {Sappey)  ............  283 

62.  Meibomian  glands  of  the  upper  lid  {Sappey)       ........  285 

63.  Human  milk-globules  from  a  healthy  woman  eight  days  after  delivery  {Funke)  .         ,  297 

64.  Colostrum  from  a  healthy  lying-in  woman  twelve  hours  after  delivery  {Funke)   .         .  302 

65.  Anatomy  of  the  nails  {Sappey)    ...........  309 

66.  Section  of  a  nail  {Sappey)  ............  310 

67.  Hair  and  hair-follicle  {Sappey)    .         .         .         .         .         .         .         .         .         .         .312 

68.  Root  of  the  hair  {Sappey) 313 

69.  Surface  of  the  palm  of  the  hand,  a  portion  of  skin  about  one-half  inch  (12.5   milli- 

meters) square  {Sappey)       ...........  316 

70.  Longitudinal  section  of  the  kidney  {Sappey)        ........  323 

71.  Longitudinal  section  of  the  pyramidal  substance  of  the  kidney  of  the  foetus  {Sappey)  324 

72.  Longitudinal  section  of  the  cortical  substance  of  the  same  kidney  {Sappey)        .         .  324 

73.  Section  of  collecting  tubes  of  the  kidney  {Author's  collectio?i)     .....  325 

74.  Diagram  of  the  structure  of  the  kidney  {Landois)       .......  327 

75.  Transverse  section  of  a  single  hepatic  lobule  {Sappey)         ......  358 

76.  Bile-capillaries  between  the  liver-cells  {Pfeiffer)           .......  360 

77.  Racemose  glands  attached  to  the  biliary  ducts  of  the  pig  {Sappey)     ....  361 

78.  Gall-bladder,  hepatic,  cystic  and  common  ducts  {Sappey)    ......  362 

79.  Thyroid  and  thymus  glands  (^a//^/)  ..........  388 

80.  Ciliated  epithelium  {Engehnann)        .         .         .         .         .         .         .         .         .  -413 

81.  White  fibrous  tissue;    one  end  of  the  bundle  has  been  teased  to  display  the  compo- 

nent fibrillse  {Piersol)  ............  415 

82.  Elastic  fibres  isolated;    from  the  adventitia  of  the  aorta  {Piersol,  after  Schiefferdecker)  416 

83.  Portion  of  the  elastic  tissue  of  the  intima  of  the  human  aorta;    the  fibres  are  so  broad 

and  so  closely  grouped  that  they  constitute  an  elastic  sheet  —  fenestrated  mem- 
brane of  Henle — {Piersol)          ..........  416 

84.  Muscular  fibres  from  the  urinary  bladder  of  the  human  subject  {Sappey)    .         .         -417 


LIST    OF    TEXT-ILLUSTRATIONS 


XXlll 


FIG. 

85.  Muscular  fibres  from  the  aorta  of  the  calf  (^Sappey) 

86.  Muscular  fibres  from  the  uterus  of  a  woman  who  died  in  the  ninth  month  of  utero 

gestation  {Sappey)        ........... 

87.  Vascular  canals  and  lacunse  seen  in  a  longitudinal  section  of  the  humerus  (Sappey) 

88.  Vascular  canals  and  lacunae  seen  in  a  transverse  section  of  the  humerus  {Sappey) 

89.  Vertical  section  of  diarthrodial  cartilage  {Sappey)     ...... 

90.  Vertical  section  of  the  human  larynx,  showing  the  vocal  chords  {Sappey) 

91.  Posterior  view  of  the  muscles  of  the  larj'nx  {Sappey)         ..... 

92.  Lateral  view  of  the  muscles  of  the  larynx  {Sappey)  ...... 

93.  Glottis   seen  with   the   laryngoscope    during   the   emission    of  high-pitched   sounds 

{Le  Bon) 

94.  Appearance  of  the  vocal  chords  in  the  production  of  the  chest-voice  {Mandl) 

95.  Appearances  of  the  vocal  chords  in  the  production  of  the  falsetto  voice  {Mills) 

96.  MeduUated  nerve-fibres  {Pieisol)       .... 

97.  Gold-stained  axis-cylinder  {Piersol)  .... 

98.  Nodes  of  Ranvier  and  lines  of  Fromann  {Ranvier)  . 

99.  Fibres  of  Remak  {Hobin)  ..... 
100.  Branching  of  a  nerve  in  the  abdominal  muscle  of  a  mouse  {Sobotta) 
lOi.  Motor  end-plates  from  a  muscle  of  a  lizard  {Sobotta) 

102.  Transverse  section  of  a  corpuscle  of  Vater  {Author's  collection) 

103.  Longitudinal  section  of  a  corpuscle  of  Vater  {Sappey) 

104.  Tactile  corpuscle  from  the  human  corium  {Bohm  and  Devidoff) 

105.  Corpuscle  of  Krause  from  the  human  conjunctiva  {Dogiel) 

106.  Papillse  of  the  skin  of  the  palm  of  the  hand  {Sappey) 

107.  Unipolar  cell  from  the  Gasserian  ganglion  {Schwalbe) 

108.  Unipolar  cell  with  a  spiral  fibre;    bipolar  nerve-cell  {Landois)  . 

109.  Sympathetic  ganglion-cell  from  man  (AVk  a«(/i?f&««)    . 
no.  Cell  from  the  electric  lobe  of  the  torpedo  {Schultze) 

111.  Nerve-cells,  glia-cells  and  neuroglia  from  the  spinal  cord  of  the  calf 

112.  Diagram  of  a  nerve-cell  to  show  Nissl  granules  {R.  y  Cajal)    . 

113.  Method  of  testing  excitability  in  electrotonus  (Za«a'(?zj)   . 

114.  Cervical  portion  of  the  spinal  cord  (Zf^iVxc-^y^/if) 

115.  Dorsal  portion  of  the  spinal  cord  (//zV^fir/z/^/^) 

116.  Inferior  portion  of  the  spinal  cord,  and  cauda  equina  {Hirsdifeld) 

117.  Roots  of  the  cranial  nerves  ( Hirschfeld)  ..... 

118.  Distribution  of  the  motor  oculi  communis  {Hirschfeld)     . 

119.  Distribution  of  the  patheticus  {Hirschfeld)        .... 

120.  Distribution  of  the  motor  oculi  externus  {Hirschfeld) 

121.  Distribution  of  the  small  root  of  the  fifth  nerve  {Hirschfeld)    . 

122.  Superficial  branches  of  the  facial  and  the  fifth  {Hirschfeld) 

123.  Chorda-tympani  nerve  {Hirschfeld^  ...... 

124.  Spinal  accessory  nerve  {Hirschfeld)  ...... 

125.  Distribution  of  the  sublingual  nerve  {Sappey)  .... 

126.  Principal  branches  of  the  large  root  of  the  fifth  nerve  {Robin) 

127.  Ophthalmic  di\dsion  of  the  fifth  {Hirschfeld)    .... 

128.  Superior  maxillary  division  of  the  fifth  {Hirschfeld)  . 

129.  Inferior  maxillary  division  of  the  fifth  {Hirschfeld)  . 

130.  Anastomoses  of  the  pneumogastric  {Hirschfeld) 

131.  Distribution  of  the  pneumogastric  {Hirschfeld) 

132.  Transverse  section  of  the  spinal  cord  of  a  child  six  months  old,  at  the  middle  of  the 

lumbar  enlargement,  treated  with  potassium  auric  chloride  and  uranium  nitrate 
{Gerlach) 548 


{Lavdowsky) 


xxiv  LIST   OF   TEXT-ILLUSTRATIONS 

FIG.  PAGE 

133.  Diagram  of  the  columns  of  the  cord  .........  552 

134.  View  of  the  structures  displayed  on  the  right  side  of  a  median  longitudinal  section 

of  the  brain  —  semidiagrammatic          .........  566 

135.  Vertical  section  of  the  cerebral  cortex  (J^.  y  Cajal)  .......  568 

136.  Cells  of  the  molecular  layer  of  the  cerebral  cortex  {R.  y  Cajal)        ....  568 

137.  Diagrammatic  section  through  the  cerebral  cortex  (A',  jc  Cajal)         ....  569 

138.  Cells  with  short  neurites  in  the  cerebral  cortex  (A'.  /  Cajal)      .....  569 

139.  Lateral  surface  of  the  brain  {Dalton)         .         .         .         .  .         .         .         .         •  57° 

140.  Median  section  of  the  brain  (^Dalton)        .........  570 

141.  Horizontal  section  of  the  brain  {Dalton)  .........  574 

142.  Vertical  section  of  the  brain  {Dalton)        .........  576 

143.  Diagrammatic  representation  of  the  direction  of  some  of  the  fibres  of  the  cerebrum 

{Le  Bon) 581 

144.  Motor  cortical  zone  {Exner)     ...........  583 

145.  Diagram  of  a  median  section  of  the  brain  ........  584 

146.  Diagram  of  certain  motor  cortical  areas     .........  5S4 

147.  Cerebellum  and  bulb  {l/ii'sckj'eld)     ..........  593 

148.  Section  of  a  cerebellar  lamina  perpendicular  to  its  axis  (R.  y  Cajal)          .         .  .  594 

149.  Section  of  a  cerebellar  lamina  parallel  to  its  axis  (A',  y  Cajal)  .....  595 

150.  Cell  of  Purkinje  {^Learning)        ...........  596 

151.  Anterior  view  of  the  bulb  (^Sappey)   ..........  599 

152.  Floor  of  the  fourth  ventricle  (^Hirschfeld)  ........  600 

153.  Cervical  and  thoracic  portions  of  the  sympathetic  {Sappey) 608 

154.  Lumbar  and  sacral  portions  of  the  sympathetic  {Sappey) 609 

155.  Map  showing  the  relative  distribution  of  the  sensibility  to  touch,  warmth  and  cold 

in  the  palm  of  the  left  hand  (Co/(/f<://^/(/(7r) 630 

156.  Olfactory  ganglion  and  nerves  {Hi7-sc/ifeld )       ........  632 

157.  Vertical  section  of  the  olfactory  membrane  of  an  executed  criminal — Golgi  method 

{Zimmermann  a?id  Sobviia)         ..........  633 

158.  Glosso-pharyngeal  nerve  {Sappey)     ..........  640 

159.  Papillae  of  the  tongue  {Sappey) 642 

160.  Medium-sized  circumvallate  papilla  {Sappey)    ........  643 

161.  Fungiform,  filiform,  and  hemispherical  papillae  {Sappey) 643 

162.  Transverse  section  of  a'taste-bud  from  a  rabbit  {Sobotla)  ......  645 

163.  Vertical  section  of  a  taste-bud  {Sobotla)    .........  645 

164.  Optic  tracts,  commissure  and  nerves  {Hirschfeld)     .......  647 

165.  Diagram  of  the  decussation  of  fibres  at  the  optic  commissure 648 

166.  Choroid  coat  of  the  eye  {Sappey)       .         .         .         .         .         .         .         .         .         '651 

167.  Ciliary  muscle  {Sappey)     ............  653 

168.  Diagram  of  the  retina  {Kallius')        ..........  658 

169.  Bloodvessels  of  the  retina  {Loring)  ..........  660 

170.  Crystalline  lens,  anterior  view  {Babiichin)          .         .         .         .         .         .         .  .661 

171.  Section  of  the  crystalline  lens  {Babuchin)  .         .  .         .         .         .         .         .661 

172.  Zone  of  Zinn  {Sappey) 663 

173.  Diagrammatic  section  of  the  eye        ..........  665 

174.  Refraction  by  convex  lenses       .         .          .  .         .         .         .         .         .         .         .671 

175.  Achromatic  lens  .............  674 

176.  Section  of  the  lens  etc.,  showing  the  mechanism  of  accommodation  {Pick)        .         .  688 

177.  Field  of  vision  of  the  right  eye,  as  projected  by  the  patient  on  the  inner  surface  of 

a  hemisphere,  the  pole  of  which  forms  the  object  of  regard  —  semidiagrammatic 

{Landolt) .  690 

178.  Binocular  field  of  vision  {B'orsler)     ..........  693 


LIST    OF   TEXT-ILLUSTRATIONS  xxv 

FIG.  PAGE 

179.  Muscles  of  the  eyeball  (^Sap'pey)         ..........  699 

180.  Diagram  illustrating  the  action  of  the  muscles  of  the  eyeball  (^Fick)          .         .         .  701 

181.  Lachrymal  and  Meibomian  glands  (Sa/>J>ey)       ........  708 

182.  Lachrymal  canals,  lachrymal  sac  and  nasal  canal,  opened  by  their  anterior  portion 

(Sappey) 709 

183.  The  pinna  (Sappey)  .............  713 

184.  Posterior  view  of  a  mold  in  wax  of  the  cavity  of  the  concha  and  the  external  audi- 

tory meatus  (Sappey)   .         .         .         .         .         .  .  .  .  .  .  .714 

185.  General  view  of  the  organ  of  hearing  {Sappey)          .......  716 

186.  Ossicles  of  the  tympanum  {jiiodified from  Ri'idinger)  .         .         .         .         .         -1^1 

187.  The  right  temporal  bone,  the  petrosal  portion  removed,  showing  the  ossicles  seen 

from  within.     From  a  photograph  {Kildingej')     .         .         .         .  .  .  .718 

188.  The  left  bony  labyrinth  of  a  new-born  child,  forward  and  outward  view.     From  a 

photograph  {Rudhiger)        ...........  720 

189.  Resonators  of  Helmholtz  ............  729 

190.  Right   membrana   tympani,   seen   from  within.      From  a  photograph   and  slightly 

reduced  {Riidinger)    ............  735 

191.  Diagram  of  the  labyrinth.     From  a  photograph  and  slightly  reduced  {Riidinger)     .  743 

192.  Otoliths  from  various  animals  {Niidinger)           ........  744 

193.  Section  of  the  first  turn  of  the  spinal  canal  of  a  cat  newly  born.     Section  of  the 

cochlea  of  a  human  foetus  at  the  fourth  month.     From  a  photograph  and  slightly 

reduced  {Nildivger)     ............  745 

194.  Distribution  of  the  cochlear  nerve  in  the  spiral  lamina.     The  cochlea  is  from  the 

right  side  and  is  seen  from  its  antero-inferior  part  {Sappey)          ....  747 

195.  The  two  pillars  of  the  organ  of  Corti  {Sappey)          .......  748 

196.  Vertical  section  of  the  organ  of  Corti  of  the  dog  (  Waldeyer)   .....  749 

197.  Uterus,  Fallopian  tubes  and  ovaries,  posterior  view  {Sappey)     .....  755 

198.  Ovum  of  the  cat,  within  the  ovary  (  fVi/son)     ........  758 

199.  Virgin  uterus;    anterior  view;    median  longitudinal  section;    transverse  longitudinal 

section  {Sappey)  .............  760 

200.  Muscular  fibres  of  the  uterus  {Sappey)       .         .         .         .         .         .         .         .         .761 

201.  Superficial  fibres  of  the  anterior  surface  of  the  uterus  {Liegeois)        ....  762 

202.  Inner  layer  of  the  muscular  fibres  of  the  uterus  {Liegeois)          .....  763 

203.  Uterine  and  utero-ovarian  veins  {Sappey)           ........  764 

204.  Fallopian  tube  (  Williams,  after  Sappey)  .........  764 

205.  External  erectile  organs  of  the  female  {Liegeois)       .......  765 

206.  Deutoplasra-forming  ovum  from  a  Graafian  follicle  of  a  woman  twenty-seven  years 

old  {Nagel)           .............  767 

207.  Ovum  from  a  Graafian  follicle  of  a  woman  thirty  years  old  {Nagel)  ....  768 

208.  Primordial  ovum,  with  two  germinal  vesicles  and   follicular  epithelium;    from  the 

ovary  of  a  new-born  child  {Nagel)       .........  769 

209.  Portion  of  an  ovary,  showing  a  corpus  luteum  of  pregnancy  (  IVillianis)  .         .         .  775 

210.  Lobes  of  the  testicle  and  epididymis  {Sappey) 777 

211.  Interstitial  gland  of  the  testicle  (.5o?««  rt«</^«ri?/) 779 

212.  Vesiculae  seminales,  vasa  deferentia  and  ejaculatory  ducts  {Sappey)  ....  780 

213.  Spermatozoids,  spermatic  crystals  and  leucocytes  {Peye?-)  ......  784 

214.  Y{Mmz.ns-^ermz.\.ozo\d%  {Retziits  and  /ensefi)      ........  784 

215.  Diagram  showing  stages  of  spermatogenesis  as  seen  in  different  sectors  of  a  seminif- 

erous tubule  of  a  rat  {McMiirrich,  after  Leuhossek)     ......  785 

216.  Germ-nuclei  of  the  thread-worm  —  ascaris  megalocephala  (i5(7Z'f;'?)  .         .         .         .  790 

217.  Karyokinesis  {Roveri)        .         .         .         .         .         .         .         .         .         .         .         .  791 

218.  Cell-division  ( Wilson) 792 


xxvi  LIST   OF   TEXT-ILLUSTRATIONS 

FIG.  PAGE 

219.  Formation  of  the  blastodermic  vesicle  (j.ian  Benedeii)      '  .         .         .         .         .         .  796 

220.  Four  stages  in  segmentation  of  the  ovum  of  a  mouse  (^Soholta) .....  797 

221.  Later  stages  of  segmentation  of  the  ovum  of  a  bat  {van  Beneden)    ....  798 

222.  Embryonic  shield  of  a  rabbit,  showing  the  primitive  streak  and  the  medullary  groove 

above  (^Kollmann)       ............  800 

223.  Transverse  section  of  the  embryonic  area  of  a  dog's  ovum  of  about  fifteen  days 

{Bonnet) 801 

224.  Five  diagrammatic   representations  of  the  formation    of  membranes  in  mammalia 

{Kolliker) 803 

225.  Embryo  of  twenty  to  twenty-five  days  i^Coste)    ........  807 

226.  Human  embryo  of  the  fourth  to  the  fifth  week  —  prepared  by  Dr.  G.  R.  Corson,  of 

Savannah,  Ga.  {Gage).         ...........  808 

227.  Seventeen  days'  gravid  uterus  —  from  the  Anatomical  Museum  of  Johns  Hopkins 

University  —  embryo  drawn  relatively  too  large  {Williams)         ....  812 

228.  Early  stage  of  development  of  the  chick  (^^/'t?//?  aMdfj9rMc-yJf) 817 

229.  Transverse  section  near  the  head  {^Seboth  and  BrUcke)       ......  817 

230.  Later  stage  of  development  of  the  chick  (5^/;o/'/i  rt«t/ i5rMf/&^) 818 

231.  The  first  six  cervical  vertebrae  of  the  embryo  of  a  rabbit  {Ro/nii)      ....  819 

232.  Human  embryo  about  one  month  old,  showing  the  large  size  of  the  head  and  upper 

parts  of  the  body,  the  twisted  form  of  the  spinal  column,  the  rudimentary  condi- 
tion of  the  upper  and  lower  extremities  and  the  rudimentary  tail  at  the  end  of 

the  spinal  column  {Dalton).         ..........  820 

233.  Development  of  the  nervous  system  of  the  chick  (  Wagner)      .....  823 

234.  Development  of  the  spinal  cord  and  brain  of  the  human  subject  (^Tiedemann)          .  824 

235.  Foetal  pig,  showing  a  loop  of  intestine  forming  an  umbilical  hernia  {Dalton)    .         .  827 

236.  Formation  of  the  bronchial  ramifications  and  of  the  pulmonary  cells  (^Rathke  and 

J.  Miiller) 829 

237.  Mouth  of  a  human  embryo  of  twenty-five  to  twenty-eight  days  (Coj/^)      .         .         .  83a 

238.  Mouth  of  a  human  embryo  of  thirty-five  days  {Caste)        ......  831 

239.  Mouth  of  a  human  embryo  of  forty  days  {Coste)        .......  831 

240.  Temporary  and  permanent  teeth  {Sappey)          ........  834 

241.  Foetal  pig  f  of  an  inch  (16  millimeters)  long  {Dalton)     ......  836 

242.  Diagrammatic  representation  of  the  genito-urinary  system  {Henle)  ....  838 

243.  Area  vasculosa  of  a  rabbit  of  ten  days  {yati  Beneden  and  Julin)       ....  840 

244.  Area  vasculosa  of  a  rabbit  of  eleven  days  {van  Beneden  and  Julin)         .         .         .  841 

245.  Arterial  arches  in  man  and  mammals  {modified from  Rathke)    .....  844 

246.  Diagram  of  the  foetal  circulation  (^Kallmann)  ........  847 

247.  Cholesterin  extracted  from  meconium         .........  855 


PART  I 

INTRODUCTION  —  THE  BLOOD  —  CIRCULATION 
—  RESPIRATION— ALIMENTATION  — DIGES- 
TION—ABSORPTION— SECRETION  AND  EX- 
CRETION —  METABOLISM  —  NUTRITION  — 
ANIMAL    HEAT 


INTRODUCTION 


The  ameba  proteus  —  Protoplasm  —  The  typical  animal  cell  —  Karyokinesis  (Mitosis)  — 
Prophases  —  Metaphase  —  Anaphase  —  Telophases  —  Amitosis  —  Ehrlich's  side-chain 
hypothesis  —  Immunity  —  Receptors  —  Passive  and  active  immunity  —  C)i;olysis  —  Alexins 
(Complements) — Amboceptors  (Immune  bodies)  — Antibodies — Precipitins — Agglutins. 

The  Ameba  Pivteiis.  —  It  seems  natural  and  logical,  as  an  introduc- 
tion to  human  physiology,  to  begin  with  the  ameba  proteus.  This  is 
the  simplest  form  of  distinct  and  independent  animal  existence,  and  it 
closely  resembles  the  typical  animal  cell.     This  rhizopod  is  practically 

r      '     -) 


'  '.^y-^ii-^f^,-/'' 


V^ 


-A 


Fig.  I. — Ameba  pro  feus,  X  280  (Sedgwick  and  Wilson). 

n,  nucleus  ;  -um,  water-vacuoles ;    cv,  contractile  vacuole  ;  fv,  food-vacuole. 
Ectoplasm  and  pseudopods  are  not  shown  in  this  figure. 

a  single  cell  without  a  distinct  investing  membrane.  It  is  capable  of 
appropriating  nutrient  matters  and  of  multiplication.  It  is  little  more 
than  a  mass  of  protoplasm,  a  name  derived  from  the  Greek  words 
7r/3WTo?  (first)  and  TrXdcrfxa  (form)  applied  to  the  substance  of  many  of 
the  cells  and  tissues  of  adult  animals  high  in  the  scale. 

The  ameba  is  a  mass  of  contractile  matter,  with  a  nucleus,  fine  and 
coarse  granules,  and  cavities  called  vacuoles,  some  of  which  are  con- 
tractile.      In    addition,    there    are   vacuoles   that    contain    granules   of 


2  INTRODUCTION 

nutritive  matter,  called  food-vacuoles,  and  others  called  water-vacuoles. 
The  ameba  itself  is  surrounded  with  protoplasm  (ectoplasm),  which,  by- 
alternate  extension  and  contraction  of  processes  called  pseudopods, 
enables  it  to  move  slowly  from  place  to  place.  These  creeping  move- 
ments are  observed  in  some  animal  cells  and  are  called  ameboid. 

Protoplasm.  —  The  various  substances  known  collectively  as  proto- 
plasm constitute  the  basis  of  life,  both  vegetable  and  animal.  It  is 
composed  mainly  of  carbon,  hydrogen,  oxygen  and  nitrogen ;  but  the 
composition  of  its  molecule  is  constantly  changing,  and  consequently 
it  has  no  fixed  and  definite  chemical  composition.  In  this  respect  it  is 
in  a  condition  known  as  labile.  In  studying  the  structure  and  composi- 
tion of  animal  cells,  it  will  be  seen  that  the  general  term  "  protoplasm," 
aside  from  the  so-called  proteids,  includes  many  substances  known 
under  different  names  intended  to  express,  more  or  less  accurately, 
different  properties  and  relations.  The  typical  animal  cell,  indeed,  is 
composed  of  many  of  these  substances  called  by  different  names. 

The  Typical  Animal  Cell}  —  Plgure  2  represents  diagrammatically  an 
animal  cell.  This  is  somewhat  more  complex  in  its  structure  than  the 
ameba.  Its  basis  is  a  clear  protoplasm  (hyaloplasm)  contained  in  the 
meshes  of  a  reticulum  (spongioplasm)  with  minute  granules  (micro- 
somes), the  whole  being  called  cytoplasm.  In  the  cytoplasm  are  little 
globules  (plastids)  and  usually,  also,  dark  granules  or  globules  of  vari- 
able size  (metaplasm).  The  most  important  structure  in  the  cytoplasm  is 
the  "attraction-sphere,"  containing  two  little  bodies  called  centrosomes. 
The  cell  itself  is  surrounded  with  a  delicate  membrane  composed  of 
condensed  hyaloplasm.  In  the  cell,  near  its  centre,  is  a  rounded 
nucleus  with  a  highly  refracting  nucleolus,  the  nucleus  being  sur- 
rounded with  a  membrane  and  presenting  a  very  fine  reticulum  formed 
of  "  linin  "  fibres,'^  that  are  not  seen,  however,  unless  brought  out  by 
reagents.  The  nucleus  also  contains  relatively  coarse  threads  of  chro- 
matin, a  substance  chemically  identical  with  nuclein.  The  substance 
of  the  nucleus  is  sometimes  spoken  of  as  the  linin.  A  collection  of 
chromatin  also  is  observed  in  the  nucleus,  called  the  karyosome.  The 
substance  of  the  nucleus  is  called  karyoplasm,  or  linin.     The  cell  itself 

^  The  apparent  logical  necessity  of  studying  the  cell  as  an  introduction  to  human  physiology 
is,  perhaps,  to  be  regretted  for  one  reason;  and  that  is  a  redundancy  of  nomenclature,  always 
somewhat  confusing.  Wilson,  in  his  work  on  The  Cell,  gives  a  glossary  with  two  hundred 
different  names  that  have  been  applied  to  parts  of  the  cell  and  its  processes  of  origin,  develop- 
ment and  multiplication,  only  seventeen  of  which  are  classed  as  obsolete.  I  have  striven, 
however,  to  minimize  this  difficulty  by  adopting,  so  far  as  possible,  only  names  that  are  in  com- 
mon use  and  to  be  found  in  modern  works  on  anatomy. 

2  Linin-elements  may  be  seen  in  cells  fixed  with  Flemming's  solution  and  stained  with 
picrocarmin.  Poljakoff,  "Biologie  der  Zelle,"  Archiv  fiir  mikroscopische  Anatomie,  Bonn, 
1900,  Bd.  LVI,  S.  651  et  seq. 


KARYOKINESIS 


usually  presents  one  or  more  vacuoles.  The  uses  and  properties  of 
these  various  parts  will  appear  in  the  study  of  karyokinesis  (mitosis), 
or  indirect  cell-division  ;  and  the  structures  just  described  are  observed 
in  what  is  known  as  the  "  resting  "  cell. 

All  animal  tissues,  organs  and  systems  are  composed  of  cells  derived 
originally  from  a  single  female  cell,  the  ovum,  fertilized  by  union  with 
a  male  cell,  and  are  produced  by  indirect  cell-division.  "  It  has  been 
estimated  that  the  number  of  cells  entering  into  the  composition  of 
the  body  of    an  adult  human  being  is   about   26,500,000,000,000,000" 


Attractfon-spherii  enclosing  two  centrosomes. 


Nucleus 


Plasmosome,  or 

true 

nucleolus 

Chromatin- 

network 

Linin-network 

Karyosome, 
net-knot,  or 
chromatin- 
nucleolus 


Plastids  lying  in  the 
cytoplasm 


Vacuole 


Pa5;sive  bodies  (meta- 
plasm  or  paraplasm) 
suspended  in  the  cy- 
toplasmic mesh  work 


Fig.  2.  —  Diagram  of  a   Cell  (Wilson). 

Its  basis  consists  of  a  thread-work  (mitome,  or  reticulum)  composed  of  minute  granules  (micro- 
somes) and  traversing  a  transparent  ground-substance. 

(McMurrich).  In  the  adult  the  cells  appropriate  different  substances, 
organic  and  inorganic,  become  specialized  and  are  arranged  into  differ- 
ent tissues  and  organs  possessing  varied  functions.  The  one  function 
or  property,  however,  which  all  cells  have  in  common,  is  that  of  assimi- 
lating nutritive  matters  to  supply  loss  by  the  constant  changes  charac- 
teristic of  living  structures.  The  changes  that  involve  the  breaking  down 
of  living  substance  are  known  as  katabolic.  The  process  of  repair  is 
called  anabolism. 

Karyokinesis  (Mitosis) 

Prophases.  —  Indirect  cell-division  begins  with  a  separation  of  the 
attraction-sphere  into  two,  each   one  carrying  a  centrosome,  or  polar 


INTRODUCTION 


body.  The  two  spheres  separate  from  each  other  and  send  out  radiat- 
ing filaments,  forming  a  double  star,  called  the  amphiaster.  They  are 
connected   together,    however,  by  filaments   in   the   form   of    a    spindle 


Fig.  3.  —  Diagram  showing  the  prophases  of  katyokinesis  (Wilson). 

A,  resting-cell :  c,  attraction-sphere  containing  two  centrosomes.  B,  early  prophase,  the  nucleus 
containing  a  continuous  spirem,  the  nucleolus  still  present:  a,  amphiaster.  C,  disappearance  of  the 
primary  spindle  and  passage  of  the  centrosomes  to  opposite  poles  of  the  nucleus  (the  nucleolus  has 
disappeared) .  D,  another  type  of  prophase,  in  which  the  primary  spindle  persists.  J£,  later  prophase, 
in  which  a  new  spindle  is  formed  within  the  nucleus.  F,  completion  of  the  karyokinetic  figure: 
ep,  equatorial  plane  of  chromosomes. 

(the  central  spindle),  which  lies  next  the  nucleus,  gradually  encroach- 
ing upon  it.  The  substance  of  the  amphiaster  and  the  spindle  is  called 
archoplasm.     As  the  spindle  is  formed,  the  membrane  of  the  nucleus 


ANAPHASE  5 

disappears  and  the  threads  of  chromatin  become  thicker.  Sometimes  the 
original  spindle  remains ;  but  often  it  disappears  and  is  replaced  with  a 
new  spindle  formed  within  the  nucleus.  In  many  cells  the  chromatin 
during  the  formation  of  the  amphiaster  assumes  the  form  of  a  loose  skein 
between  the  two  attraction-spheres,  called  the  spirem.  This  is  described 
^by  some  writers  as  the  spirem  stage. 

The  threads  of  chromatin  now  separate  into  a  number  of  shorter 
threads  called  chromosomes,  which  arrange  themselves  in  the  equator  of 
the  spindle,  forming  the  equatorial  plate.  This  completes  the  forma- 
tion of  what  is  known  as  the  mitosic  or  karyokinetic  figure.  The 
changes  just  described  constitute  the  prophases  of  karyokinesis.  All 
embryologists  agree  that  after  the  division  of  the  chromatic  threads  the 
number  of  resulting  chromosomes  for  each  species  of  plant  or  animal  is 
fixed  and  characteristic;  and  this  is  true  after  division  of  all  its  cells 
(Wilson).  The  number  in  man  is  thought  to  be  sixteen  ;  in  sharks  it  is 
thirty-six ;  and  in  ascaris  it  is  four  or  even  two.  Wilson  gives  a  list  of 
forty-seven  species  in  which  the  number  has  been  noted  by  various 
investigators.  It  is  a  curious  fact,  also,  that  the  number  is  always  divis- 
ible by  two.  In  fertilization,  the  number  in  the  male  and  in  the  female 
pronucleus  is  reduced  one-half  ;  so  that  the  cleavage-nucleus,  which 
results  from  the  union  of  the  two  pronuclei,  contains  the  same  number 
of  chromosomes  as  did  the  original  ovarian  nucleus. 

Metaphase.  —  The  prophases  just  described  are  preparatory  to  the 
processes  resulting  in  cell-division,  which  begin  with  a  splitting  of  each 
chromosome  lengthwise  into  two.  This  is  called  metakinesis,  or  the 
metaphase. 

Anaphase. —  The  arrangement  of  the  chromosomes  in  the  equatorial 
plane  of  the  spindle  is  different  in  different  species  of  animals.  In 
many  instances  they  take  the  form  of  the  letter  V  and  are  arranged  in 
a  cluster  with  their  angles  directed  inward,  so  that  the  group  forms 
a  sort  of  star.  With  this  arrangement,  the  cell  is  in  what  is  called 
the  monaster  stage,  and  this  stage  often  comes  before  the  splitting  of 
the  threads.  Following  this,  the  chromosomes  pass  one-half  each,  to  the 
attraction-spheres,  around  which  they  are  grouped  preparatory  to  the 
formation  of  the  daughter-nuclei.  This  is  called  by  some  the  diaster 
stage.  In  this  stage,  filaments  pass  between  the  two  masses  of  chromo- 
somes (interzonal  fibres)  and  form  the  central  spindle.  The  grouping 
of  the  chromosomes  around  the  two  attraction-spheres  marks  the  ana- 
phase. It  is  probable  that  in  most  cells  the  fibres  of  the  central  spindle 
are  of  new  origin  and  are  not  derived  from  the  spindle  of  the  amphi- 
aster. Lying  in  the  equatorial  plane  of  the  central  spindle  is  a  group 
of  granules,  constituting  the  mid-body. 


INTRODUCTION 


Some  writers  describe  what  is  called  the  dispirem  stage,  in  which  the 
daughter-chromosomes  unite  into  a  single  thread  in  the  form  of  a  loose 
skein  around  each  attraction-sphere.  In  any  event,  after  the  for- 
mation of  the  diaster,  all  begin  to  divide,  entering  on  what  are  called 
telophases. 

Telophases.  —  The  changes  that  follow  the  dispirem  stage  are  simple, 
and  constitute  the  final  processes  of  karyokinesis  (telophases).     Each 


Fig.  4.  —  Diagram  of  the  later  phases  0/ haryokiiiesis  (Wilson). 

G,  metaphase  :  ^/,  splitting  of  the  chromosomes;  ;/,  the  cast-off  nucleolus,  //.anaphase:  ^/;  inter- 
zonal fibres,  or  central  spindle,  between  the  diverging  daughter-chromosomes.  /,  telophase,  showing 
beginning  division  of  the  cell-body,  and  the  mid-body  in  the  equatorial  plane  of  the  spindle.  /,  division 
completed. 

collection  of  chromosomes  becomes  surrounded  with  cytoplasm  and  finally 
with  a  membrane ;  and  thus  two  daughter-nuclei  are  formed  by  division 
of  the  original  nucleus  of  the  parent-cell.  The  chromosomes  now  con- 
stitute the  chromatic  substance  of  the  daughter-nuclei,  a  highly  refracting 
nucleolus  is  developed  and  a  new  attraction-sphere  with  two  centrosomes 
makes  its  appearance  in  the  cytoplasm.     The  parent-cell  has  become 


TELOPHASES 


B 


'\ 


C 


I. 


/ 


:.'lf 


'<,'■  ^^-fr* 


.L> 


Fig.  5. —  Six  phases  of  karyokinesis  of  the  egg  of  the  sea-ia-chin   (Wilson). 


8 


INTRODUCTION 


completely  divided ;  and  the  daughter-cells  are  themselves  capable  of 
karyokinetic  division,  and  so  on  until  the  cells  thus  produced  lose  this 
power  and  die  of  old  age. 

It  is  possible  for  a  single  observer  to  watch  the  process  of  karyo- 
kinesis  through  all  its  phases,  which  is  found  to  occupy  half  an  hour  to 
three  hours ;  but  the  different  stages  are  more  easily  studied  in  hard- 
ened and  stained  preparations. 

Figure  5  is  a  reproduction,  reduced  one-half,  of  plates  selected  from 
the  superb  Atlas  of  the  Fertilization  and  Karyokinesis  of  the  Ovum,  by 
Professor  Edmund  B.  Wilson,  of  Columbia  University.  These  are  faith- 
ful reproductions  of  photographs  of  the  actual  processes  in  the  naked 
egg  of  the  sea-urchin  {Toxopnenstes  variegatiis\  all  magnified  in  the 
original  looo  diameters  except  C,  which  is  magnified  3000  diameters. 

A,  X  500,  is  the  ovarian  ^gg,  before  maturation,  with  the  germinal 
vesicle  (nucleus)  and  the  germinal  spot  (nucleolus);  B,  x  500,  shows 
the  formation  of  the  asters  and  the  origin  of  the  spindle  (one  of  the  late 
prophases);  C,  x  1500,  shows  the  splitting  and  separation  of  the 
chromosomes  (metaphase) ;  D,  x  500,  shows  the  beginning  divergence 
of  the  daughter-chromosomes  (early  anaphase) ;  E,  x  500,  shows  com- 
plete divergence  of  the  daughter-chromosomes  (final  anaphase)  ;  F,  x  500, 

shows  division  of  the  0.^,^  nearly 
completed  and  re-formation  of  the 
daughter-nuclei  (telophase). 

Amitosis.  —  Exceptionally, 
certain  cells  undergo  direct,  or 
amitotic  division,  there  being  no 
formation  of  chromosomes,  spi- 
rems  or  spindles,  and  the  centro- 
somes  taking  no  part  in  the 
process.  In  amitosis  the  nuclei 
enlarge  and  there  is  a  consider- 
able increase  in  its  chromatin. 
The  nuclei  then  become  con- 
stricted and  finally  divide  into 
two,  the  cell  itself  afterward  fol- 
lowing this  division. 

The  physiological  significance 
of  amiosis  is  obscure ;  and  the 
process  has  been  the  subject  of  much  study  and  speculation.  The  chief 
point  of  interest,  concerning  which  there  is  considerable  doubt,  is  the  re- 
lation of  the  centrosome  and  the  attraction-sphere  to  this  process  ;  but  it 
is  the  opinion  of  most  embryologists  that  the  nucleus  alone  is  involved, 


Fig.  6. 


-Groups  of  cells  with  amitotically  dividing 
nuclei  (Wilson,  after  Wheeler). 


IMMUNITY  9 

the  centrosome  being  inactive,  except,  perhaps,  in  amitosis  of  spermatids 
and  some  leucocytes.  At  present  the  most  reasonable  view  of  amitosis 
is  that  cells  dividing  in  this  way  are  in  process  of  degeneration  and  are 
approaching  the  end  of  division  of  any  kind. 

Ehrlich's  Side-chain  Hypothesis 

This  hypothesis  is  supposed  by  some  physiologists  to  account  for  the 
processes  involved  in  the  nutrition  and  multiplication  of  animal  cells. 
It  may  be  diagrammatically  illustrated  by  supposing  that  the  cell  sends 
out  from  its  surface  little  prominences  in  the  form  of  a  side  chain. 
These  hypothetical  prominences  are    called  receptors,  although    their 

Prote/'of 


Molecule 


Fig.  7.  —  Animal  cell  with  three  receptors,  one  each  for  carbohydrates,  proteids  and  fats. 

form  has  been  inferred  rather  than  seen.  The  different  receptors 
have  affinities  for  special  nutrient  matters ;  for  example,  there  are  cer- 
tain receptors  that  have  an  affinity  for  proteid  molecules,  others  for 
carbohydrates,  and  others  for  fats.  When  the  affinity  of  a  special 
receptor  is  satisfied  by  the  appropriation  of  the  special  molecule  with 
which  it  is  combined,  a  new  receptor  is  sent  out,  with  the  same  affinity, 
and  so  on  until  the  nutritive  requirements  of  the  cell  are  satisfied.  The 
same  process  goes  on  between  the  carbohydrate  molecules  and  the 
fat  molecules  and  their  appropriate  receptors  ;  and  thus  the  cell  is 
nourished. 

Immunity 

The  side-chain   hypothesis    leads  naturally  to    a  theory  of  the  de- 
struction of  cells  by  the  action  of  toxins ;    and    this,  to    a    theory  of 


lO  INTRODUCTION 

immunity.     A  toxic    molecule  may  be  assimilated    through    a    special 

receptor,  either  damaging  or  destroying    the    cell ;    but  if  there  exist 

no    receptors   that    have    an    affinity    for    a    certain  toxin,  the    cell  is 

immune  to  that  special  toxic  molecule.     A  toxic  molecule  is  supposed 

to  have  two  groups  of  affinities  :   i.  a  toxophorous  group,  which  does 

damage  to   the  cell ;    2.    a   haptophorous,  or   combining   group,  which 

had  an  affinity  for  its  special  receptor.     Figure  8  represents  diagram- 

matically    a    toxic    molecule.      The    shaded 

_         ,  portion  is  the  toxophorous  group,  and  the 

ToxophoKOus    \  .  '^  &       t' 

proup  clear     portion,    the     haptophorous     group. 

These  toxic  molecules  may  unite  with  their 

special  receptors  and  be  thrown  off  by  the 

Haptophorous        cell    into    the    blood-current.      When    this 

pKOup  occurs,  the  toxins    do    not   reach  the  cell; 

but  their  affinities  are  neutralized  and  they 

become  innocuous.      If,  however,  the  toxic 

Fig.  8.  —  Diagram  of  a  toxic  molecule.  ,  ,  ,  i  i  t 

molecules  are  too  abundant  to  be  thus  dis- 
posed of,  they  may  enter  the  cell  through  the  appropriate  receptors 
and  destroy  it.  The  throwing  off  of  combined  receptors  and  toxins  in 
this  way  is  a  protective  process,  but  it  is  limited. 

Receptors.  —  When  cells  are  attacked  by  toxins,  there  is  a  great 
over-production  of  receptors,  and  many  of  them  are  thrown  off  without 
having  formed  a  union  with  toxic  molecules.  Thus,  receptors  float- 
ing in  the  blood  still  have  an  affinity  for  special  toxins,  which  they 
break  up  and  render  innocuous.  In  this  way  they  protect  the  cells, 
acting  as  antitoxins.     This  process  is  roughly  illustrated  in  Figure  9. 

Passive  and  Active  Immunity. — What  is  known  as  passive  immu- 
nity is  secured  by  introducing  into  the  body  of  an  animal  a  serum 
containing  a  protective  substance  that  acts  as  an  antitoxin.  The  anti- 
toxin consists  of  receptors  that  have  been  formed  in  excess  and  thrown 
off  into  the  blood-serum,  which  thereby  becomes  antitoxic.  These 
antitoxic  receptors  combine  with  and  neutralize  the  toxins.  Passive 
immunity  is  produced  promptly  but  soon  passes  away.  It  is  called 
passive  immunity  for  the  reason  that  the  immunizing  bodies  have  been 
produced  by  another  animal,  the  animal  thus  rendered  immune  being 
passive  and  simply  receiving  the  immunizing  receptors.  Active  immu- 
nity is  a  much  slower  process  and  is  more  lasting.  In  this  form  of 
immunity  the  animal  produces  its  own  antitoxin.  Receptors  unite  with 
toxic  molecules,  are  thrown  off  into  the  blood,  become  innocuous  and  are 
eliminated  through  the  emunctories.  In  addition,  new  receptors  (anti- 
toxins) are  produced  in  large  excess  (over-production)  and  are  thrown  off 
by  the  cells  into  the  blood.     They  thus  exist  in  the  blood,  ready  to  neu- 


ALEXINS   (COMPLEMENTS) 


II 


tralize  the  special  toxins  for  which  they  have  an  affinity.     Such  an  animal 
is  in  a  condition  of  active  immunity,  having  itself  produced  the  immu- 


cy.eeReceptoi's-that 

have. become 

Antitoxins 


/attach  edRecepto^-^ 


^  %%\rcL 


Pig.  p. —  Toxins  attached  to  receptors  ;  free  receptors   (antitoxins^  ;  antitoxins  united  with  toxins. 


Alexin 
(Complement) 

AmboceptoK- 
(immune  body) 

Receptor 


nizing  agents  ;  it  has  a  serum,  however,  that  may  be  introduced  into 
another  animal,  rendering  it  passively  immune.  Both  active  and  passive 
immunity  are  antitoxic,  as  distinguished 
from  bacteriolytic  immunity,  in  which  lat- 
ter, bacteria  are  dissolved  and  destroyed. 
Cytolysis.  —  The  serum  of  one  species 
of  animal  injected  into  the  vessels  of 
an  animal  of  different  species  may  dis- 
solve the  red  corpuscles  of  the  second 
animal.  This  is  called  laking  of  blood ; 
and  the  serum  is  then  said  to  be  lytic. 
This,  however,  is  not  true  of  the  Guinea 
pig  and  the  rabbit ;  but  the  serum  of 
the  Guinea  pig  may  be  adapted  to  the 
blood  of  the  rabbit  and  rendered  lytic 
for  such  blood.  This  is  called  hemo- 
lysis; and  the  Guinea  pig's  serum  which 
has  been  rendered  lytic  for  rabbit's  pjg  ■i,^,— Alexin  [complement)  com- 
corpuscles  is  lytic  for  these  and  for  no  ^''"^'^  "'^'^'^  ^'^^  receptor  through  the  ambo- 

■'  ceptor  {immune  body) . 

other  corpuscles. 

Alexins  {Coniplanents). — The  lytic  properties  of  the  Guinea  pig's 
serum  for  rabbit's  corpuscles  may  be  neutralized  by  exposing  it  for  half 


12 


INTRODUCTION 


an  hour  to  a  temperature  of  56°  C.  (about  133°  Fahr.) ;  but  the  lytic 
power  may  be  restored  by  adding  fresh  serum  of  the  normal  Guinea 
pig.  These  experimental  facts  are  thought  to  show  that  there  are  two 
substances  in  lytic  blood,  which  act  together  :  one  of  these  substances  is 
stable  or  active  at  56°  C,  and  the  other,  which  exists  in  normal  serum, 
becomes  inert  at  56°  C.  The  stable  substance  —  active  at  56°  C.  —  is  the 
so-called  immune  body  (amboceptor).  The  unstable  substance,  inert  at 
56°  C,  is  the  alexin.  The  immune  body  may  be  obtained  free  from 
alexin  by  the  application  of  heat.  The  alexin  may  be  obtained,  by  cer- 
tain processes,  free  from  the  immune  body.     In  cytolysis,  however,  the 


Alexin 
)(Com  pie  merit; 

inticoinplement 

,  Amboceptor 
(immune  body) 
^Receptoc     ^ 


Alexin 

((Complement) 
)  Amboceptor 
(immune  boay) 

Anti-immune  body 
Receptor 


Fig.  II.  —  Anticomplement protecting  there- 
ceptor  by  uniting  with  the  co7nplement  (alexin) . 


Fig.  12. —  Anti-immune  body  protecting  the  re- 
ceptor by  uniting  with  the  immune  body. 


two  bodies  —  alexin  (complement)  and  the  immune  body  —  must  act 
together.  It  is  assumed  that  the  alexin  cannot  combine  directly  with 
receptors,  but  that  it  can  combine  with  the  immune  body  and  through  it 
with  the  receptors. 

Immune  Bodies  {Amboceptors^.  —  The  immune  body  has  two  afifini- 
ties,  one  for  the  complement  and  one  for  the  receptor  ;  and  it  is  on 
account  of  this  property  that  it  is  called  the  amboceptor.  Figure  10  is 
a  rough  illustration  of  this  theory.  The  alexin  is  often  called  the  com- 
plement, and  the  immune  body  (amboceptor),  the  interbody. 

Antibodies.  —  Experiments  have  shown  that  in  the  body  of  an 
animal  ^in  which  serum  containing  alexins  and  amboceptors  has  been 


AGGLUTINS  1 3 

introduced,  the  cells  produce  what  are  called  antibodies,  which  secure 
immunity.  The  antibody  (anticomplement)  may  have  a  dominating 
affinity  for  the  complement,  unite  with  it  and  prevent  the  union  of  the 
complement  with  the  amboceptor ;  or  it  may  unite,  in  the  same  way, 
with  the  amboceptor  and  prevent  its  union  with  the  receptor,  when  it 
is  called  the  anti-immune  body.  In  either  event  it  protects  the  cell 
from  the  alexin. 

Figure  1 1  shows  the  antibody  (anticomplement)  united  with  the 
alexin,  preventing  a  union  of  the  alexin  with  the  amboceptor.  Figure 
12  shows  the  antibody  (anti-immune  body)  united  with  the  amboceptor, 
preventing  a  union  of  the  alexin  with  the  receptor. 

Precipitins.  —  It  is  possible  to  produce,  in  an  adapted  animal,  sub- 
stances known  as  precipitins ;  and  these  have  been  used  as  tests  for 
different  kinds  of  blood.  The  blood-serum  of  an  adapted  animal,  if 
added  to  the  blood  used  in  adaption,  produces  a  copious  precipitate, 
which  does  not  occur  with  other  mixtures. 

Agglutins. — When  the  blood  of  an  animal  is  adapted  to  the  red 
blood-corpuscles  of  an  animal  of  a  different  species  by  repeated  intra- 
peritoneal injections,  the  blood-serum  of  the  adapted  animal  becomes 
agglutinative,  not  only  for  the  blood-cells,  but  for  other  cells  as  well, 
belonging  to  the  animal  whose  blood  has  been  used  in  the  process  of 
adaption ;  but  no  agglutination  occurs  in  cells  from  other  sources.  This 
process  of  agglutination,  however,  is  not  protective. 


CHAPTER    I 

THE   BLOOD 

Importance  of  the  blood  —  Quantity  of  blood  —  Opacity  —  Taste  —  Reaction  —  Specific  grav- 
ity—  Temperature  —  Color  —  Laking  of  blood  —  Blood-corpuscles — Red  corpuscles. — 
Hemoglobin  —  Precipitin-test  for  blood  —  Development  of  red  corpuscles — Leucocytes 
—  Lymphocytes  —  Blood-platelets  —  Plasma  and  serum  —  Fibrinogen  —  Serum-globulin  — 
Serum-albumin  —  Extractives  and  salts  —  Coagulation  of  the  blood  —  Prothrombin  and 
thrombin  —  Uses  of  coagulation. 

Importance  of  the  Blood.  —  With  the  progress  of  knowledge  and  the 
accumulation  of  facts  in  physiology,  the  importance  of  the  blood  in  its 
relation  to  the  processes  of  animal  life  becomes  more  and  more  thor- 
oughly understood  and  appreciated.  The  blood  is  the  most  abundant 
and  highly  organized  of  the  liquids  of  the  body,  providing  materials  for 
the  re-formation  of  all  parts,  without  exception,  receiving  the  products 
of  their  katabolism  and  conveying  them  to  the  proper  organs  by  which 
they  are  removed  from  the  system.  These  processes  require,  on  the 
one  hand,  constant  renewal  of  nutritive  constituents,  and,  on  the  other, 
constant  purification  by  the  prompt  removal  of  effete  matters.  Those 
tissues  in  which  the  processes  of  nutrition  are  active  are  supplied  with 
blood  by  mean^  of  vessels ;  but  some,  less  highly  organized,  like  the 
epidermis,  hair,  cartilage,  etc.,  which  are  called  extravascular  because 
they  are  not  penetrated  by  vessels,  are  none  the  less  dependent  on  the 
blood,  as  they  imbibe  nutritive  matters  from  the  blood  of  adjacent 
parts. 

The  importance  of  the  blood  in  the  processes  of  animal  life  is  evi- 
dent ;  and  in  animals  in  which  nutrition  is  active,  death  is  the  immediate 
result  of  its  abstraction  in  large  quantity.  Its  importance  to  life  in  this 
regard  can  readily  be  demonstrated  by  experiments  on  the  inferior  ani- 
mals. If,  in  a  small  dog,  a  canula  is  adapted  to  a  syringe  introduced 
through  the  right  jugular  vein  into  the  right  side  of  the  heart,  and  a  great 
part  of  the  blood  is  suddenly  withdrawn,  immediate  suspension  of  all  the 
so-called  vital  processes  is  the  result ;  and  if  the  blood  is  afterward 
returned  to  the  system,  the  animal  is  as  suddenly  revived. 

Certain  conditions,  one  of  which  is  diminution  of  the  heart's  action 
after  copious  hemorrhage,  prevent  the  escape  of  all  the  blood  from  the 
body,  even  after  division  of  the  largest  arteries ;  but  after  the  arrest  of 

14 


QUANTITY   OF    BLOOD  1 5 

the  functions,  which  follows  copious  discharges  of  this  liquid,  life  may 
be  restored  by  injecting  into  the  vessels  the  same  blood  or  fresh  blood 
from  another  animal  of  the  same  species.  This  observation,  which  was 
first  made  on  the  inferior  animals,  has  been  applied  to  the  human  sub- 
ject; and  it  has  been  ascertained  that  in  patients  sinking  under  hemor- 
rhage, the  introduction  even  of  a  few  ounces  of  fresh  blood  may  restore 
the  functions  for  a  time  and  sometimes  permanently. 

Quantity  of  Blood.  — •  The  determination  of  the  entire  quantity  of 
blood  contained  in  the  body  has  long  engaged  the  attention  of  physiolo- 
gists, without,  however,  absolutely  definite  results.  This  fact  shows  the 
extent  of  the  obstacles  to  be  overcome  before  the  question  can  be 
absolutely  settled.  The  chief  difficulty  is  that  all  the  blood  is  not  dis- 
charged from  the  body,  even  after  division  of  the  great  arteries,  as 
after  decapitation,  and  no  entirely  accurate  means  have  been  devised 
for  estimating  the  quantity  that  remains  in  the  vessels.  A  process 
devised  by  Haldane  and  Lorrain  Smith  is  open,  perhaps,  to  as  few 
serious  objections  as  any.  This  method  takes  account  of  the  hemoglo- 
bin, a  constant  constituent  of  the  red  blood-corpuscles.  Hemoglobin 
combines  with  carbon  monoxide  in  definite  proportions,  which  are  about 
equal  to  the  oxygen  capacity  of  the  blood-corpuscles.  A  man  is  made  to 
breathe  a  measured  volume  of  this  gas,  and  the  percentage  saturation  is 
determined.  From  this  it  is  easy  to  calculate  the  proportion  of  carbon 
monoxide  which  would  be  required  to  saturate  the  hemoglobin  contained 
in  the  entire  mass  of  blood.  It  remains  only  to  estimate  the  quantity  of 
carbon  monoxide  absorbed,  and  then  it  is  not  difiEicult  to  calculate  the 
quantity  of  this  gas  that  would  be  required  to  saturate  the  entire  mass  of 
blood.  Such  calculations  have  resulted,  from  observations  on  fourteen 
healthy  persons,  in  the  estimate  that  the  entire  mass  of  blood  is  equal  to 
about  one-twentieth  part  of  the  weight  of  the  body,  which  is  much  less 
than  estimates  previously  made. 

Prolonged  abstinence  from  food  has  a  notable  effect  in  diminishing 
the  quantity  of  blood,  except  when  large  quantities  of  liquids  have  been 
taken  ;  and  the  reverse  is  true  after  the  ingestion  of  food  and  drink  in 
abundance.  The  quantity  of  blood,  also,  is  notably  large  in  persons  of 
plethoric  habit.  Wrisberg  reported  the  case  of  a  female  criminal  from 
whom  nearly  twenty-one  and  a  half  pounds  (9745  grams)  of  blood  flowed 
after  decapitation.  It  is  not  possible  to  form  a  definite  idea  of  the 
quantity  of  blood  during  digestion,  but  it  must  be  considerably  greater 
than  in  a  fasting  condition.  The  percentage  of  blood  that  can  be  drawn 
from  the  body  without  producing  death  varies  greatly.  A  withdrawal 
of  twenty  per  cent  usually  is  tolerated  ;  but  a  loss  of  thirty  per  cent  is 
almost  invariably  fatal. 


l6  THE    BLOOD 

Opacity.  —  The  opacity  of  the  blood  depends  on  the  fact  that  it  is 
not  a  homogeneous  Hquid,  but  is  composed  of  plasma  and  corpuscles, 
both  of  which  are  nearly  transparent  but  which  have  each  a  different 
refractive  index.  The  rays  of  light,  consequently,  can  not  pass  through 
the  liquid,  and  the  mixture  is  opaque. 

Odor.  —  The  blood  has  a  faint  but  characteristic  odor.  This  may  be 
developed  so  as  to  be  quite  distinct,  by  the  addition  of  a  few  drops  of 
sulphuric  acid,  when  the  odor  peculiar  to  the  animal  from  which  the 
blood  has  been  taken  becomes  very  marked. 

Taste.  —  The  taste  of  the  blood  is  distinctly  saline,  on  account  of  a 
number  of  salts  contained  in  the  plasma,  and  particularly  of  a  consider- 
able proportion  —  three  to  four  parts  per  thousand —  of  sodium  chloride. 

Reaction.  — -  The  reaction  of  the  blood  in  health  is  distinctly  alkaline  ; 
but  it  is  not  always  easy  to  demonstrate  this,  on  account  of  the  red  color 
of  the  corpuscles,  which  obscures  the  reaction.  If,  however,  a  drop  of 
blood  is  put  upon  glazed  reddened  litmus  paper  and  is  then  lightly 
wiped  off  with  a  soft  sponge,  a  spot  remains  that  is  of  a  distinctly  blue 
color.  The  alkaline  reaction  is  due  to  the  presence  of  sodium  carbonate 
and  sodium  phosphate  in  the  plasma. 

Specific  Gravity. — The  specific  gravity  of  defibrinated  blood  is 
between  1.055  '^'^^  1.062,  varying  considerably  with  conditions  of  the 
digestive  organs. 

Temperature.  —  The  temperature  of  the  blood  usually  is  given  as 
between  98°  and  100°  Fahr.  (36.67°  and  37.78°  C);  but  experiments 
have  shown  that  it  varies  considerably  in  different  vessels,  indepen- 
dently of  exposure  to  external  refrigerating  influences.  The  blood  is 
warmer  in  the  right  than  in  the  left  cavities  of  the  heart.  With  few 
exceptions,  it  is  warmer  in  the  arteries  than  in  the  veins.  It  is  warmer 
in  the  portal  vein  than  in  the  abdominal  aorta.  It  is  constantly  warmer 
in  the  hepatic  veins  than  in  the  portal  vein.  The  blood  is  warmest, 
indeed,  in  the  hepatic  veins,  where  it  has  a  temperature  of  ioi°  to  107° 
Fahr.  (38.33°  to  41.67°  C). 

Color.  —  The  color  of  the  blood  is  due  to  the  red  corpuscles.  In  the 
arterial  system  the  color  is  uniformly  red.  In  the  veins  it  usually  is 
dark  blue  but  sometimes  almost  black.  The  color  in  the  veins,  however, 
is  not  constant.  Many  years  ago,  John  Hunter  observed,  in  a  case  of 
syncope,  that  the  blood  obtained  by  venesection  was  bright  red.  The 
color  of  the  venous  blood  depends  on  the  condition  of  the  organ  or 
part  from  which  it  is  returned.  The  red  color  of  venous  blood  was  first 
noticed  by  Bernard  in  the  renal  veins,  where  it  contrasts  strongly  with 
the  black  blood  in  the  ascending  vena  cava.  When  the  excito-secretory 
nerve  of  the  submaxillary  gland  is  faradized,  the  blood  coming  from  the 


BLOOD-CORPUSCLES 


17 


gland  is  bright  red.     Inasmuch  as  the  red  color  of  the  blood  depends  on 

the  presence  of  oxygen  in  the  red  corpuscles,  the  loss  of  oxygen  which 

occurs  as  the  result  of  the  katabolic  processes  in  the  gland  changes  the 

blood  from  red  to  blue  ;  but  if  the  quantity  of  blood  passing  through  the 

gland  is  so  great  that  this  change  is   much   diminished,  the  red  color 

of  the  arterial  blood  remains. 

Although   oxygen   is   replaced 

by  carbon  dioxide  in  molecular 

katabolism,     the     quantity     of 

oxygen  lost  in  this  process  is 

not    sufficient   to   produce   the 

change  from  red   to  blue,   on 

account  of  the  great   activity 

in  the  local  circulation,  which 

occurs  during  secretion. 

Laking  of  Blood.  —  When 
serum  from  the  blood  of  one 
animal  is  added  to  the  blood 
of  another  animal  of  a  differ- 
ent species,  a  curious  phe- 
nomenon is  presented,  called 
the  laking  of  blood.  The  red 
corpuscles  are  broken  up  and 
the  hemoglobin  appears  in 
solution,  leaving  the  filmy  remains  —  called  the  ghosts  of  the  corpuscles 
—  to  settle  to  the  bottom  of  the  vessel.  This  is  merely  a  solution  of 
the  coloring  matter,  which  is  freed  from  the  stroma  of  the  corpuscles 
and  gives  the  peculiar  color  to  the  solution.  A  phenomenon  analogous 
to  the  laking  of  blood  was  observed  by  Rollett.  By  alternately  freezing 
and  thawing  blood,  he  succeeded  in  extracting  the  hemoglobin.  When 
afterward  warmed  and  liquefied,  the  solution  was  dark  and  transparent, 
with  the  corpuscles  entirely  decolorized. 

Blood-corpuscles 

In  1661,  Malpighi,  with  the  imperfect  lenses  at  his  command,  dis- 
covered the  blood-corpuscles  of  the  hedgehog.  Leeuwenhock  saw  the 
human  blood-corpuscles  in  1673  and  described  them  in  a  communication 
to  the  Philosophical  Society  in  1674.  William  Hewson  discovered  the 
leucocytes  about  a  century  later.  Neumann,  of  Konigsburg,  and 
Bizzozero,  of  Turin,  described  the  blood-platelets  about  1868.  Since 
that  time,  three  varieties  of  corpuscles  have  been  recognized  in  human 
blood. 

c 


Fig.  13.  —  Blood  of  Guinea  pig,  spread  and  dried  on 
glass  cover,  X  1450  (Sternberg). 

The  corpuscles  of  the  Guinea  pig  have  the  same  form 
as  human  corpuscles,  but  are  a  little  smaller,  measuring 
about  jg'jB  of  an  inch  (7  m)  in  diameter. 


l8  THE    BLOOD 

Red  Corpuscles.  —  The  red  blood-corpuscles  (erythrocytes)  constitute 
about  fifty  per  cent  of  the  entire  mass  of  blood.     (Flint,  1863.)     Their 


Fig.   14.- — Blood-corpuscles  from  certain  of  the  inferior  animals,  compared  with  corpuscles  from  the 

human  subject,  X  700. 

The  measurements  in  these  figures  are  taken  from  Gulliver  (1841),  and  for  the  elliptical  cells  the 
long  diameters  are  given.  In  the  original  article  by  Gulliver  about  five  hundred  measurements  are  given. 
I  published  one  hundred  of  these  in  the  Physiology  of  Man,  1866,  Vol.  I,  p.  113.  For  the  conven- 
ience of  readers,  the  English  measurements  have  been  reduced  to  microns. 

A.  Man,  j^'bo  inch  =  8.0  /^.  jl/.  Lizard,  is'sb  inch  =  16.3  >i. 

B.  Whale,  jn'gg  inch  =  8.2  m.  N.  Snake,  f^Vi  inch  =  20.0  t^. 

C.  Elephant,  ^-Vs  inch  =  9.2  m.  O.  Crocodile,  1531  inch  =  20.6  n. 

D.  Mouse,  :fi^5  inch  =  6.0  ^t.  P.  Toad,  jo'jrj  inch  =  24.3  m. 

E.  Horse,  jeoa  inch  =  5.5  h.  Q.  Triton,  sU  inch  =  31.2  m. 

F.  Musk-deer,  usis  inch       =    2.0  m.  K.  Proteus,  iJg  inch  =  63.5  i^.. 

G.  Camel,  ji'jj  inch  =    8.1  /n.  S.  Perch,  j^'ei  inch  =  10.3  m. 
//.  Humming-bird,  5b'e5  inch  =    9.6  fi.                                  T.  Pike,  in'on  inch  =  12.7  m. 

/.  Pheasant,  n'ls  inch  =  12.0  /^.  U.  Electric  eel,  itVs  inch  =  14.8  m. 

A'.   Pigeon,  53'fj  inch  =  ii.o  n.  V.  Shark,  1^43  inch  =  22.2  ^. 

L.  Ostrich,  isjj  inch  =  15.4  /n. 

form  is  peculiar  and  distinctive.  Many  are  circular,  and  thinner  at  the 
central  portion  than  at  the  periphery,  where  the  stroma  is  more  dense 
and  consistent. 


RED    CORPUSCLES 


19 


The  corpuscles  of  cold-blooded  animals,  birds,  and  the  camelidae  are 
oval,  and  with  the  exception  of  the  camelidae  are  nucleated.  The  cor- 
puscles of  the  camelidae  are  biconvex. 

The  color  of  the  red  corpuscles  by  transmitted  light  is  pale  and 
faintly  yellowish,  and  is  due  to  hemoglobin,  which  constitutes  about 
95.5  per  cent  of  their  substance  (see  Plate  II,  Fig.  2).  Their  specific 
gravity  is  about  1088.  In  the  blood  of  the  horse  —  which  coagulates 
slowly — the  corpuscles  readily  gravitate  to  the  bottom  of  a  vessel, 
leaving  a  clear  plasma  above. 

The  number  of  corpuscles  in  a  given  volume  may  be  easily  calcu- 
lated by  means  of  an  instrument  called  the  hemacytometer.  This  is  an 
apparatus  for  counting  the  cor- 
puscles in  a  measured  space 
filled  with  blood  properly  diluted 
and  the  corpuscles  evenly  dis- 
tributed in  the  mixture.  The 
results  of  modern  observers 
agree  remarkably  with  those  of 
Vierordt  (1852),  Walker  (1854), 
and  Malassez(i872),  the  general 
estimate  being  about  5,000,000 
corpuscles  in  a  cubic  millimeter 
(one  millimeter  =  ^.^  inch)  of 
blood.  Various  saline  solutions 
are  used  in  diluting  the  blood, 
having  a  specific  gravity  of  1020 
to  1025.  The  Thoma-Zeiss  ap- 
paratus is  the  one  most  used 
in  chemical  observations ;  and 
this  is  merely  a  convenient  modification  of  the  method  of  Vierordt 
and  Walker  and  Malassez,  which  it  is  unnecessary  to  describe  in  detail. 
The  proportion  of  corpuscles  is  greater  in  the  veins  than  in  the  arteries, 
the  blood  of  the  splenic  veins  presenting  the  highest  number.  In 
womien  the  corpuscles  number  about  4,500,000  in  a  cubic  millimeter. 
The  number  of  corpuscles  is  gradually  increased  during  fifteen  or 
twenty  days'  sojourn  in  high  altitudes.  At  an  altitude  of  about  14,500 
feet  (4392  meters)  the  number  per  cubic  millimeter  was  8,000,000 
(Viault). 

A  short  time  after  blood  has  been  drawn  from  the  vessels,  the  cor- 
puscles usually  show  a  tendency  to  arrange  themselves  in  rows  like 
rouleaux  of  coin.  This  is  due  to  the  exudation  of  a  sticky  substance 
which  causes  them  to  adhere  together  by  their   flat   surfaces.      Under 


Fig.  15.  —  Human    blood-corpuscles    in    rouleaux, 
X  840  (Stratford). 

This  figure  shows  fresh  corpuscles,  most  of  them 
arranjied  in  rows. 


20  THE   BLOOD 

the  influence  of  reagents  the  corpuscles  undergo  certain  changes  in 
form  and  appearance.  A  physiological  salt-solution  prevents  the 
arrangement  in  rouleaux  ;  and  if  a  stronger  solution  is  used,  the  corpus- 
cles shrink  and  become  irregular  in  form  and  crenated.  In  pure  water 
and  in  dilute  alkaline  solutions,  the  red  corpuscles  dissolve  slowly  and 
finally  disappear.  A  two  per  cent  solution  of  tannic  or  boric  acid 
decolorizes  the  corpuscles,  and  the  coloring  matter  appears  in  the 
form  of  small  globules.  The  stroma  of  the  corpuscles  is  gradually 
broken  up  by  the  addition  of  chloroform.  Under  the  influence  of  a 
feeble  electric  current  the  corpuscles  become  crenated  and  covered 
with  httle  granules.  The  diameter  of  the  red  corpuscles  is  fairly  uni- 
form, measuring  about  32V0  ^^  ^^  ^^^^  i7f^  ^^  ^^)-  Their  thickness  at 
the  periphery  is  about  3-2  0o"o  ^^  ^"  ^^^^  (^  '"')>  ^^^^  ^^  ^^Y  given  speci- 
men of  blood  there  are  a  few  small  immature  corpuscles,  sometimes 
called  microcytes. 

The  anatomical  structure  of  the  red  corpuscles  is  very  simple.  The 
hemoglobin  is  enclosed  in  a  delicate  transparent  and  elastic  filmy  net- 
work, or  stroma,  which  appears  as  the  "  ghosts  "  of  the  corpuscles  after 
the  coloring  matter  has  been  removed,  as  in  the  laking  of  blood.  Of  the 
chemistry  of  the  red  corpuscles  as  compared  with  the  chemistry  of  the 
plasma,  there  is  little  to  be  said.  The  organic  matter  is  in  the  form  of  what 
is  known  as  a  nucleo-proteid.  The  principal  salts  are  sodium  and  potas- 
sium chlorides,  and  in  human  blood,  potassium  chloride  is  the  more 
abundant.  Cholesterin  is  always  found  associated  with  the  other 
extractives,  including  a  notable  proportion  of  lecithin. 

Hemoglobin 

The  molecule  of  hemoglobin,  at  least  in  the  blood  of  the  dog,  is 
of  very  large  size,  amounting  to  16,669  (Jaquet  and  Hufner).  The 
empyrical  formula  is  C758Hi203Ni95S;jFeO2i8.  There  may  be  obtained 
from  the  blood  a  considerable  number  of  so-called  derivatives  of  hemo- 
globin. The  most  important  of  these  is  hematin,  the  detection  of  which 
is  regarded  as  one  of  the  most  reliable  tests  for  blood.  If  the  dried 
blood  from  a  suspected  stain  is  boiled  with  a  few  drops  of  glacial 
acetic  acid,  on  cooling,  hemin  crystals  will  appear,  formed  by  the  split- 
ting of  hemoglobin  into  hemin,  or  hemochromogen,  and  globin.  The 
formula  for  hematin  hydrochlorate  (hemin)  is  C.35H;,5N4FeC104  (Morner). 
Other  derivatives  are  hematoporphyrin  (an  iron-free  hematin),  hematoidin, 
which  closely  resembles  bilirubin,  and  compounds  of  hemoglobin  with 
oxygen,  carbon  monoxide  and  nitrous  oxide.  It  is  in  the  form  of  oxy- 
hemoglobin that  oxygen  is  carried  by  the  blood  to  the  tissues.     These 


DEVELOPMENT    OF    THE    RED    CORPUSCLES  21 

various  derivatives  of  hemoglobin  may  be  recognized  by  their  absorption- 
bands  in  the  spectrum.  Methemoglobin,  formed  by  adding  potassium 
ferricyanide  or  amyl  nitrite  to  the  blood,  contains  the  same  proportion 
of  oxygen  as  oxyhemoglobin,  but  in  a  different  form  of  combination 
(see  Plate  II,  Fig.  2). 

Precipitin-Test  for  Blood.  —  A  test  for  blood,  which  surpasses  in 
delicacy  any  known  test  for  any  known  substance,  depends  on  the 
property  of  blood-serum,  adapted  to  a  certain  species  of  animal,  of 
forming  a  precipitate  when  mixed  with  the  blood  of  the  adapted  ani- 
mal. This,  it  is  said,  will  detect  the  presence  of  blood  of  a  given 
species  of  animal  in  the  proportion  of  one  part  in  fifty  thousand.  The 
following  illustrates  the  operation  of  this  test :  Repeated  daily  injec- 
tions of  human  blood-serum  are  made  into  the  peritoneal  cavity  of  a 
rabbit  for  seven  or  eight  days.  In  this  way  the  blood  of  the  rabbit 
becomes  adapted  to  the  human  blood.  A  little  blood-serum  of  the 
rabbit  is  now  to  be  mixed  with  a  small  quantity  of  a  salt-solution  of 
the  suspected  blood.  If  the  specimen  is  from  the  human  subject  or 
one  of  the  primates,  the  mixture  will  present  an  abundant  precipitate. 
If  there  should  be  no  precipitate,  it  is  certain  that  the  specimen  does 
not  contain  human  blood. 


Development  of  the  Red  Corpuscles 

In  the  circular  area  that  surrounds  the  embryo  in  the  earliest  stages 
of  development,  called  the  area  vasculosa,  bodies  make  their  appear- 
ance that  afterward  take  on  the  characters  of  the  red  blood-corpuscles. 
In  the  process  of  formation  of  this  area,  nucleated  mesoblastic  cells 
branch  out  in  various  directions  to  form  a  sort  of  network,  which  is 
afterward  changed  into  a  connected  system  of  vessels.  Nucleated 
bodies  then  collect  in  certain  parts  of  this  network,  which  become  sur- 
rounded with  protoplasm  and  afterward  are  colored  with  hemoglobin. 
At  first  there  are  no  regular  movements  in  the  area  vasculosa ;  but  a 
rudimentary  heart  is  soon  formed  by  a  twisting  of  the  great  central 
vessel  upon  itself,  and  the  currents  of  the  circulation  become  estab- 
lished. During  this  time  the  blood-cells  are  capable  of  ameboid  move- 
ments and  undergo  multiplication  by  karyokinesis.  They  are  at  first 
white  and  nucleated,  but  soon  become  colored,  the  nuclei  remaining. 
These  first-formed  embryonic  corpuscles  (erythroblasts)  measure  2  5V0" 
to  ^5^0"  of  an  inch  (10  /x  to  16  /u.)  in  diameter. 

As  the  liver,  spleen,  thymus  and  lymphatic  glands  are  developed, 
they  assume  the  function  of  producing  red  blood-corpuscles,  which  also 
multiply  by  karyokinesis  in  the  substance  of  these  organs.    In  the  foetus 


22  THE    BLOOD 

the  marrow  of  all  the  bones  is  red  ;  but  in  the  adult,  red  marrow  exists 
in  the  cancellated  structure  of  the  fiat  bones  only.  It  has  been  shown 
that  the  red  marrow  is  the  most  efficient  agent  in  the  formation  of  cor- 
puscles. In  the  adult  the  corpuscles  are  developed  largely  in  the 
marrow  of  the  ribs.  In  this  situation,  large  pale  cells  make  their 
appearance,  which  soon  become  partly  colored  with  hemoglobin.  The 
protoplasm,  thus  colored,  afterward  separates  into  smaller  bodies,  cup- 
shaped  at  first,  which  eventually  take  on  the  characters  of  the  red 
corpuscles.  Mingled  with  these  —  which  may  be  called  mature  cor- 
puscles—  are  smaller  bodies,  containing  hemoglobin,  that  are  capable 
of  ameboid  movements.  It  is  probable  that  red  corpuscles  are  produced 
from  similar  cells  developed  in  the  liver,  spleen,  thymus  and  lymphatic 
glands,  at  least  in  adult  animals  (see  Plate  I,  showing  cells  in  bone- 
marrow). 

Leucocytes  and  Lymphocytes 

In  addition  to  the  red  blood-corpuscles,  at  least  five  varieties  of  white 
corpuscles  have  been  studied  and  described  in  the  human  blood.  The 
proportion  of  these  corpuscles  to  the  red  varies  in  different  persons  and 
at  different  times  of  the  day.  It  is  usually  as  one  to  five  hundred, 
or  about  ten  thousand  in  a  cubic  millimeter.  These  bodies,  which  were 
first  described  by  Hensen,  are  white,  globular  and  nucleated. 

Leucocytes.  —  The  first  variety  of  leucocytes  constitutes  about 
seventy-two  per  cent  of  the  total  number.  These  are  described  under 
the  name  of  large  polynuclear  neutrophiles.  They  often  contain  two  or 
more  nuclei,  and  their  cytoplasm  presents  granules  that  have  an  affinity 
for  neutral  aniline  dyes  —  hence  their  name.  They  probably  are  pro- 
duced largely  in  the  red  marrow  of  bones.  They  are  capable  of 
ameboid  movements  and  of  incorporating  in  their  substance  and  de- 
stroying foreign  particles.  For  this  reason,  as  well  as  on  account 
of  their  great  number  in  the  blood,  they  are  regarded  as  more 
important  than  other  bodies  of  a  similar  nature.  It  is  thought  pos- 
sible that  these  leucocytes  are  capable  of  protecting  the  organism 
against  pathogenic  bacteria,  acting  as  phagocytes.  They  are  consid- 
erably larger  than  the  red  corpuscles,  measuring  about  25V0  ^^  ^^  \x\q}cs. 
(10  /x)  in  diameter. 

The  second  variety  is  known  as  large  mononuclear  leucocytes. 
These  also  are  larger  than  the  red  blood-corpuscles.  They  may  be 
polynuclear  leucocytes  in  a  transitional  condition,  the  nucleus  finally 
assuming  the  forms  noted  in  the  first  variety.  The  protoplasm  sur- 
rounding the  single  nucleus  in  these  bodies  is  clear,  and  this  variety 
has  received  the  name  of  myelocytes.     They  probably  are  developed 


BLOOD-PLATELETS  23 

in  the  cancellated  structure  of  the  bones.  They  constitute  about  three 
per  cent  of  the  total  number  of  leucocytes. 

The  third  variety  is  called  eosinophiles,  on  account  of  their  affinity 
for  acid  dyes,  which  strongly  color  the  large  granules  contained  in 
their  protoplasm.  They  also  probably  are  derived  from  the  red  marrow 
of  the  bones.  They  constitute  one  or  two  per  cent  of  the  total  number 
of  leucocytes. 

In  addition  to  the  three  varieties  of  leucocytes  just  described,  a 
fourth  variety,  called  basophihc,  is  sometimes  observed.  These  have 
an  affinity  for  basic  aniline  dyes. 

These  four  varieties  of  leucocytes  —  probably  by  virtue  of  their 
ameboid  movements  - —  when  they  lie  for  a  considerable  time  in  contact 
with  the  walls  of  the  bloodvessels  are  capable  of  passing  through 
without  solution,  of  continuity  in  the  vessels  themselves.  They  thus 
frequently  pass  out  into  inflammatory  foci.  They  creep  about  in  the 
tissues  and  are  then  called  migratory  or  wandering  cells. 

Lyviphocytes.  —  The  fifth  variety  is  known  under  the  name  of 
lymphocytes.  They  exist  in  the  form  of  a  rather  small  rounded 
nucleus  surrounded  with  clear  cytoplasm.  They  constitute  about 
twenty-three  per  cent  of  the  total  number  of  white  corpuscles. 

The   live  varieties  of  white  corpuscles  are  produced   chiefly  in  the 

red   marrow,   but    they   also   appear  de  novo  in   the  substance   of    the 

lymphadenoid  tissues,   the   spleen,  thymus   and  the  lymphatic   glands. 

Treated  with  water  or  acetic  acid,  they  swell  and  their  nuclei  become 

more   prominent.       They   are    dissolved    in    dilute    alkalis.       Although 

they  undoubtedly  are  developed  in  the  red  marrow,  the  spleen,  thymus 

and   lymphatic  glands  —  situations   in    which  the    red   corpuscles    first 

make  their  appearance  —  the  idea  that  they  are  finally  developed  into 

red  corpuscles,  which  at   one   time  obtained,  has  been   abandoned  (see 

Plate  I). 

Blood-platelets 

In  addition  to  the  leucocytes,  Httle  homogeneous,  ovoid,  grayish,  flat- 
tened bodies  ly^oo  to  10^00  ^^  ^^  ^"^^  ^^-5  ^^  ^-5  *")  i^  diameter, 
have  been  observed  and  described  under  the  name  of  blood-platelets 
(Bizzozero).  These  bodies  exist  in  the  blood  in  the  proportion  of  one 
to  about  fifteen  to  twenty  red  disks,  or  180,000  to  600,000  in  a  cubic 
millimeter.  Their  origin  is  somewhat  obscure,  but  it  is  thought  that 
their  chief  source  is  from  the  red  corpuscles,  which  extrude  a  globular 
matter  having  reactions  like  the  nucleo-proteids.  Their  function  is 
equally  obscure ;  but  it  is  probable  that  they  are  concerned  in  some 
way  in  the  production  of  prothrombin  and  are  instrumental  in  bringing 
about  coagulation  of  the  blood  (see  Plate  II,  Fig.  i). 


24 


THE    BLOOD 


In  addition  to  the  structures  in  the  blood  already  described,  the 
plasma  often  contains  minute  fatty  granules,  especially  during  diges- 
tion, such  as  are  found  in  large  quantity  in  chyle  and  in  smaller  quan- 
tity in  lymph.  The  lymph,  like  the  blood,  is  composed  of  plasma  and 
corpuscles,  the  latter  being  chiefly  in  the  form  of  lymphocytes ;  and  the 
lymph  also,  like  the  blood,  is  capable  of  coagulation.  Blood-platelets, 
however,  have  not  been  observed  in  lymph. 

Plasma  and  Serum 

Before  coagulation,  the  blood  is  composed  of  a  relatively  clear 
plasma  holding  the  corpuscles  in  suspension.  After  coagulation,  the 
clot,  enclosing  the  corpuscles,  separates  and  leaves  the  serum,  which 
is  the  plasma  less  the  constituents  that  form  fibrin.  The  plasma  is 
slightly  yellowish,  alkaline  and  of  a  specific  gravity  of  1026  to  1029.  It 
contains  proteids,  extractives  (including  fats)  and  inorganic  salts.  The 
proteids  consist  of  fibrinogen,  paraglobulin  (serum-globulin)  and  serum- 
albumin  ;  and  their  proportion  is  about  eight  parts  per  thousand. 

Fibrinogen.  —  Fibrinogen  (Cio8Hjg2N3oS034)  ^^  ^  globulin ;  but 
it  is  distinguished  from  the  other  globulins  of  the  plasma  by  its  be- 
havior in  the  presence  of  certain  reagents.  It  is  precipitated  by  half- 
saturation  of  the  plasma  with  sodium  chloride  and  is  coagulated  at  a 
relatively  low  temperature,  133°  Fahr.  (56°  C).  Under  the  influence 
of  the  so-called  fibrin-ferment,  its  molecule  splits  into  fibrin,  which  is 
insoluble,  and  a  soluble  globulin.  Its  proportion  in  the  blood  is  about 
three  parts  per  thousand. 

Serum-globulin.  —  Serum -globulin  (CinHiggNaoSOgg  -|-  \  H2O)  exists  in 
the  blood  in  the  proportion  of  about  thirty-one  parts  per  thousand.  It 
coagulates  at  a  temperature  of  about  158°  Fahr.  (70°  C).  It  may  be 
separated  from  the  neutral  salts  by  dialysis.  Both  fibrinogen  and  serum- 
globulin  are  precipitated  by  magnesium  sulphate.  It  directly  or  in- 
directly nourishes  the  proteids  of  the  tissues,  perhaps  undergoing 
previously  a  change  into  serum-albumin.  It  may  be  derived  from  food, 
but  it  is  thought  by  some  to  be  a  product  of  disintegration  of  leucocytes. 

Serum-albumin.  —  Serum-albumin  (C78H122N20SO24)  is  the  most  impor- 
tant nutritive  proteid  of  the  blood.  It  is  the  only  proteid  that  is  not 
precipitated  by  magnesium  sulphate.  It  coagulates  at  a  temperature  of 
158°  Fahr.  (70°  C).  Its  proportion  in  the  blood  is  about  forty-five  parts 
per  thousand.  It  is  probable  that  it  is  not  a  simple  albumin  but  is 
composed  of  two  or  three  different  albumins.  It  is  highly  osmotic,  a 
property  that  distinguishes  it  from  ordinary  egg-albumin. 


COMPOSITION    OF    BLOOD-PLASMA 


25 


o 


Wl 

O 


}  1.475  psi'ts  per  1000. 


a        i 


TABLE    OF   COMPOSITION    OF   BLOOD-PLASMA 
Specific  gravity,  1028. 

r  Water,  779  parts  per  1000  in  the  male;    791  parts  per  1000  in  the  female. 

Sodium  chloride,  3  to  4  parts  per  1000. 

Potassium  chloride,  0.359  parts  per  looo. 

Ammonium  chloride,  proportion  not  determined. 

Potassium  sulphate,  0.2S8  parts  per  1000. 

Sodium  sulphate,  proportion  not  determined. 

Potassium  carbonate,  proportion  not  determined. 

Sodium  carbonate  (with  sodium  bicarbonate),  1.200  parts  per  looo. 

Magnesium  carbonate,  proportion  not  determined. 

Calcium  phosphate  of  the  bones,  and  neutral  phosphate,  'i 

Magnesium  phosphate,  I 

Potassium  phosphate,  !■  1.500  parts  per  looo. 

Ferric  phosphate  (probable),  | 

Basic  phosphates  and  neutral  sodium  phosphate,  J 

.  Silica,  copper,  lead  and  magnesia,  traces  occasionally. 

r  Sodium  lactate,  proportion  not  determined. 

Calcium  lactate  (probable),  proportion  not  determined. 

Sodium  oleate,        1 
-;'         "        palmitate,  I 
i         "        stearate, 
"        valerate, 
(^        "        butyrate, 

r  Olein,  I 

i   Palmitin,  | 

I   Stearin,  ) 

-!   Lecithin,  containing  nitrogen  and  called  phosphorized  fatty  matter,  0.400  parts  per  lOOO. 

I  Glucose,  0.002  parts  per  1000. 

I   Glycogen,  proportion  not  determined. 

i,  Inosit,  proportion  not  determined. 

r  Carbon  dioxide  in  solution. 
Urea,  0.177  parts  per  1000,  in  arterial  blood;   o.oSS,  in  the  blood  of  the  renal  vein. 
Sodium  urate,  proportion  not  determined. 
Potassium  urate  (probable),  proportion  not  determined. 
Calcium  urate,  • ' 

Magnesium  urate,        ' 
Ammonium  urate,        ' 
Sodium  sudorates,  etc., 
Inosates, 
Oxalates, 
Creatin, 
Creatinin, 
Leucin, 
Xanthin, 
Hypoxanthin, 
Cholesterin,  0.455  ^'^  °-75i  parts  per  1,000,  in  the  entire  blood  (Flint). 

r  Fibrinogen,  3  parts  per  1000. 

Serum-albumin,  45  parts  per  1000. 

Serum-globulin,  31  parts  per  1000. 
i.  Peptones,  4  parts  per  1000.  '< 

Coloring  matters  of  the  plasma,  proportion  and  characters  not  determined. 


26  THE    BLOOD 

Extractives  and  Salts 

Grouped  under  the  head  of  extractives,  may  be  included  various 
nitrogenous  and  non-nitrogenous  matters,  such  as  urea,  urates,  creatin, 
creatinin,  xanthin,  hypoxanthin,  the  lecithins,  fats,  waxes,  sugar  and 
cholesterin.  In  addition,  inorganic  salts  exist  in  the  proportion  of  six 
to  eight  parts  per  thousand.  The  most  abundant  of  the  inorganic  salts 
is  sodium  chloride,  the  proportion  of  which  is  sixty  to  ninety  per  cent 
of  the  total  saline  matters.  Potassium  chloride  is  found  in  much 
smaller  quantity  and  exists  chiefly  in  the  red  corpuscles.  The  other 
saline  matters  are  in  the  form  of  sulphates  and  phosphates.  Calcium 
salts  are  present  and  are  important  in  connection  with  coagulation. 
Gases  are  in  solution  or  in  a  condition  of  feeble  combination.  Of  the 
gases,  carbon  dioxide  is  important  in  retaining  certain  of  the  salts  in 
solution. 

Coagulation  of  the  Blood 

The  blood  remains  liquid  so  long  as  it  is  contained  in  the  vessels 
and  the  circulation  is  not  interrupted  ;  but  soon  after  circulation  ceases 
or  the  blood  is  drawn  from  the  body,  it  coagulates,  or  "sets"  into  a 
jelly-like  mass.  In  a  few  hours,  contraction  of  the  clot  will  have  taken 
place,  and  a  clear  straw-colored  serum  is  then  expressed.  The  serum 
contains  all  the  constituents  of  the  blood  except  the  corpuscles  and  the 
fibrin-factors,  which  together  form  the  clot.  In  the  human  subject, 
when  the  blood  is  received  into  a  moderately  deep,  smooth  vessel,  the 
phenomena  of  coagulation  present  themselves  in  the  following  order  : 

First,  a  gelatinous  pellicle  forms  on  the  surface,  which  occurs  in  one 
minute  and  forty-five  seconds  to  six  minutes ;  in  two  to  seven  minutes, 
a  gelatinous  layer  has  formed  next  the  sides  of  the  vessel ;  the  whole 
mass  of  blood  becomes  of  a  jelly-like  consistence  in  seven  to  sixteen 
minutes.  Contraction  then  begins,  and  drops  of  clear  serum  make  their 
appearance  on  the  surface  of  the  clot.  This  liquid  increases  in  quantity, 
and  in  ten  or  twelve  hours  separation  is  complete.  The  clot,  which  is 
heavier,  sinks  to  the  bottom  of  the  vessel,  unless  it  contains  bubbles  of 
gas  or  the  surface  is  very  concave.  In  most  warm-blooded  animals 
the  blood  coagulates  more  rapidly  than  in  man.  Coagulation  is  pecul- 
iarly rapid  in  the  blood  of  birds,  and  sometimes  it  takes  place  almost 
instantaneously.  Coagulation  is  more  rapid  in  arterial  than  in  venous 
blood.  In  the  former,  the  proportion  of  fibrin  formed  is  notably  greater 
and  the  characters  of  the  fibrin  are  somewhat  different.  A  solution  of 
sodium  chloride  dissolves  the  fibrin  of  venous  blood  but  does  not  dis- 
solve the  fibrin  of  an  arterial  clot. 


COAGULATION    OF   THE    BLOOD 


27 


The  relative  proportions  of  serum  and  clot  are  variable,  unless  that 
portion  of  the  serum  retained  between  the  meshes  of  the  coagulated 
mass  is  included  in  the  estimate.  As  the  clot  is  composed  of  corpuscles 
and  fibrin,  and  as  these  in  their  moist  state  represent,  in  general  terms, 
about  one-half  of  the  blood,  it  may  be  stated  that  after  coagulation,  the 
actual  proportions  of  clot  and  serum  are  about  equal.  Simply  taking 
the  serum  that  separates  spontaneously,  there  is  a  large  quantity,  when 
the  clot  is  densely  contracted,  and  a  smaller  quantity,  when  it  is  loose 
and  soft.     Usually  the  clot  retains  about  one-fifth  of  the  serum. 

On  removing  the  clot,  after  the  separation  of  the  serum  is  complete, 
it  presents  a  gelatinous  consistence,  and  is  more  or  less  firm  according 
to  the  degree  of  contraction.  As  a  general  rule,  when  coagulation  has 
been  rapid,  the  clot  is  soft  and  but  slightly  contracted.  When,  on  the 
other  hand,  coagulation  has  been  slow,  the  clot  contracts  for  a  long  time 
and  is  much  denser.  When  coagulation  is  slow,  the  clot  frequently 
presents  what  is  known  as  the  buffed  and  cupped  appearance. 

Blood  flowing  slowly  from  a  small  opening  in  a  vessel  coagulates  more 
rapidly  than  when  it  is  discharged  in  a  full  stream  from  a  large  opening. 
If  received  into  a  shallow  vessel,  it  coagulates  much  more  rapidly  than 
in  a  deep  vessel.  If  the  inner  surface  of  the  vessel  is  rough,  coagula- 
tion is  more  rapid  than  when  it  is  smooth  and  polished.  If  the  blood  as 
it  flows  is  received  on  a  cloth  or  a  bundle  of  twigs,  it  coagulates  almost 
instantaneously.  In  short,  it  appears  that  conditions  that  favor  evapora- 
tion from  the  blood  hasten  its  coagulation. 

Coagulation  of  the  blood  is  prevented  by  rapid  freezing,  but  it  occurs 
afterward  if  the  blood  is  carefully  thawed.  Between  32°  and  140°  Fahr. 
(0°  and  60°  C),  elevation  of  temperature  increases  the  rapidity  of 
coagulation. 

Various  chemical  substances  retard  or  prevent  coagulation.  Among 
these  may  be  mentioned  potassium  and  sodium  hydrate,  sodium  carbo- 
nate, ammonium  carbonate,  potassium  carbonate,  ammonia,  and  sodium 
sulphate.  In  the  menstrual  flow  the  blood  remains  liquid  on  account  of 
mixture  with  the  abundant  secretions  of  the  vagina. 

The  blood  coagulates  in  the  vessels  after  death,  though  less  rapidly 
than  when  drawn  from  the  body.  It  occurs  in  twelve  to  twenty-four 
hours  after  circulation  has  ceased,  and  the  blood  then  is  found  chiefly  in 
the  venous  system.  The  existence  of  projections  into  the  calibre  of 
vessels  or  the  passage  of  a  fine  thread  through  an  artery  or  vein  will 
determine  the  formation  of  a  small  coagulum  on  the  foreign  substance, 
while  the  circulation  is  neither  interrupted  nor  retarded.  In  the  present 
state  of  knowledge,  explanation  of  these  facts  is  difificult  if  not  impos- 
sible.    The  process,  under  these  conditions,  cannot  be  subjected  to  direct 


28  THE    BLOOD 

experiment  as  in  the  case  of  blood  coagulating  out  of  the  body.  Leech- 
drawn  blood  remains  liquid  in  the  body  of  the  animal ;  and  the  blood 
flowing  from  a  leech-bite  presents  the  same  persistent  fluidity.  This 
explains  the  well-known  fact  that  this  insignificant  wound  gives  rise  to 
considerable  hemorrhage. 

With  the  intention  to  simplify  as  much  as  possible  the  exposition  of 
the  theory  of  coagulation  and  to  remove  sources  of  confusion,  I  shall 
adopt  in  its  description  the  theory  of  Schmidt  as  modified  chiefly  by 
the  researches  of  Hammarsten  and  LiUenfeld.  In  this  theory  it  is  as- 
sumed that  a  substance  is  developed  in  coagulating  blood  that  is  capable 
of  reacting  with  fibrinogen  to  produce  fibrin.  By  the  disintegration  of  cer- 
tain of  the  leucocytes  and  the  blood-platelets,  a  nucleo-albumin  is  given 
off,  which  unites  with  calcium  to  form  thrombin.  This  nucleo-albumin  is 
called  prothrombin.  In  the  reaction  that  results  in  the  formation  of 
fibrin,  the  fibrinogen  molecule  is  split  into  a  body  that  unites  with  throm- 
bin, leaving  a  new  substance  called  fibrin-globulin.  Sixty  to  ninety  per 
cent,  however,  of  the  fibrinogen  molecule  enters  into  the  composition  of 
fibrin.  The  presence  of  calcium  salts  is  necessary  to  the  change  of  pro- 
thrombin into  thrombin  ;  but  Hammarsten  has  succeeded  in  producing  a 
fibrin  containing  only  0.005  P^r  cent  of  calcium.  The  agency  of  the 
blood-platelets  in  the  production  of  fibrin  can  hardly  be  doubted.  Micro- 
scopical observations  have  revealed  filaments  of  fibrin  radiating  from 
these  bodies  partially  disintegrated.  The  formation  of  fibrin,  indeed, 
may  be  simply  described  as  follows  :  — 

Prothroinbiu  and  ThroDibin.  —  As  the  result  of  disintegration  of 
blood-platelets  (Lilienfeld)  and  of  certain  leucocytes,  a  nucleo-albumin 
is  formed  called  prothrombin ;  prothrombin  unites  with  calcium  to 
form  thrombin  ;  finally,  thrombin  splits  the  molecule  of  fibrinogen,  com- 
bines with  part  of  this  molecule  to  form  fibrin  and  leaves  a  part  that  is 
called  fibrin-globulin. 

Uses  of  Coagulation.  —  The  property  of  the  blood  under  consideration 
has  an  important  office  in  the  arrest  of  hemorrhage.  The  effect  of  ab- 
sence of  or  great  diminution  in  coagulability  is  exemplified  in  instances 
of  what  is  called  the  hemorrhagic  diathesis,  or  hemophilia,  a  condition 
in  which  slight  wounds  are  followed  with  alarming  and  sometimes  fatal 
hemorrhage.  This  condition  may  exist  for  years  and  is  not  character- 
ized by  any  peculiar  symptoms  except  an  obstinate  flow  of  blood  from 
slight  wounds. 

Hemophilia  is  the  most  striking  example  in  medicine  of  transmis- 
sion by  inheritance.  It  has  been  traced  through  successive  generations 
in  a  single  family  for  more  than  two  hundred  years.  It  affects  males 
much  more  frequently  than  females,  the  ratio  being  more  than  ten  to 


USES    OF   COAGULATION  29 

one.  It  is  a  curious  fact  that  the  diathesis  comes  through  the  females, 
who  are  not  themselves  "bleeders."  The  daughters  transmit  it  to  their 
sons,  but  male  bleeders  seldom  transmit  the  diathesis  except  to 
daughters,  whose  sons  usually  are  bleeders.  It  has  also  been  observed 
that  the  females  in  bleeder-families  are  very  prolific.  Hemophilia  may 
develop  spontaneously,  without  heredity,  but  it  nearly  always  is 
congenital. 

During  coagulation,  fibrin  assumes  a  filamentous  form,  presenting, 
under  the  microscope,  the  appearance  of  rectilinear  fibrillae.  These 
fibrillae  gradually  increase  in  number,  and  as  contraction  of  the  clot 
occurs,  they  become  irregularly  crossed.  They  are  always  straight, 
however,  and  never  assume  the  wavy  appearance  characteristic  of  true 
fibrous  tissue. 

The  blood  of  the  renal  and  hepatic  veins,  capillary  blood,  and  the 
blood  which  passes  from  the  capillary  system  into  the  veins  after  death 
usually  does  not  coagulate  or  coagulates  very  imperfectly ;  in  other 
words,  blood  from  these  parts  does  not  readily  form  fibrin.  The  reason 
of  this  peculiarity  is  not  known  ;  but  the  fact  affords  a  partial  explanation 
of  the  normal  fluidity  of  the  blood ;  for  this  liquid,  passing  over  the 
entire  course  of  the  circulation  in  about  thirty  seconds,  seems  to  be  los- 
ing its  coagulability  in  its  passage  through  the  liver,  kidneys,  and  the 
general  capillary  system  as  fast  as  its  coagulability  is  increased  in  the 
other  parts.  Taking  into  consideration  the  rapidity  of  the  circulation, 
it  is  evident  that  coagulation  can  not  take  place  while  the  normal  circu- 
lation is  maintained  and  while  the  blood  is  undergoing  the  changes 
incident  to  general  metabolism. 


CHAPTER    II 

CIRCULATION    OF   THE    BLOOD    THROUGH    THE    HEART 

Discovery  of  the  circulation  —  Physiological  anatomy  of  the  heart  —  Tricuspid  valve  —  Pul- 
monic valves  —  Mitral  valve  —  Aortic  valves — Movements  of  the  heart  —  Cardiac  cycle 
—  Sounds  of  the  heart  —  Frequency  of  the  heart's  action  —  Cause  of  the  rhythmical  con- 
tractions of  the  heart  —  Accelerator  nerves  —  Direct  inhibition  of   the  heart  —  Work  of 

the  heart. 

Harvey  "set  forth  for  the  first  time  his  discovery  of  the  circula- 
tion," in  his  pubHc  lectures  in  1616.  In  1628,  he  published  the  Excr- 
citatio  Atiatouiica  dc  Motu  Cordis  ct  Sanguinis  in  Aninialibus.  This 
discovery,  from  the  isolated  facts  bearing  upon  it  observed  by  anato- 
mists to  its  culmination  in  the  experiments  of  Harvey,  illustrates  so 
well  the  gradual  development  of  physiological  truth,  that  it  does  not 
seem  out  of  place  to  begin  the  study  of  the  circulation  with  a  brief 
sketch  of  its  history. 

The  facts  bearing  on  the  circulation,  developed  before  the  time  of 
Harvey,  are  chiefly  anatomical.  The  writings  of  Hippocrates  are 
indefinite  on  all  points  connected  with  the  circulatory  system  ;  and  no 
clear  and  positive  statements  are  to  be  found  in  ancient  works  before 
the  time  of  Aristotle.  The  book  of  Aristotle  most  frequently  quoted 
by  physiologists  is  '^vs,  History  of  Animals  ;  and  in  this  occurs  a  passage 
which  seems  to  indicate  that  he  thought  that  air  passed  from  the  lungs 
to  the  heart ;  but  in  his  work,  De  Partibiis  Aninialimn,  it  is  stated  that 
there  are  two  great  bloodvessels,  the  vena  cava  and  aorta,  arising  from 
the  heart,  and  that  the  aorta  and  its  branches  carry  blood.  Galen, 
however,  demonstrated  experimentally  the  presence  of  blood  in  the 
arteries,  by  including  a  portion  of  one  of  these  vessels  between  two 
ligatures,  in  a  living  animal ;  but  his  ideas  of  the  communication  be- 
tween the  arteries  and  veins  were  erroneous,  for  he  believed  in  the 
existence  of  small  orifices  in  the  septum  between  the  ventricles  of  the 
heart,  a  mistake  that  was  corrected  by  Vesalius  about  the  middle  of 
the  sixteenth  century. 

In  1546,  seven  years  before  the  description  of  the  pulmonary  circu- 
lation'by  Servetus,  Rabelais,  probably  the  most  learned  man  of  his 
time,  gave  a  very  fair  description  of  the  circulation  of  the  blood 
through  the  lungs.     An  account  of  this,  with  a  literal  translation  from 

30 


DISCOVERY    OF    THE    CIRCULATION  3 1 

the  book  Treating  of  the  Heroic  Deeds  and  Sayings  of  the  Good  Pantag- 
ruel,  was  published  in  1903  (Flint). 

In  1553,  Michael  Servetus,  who  is  commonly  regarded  as  the  dis- 
coverer of  the  passage  of  the  blood  through  the  lungs,  or  the  pulmonary- 
circulation,  described  the  course  of  the  blood  through  the  lungs,  from 
the  right  to  the  left  side  of  the  heart.  This  description,  complete  as 
it  is,  was  merely  incidental  to  the  development  of  a  theory  in  regard 
to  the  formation  of  the  soul  and  the  production  of  what  were  called 
animal  and  vital  spirits  {spiritus). 

A  few  years  later,  Colombo,  professor  of  anatomy  at  Padua,  and 
Cesalpinus,  of  Pisa,  described  the  passage  of  the  blood  through  the 
lungs,  probably  without  a  knowledge  of  what  had  been  written  by 
Servetus.  To  Cesalpinus  is  attributed  the  first  use  of  the  expression 
"circulation  of  the  blood";  and  he  also  remarked  that  after  ligature 
or  compression  of  a  vein,  the  swelling  is  always  below  the  point  of 
obstruction. 

The  history  of  the  discovery  of  the  valves  in  the  veins  is  somewhat 
obscure,  although  priority  of  observation  is  almost  always  conceded 
to  Fabricius.  As  regards  this  point,  only  the  dates  of  published  me- 
moirs are  to  be  considered,  notwithstanding  the  assertion  of  Fabricius 
that  he  had  seen  the  valves  in  1574.  In  1545,  Etienne  described,  in 
branches  of  the  portal  vein,  "valves,  which  he  called  apophyses,  and 
which  he  compared  to  the  valves  of  the  heart."  In  1551,  Amatus 
Lusitanus  published  a  letter  from  Cannanus,  in  which  it  is  stated  that 
he  had  found  valves  in  certain  of  the  veins.  In  1563,  Eustachius  pub- 
lished an  account  of  the  valves  of  the  coronary  vein.  In  1586,  a  clear 
account,  by  Piccolhominus,  of  the  valves  of  the  veins  was  published. 
Fabricius  gave  the  most  accurate  descriptions  and  delineations  of  the 
valves,  and  his  first  publication  is  said  to  have  appeared  in  1603.  He 
demonstrated  the  valves  to  Harvey,  at  Padua ;  and  it  is  probable  that 
this  was  the  origin  of  the  first  speculations  by  Harvey  on  the  mechan- 
ism of  the  circulation. 

In  the  work  of  Harvey  are  described  first  the  movements  of  the 
heart,  which  he  exposed  and  studied  in  living  animals.  He  described 
minutely  all  the  phenomena  that  accompany  its  action ;  its  diastole, 
when  it  is  filled  with  blood,  and  its  systole,  when  the  ventricles  con- 
tract simultaneously,  and  "by  an  admirable  adjustment  all  the  internal 
surfaces  are  drawn  together,  as  if  with  cords,  and  so  is  the  charge  of 
blood  expelled  with  force."  From  the  description  of  the  action  of 
the  ventricles,  he  passed  to  the  auricles,  and  showed  how  these,  by 
their  contraction,  filled  the  ventricles  with  blood.  By  experiments  on 
serpents  and   fishes,  he  proved  that  the  blood  fills  the  heart  from  the 


32  CIRCULATION    OF    THE    BLOOD 

veins  and  is  sent  out  into  the  arteries.  Exposing  the  heart  and  the 
great  vessels  in  these  animals,  he  applied  a  ligature  to  the  veins,  which 
had  the  effect  of  cutting  off  the  supply  from  the  heart  so  that  it  became 
pale  and  flaccid  ;  and  by  removing  the  ligature  the  blood  could  be  seen 
flowing  into  the  organ.  When,  on  the  other  hand,  a  ligature  was  appUed 
to  the  artery,  the  heart  became  unusually  distended,  which  continued 
so  long  as  the  obstruction  remained.  When  the  Hgature  was  removed, 
the  heart  soon  returned  to  its  normal  condition.  Harvey  completed 
his  description  of  the  circulation  by  experiments  showing  the  course 
of  the  blood  in  the  arteries  and  veins  and  the  uses  of  the  valves  of  the 
veins.  By  these  simple  observations  the  chain  of  experimental  evi- 
dence establishing  the  fact  of  the  circulation  of  the  blood  was  com- 
pleted. 

Although  Harvey  accurately  described  the  course  of  the  blood 
and  left  no  doubt  as  to  the  communication  between  the  arteries  and 
veins,  it  remained  for  others  actually  to  see  the  blood  in  movement  and 
follow  it  from  one  system  of  vessels  to  the  other.  In  1661,  Malpighi 
saw  the  blood  circulating  in  the  vessels  of  the  lung  of  a  living  frog, 
examining  it  with  magnifying  glasses;  and  a  little  later,  Leeuwenhoek 
saw  the  circulation  in  the  wing  of  a  bat.  These  observations  completed 
the  discovery  of  the  circulation. 

In  man  and  in  the  warm-blooded  animals,  the  organism  requires 
blood  that  has  been  oxygenated  in  the  lungs ;  and  to  meet  this  demand 
fully,  the  circulatory  system  is  divided  into  pulmonic  and  systemic. 
The  heart  is  double,  having  a  right  side  and  a  left  side,  which  are 
entirely  distinct  from  each  other.  The  right  heart  receives  the  blood 
as  it  is  brought  from  the  general  system  by  the  veins  and  sends  it  to  the 
lungs  ;  the  left  heart  receives  the  blood  from  the  lungs  and  sends  it  to 
the  general  system.  It  must  be  borne  in  mind,  however,  that  although 
the  two  sides  of  the  heart  are  distinct  from  each  other,  their  action  is 
simultaneous ;  and  in  studying  the  motions  of  the  heart,  it  will  be 
found  that  the  blood  is  sent  at  the  same  time  from  the  right  side 
to  the  lungs  and  from  the  left  side  to  the  system.  It  will  not  be 
necessary,  therefore,  to  separate  the  two  circulations  in  the  study  of 
their  mechanism  ;  for  the  simultaneous  action  of  both  sides  of  the 
heart  renders  it  possible  to  study  its  action  as  a  single  organ ;  and  the 
constitution  and  operations  of  the  two  kinds  of  vessels  do  not  present 
any  material  differences. 

There  are  three  kinds  of  bloodvessels  :  arteries,  which  carry  blood 
from  the  heart  to  the  general  system  ;  capillaries,  w^hich  distribute  the 
blood  in  the  parts ;  and  veins,  which  return  the  blood  from  the  general 
system  to  the  heart. 


PHYSIOLOGICAL   ANATOMY    OF    THE    HEART 


33 


Physiological  Anatomy  of  the  Heart.  —  The  heart  of  the  human  sub- 
ject is  a  pear-shaped  muscular  organ,  situated  in  the  thoracic  cavity,  its 
base  lying  in  the  median  line  and  its  apex  at  the  fifth  intercostal  space, 
three  inches  (7.6  centimeters)  to  the  left  of  the  median  line,  or  one  inch 
(2.5  centimeters)  within  the  line  of  the  left  nipple.  The  weight  of  the 
heart  is  ten  to  twelve  ounces  (283  to  340  grams)  in  the  male,  and  eight 
to  ten  ounces  (227  to  283  grams)  in  the  female.  It  has  four  distinct 
cavities,  —  a  right  and  a  left  auricle  and  a  right  and  a  left  ventricle,  the 
ventricles  being  the  more  capacious.  The  heart  is  held  in  place  by  the 
attachment  of  the  great 
vessels  to  the  posterior 
wall  of  the  thorax ;  while 
the  apex  is  free  and  is 
capable  of  a  certain  ex- 
tent of  movement.  The 
entire  organ  is  enveloped 
in  a  fibrous  sac  called 
the  pericardium.  This 
sac  is  lined  with  a  serous 
membrane,  which  is  at- 
tached to  the  great  ves- 
sels at  the  base  and  is 
reflected  over  the  sur- 
face of  the  heart.  This 
membrane  is  lubricated 
with  about  a  drachm 
(3.7  cubic  centimeters) 
of  liquid,  so  that  the 
movements  of  the  heart 
are  attended  with  but 
slight  friction.  The  se- 
rous pericardium  does  not  present  any  differences  from  serous  mem- 
branes in  other  situations,  which  form  a  part  of  the  great  lymphatic 
system.  The  cavities  of  the  heart  are  lined  with  a  smooth  membrane, 
called  the  endocardium,  which  is  continuous  with  the  lining  membrane 
of  the  bloodvessels. 

The  right  auricle  receives  the  blood  from  the  venae  cavae  and  empties 
it  into  the  right  ventricle.  The  auricle  consists  of  a  principal  cavity,  or 
sinus,  as  it  is  called,  with  a  little  appendix,  called,  from  its  resemblance 
to  the  ear  of  a  dog,  the  auricular  appendix.  It  presents  two  large  open- 
ings, for  the  vena  cava  ascendens  and  the  vena  cava  descendens  respec- 
tively, with  a  small  opening  for  the  coronary  vein.     It  also  has  another 


Fig.  16.  — Heart  in  situ  (Dalton,  in  Flint,  On  the  Heart). 

a,  b,  c,  d,  e,  ribs ;  i,  2,  3,  4,  5,  intercostal  spaces  ;  vertical  line, 
median  line ;  triangle,  superficial  cardiac  region ;  X  on  the  fourth 
rib,  nipple. 


34 


CIRCULATION    OF   THE    BLOOD 


large  opening,  called  the  auriculo-ventricular  opening,  through  which  the 
blood  flows  into  the  ventricle.  The  auricular  walls  are  thinner  than  the 
walls  of  the  ventricles,  measuring  about  one  line  (2.1  millimeters).  They 
are  composed  of  muscular  fibres  arranged  in  two  layers,  one  of  which,  the 
external,  is  common  to  both  auricles,  and  the  other,  the  internal,  is  proper 
to  each.  These  muscular  fibres,  although  involuntary  in  their  action, 
belong  to  the  striated  variety  and  are  nearly  the  same  in  structure  as 
the  fibres  of  the  ventricles.  Some  of  the  auricular  fibres  are  looped, 
arising  from  a  cartilaginous  ring  which  separates  the  auricles  and  ven- 
tricles and  passing  over  the  auricles ;  and  others  are  circular,  surround- 
ing the  auricular  ap- 
pendages and  the 
openings  of  the  veins, 
extending,  also,  for  a 
short  distance  along 
the  course  of  these 
vessels.  One  or  two 
valvular  folds  are 
found  at  the  orifice 
of  the  coronary  vein, 
preventing  a  reflux  of 
blood ;  but  there  are 
no  valves  at  the  ori- 
fices of  the  venae 
cavae. 

The  left  auricle 
receives  the  blood 
from  the  lungs  by  the 
pulmonary  veins.  It 
does  not  differ  mate- 
rially in  its  anatomy 
from  the  right.  It  is 
a  little  smaller,  and  its  walls  are  thicker,  measuring  about  a  hne  and  a 
half  (3.15  milHmeters).  It  has  four  openings  by  which  it  receives  blood 
from  the  four  pulmonary  veins.  These  openings  have  no  valves.  Like 
the  right  auricle,  it  has  a  large  opening  through  which  blood  flows  into 
the  corresponding  ventricle.  The  arrangement  of  the  muscular  fibres  is 
essentially  the  same  as  in  the  right  auricle.  In  adult  life  the  cavities  of 
the  auricles  are  distinct  from  each  other.  Before  birth  they  communi- 
cate by  a  large  opening,  the  foramen  ovale,  and  the  orifice  of  the  inferior 
vena  cava  is  provided  with  a  membranous  fold,  the  Eustachian  valve, 
which  serves  to  direct  the  blood  from  the  lower  part  of  the  body  through 


Fig.  17.  — Muscular  fibres  of  the  auricles  (Bonamy  and  Beau). 

I,  right  auricle  ;  2,  inferior  vena  cava;  3,  superior  vena  cava; 
4,  coronary  vein;  5,  left  auricle ;  6,  6,  left  pulmonary  veins;  7,  7, 
right  pulmonary  veins  ;  8,  8,  muscular  fibres  surrounding  the  right  and 
left  auriculo-ventricular  openings;  9,  muscular  fibres  surrounding  the 
opening  of  the  superior  vena  cava;  10,  muscular  fibres  surrounding 
the  opening  of  the  inferior  vena  cava  ;  11,  12,  12,  12,  12,  circular  fibres 
surrounding  the  openings  of  the  pulmonary  veins. 


PHYSIOLOGICAL   ANATOxMY    OF    THE    HEART 


35 


the  opening  into  the  left  auricle.     After  birth  the  foramen  ovale  is  closed 
and  the  Eustachian  valve  gradually  disappears. 

The  ventricles,  in  the  human  subject  and  in  warm-blooded  animals, 
constitute  the  bulk  of  the  heart.  They  have  a  capacity  somewhat  greater 
than  that  of  the  auricles  and  are  provided  with  thick  muscular  walls. 
The  action  of  this  portion  of  the  heart  sends  the  blood,  on  the  one 
hand,  to  the  lungs  and 
back  to  the  left  side  of 
the  heart,  and  on  the 
other,  through  the  en- 
tire system  of  the  greater 
circulation,  to  the  right 
side. 

The  capacity  of  the 
cavities  in  the  right  side 
of  the  heart  is  one-tenth 
to  one-eighth  greater 
than  that  of  the  corre- 
sponding cavities  on  the 
left  side.  The  capacity 
of  the  ventricles  exceeds 
that  of  the  auricles  by 
one-fourth  to  one-third. 
The  absolute  capacity  of 
the  left  ventricle,  when 
distended  to  its  utmost, 
is  4.8  to  7  ounces  (143  to 
212  cubic  centimeters). 
This  is  much  greater 
than  most  estimates, 
which  place  the  capacity 
of  each  of  the  various 
cavities,  moderately  dis- 
tended,  at   about   three 


Fig.  18.  —  Heart,  anterior  view  (Bonamy  and  Beau). 

I,  right  ventricle  ;  2,  left  ventricle  ;  3,4,  right  auricle ;  5,6,  left 
auricle;  7,  pulmonary  artery;  8,  aorta;  9,  superior  vena  cava; 
10,  anterior  coronary  artery;  11,  branch  of  the  coronarj'  vein; 
12,  12,  12,  lymphatic  vessels. 


ounces  (90  cubic  centimeters).  Notwithstanding  the  disparity  in  the 
extreme  capacity  of  the  various  cavities,  the  quantity  of  blood  which 
enters  these  cavities  necessarily  is  equal  to  that  which  is  expelled. 
This  is  estimated  at  about  three  ounces  (90  cubic  centimeters). 

The  cavities  of  the  ventricles  are  conoidal,  the  right  being  broader 
and  shorter  than  the  left,  which  latter  extends  to  the  apex.  The  inner  sur- 
faces of  both  cavities  are  marked  by  ridges  and  papillae,  called  columnse 
carneae.      Some  of   these  are  fleshy  ridges  projecting  into   the   cavity; 


36 


CIRCULATION    OF   THE    BLOOD 


Others  are  columns  attached  by  either  extremity  and  free  at  the  central 
portion ;  and  others  are  papillae,  giving  origin  to  the  chordae  tendineae, 
which  are  attached  to  the  free  borders  of  the  auriculo-ventricular  valves. 
These  fleshy  columns  interlace  in  every  direction  and  give  the  inner 
surfaces  of  the  cavities  a  reticulated  appearance.      This   arrangement 


Fig.  19.  —  Left  cavities  of  the  heart  (Bonamy 
and  Beau). 

1,  left  ventricular  cavity ;  2,  initrul  valve; 
3,  4,  columnes  carnecB  ;  5,  aortic  opening  ;  6,  aorta  ; 
7,  8,  9,  aortic  valves  ;  10,  right  ventricular  cavity; 
II,  interventricular  septum  ;  12,  pulmonary  ar- 
tery; 13,  14,  pulmonic  valves;  15,  left  auricular 
cavity ;  16,  16,  right  pulmonary  veins,  with  17,  17, 
openings  of  the  veins ;  18,  section  of  the  coronary 


Fig.  20.  —  ^'s  ,f  the  heart  (Bonamy 

and  Beau) . 

I,  r/ght  ventricular  cavity  ;  2,  posterior  cur- 
tain of  the  tricuspid  valve ;  3,  right  auricular 
cavity  ;  4,  columncB  carnea  of  the  right  auricle  ; 
5,  section  of  the  coronary  vein;  6,  Eustachian 
valve  ;  7,  ring  of  Vieussens  ;  8,  fossa  ovalis; 
9,  superior  vena  cava ;  10,  inferior  vena  cava ; 
II,  aorta;  12,  12,  right  pulmonary  veins. 


facilitates  the  complete  emptying    of    the  ventricles  during  their  con- 
traction. 

The  walls  of  the  left  ventricle  are  thicker  than  those  of  the  right 
side.  The  average  thickness  of  the  right  ventricle  at  the  base  is  two  and 
a  half  lines  (5.25  millimeters),  and  the  thickness  of  the  left  ventricle  at 
the  corresponding  part  is  seven  lines  (14.7  millimeters),  or  a  little  more 
than  half  an  inch. 


PHYSIOLOGICAL   ANATOMY  OF   THE    HEART 


37 


The  arrangement  of  the  muscular  fibres  of  the  ventricles  is  more 
regular  than  in  the  auricles  ;  but  their  direction  cannot  be  well  made 
out  unless  the  heart  has  been  boiled  for  a  number  of  hours,  when  part 
of  the  intermuscular  tissue  is  dissolved.  They  present  two  principal 
layers,  —  a  superficial  layer  common  to  both  ventricles,  and  a  deep  layer 
proper  to  each  ventricle.  The  superficial  fibres  pass  obliquely  from  right 
to  left  from  the  base  above  to  the  apex  below ;  here  they  take  a  spiral 
course,  become  deep  and  pass 
into  the  interior  to  form  the 
columnae  carneae.  These  fibres 
envelop  both  ventricles.  They 
may  be  said  to  arise  from  car- 
tilaginous rings  that  surround 
the  auricuio-ventricular  ori- 
fices. The  external  surface 
of  the  heart  is  marked  by  a 
groove  that  indicates  the  divi- 
sion between  the  two  ventri- 
cles. The  deep  fibres  are 
circular,  or  transverse,  and 
surround  each  ventricle  sepa- 
rately. 

The  muscular  tissue  of  the 
heart  is  of  a  deep  red  color 
and  resembles,  in  its  gross 
characters,  the  tissue  of  ordi- 
nary voluntary  muscles ;  but 
as  already  intimated,  it  pre- 
sents certain  peculiarities  in 
its  minute  anatomy.  The 
fibres  are  considerably  smaller 
and  are  more  granular  than 
those  of  ordinary  muscles. 
They  are,  moreover,  connected  with  each  other  by  short  inosculating 
branches  and  have  no  sarcolemma.  The  muscular-fibre  cells  have 
each  a  single  oval  nucleus  which  presents  a  network  of  chromatin. 
Sometimes,  though  rarely,  a  cell  contains  two  nuclei.  The  cells  are 
joined  together  by  their  ends  with  what  seems  to  be  a  cement-sub- 
stance, with  delicate  protoplasmic  processes  extending  between  two  con- 
tiguous cells.  The  branching  fibres  form  a  close  muscular  reticulum  in 
the  meshes  of  which  are  bloodvessels,  nerves  and  a  small  quantity  of 
areolar  tissue.     This  arrangement  favors  the  complete  expulsion  of  the 


Fig.  21.  —  Muscular  fibres  of  the  ventricles  (Bonamy 
and  Beau). 

I,  superficial  fibres  common  to  both  ventricles ;  2,  fibres 
of  the  left  ventricle  ;  3,  deep  fibres  passing  upward  toward 
the  base  of  the  heart ;  4,  fibres  penetrating  the  left  ven- 
tricle. 


38 


CIRCULATION    OF   THE    BLOOD 


contents  of  the  cavities,  especially  the  ventricles,  with  each  systole  (see 
Plate  II,  Fig.  3). 

The  distribution  of  the  nerves  to  the  heart  and  the  arrangement 
of  the  ganglia  and  nerve-terminations  in  its  substance  will  be  de- 
scribed in  connection  with  the  influence  of  the  nervous  system  on  the 
circulation. 

Each  ventricle  has  two  orifices,  — one  by  which  it  receives  blood  from 
the  auricle,  and  the  other  by  which  the  blood  passes  from  the  right  side 
to  the  lungs  and  from  the  left  side  to  the  general  system.  All  these 
openings  are  provided  with  valves,  which  are  so  arranged  as  to  allow 
the  blood  to  flow  in  but  one  direction. 

Tricuspid  Valve. — This  valve  is  situated  at  the  right  auriculo-ven- 
tricular  opening.     It  has  three  curtains,  formed  of  a  thin  but  resisting 

membrane,  which  are  at- 
tached around  the  open- 
ing. Their  free  borders 
are  attached  to  the  chordae 
tendineae. 

TJie  Pulmonic  Valves. 
—  The  three  pulmonic 
valves,  also  called  the 
semilunar  or  the  sigmoid 
valves  of  the  right  side, 
are  situated  at  the  orifice 
of  the  pulmonary  artery. 
They  are  strong  mem- 
branous pouches,  with 
their    convexities,     when 

I,  right  auriculo-ventiicular  opening,  closed  by  the  tricuspid 

valve  ;  2,  left  auriculo-ventricular  opening,  closed  by  the  mitral  cloSCd,  lookmg  tOWard  the 

valve;    4,  fibrous  ring;    5,  aortic  opening  and  valves;    6,  pul-  vpntnrlp  Thpv    are    at- 

nionic  opening  and  valves ;  8,  9,  muscular  fibres.  *  -^ 

tached  to  the  borders  of 
the  orifice  of  the  pulmonary  artery,  and  when  closed,  their  free  edges 
meet  and  prevent  regurgitation  of  blood.  At  the  centre  of  the  free 
border  of  each  valve  is  a  little  body  called  the  corpuscle  of  Arantius. 
Just  above  the  attached  margins  of  the  valves,  the  vessel  presents  three 
dilatations,  or  sinuses,  called  sinuses  of  Valsalva.  The  corpuscles  of 
Arantius  aid  in  the  close  adaptation  of  the  free  borders  of  the  valves  to 
each  other  to  prevent  regurgitation  of  blood. 

Mitral  Valve.  —  The  mitral  valve,  sometimes  called  the  bicuspid,  is 
situated  at  the  left  auriculo-ventricular  orifice.  It  is  attached  to  the  bor- 
ders of  this  opening,  and  its  free  margins  are  held  in  place,  when  the 
valve  is  closed,  by  the  chordae  tendineae,  to  which  they  are  attached.     It 


Fig.  22.  —  Valves  of  the  heart  (Bonamy  and  Beau). 


MOVEMENTS    OF   THE    HEART  39 

presents  no  material  difference  from  the  tricuspid  valve,  except  that  it  is 
divided  into  two  curtains  instead  of  three. 

Aortic  Valves.  —  The  three  aortic  semilunar  valves  are  the  same  in 
their  arrangement  as  the  pulmonic  valves.  They  prevent  regurgitation 
from  the  aorta  into  the  left  ventricle. 


Movements  of  the  Heart 

Dilatation  of  the  cavities  of  the  heart  is  called  diastole,  and  con- 
traction, systole.  A  complete  revolution,  or  cycle  of  the  heart  consists 
in  the  filling  and  emptying  of  all  its  cavities,  during  which  they  pre- 
sent alternations  of  rest  and  contraction.  As  these  occupy  less  than 
one  second,  it  is  evident  that  their  exact  relations  to  each  other  require 
careful  study. 

Except  during  the  short  time  occupied  in  contraction  of  the  auricles, 
these  cavities  are  constantly  receiving  blood,  on  the  right  side  from  the 
venae  cavas  and  on  the  left  side  from  the  pulmonary  veins.  When  the 
auricles  have  become  fully  distended,  they  contract  and  send  the  blood 
on  the  right  side  into  the  right  ventricle  and  on  the  left  side  into  the 
left  ventricle.  During  this  contraction,  the  blood  ceases  to  flow  from 
the  veins  into  the  auricles,  and  a  small  quantity  is  regurgitated,  as 
the  openings  are  not  provided  with  valves ;  but  the  arrangement  of  the 
muscular  fibres  of  the  auricles  around  the  openings  of  the  veins  limits 
this  regurgitation,  and  the  greater  part  of  the  blood  is  forced  into  the 
ventricles. 

Immediately  following  contraction  of  the  auricles,  there  is  contraction 
of  the  ventricles.  This  is  the  chief  active  operation  of  the  heart,  and  it 
usually  is  spoken  of  as  the  systole.  Regurgitation  of  blood,  during  con- 
traction of  the  ventricles,  is  prevented  by  closure  of  the  auriculo-ventric- 
ular  valves.  This  act  accompUshed,  the  heart  has  a  period  of  rest,  the 
blood  flowing  into  the  auricles  and  from  them  very  slowly  into  the  ven- 
tricles, until  the  auricles  are  again  completely  filled,  when  another  cycle 
of  the  heart  begins. 

The  position  of  the  heart  in  the  thoracic  cavity  is  with  its  base 
directed  slightly  to  the  right  and  its  apex  to  the  left.  The  movement 
of  the  apex  from  left  to  right  is  a  necessary  consequence  of  the  direc- 
tion of  the  superficial  fibres  from  right  to  left.  The  fibres  on  the  ante- 
rior surface  are  longer  than  the  posterior  fibres,  and  therefore  the  point 
of  the  heart  is  moved  upward  and  to  the  right  during  their  contraction. 
In  the  ventricular  systole,  the  heart  itself  is  propelled  forward  by  the 
sudden  distention  of  the  great  vessels  at  the  base,  aided  by  the  recoil  of 
the  ventricles.     By  reason  of  the  spiral  course  of  the  superficial  fibres  of 


40  CIRCULATION    OF   THE    BLOOD 

the  ventricles,  their  contraction  produces  a  twisting  of  the  point  upon 
itself.     An  untwisting  occurs  during  the  ventricular  diastole. 

If  the  heart  is  grasped  with  the  hand  during  its  action,  it  is  observed 
that  the  systole  is  attended  with  a  palpable  hardening.  Like  any  other 
muscle,  the  heart  is  sensibly  hardened  during  contraction. 

The  projection  of  the  point  of  the  heart  forward  during  the  systole  is 
not  due  to  elongation  of  the  ventricles.  When  the  ventricles  contract, 
their  transverse  diameter  is  slightly  diminished  and  the  antero-posterior 
diameter  is  correspondingly  increased.  The  ventricles  themselves  are 
sensibly  shortened  during  their  systole. 

Cardiac  Cycle.  —  A  cardiac  cycle  includes  the  alternate  contraction 
and  dilatation  of  its  several  cavities.  It  is  to  be  remembered  that  the 
two  sides  of  the  heart  act  together.  Dividing  the  cycle  into  eighths  and 
beginning  with  the  contraction  of  the  auricles,  the  following  represents 
a  complete  revolution  :  one-eighth,  the  auricles  contract  and  the  ven- 
tricles dilate  ;  three-eighths,  the  ventricles  contract  and  the  auricles  are 
passive;  four-eights,  the  auricles  dilate  and  the  ventricles  are  passive. 
If  the  condition  of  the  walls  of  the  several  cavities  is  now  compared  with 
the  condition  of  the  valves,  it  will  be  found  that  the  auriculo-ventricular 
valves  are  closed  during  the  three-eighths  of  the  cycle  occupied  in  con- 
traction of  the  ventricles,  and  the  semilunar  valves  are  open  ;  and  that  the 
semilunar  valves  are  closed  during  the  remaining  five-eighths  of  the  cycle, 
while  the  auriculo-ventricular  valves  are  open.  It  is  possible,  also,  to 
connect  the  action  of  the  valves  with  the  condition  of  the  walls  of  the 
different  cavities,  and  the  direction  of  the  blood-currents  with  what  are 
known  as  the  heart-sounds. 

Sounds  of  the  Heart.  —  The  first  sound  of  the  heart  accompanies  con- 
traction of  the  ventricles.  It  is  heard  at  its  maximum  of  intensity  over 
the  apex  in  the  fifth  intercostal  space  and  is  conducted  upward  toward 
the  base.  This  is  a  compound  sound.  Its  elements  are,  vibration  of  the 
mitral  and  tricuspid  valvular  curtains  at  the  time  of  their  closure,  a  sound 
due  to  muscular  contraction  and  an  impression  conveyed  to  the  ear  from 
the  impulse  of  the  heart  against  the  walls  of  the  chest.  The  first  sound 
is  relatively  low  in  pitch,  prolonged  and  "  booming."  Its  low  pitch  is 
due  to  the  length  of  the  free  borders  of  the  valvular  curtains  as 
compared  with  the  semilunar  valves  :  the  prolongation  of  the  sound  is 
attributed  to  the  prolongation  of  the  ventricular  contraction  during 
three-eighths  of  the  cardiac  cycle  ;  the  impulsion  element  comes  from 
the  striking  of  the  apex  against  the  thoracic  walls. 

The  second  sound  which  follows  the  first — practically  without  an  inter- 
val—  is  relatively  high  in  pitch  and  is  shorter  than  the  first  sound.  This 
is  a  simple  sound  and  is  due  to  the  vibration  of  the  valves  during  their 


FREQUENCY    OF    THE    HEART'S    ACTION  41 

closure.  It  is  relatively  high  in  pitch  on  account  of  the  shorter  length 
of  the  free  borders  of  the  valves.  It  is  heard  at  its  maximum  of  inten- 
sity over  the  semilunar  valves  on  either  side  of  the  upper  part  of  the 
sternum  and  is  conducted  upward  along  the  great  vessels. 

Placing  the  stethoscope  over  the  apex  of  the  heart  and  a  little  to  the 
left,  it  is  possible  to  distinguish  the  sound  produced  by  closure  of  the 
mitral  valve  ;  and  with  the  stethoscope  just  below  the  ensiform  cartilage, 
the  sound  produced  by  the  tricuspid  valve  may  be  distinguished.  In 
the  same  way,  if  the  stethoscope  is  placed  a  little  to  the  right  of  the 
sternum,  near  the  aortic  valves,  the  sound  produced  by  these  valves  may 
be  distinguished,  while  to  the  left  of  the  sternum,  near  the  pulmonic 
valves,  the  sound  produced  by  these  valves  becomes  more  distinct. 

A  cardiac  cycle  with  reference  to  the  heart-sounds  is  somewhat 
different  from  the  cycle  described  with  reference  to  the  contractions  of 
the  heart.  The  cycle,  as  it  relates  to  the  sounds,  is  as  follows :  during 
four-eighths  of  the  cycle,  the  first  sound  is  heard ;  this  is  followed  im- 
mediately by  the  second  sound,  which  occupies  three-eighths  of  the  cycle. 
One-eighth  of  the  cycle  is  silence. 

It  is  of  great  importance  to  connect  the  heart-sounds  with  the  blood- 
currents.  During  the  first  sound,  the  auriculo-ventricular  valves  are 
closed,  the  semilunar  valves  are  open,  and,  as  a  consequence,  the  blood 
is  flowing  from  the  left  ventricle  into  the  aorta  and  from  the  right 
ventricle  into  the  pulmonary  artery.  During  the  second  sound,  the 
blood  is  flowing  into  the  auricles,  a  small  quantity  is  passing  into  the 
ventricles,  the  semilunar  valves  are  closed  and  the  auriculo-ventricular 
valves  are  open. 

Freqiiency  of  the  Heart's  Action.  —  The  number  of  pulsations  of 
the  heart  is  not  far  from  70  per  minute  in  an  adult  male  and  is  be- 
tween 70  and  80  in  the  female.  There  are  cases,  however,  in  which 
the  pulse  is  normally  much  slower  or  more  frequent  than  this,  a  fact 
that  must  be  remembered  when  examining  the  pulse  in  disease.  It 
is  said  that  the  pulse  of  Napoleon  I  was  only  40  per  minute,  and 
that  the  pulse  of  Sir  William  Congreve  was  never  less  than  128 
per  minute  in  health.  It  is  not  unfrequent  to  find  a  normal  pulse  of 
a  hundred  or  more  a  minute  ;  but  in  the  cases  reported  in  which  the 
pulse  has  been  found  to  be  40  or  less,  it  is  possible  that  each  alter- 
nate beat  of  the  heart  was  so  feeble  as  to  produce  no  perceptible 
arterial  pulsation.  In  such  instances,  the  fact  may  be  ascertained 
by  listening  to  the  heart  while  the  finger  is  placed  upon  the  artery. 

In  both  the  male  and  the  female,  observers  have  constantly  found 
a  difference  in  the  rapidity  of  the  heart's  action  at  different  periods  of 
life.     The  pulsations  of  the  heart  in  the  foetus  are  about  140  per  minute. 


42  CIRCULATION    OF    THE    BLOOD 

At  birth  the  pulse  is  136.  It  gradually  diminishes  during  the  first 
year  to  about  128.  The  second  year,  the  diminution  is  quite  rapid,  107 
being  the  mean  frequency  at  two  years  of  age.  After  the  second  year, 
the  frequency  progressively  diminishes  until  adult  life,  when  it  is  at 
its  minimum,  which  is  about  70  per  minute.  At  the  later  periods  of 
life  the  movements  of  the  heart  become  slightly  accelerated,  ranging 
between   75  and  80. 

During  early  life  there  is  no  marked  and  constant  difference  in  the 
rapidity  of  the  pulse  in  the  sexes ;  but  near  the  age  of  puberty  the 
development  of  the  peculiarities  relating  to  sex  is  accompanied  with  an 
acceleration  of  the  heart's  action  in  the  female,  which  continues  into 
old  age. 

The  condition  of  the  digestive  system  has  a  marked  influence  on  the 
rapidity  of  the  pulse,  and  there  usually  is  an  increase  of  five  or  ten 
beats  per  minute  after  each  meal.  Prolonged  fasting  diminishes  the 
frequency  of  the  pulse  by  about  twelve  beats.  Alcohol  first  diminishes 
and  afterward  accelerates  the  pulse.  Coffee  is  said  to  accelerate  the 
pulse  in  a  marked  degree.  It  has  been  ascertained  that  the  pulse  is 
accelerated  in  a  greater  degree  by  animal  than  by  vegetable  food. 

It  has  been  observed  that  the  position  of  the  body  has  a  decided 
influence  on  the  rapidity  of  the  pulse.  In  the  male,  there  is  a  differ- 
ence of  about  10  beats  between  standing  and  sitting,  and  15  beats 
between  standing  and  the  recumbent  posture.  In  the  female,  the 
variations  with  position  are  not  so  great.  The  average  is,  for  the 
male:  standing,  81  ;  sitting,  71  ;  lying,  66;  —  for  the  female  :  standing, 
91;  sitting,  84;  lying,  80.  These  are  given  as  averages  of  a  large 
number  of  observations.  There  were  a  few  instances,  however,  in 
which  there  was  scarcely  any  variation  with  posture,  and  some  in  which 
the  variation  was  much  greater  than  the  average.  In  the  inverted 
posture,  the  pulse  was  found  to  be  reduced  about  15  beats  (Guy). 

The  question  at  once  suggests  itself  whether  the  acceleration  of  the 
pulse  in  sitting  and  standing  may  not  be  due,  in  some  measure,  to  the 
muscular  effort  required  in  making  the  change  of  posture.  This  is 
answered  by  the  experiments  of  Guy,  in  which  the  subjects  were  placed 
on  a  revolving  board  and  the  position  of  the  body  was  changed  without 
any  muscular  effort.  Nearly  the  same  results  as  those  cited  above 
were  obtained  in  these  experiments.  In  a  single  observation,  the  pulse, 
standing,  was  89;  lying,  jy;  difference,  12.  With  the  posture  changed 
without  muscular  effort,  the  results  were  as  follows:  standing,  ^y \ 
lying,  74;  difference,  13.  Different  explanations  of  these  variations 
have  been  offered  by  physiologists ;  but  Guy  seems  to  have  settled 
experimentally  the  fact   that   the  acceleration  is   due    in    part   to   the 


INFLUENCE    OF    RESPIRATION    ON    THE    HEART  43 

muscular  effort  required  to  maintain  the  body  in  the  sitting  and  stand- 
ing positions.  The  following  are  the  results  of  experiments  bearing  on 
this  point. 

"  I.  Difference  between  the  pulse  in  the  erect  posture,  without 
support,  and  leaning  in  the  same  posture,  in  an  average  of  twelve  ex- 
periments on  the  writer,  12  beats;  and  on  an  average  of  eight  experi- 
ments on  other  healthy  males,  8  beats. 

"  2.  Difference  in  the  frequency  of  the  pulse  in  the  recumbent  pos- 
ture, the  body  fully  supported,  and  partially  supported,  14  beats  on  an 
average  of  five  experiments. 

"  3.  Sitting  posture  (mean  of  ten  experiments  on  the  writer),  back 
supported,  80 ;  unsupported,  87 ;  difference,  7  beats. 

"  4.  Sitting  posture  with  the  legs  raised  at  right  angles  with  the  body 
(average  of  twenty  experiments  on  the  writer),  back  unsupported,  86  ; 
supported,  68  ;  difference,  18  beats.  An  average  of  fifteen  experiments 
of  the  same  kind  on  other  healthy  males  gave  the  following  numbers : 
back  unsupported,  80;  supported,  68  ;  a  difference  of  12  beats." 

Muscular  exercise  increases  the  frequency  of  the  pulsations  of  the 
heart ;  and  the  experiments  just  cited  show  that  the  difference  in  rapidity, 
which  is  by  some  attributed  to  change  in  posture,  —  some  positions,  it 
is  fancied,  offering  fewer  obstacles  to  the  current  of  blood  than  others, 
—  is  due  mainly  to  muscular  exertion.  According  to  Bryan  Robinson 
(1734),  a  man  in  the  recumbent  posture  has  64  pulsations  per  minute; 
sitting,  68 ;  after  a  slow  walk,  y8 ;  after  walking  four  miles  in  an  hour, 
100;  and  140  to  150  after  running  as  fast  as  he  could. 

The  influence  of  sleep  on  the  action  of  the  heart  reduces  itself 
almost  entirely  to  the  proposition  that  during  this  condition  there 
usually  is  entire  absence  of  muscular  effort,  and  consequently  the 
number  of  beats  is  less  than  when  the  individual  is  awake.  It  has 
been  found  that  there  is  no  difference  in  the  pulse  between  sleep  and 
perfect  quiet  in  the  recumbent  posture.  This  was  noted  in  the 
adult  male ;  but  there  is  a  marked  difference  in  females  and  young 
children,  the  pulse  being  always  slower  during  sleep  (Ouetelet). 

The  influence  of  extremes  of  temperature  on  the  heart  is  very 
decided.  The  pulse  may  be  doubled  by  remaining  a  very  few  min- 
utes exposed  to  extreme  heat.  Bence  Jones  and  Dickinson  have  ascer- 
tained that  the  pulse  may  be  much  reduced  in  frequency,  for  a  short 
time,  by  the  cold  douche.  It  has  also  been  remarked  that  the  pulse  is 
more  rapid  in  warm  than  in  cold  climates. 

Influence  of  Respiration  on  the  Action  of  the  Heart.  —  The  relations 
between  the  circulation  and  respiration  are  very  intimate,  and  one 
process  can  not  go   on  without  the  other.       If   circulation  is  arrested. 


44  CIRCULATION    OF   THE    BLOOD 

the  muscles,  being  no  longer  supplied  with  fresh  blood,  soon  lose  their 
contractility  and  respiration  ceases.  Circulation,  also,  is  impossible  if 
respiration  is  permanently  arrested.  When  respiration  is  imperfectly 
performed,  the  action  of  the  heart  is  slow  and  labored.  The  effects  of 
arrest  of  respiration  are  marked  in  all  parts  of  the  circulatory  system, 
arteries,  capillaries  and  veins ;  but  the  disturbances  thus  produced  all 
react  on  the  heart. 

If  the  heart  is  exposed  in  a  living  animal  and  artificial  respiration 
is  kept  up,  although  the  pulsations  are  increased  in  frequency  and 
diminished  in  force,  after  a  time  they  become  regular  and  continue  thus 
so  long  as  air  is  adequately  supplied  to  the  lungs.  Under  these  condi- 
tions, respiration  is  under  control  and  the  effects  of  its  arrest  on  the 
heart  can  easily  be  studied.  If  respiration  is  interrupted,  the  following 
changes  in  the  action  of  the  heart  are  observed :  For  a  few  seconds 
pulsations  go  on  as  usual ;  but  in  about  a  minute  they  begin  to  diminish 
in  frequency.  At  the  same  time,  the  heart  becomes  engorged  with 
blood  and  the  distention  of  its  cavities  rapidly  increases.  For  a  time 
its  contractions  are  competent  to  discharge  the  entire  contents  of  the 
left  ventricle  into  the  arterial  system,  and  a  cardiometer  applied  to  an 
artery  then  indicates  an  increase  in  the  blood-pressure.  A  correspond- 
ing increase  in  the  movements  of  the  mercury  will  be  noted  at  each 
contraction  of  the  heart,  indicating  that  the  organ  is  acting  with  abnor- 
mal vigor.  If  respiration  is  still  interrupted,  the  engorgement  becomes 
intense,  the  heart  at  each  diastole  being  distended  to  its  utmost  capacity. 
It  now  becomes  incapable  of  emptying  itself,  the  contractions  become 
unfrequent,  perhaps  three  or  four  in  a  minute,  and  are  progressively 
enfeebled.  The  organ  is  dark,  almost  black,  owing  to  the  circulation 
of  venous  blood  in  its  substance.  If  respiration  is  not  resumed,  this 
distention  continues,  the  contractions  become  less  frequent  and  more 
feeble  and  in  a  few  minutes  they  cease. 

The  arrest  of  the  action  of  the  heart,  under  these  conditions,  is 
chiefly  mechanical.  The  unaerated  blood  passes  with  difficulty  through 
the  capillaries  of  the  system,  and  as  the  heart  is  constantly  at  work,  the 
arteries  become  greatly  distended.  This  is  shown  by  the  great  increase 
in  the  pressure  while  the  arteries  are  filled  with  black  blood.  If,  now, 
the  heart  and  great  vessels  are  closely  examined,  the  order  in  which 
they  become  distended  is  readily  observed.  These  phenomena  show 
that  in  asphyxia  the  obstruction  to  the  circulation  begins,  not  in  the 
lungs,  but  in  the  capillaries  of  the  system  and  is  propagated  backward 
to  the  heart  through  the  arteries.  The  distention  of  the  heart  in  as- 
phyxia is  therefore  due  to  the  fact  that  unaerated  blood  cannot  circulate 
freely  in  the    systemic   capillaries.      When  thus   distended,  the  heart 


CAUSE  OF  RHYTHMICAL  CONTRACTIONS  OF  THE  HEART   45 

becomes  paralyzed,  like  any  muscle  after  a  severe  strain.  It  is  probable 
that  the  impediment  to  the  capillary  circulation  results  from  contraction 
of  the  arterioles  of  supply,  due  to  irritation  produced  by  the  excess  of 
carbon  dioxide  in  the  blood. 

Cause  of  tJie  Rhythmical  Contractions  of  the  Heart.  —  The  heart  in 
its  structure  bears  a  close  resemblance  to  the  voluntary  muscles  ;  but  it 
has  a  constant  office  to  perform  and  seems  to  act  without  external 
stimulation.  Its  action  resembles,  in  this  regard,  the  movements  of 
cilia.  The  movements  of  the  heart  are  involuntary.  Its  pulsations 
can  be  neither  arrested,  retarded  nor  accelerated  directly  by  an  effort 
of  the  will,  except,  of  course,  when  retarded  by  voluntary  arrest  of 
respiration  or  accelerated  by  violent  muscular  exercise  or  other  indirect 
means.  Its  property  of  rhythmical  contraction,  however,  seems  to 
depend  on  the  circulation  of  blood  in  its  substance.  If  the  coronary 
arteries  are  tied,  the  heart  ceases  to  beat  in  about  twenty-three  minutes 
(Erichsen).  The  regular  and  efficient  contractions  of  the  heart,  also, 
are  promoted  by  the  passage  of  blood  through  its  cavities.  Although 
the  heart  removed  from  the  body  will  continue  to  contract  spontaneously 
and  rhythmically  for  a  time,  its  contractions  soon  cease,  at  least  in 
warm-blooded  animals ;  but  during  intervals  of  rest,  a  contraction  may 
be  excited  by  direct  stimulation.  The  nature  of  the  liquid  passing 
through  the  heart  has  an  influence  on  the  character  of  its  contractions. 
When  blood  passes  through  its  cavities,  the  pulsations  are  regular  and 
powerful ;  but  if  water  is  substituted,  the  beats  become  more  frequent 
and  are  not  so  vigorous  (Flint,  1861). 

It  is  certain  that  the  muscular  tissue  of  the  heart  has  an  inherent 
property  of  rhythmical  contraction.  Under  normal  conditions,  this  con- 
traction seems  to  be  propagated  from  the  auricles  to  the  ventricles ;  but 
it  is  also  true  that  the  contractions  of  the  heart  are  regulated  through 
the  nervous  system.  When  the  heart  is  divided  transversely  at  about  the 
middle  of  the  ventricles,  the  upper  portion  continues  to  pulsate,  while 
the  lower  portion  does  not.  The  lower  portion,  however,  still  possesses 
contractihty  and  will  respond  to  direct  stimulation.  This  is  thought  to 
be  due  to  sympathetic  ganglia  that  exist  in  the  upper  part,  but  not  in 
the  lower  part  of  the  ventricles.  In  the  frog  there  are  three  sympathetic 
ganglia  situated  near  the  auricles  :  one,  the  ganglion  of  Remak,  is  at  the 
point  where  the  inferior  vena  cava  opens  into  the  right  auricle ;  another 
is  between  the  left  auricle  and  the  right  ventricle  ;  another  is  between  the 
two  auricles.  In  man  there  is  a  chain  of  ganglia  between  the  auricles 
and  the  ventricles.  It  is  probable  that  these  ganglia  are  important  in 
regulating  the  action  of  the  heart. 

In  view  of  the  results  of  experiments  on  the  cold-blooded    animals 


46  CIRCULATION    OF    THE    BLOOD 

especially,  it  may  be  stated  that  the  muscular  fibres  of  the  auricles  and 
of  the  upper  part  of  the  ventricles  have  the  property  of  intermittent  and 
regular  contraction,  which  is  dependent,  to  a  great  extent,  on  the  influ- 
ence of  the  so-called  motor  ganglia  of  the  heart ;  and  that  the  wave  of 
contraction  is  transmitted  to  the  lower  portion  of  the  ventricles,  the  fibres 
of  which  do  not  seem  to  possess  the  property  of  independent  contraction. 
The  muscular  tissue  of  the  heart,  however,  may  be  thrown  into  contrac- 
tion during  diastole  by  the  application  of  a  stimulus,  a  property  observed 
in  all  muscular  fibres.  The  excitability  manifested  in  this  way  is  more 
marked  in  the  interior  than  on  the  exterior  of  the  organ.  Blood  in  con- 
tact with  the  lining  membrane  of  the  heart  acts  as  a  stimulus  in  a  re- 
markable degree  and  is  even  capable  of  restoring  excitability  after  it  has 
become  extinct.  The  passage  of  blood  through  the  heart  is  a  natural 
stimulus  and  is  an  important  element  in  the  production  of  regular  pul- 
sations, although  it  does  not  endow  the  fibres  with  their  contractile 
properties.^ 

Accelerator  Nerves.  —  Experiments  on  the  influence  of  the  sympa- 
thetic nerves  on  the  heart  have  not  been  entirely  satisfactory.  It  has  been 
observed  that  the  action  of  the  heart  is  arrested  by  destroying  the  car- 
diac plexus;  but  in  regard  to  this,  the  difficulty  of  the  operation  and  the 
disturbance  of  the  heart  consequent  on  the  necessary  manipulations 
must  be  taken  into  account.  It  has  been  shown,  however,  that  stimula- 
tion of  the  sympathetic  in  the  neck  has  the  effect  of  accelerating  the  car- 
diac movements. 

In  the  bulb  is  a  centre,  stimulation  of  which  increases  the  rapidity 
of  the  heart's  action  ;  and  from  this  centre,  fibres  descend  in  the  substance 
of  the  spinal  cord,  pass  out  with  the  communicating  branches  of  the 
lower  cervical  and  upper  dorsal  nerves  to  the  sympathetic  and  go  to  the 
cardiac  plexus.  In  the  cat,  the  accelerator  fibres  pass  through  the  first 
thoracic  sympathetic  ganglion.  Taking  all  precautions  to  eliminate  the 
influence  of  variations  in  blood-pressure,  it  has  been  shown  that  after 
division  of  the  pneumogastrics,  stimulation  of  the  accelerator  fibres  in- 
creases the  number  of  beats  of  the  heart.  This  action  is  direct  and  not 
reflex. 

1  The  well-known  experiments  of  Stannius,  published  in  1852,  have  lately  received  much 
attention.  In  these  observations  it  was  found  that  a  ligature  applied  exactly  at  the  line  of  junc- 
tion of  the  sinus  venosus  with  the  right  auricle,  in  the  frog,  arrests  for  a  time  the  contractions 
of  other  parts  of  the  heart,  while  the  sinus  continues  to  beat  regularly  ;  but  the  walls  of  the  other 
cavities  will  contract  under  direct  stimulation.  The  wave  of  contraction  seems  to  pass  from  the 
sinus  to  the  auricle  and  ventricle.  If,  now,  another  ligature  is  applied  to  the  line  of  junction  of 
the  auricle  with  the  ventricle,  the  ventricle  resumes  its  rhythmical  contractions,  while  the  auricle 
continues  at  rest.  Exjjlanations  of  these  phenomena  —  which  are  not  observed  in  animals  higher 
in  the  scale — are  so  unsatisfactory  that  it  does  not  seem  worth  while  to  discuss  them  in  the  body 
of  the  text. 


INHIBITION    OF    THE    HEART  47 

Direct  Inhibition  of  the  Heart.  —  Division  of  the  pneumogastric 
nerves  in  the  neck  increases  the  frequency  and  diminishes  the  force  of 
the  contractions  of  the  heart.  To  anticipate  a  little  of  the  history  of 
the  pneumogastric  nerves,  it  may  be  stated  that  while  they  are  exclu- 
sively sensory  at  their  origin,  they  receive,  after  having  emerged  from 
the  cranial  cavity,  a  number  of  communicating  filaments  from  various 
motor  nerves.  That  they  influence  certain  muscles,  is  shown  by  the 
paralysis  of  these  muscles  after  division  of  the  nerves  in  the  neck,  as, 
for  example,  arrest  of  the  movements  of  the  glottis. 

A  moderate  faradic  current  passed  through  both  pneumogastrics 
arrests  the  action  of  the  heart  in  diastole.  This  observation  has 
been  made  on  living  animals,  both  with  and  without  exposure  of  the 
heart ;  and  this  kind  of  action  is  known  as  inhibitory,  or  restraining. 
Its  nervous  mechanism  is  direct  and  not  reflex ;  and  the  inhibitory 
influence  is  conveyed  to  the  heart  through  filaments  in  the  pneumo- 
gastrics, derived  from  the  spinal  accessory. 

It  is  said  that  direct  stimulation  of  the  bulb  has  the  same  effect  on 
the  heart  as  stimulation  of  the  pneumogastrics ;  but  it  is  difficult  to 
limit  the  stimulation  to  a  particular  point  in  the  bulb  and  to  avoid  com- 
phcating  conditions.  A  sufficiently  powerful  stimulus  applied  to  one 
pneumogastric  will  arrest  the  cardiac  pulsations,  and  in  some  animals 
the  inhibitory  action  is  confined  to  the  ner\'e  of  the  right  side.  It  is 
not  known  that  any  such  difference  between  the  two  nerves  exists  in 
the  human  subject,  and  certainly  there  is  no  marked  difference  in  most 
of  the  mammalia. 

If  both  pneumogastrics  are  faradized  for  two  or  three  minutes,  the 
contractions  of  the  heart  return,  even  though  the  stimulation  is  con- 
tinued, provided  the  current  be  not  too  powerful  but  of  sufficient 
strength  to  promptly  arrest  the  pulsations.  It  is  probable  that  this  is 
due  to  the  fact  that  the  conductivity  of  the  nerve  after  a  time  becomes 
exhausted  by  prolonged  excitation,  and  its  inhibitory  influence  is  for  the 
time  destroyed. 

Stimulation  of  the  pneumogastrics  in  any  part  of  their  course  is 
followed  by  the  usual  inhibitory  phenomena,  and  the  same  results  some- 
times follow  stimulation  of  the  thoracic  cardiac  branches.  It  has  also 
been  observed  that  when  the  heart's  action  has  been  arrested  and  the 
organ  is  quiescent  in  diastole,  direct  mechanical  stimulation  of  the 
heart  is  followed  by  a  single  contraction,  showing  that  the  excitability 
of  the  fibres  has  not  been  entirely  suspended. 

After    section   of   both   pneumogastrics   in  the   neck,   digitahs  fails  • 
to  diminish  the  number  of  beats   of   the  heart;    showing  that   separa- 
tion of  the  heart  from  its  connections  with  the  cerebro-spinal  nerves 


48  CIRCULATION    OF   THE    BLOOD 

removes  the  organ  from  the  characteristic  and  peculiar  effects  of  the 
poison. 

Feeble  stimulation  of  one  or  both  pneumogastrics,  when  it  produces 
any  effect,  almost  always  slows  the  action  of  the  heart.  In  some 
animals,  however,  the  pneumogastrics  contain  a  few  accelerator  fibres, 
and  feeble  excitation  sometimes  is  followed  by  a  slight  increase  in  the 
rapidity  of  the  cardiac  pulsations,  but  this  is  unusual. 

Reflex  InJiibitiou  of  the  Heart.  —  Like  most  of  the  direct  operations 
of  nerves  that  can  be  imitated  by  electric  stimulation,  the  inhibitory 
action  of  the  pneumogastrics  can  be  produced  by  reflex  action.  The 
.action  of  the  heart  may  be  arrested  in  the  frog  by  sharply  tapping  the 
exposed  intestines.  The  same  effect  has  been  produced  by  stimulation 
of  the  splanchnic  nerves  or  the  cervical  sympathetic.  In  some  animals, 
if  one  pneumogastric  is  divided  in  the  neck,  the  other  being  intact, 
stimulation  of  the  central  end  of  the  divided  nerve  will  produce  inhibi- 
tion of  the  heart  by  an  action  induced  in  the  undivided  nerve.  In  all 
these  instances  the  inhibition  is  reflex.  The  stimulation  is  carried  by 
the  afferent  fibres  of  the  nei'ves  stimulated  to  the  inhibitory  centre  in 
the  bulb  and  is  reflected  to  the  heart  through  the  efferent  fibres  of  the 
pneumogastric. 

While  moderate  stimulation  of  ordinary  sensory  nerves  is  sometimes 
followed  by  inhibition  of  the  heart,  powerful  stimulation  may  arrest  the 
cardio-inhibitory  action  of  the  pneumogastrics  as  well  as  certain  other 
reflexes. 

The  inhibitory  fibres  of  the  pneumogastrics  undoubtedly  have  an 
important  ofifice  in  connection  with  the  regulation  of  the  rapidity  and 
force  of  the  cardiac  pulsations.  It  is  important,  of  course,  that  the 
heart  should  act  at  all  times  with  nearly  the  same  force  and  frequency. 
It  has  been  seen  that  the  inherent  properties  of  its  fibres  and  the  action, 
probably,  of  the  cardiac  ganglia  are  competent  to  make  it  contract, 
and  the  necessary  intermittent  dilatation  of  its  cavities  makes  the  con- 
tractions assume  a  certain  regularity  ;  but  the  quantity  and  density  of 
the  blood  are  subject  to  considerable  variations  within  the  limits  of 
health,  which,  without  some  regulating  influence,  would  cause  varia- 
tions in  the  heart's  action  so  considerable  as  to  be  injurious.  This 
is  shown  by  the  irregular  action  of  the  heart  when  the  pneumogastrics 
have  been  divided.  These  nerves  convey  to  the  heart  a  constant 
influence,  which  may  be  compared  to  the  insensible  tonicity  imparted 
to  voluntary  muscles  by  the  general  motor  system.  When  a  set  of 
muscles  on  one  side  is  paralyzed,  as  in  facial  palsy,  their  tonicity  is 
lost,  they  become  flaccid,  and  the  muscles  on  the  other  side,  without 
any  effort  of  the  will,  distort  the  features.      An  exaggeration  of  this 


WORK    OF   THE    HEART  49 

force  may  be  imitated  by  a  feeble  faradic  current,  which  renders  the 
pulsations  of  the  heart  less  frequent  and  more  powerful,  or  it  may  be 
still  further  exaggerated  by  a  more  powerful  current,  which  arrests  the 
action  of  the  heart.  Phenomena  are  not  wanting  in  the  human  subject 
to  verify  these  views.  Causes  operating  through  the  ner\'ous  system 
frequently  produce  palpitation  and  irregular  action  of  the  heart. 
Cases  are  not  uncommon  in  which  palpitation  habitually  occurs  after 
a  full  meal.  There  are  instances  on  record  of  death  from  arrest  of  the 
heart's  action  as  a  consequence  of  fright,  anger,  grief  or  other  severe 
mental  emotions.  Syncope  from  these  causes  is  by  no  means  un- 
common. In  the  latter  instance,  when  the  heart  resumes  its  contrac- 
tions, the  nervous  shock  carried  along  the  pneumogastrics  is  sufficient 
only  to  arrest  its  action  temporarily.  When  death  takes  place,  the 
shock  is  so  great  that  the  heart  does  not  recover  from  its  effects. 

Work  of  the  Heart.  —  The  total  work  of  the  heart  is  easily  com- 
puted by  multiplying  the  weight  of  the  blood  discharged  at  each  con- 
traction of  the  ventricles  by  the  blood-pressure.  Taking  the  weight  of 
blood  discharged  by  both  ventricles  as  about  4.5  ounces  (130  grams j 
and  estimating  the  blood-pressure  as  equal  to  about  five  feet  (^1.5 
meter),  the  result  would  be  about  1.25  foot-pounds  (0.175  kilogram- 
meter)  of  work  for  each  contraction  of  the  heart.  Assuming  that  the 
heart  beats  seventy-two  times  in  a  minute,  the  total  work  for  twenty- 
four  hours  would  be  about  130,000  foot-pounds  (18,000  kilogrammeters). 
These  figures  are  given  as  representing  the  probable  w^ork  and  are  not 
to  be  taken  as  anything  more  than  approximate  estimates. 


CHAPTER   III 
CIRCULATIOxN   OF    BLOOD   IN    THE   VESSELS 

Circulation  of  blood  in  the  arteries  —  Physiological  anatomy  of  the  arteries  —  Locomotion  of  the 
arteries  and  production  of  the  pulse  —  Form  of  the  pulse  —  Pressure  of  blood  in  the  arteries 

—  Pressure  in  different  arteries  —  Influence  of  respiration  —  Influence  of  muscular  action,  etc. 

—  Influence  of  hemorrhage,  etc.  —  Rapidity  of  the  current  of  blood  in  the  arteries  —  Circula- 
tion of  blood  in  the  capillaries  —  Physiological  anatomy  of  the  capillaries  —  Pressure  of  blood 
in  the  capillaries  —  Rapidity  of  the  capillary  circulation  —  Relations  of  the  capillary  circula- 
tion to  respiration  —  Causes  of  the  capillary  circulation  —  Influence  of  temperature  on  the 
capillary  circulation  —  Circulation  of  blood  in  the  veins  —  Structure  and  properties  of  the 
veins  —  Valves  of  the  veins —  Pressure  of  blood  in  the  veins  —  Rapidity  of  the  current  of 
blood  in  the  veins  —  Causes  of  the  venous  circulation  —  Influence  of  muscular  contraction 

—  Influence  of  aspiration  from  the  thorax  —  Uses  of  the  valves  of  the  veins  —  Conditions 
that  impede  the  venous  circulation  —  Circulation  in  the  cranial  cavity  —  Circulation  in  erec- 
tile tissues  —  Derivative  circulation  —  Pulmonary  circulation  —  Circulation  in  the  walls  of 
the  heart  —  Migration  and  diapedesis  —  Rapidity  of  the  circulation  —  Phenomena  in  the 
circulatory  system  after  death. 

In  man  and  in  all  animals  with  a  double  heart,  each  cardiac  contrac- 
tion forces  a  charge  of  blood  from  the  right  ventricle  into  the  pulmonary- 
artery  and  from  the  left  ventricle  into  the  aorta ;  and  the  valves  guard- 
ing the  orifices  of  these  vessels  prevent  regurgitation  during  the  intervals 
of  contraction.  There  is,  therefore,  but  one  direction  in  which  the  blood 
can  flow  in  obedience  to  this  rhythmic  action ;  and  the  fact  that  even  in 
the  smallest  arteries  there  is  an  acceleration  in  the  current  coincident 
with  each  contraction  of  the  heart,  which  disappears  when  the  action  of 
the  heart  is  arrested,  shows  that  the  ventricular  systole  is  the  cause  of 
the  arterial  circulation.  The  supply  of  blood  regulates,  to  a  considerable 
extent,  the  processes  of  nutrition  and  has  an  important  bearing  on  the 
general  and  special  functions  ;  and  the  various  physiological  processes 
necessarily  demand  considerable  modifications  in  the  quantity  of  arterial 
blood  furnished  to  parts  at  different  times.  The  force  of  the  heart,  how- 
ever, varies  but  Uttle  within  the  limits  of  health  ;  and  the  conditions  nec- 
essary to  the  proper  distribution  of  blood  are  regulated  almost  exclusively 
by  the  arterial  system.  These  vessels  are  endowed  with  elasticity,  by 
which  the  circulation  is  considerably  facilitated,  and  with  contractility, 
by  which  the  supply  to  any  part  may  be  modified  independently  of  the 
action  of  the  heart. 

50 


CIRCULATION    OF   BLOOD    IN    THE   ARTERIES  5 1 

Circulation  of  Blood  in  the  Arteries 

The  vessels  that  carry  venous  blood  to  the  lungs  are  branches  of  a 
great  trunk  which  takes  its  origin  from  the  right  ventricle.  They  do  not 
differ  in  structure  from  the  vessels  carrying  blood  to  the  general  system, 
except  in  the  fact  that  their  coats  are  somewhat  thinner  and  more  dis- 
tensible. The  aorta,  branches  and  ramifications  of  which  supply  all  parts 
of  the  body,  is  given  off  from  the  left  ventricle.  Just  at  its  origin,  be- 
hind the  semilunar  valves,  this  vessel  has  three  sacculated  pouches  called 
the  sinuses  of  Valsalva.  Beyond  this  point  the  vessels  are  cylindrical. 
The  arteries  branch,  divide  and  subdivide,  until  they  are  reduced  to  micro- 
scopic size.  The  branches,  with  the  exception  of  the  intercostal  arteries, 
which  make  nearly  a  right  angle  with  the  thoracic  aorta,  are  given  off 
at  an  acute  angle.  As  a  rule  the  arteries  are  nearly  straight,  taking  the 
shortest  course  to  the  parts  which  they  supply  with  blood ;  and  while 
the  branches  progressively  diminish  in  size,  but  few  are  given  off  between 
the  great  trunk  and  small  vessels  that  empty  into  the  capillary  system. 
So  long  as  a  vessel  gives  off  no  branches,  its  calibre  does  not  progres- 
sively diminish ;  as  the  common  carotids,  which  are  as  large  at  their 
bifurcation  as  they  are  at  their  origin.  There  are  one  or  tw,'o  instances 
in  which  vessels,  although  giving  off  many  branches  in  their  course,  do 
not  diminish  in  size  for  some  distance ;  as  the  aorta,  which  is  as  large 
at  the  point  of  division  into  the  iliacs  as  it  is  in  the  chest,  and  the  verte- 
bral arteries,  which  do  not  diminish  in  calibre  until  they  enter  the  fora- 
men magnum.  It  has  long  been  remarked  that  the  combined  calibre  of 
the  branches  of  an  arterial  trunk  is  greater  than  that  of  the  main  vessel ; 
so  that  the  arterial  system,  as  it  branches,  increases  in  capacit}'.  A 
single  exception  to  this  rule  is  in  the  instance  of  the  common  iliacs,  the 
combined  calibre  of  which  is  less  than  the  calibre  of  the  abdominal  aorta. 

Usually  the  arteries  are  so  situated  as  not  to  be  exposed  to  pressure 
and  consequent  interruption  of  the  current  of  blood  ;  but  in  certain  situa- 
tions, as  about  some  of  the  joints,  there  is  necessarily  some  liability  to 
occasional  compression.  In  certain  parts,  also,  as  in  the  vessels  going 
to  the  brain,  particularly  in  some  of  the  inferior  animals,  it  is  necessary 
to  moderate  the  force  of  the  blood-current  on  account  of  the  delicate 
structure  of  the  organs  in  which  they  are  distributed.  Here  there  is  a 
provision  in  the  shape  of  anastomoses,  by  which,  on  the  one  hand,  com- 
pression of  a  vessel  simply  diverts  and  does  not  arrest  the  current  of 
blood,  and  on  the  other  hand,  the  current  is  rendered  more  equable  and 
the  force  of  the  heart  is  moderated. 

The  arteries  are  provided  with  fibrous  sheaths,  of  greater  or  less 
strength  as  the  vessels  are  situated  in  parts  more  or  less  exposed  to 


52  CIRCULATION    OF   THE    BLOOD 

disturbing  influences  or  accidents.  They  have  three  well-defined  coats. 
As  these  vary  considerably  in  arteries  of  different  sizes,  it  will  be  con- 
venient, in  their  description,  to  divide  the  vessels  into  three  classes :  — 

1.  The  largest  arteries;  in  which  are  included  all  that  are  larger 
than  the  carotids  and  common  iliacs. 

2.  The  arteries  of  medium  size ;  that  is,  between  the  carotids  and 
iliacs  and  the  smallest. 

3.  The  smallest  arteries;  or  those  less  than  ^  to  ^^  of  an  inch  (1.7 
to  2.1  millimeters)  in  diameter. 

The  external  coat  of  the  arteries,  called  the  tunica  adventitia,  is  the 
strongest  of  the  three.  It  is  composed  of  white  fibrous  tissue  with  a 
network  throughout  its  extent  of  yellow  elastic  fibres.  A  few  longitudi- 
nal muscular  fibres  are  found  in  this  coat.  It  is  largely  the  external  coat 
that  gives  strength  to  the  vessels.  The  nutrient  vessels  of  the  arteries 
(vasa  vasorum)  ramify  in  the  external  coat. 

The  middle  coat  is  called  the  tunica  media  and  is  composed  of  both 
muscular  and  elastic  fibres.  In  the  larger  arteries  it  is  the  thickest  coat 
of  the  three.  The  muscular  fibres  are  of  the  non-striated,  or  involuntary 
variety  and  encircle  the  vessel.  The  general  direction,  also,  of  the 
elastic  fibres  is  transverse.  These  fibres  interlace  with  each  other  in  every 
direction.  Arteries  of  different  sizes  present  differences  in  the  thickness 
and  constitution  of  the  middle  coat.  In  the  larger  vessels,  the  elastic 
elements  predominate ;  and  in  the  smaller  arteries,  the  muscular  fibres 
are  more  abundant.  In  the  very  smallest  vessels  of  supply  to  the  capil- 
lary system,  the  middle  coat  presents  muscular  fibres  only.  The  vaso- 
motor nerves  are  distributed  in  the  middle  coat. 

The  internal  coat  is  called  the  tunica  intima  and  is  composed  of  three 
layers.  This  is  sometimes  spoken  of  as  the  fenestrated  membrane  of 
Henle.  The  innermost  of  the  three  layers  of  the  intima  is  the  endothe- 
lial lining,  made  up  of  oblong  endothelial  cells  with  their  long  diameter 
in  the  direction  of  the  vessel.  Just  beneath  the  endothelial  lining  is  the 
subendothelial  layer,  composed  of  fine  branching  connective-tissue  cor- 
puscles and  fibres.  The  external  layer  of  the  intima  is  a  lamella  of  fine 
fibres  of  elastic  tissue.  These  layers  are  very  thin  in  the  smallest 
arteries  (see  Plate  III,  Figs.  2,  3,  4). 

The  elasticity  of  the  arteries  has  an  important  influence  on  the  general 
circulation.  It  provides  for  what  is  practically  a  continuous  flow  of  blood 
from  the  smallest  arteries  into  the  capillary  system.  If  it  is  possible  to 
imagine  the  arterial  system  as  consisting  of  inert  tubes,  it  is  evident  that 
the  intermittent  force  of  the  heart  would  be  quite  as  apparent  in  the 
small  as  in  the  large  arteries  ;  but  the  elasticity  of  the  walls  of  the  ves- 
sels, especially  of  the  larger  arteries,  produces  a  recoil  following  the 


PRODUCTION    OF    THE    PULSE  "  53 

contraction  of  the  ventricles,  wliicli  forces  the  blood  onward  in  the  inter- 
vals of  the  heart's  action.  This  recoil  produces  what  is  known  as  the 
dicrotic  pulse.  It  is  in  this  way  that  the  physical  property  of  elasticity 
of  the  vessels  favors  the  blood-current.  The  arteries  are  not  only  elastic 
but  contractile  ;  and  this  property,  which  gives  tonicity  to  the  vessels, 
aids  in  adapting  them  to  the  quantity  of  blood  which  they  contain  and 
regulates  the  arterial  pressure  as  well  as  the  supply  of  blood  to  different 
parts  of  the  capillary  system. 

A  study  of  the  elasticity  and  contractility  of  the  arteries  naturally  leads 
to  a  consideration  of  the  pulse.  With  each  ventricular  systole  there  is 
a  wave  of  dilatation  which  extends  from  the  aorta  to  the  smallest  arteries. 
There  is,  however,  a  slight  delay  in  the  pulse  in  the  smaller  vessels.  The 
difference  in  time  between  the  ventricular  systole  and  the  pulse  in  the 
feet  is  about  one-seventh  of  a  second. 

Locomotioji  of  the  Arteries  and  Production  of  the  Pulse.  —  With  each 
contraction  of  the  heart,  the  arteries  are  increased  in  length  and  many  of 
them  undergo  a  considerable  locomotion.  This  may  be  readily  obser\^ed 
in  vessels  that  are  tortuous  in  their  course  and  is  frequently  quite 
marked  in  the  temporal  artery  in  old  persons.  The  elongation  mav  also 
be  observed  by  watching  attentively  the  point  where  an  artery  bifurcates, 
as  at  the  division  of  the  common  carotid.  It  is  simply  the  mechanical 
effect  of  sudden  distention,  which,  while  it  enlarges  the  calibre  of  the 
vessel,  causes  an  elongation  that  is  even  miore  distinct. 

The  finger  placed  over  an  exposed  artery  or  one  that  lies  near  the 
surface  experiences  a  sensation  at  every  beat  of  the  heart  as  though  the 
vessel  were  striking  against  it.  Ordinarily  this  is  appreciated  when 
the  current  of  blood  is  subjected  to  a  certain  degree  of  obstruction,  as 
in  the  radial,  which  can  readily  be  compressed  against  the  bone.  In  an 
artery  imbedded  in  soft  parts  which  yield  to  pressure,  the  actual  dilata- 
tion of  the  vessel  being  very  slight,  pulsation  is  felt  with  difficulty  if  at  all. 
When  obstruction  of  an  artery  is  complete,  as  after  tying  a  vessel,  the 
pulsation  aboA-e  the  point  of  ligature  is  quite  marked  and  can  easily  be 
appreciated  by  the  eye.  The  explanation  of  this  exaggeration  of  the 
movement  is  the  following :  Normally,  the  blood  passes  freely  through 
the  arteries  and  produces,  in  the  smaller  vessels,  very  little  movement  or 
dilatation  ;  when,  however,  the  current  is  obstructed,  as  by  ligation  or 
even  compression  with  the  finger,  the  force  of  the  heart  is  not  sent 
through  the  vessel  to  the  periphery,  but  is  arrested  and  therefore  be- 
comes more  easily  appreciated.  In  vessels  that  have  become  undilatable 
and  incompressible  from  calcareous  deposits,  the  pulse  cannot  be  felt. 
The  character  of  the  pulse  indicates,  to  a  certain  extent,  the  condition  of 
the  heart  and  vessels. 


54  CIRCULATION   OF   THE    BLOOD 

It  is  evident  from  what  is  known  of  the  modifications  that  occur  in 
the  force  of  the  heart  and  the  quantity  of  blood  in  the  vessels,  and  from 
the  changes  which  may  take  place  in  the  calibre  of  the  arteries,  that  the 
characters  of  the  pulse  must  be  subject  to  great  variations.  Many  of 
these  may  be  appreciated  simply  by  the  sense  of  touch.  Writers  treat 
of  the  soft  and  compressible  pulse,  the  hard  pulse,  the  wiry  pulse,  the 
thready  pulse,  etc.,  as  indicating  various  conditions  of  the  arterial  system. 
The  character  of  the  pulse  in  disease,  aside  from  its  frequency,  has 
always  been  regarded  as  of  great  importance. 

Form  of  the  Pulse. — But  few  of  the  characters  of  a  pulsation,  oc- 
cupying as  it  does  only  one-seventieth  part  of  a  minute,  can  be  ascer- 
tained by  the  sense  of  touch  alone.  This  fact  has  been  appreciated  by 
physiologists;  and  within  the  last  sixty  years,  instruments  for  registering 
the  pulse  have  been  devised,  with  the  view  of  analyzing  the  dilatation 
and  movements  of  the  vessels.  The  instrument  now  used  for  this  pur- 
pose is  called  the  sphygmograph.    Vierordt  (1855)  constructed  a  complex 

apparatus,  so  arranged 
that  the  impulse  from 
an  accessible  artery,  like 
the  radial,  was  conveyed 
to  a  lever,  which  marked 
the  movement  on  a  re- 
volving cylinder.    These 

Fig.  23.  —  Trace  of  Vierordt.  '^     ■' 

traces,  hojvever,  were 
perfectly  regular  and  simply  marked  the  extremes  of  dilatation  —  exag- 
gerated, of  course,  by  the  length  of  the  lever  —  and  the  number  of 
pulsations  in  a  given  time.  The  instruments  now  in  use  differ  from 
each  other  mainly  in  the  convenience  with  which  they  are  applied,  the 
principle  in  all  being  substantially  that  of  the  sphygmograph  of  Marey. 
The  modern  instruments,  applied  to  the  radial  artery,  give  traces  quite 
different  from  those  obtained  by  Vierordt,  which  were  simply  series  of 
regular  elevations  and  depressions.  A  comparison  of  these  with  the 
traces  first  obtained  gives  an  idea  of  the  defects  that  were  remedied  by 
Marey  ;  for  it  is  evident  that  the  dilatation  and  contraction  of  the  arte- 
ries can  not  be  so  regular  and  simple  as  would  be  inferred  merely  from 
the  trace  made  by  the  instrument  of  Vierordt. 

Analyzing  the  traces  taken  by  Marey,  it  is  seen  that  there  is  a  dilata- 
tion following  the  systole  of  the  beart,  marked  by  an  elevation  of  the 
lever,  more  or  less  sudden,  as  indicated  by  the  angle  of  the  trace,  and  of 
greater  or  less  amplitude.  The  dilatation,  having  arrived  at  its  maximum, 
is  followed  by  reaction,  which  may  be  slow  and  regular,  or  may  be,  and 
ordinarily  is,  interrupted  by  a  second  and  slighter  upward  movement  of 


FORM    OF    THE    PULSE  55 

the  lever.  This  second  impulse  varies  very  much  in  amplitude.  In  some 
rare  instances,  it  is  nearly  as  marked  as  the  first  and  may  be  appreciated 
by  the  finger,  giving  the  sensation  of  a  double  pulse  following  each  con- 
traction of  the  heart.  This  is  called  the  dicrotic  pulse.  As  a  rule,  the 
first  dilatation  of  the  vessel  is  sudden  .and  is  indicated  by  an  almost 
vertical  line.  This  is  followed  by  a  comparatively  slow  reaction,  indi- 
cated by  a  gradual  descent  of  the  trace,  which  is  not,  however,  absolutely 
regular,  but  is  marked  by  a  slight  elevation  indicating  a  second  impulse. 
The  amplitude  of  the  trace,  or  the  distance  between  the  highest  and  the 
lowest  points  marked  by  the  lever,  depends  on  the  degree  of  constant 
tension  of  the  vessels.  Marey  has  found  that  the  amplitude  is  in  an 
inverse  ratio  to  the  tension ;  which  is  easily  understood,  for  when  the 
arteries  are  but  little  distended,  the  force  of  the  heart  must  be  more 
marked  in  its  effects  than  when  the  pressure  of  blood  is  greater. 

In  nearly  all  the  traces  given  by  Marey,  the  descent  of  the  lever 
indicates  more  or  less  oscillation  of  the  mass  of  blood.     The  physical 


Fig.  24.  —  Trace  of  Marey. 
Portions  of  four  traces  taken  in  different  conditions  of  the  pulse. 

properties  of  the  larger  arteries  render  this  inevitable.  As  they  yield  to 
the  distending  force  of  the  heart,  reaction  occurs  after  this  force  is  taken 
off,  and  if  the  distention  is  very  great,  gives  a  second  impulse  to  the 
blood.  This  is  quite  marked,  unless  the  tension  of  the  arterial  system 
is  so  great  as  to  offer  too  much  resistance.  One  of  the  most  favorable 
conditions  for  the  manifestation  of  dicrotism  is  diminished  tension,  which 
is  always  found  coexisting  with  a  marked  exhibition  of  this  phenomenon. 
Marey  accurately  determined  and  registered  these  various  phenomena 
and  demonstrated  that  an  important  and  essential  element  in  the  produc- 
tion of  dicrotism  is  the  tendency  to  oscillation  of  the  fluid  in  the  vessels 
during  the  intervals  between  the  contractions  of  the  heart.  This  can 
occur  only  in  a  fluid  that  has  a  certain  weight  and  acquires  a  velocity 
from  the  impulse;  and  when  air  is  introduced  into  the  apparatus,  dicro- 
tism can  not  be  produced  under  any  conditions,  as  the  fluid  does  not  pos- 
sess weight  enough  to  oscillate  between  the  impulses.  Water  showed  a 
well-marked  dicrotic  impulse  under  favorable  conditions  ;  and  with  mer- 
cury, the  oscillations  made  two,  three  or  more  distinct  impulses.  By 
these  experiments,  he  proved  that  the  blood  oscillates  in  the  vessels,  if 
this  movement  is  not  suppressed  by  too  great  pressure  or  tension.     This 


56  CIRCULATION    OF   THE    BLOOD 

oscillation  gives  the  successive  rebounds  that  are  marked  in  the  descend- 
ing line  of  the  pulse,  and  is  capable,  in  some  rare  instances  when  the 
arterial  tension  is  slight,  of  producing  a  second  rebound  of  sufficient 
force  to  be  felt  with  the  finger.  The  smallest  vessels  and  those  of 
medium  size  possess  to  an  eminent  degree  what  is  called  tonicity,  or  the 
property  of  maintaining  a  certain  continued  degree  of  contraction,  which 
is  antagonistic  to  the  distending  force  of  the  blood.  This  is  shown  by 
opening  a  portion  of  an  artery  included  between  two  ligatures  in  a  living 
animal,  when  the  contents  will  be  forcibly  discharged  and  the  calibre  of 
that  portion  of  the  vessel  be  much  diminished.  Too  great  distention  of 
the  vessels  by  pressure  of  blood  seems  to  be  prevented  by  this  constant 
action  of  the  muscular  coat;  and  thus  the  conditions  are  maintained 
that  give  to  the  pulse  the  characters  just  described. 

By  excessive  and  continued  heat,  the  muscular  structure  in  the 
arteries  may  be  dilated  so  as  to  offer  less  resistance  to  the  distending 
force  of  the  heart.  Under  these  conditions,  the  pulse,  as  felt  with  the 
finger,  will  be  found  to  be  larger  and  softer  than  normal.  Cold,  either 
general  or  local,  has  an  opposite  effect ;  the  arteries  become  contracted, 
and  the  pulse  assumes  a  harder  and  more  wiry  character.  As  a  rule, 
prolonged  contraction  of  the  arteries  is  followed  by  relaxation,  as  is  seen 
in  the  full  pulse  and  glow  of  the  surface  observed  in  reaction  after  expos- 
ure to  cold. 

Pressure  of  Blood  in  the  Arteries 

The  reaction  of  the  elastic  walls  of  the  arteries  during  the  intervals 
of  the  heart's  action  gives  rise  to  a  certain  degree  of  pressure,  by  which 
the  blood  is  continually  forced  toward  the  capillaries.  The  discharge  of 
blood  into  the  capillaries  has  a  constant  tendency  to  diminish  this  pres- 
sure ;  but  the  contractions  of  the  left  ventricle,  by  forcing  repeated  charges 
of  blood  into  the  arteries,  have  a  compensating  action.  By  the  equilib- 
rium between  these  two  agencies,  a  certain  tension  is  maintained  in  the 
arteries,  which  is  called  the  arterial  pressure. 

The  first  experiments  in  regard  to  the  extent  of  the  arterial  pressure 
were  made  by  Hales,  and  were  published  in  1733.  This  observer, 
adapting  a  long  glass  tube  to  the  artery  of  a  living  animal,  ascertained 
the  height  of  the  column  of  blood  that  could  be  sustained  by  the  arte- 
rial pressure.  In  experiments  on  the  carotid  of  the  horse,  the  blood 
mounted  to  the  height  of   eight  to  ten  feet  (243  to  304  centimeters). 

If  a  large  artery,  like  the  carotid,  is  exposed  in  a  living  animal,  and 
a  metallic  point,  connected  with  a  vertical  tube  of  smaller  calibre  and 
seven  or  eight  feet  (213  or  243  centimeters)  long  by  a  bit  of  elastic  tub- 
ing, is  secured  in  the  vessel,  the  blood  will  rise  to  the  height  of  about 


PRESSURE   OF    BLOOD    IN    THE    ARTERIES  57 

five  feet  (1.5  meters)  and  remain  at  this  point  almost  stationary,  indicat- 
ing, by  a  slight  pulsatile  movement,  the  action  of  the  heart.  Carefully 
watching  the  level  in  the  tube,  in  addition  to  the  rapid  oscillation  coinci- 
dent with  the  pulse,  another  oscillation  will  be  observed,  which  is  less 
frequent  and  which  corresponds  with  the  movements  of  respiration.  The 
pressure,  as  indicated  by  an  elevation  of  the  liquid,  is  slightly  increased 
during  expiration  and  diminished  during  inspiration.  In  such  experi- 
ments, it  is  necessary  to  fill  part  of  the  tube,  or  whatever  apparatus  is 
used,  with  a  solution  of  sodium  carbonate,  in  order  to  prevent  coagula- 
tion of  the  blood  as  it  passes  out  of  the  vessels.  The  experiment  with 
the  long  tube  gives,  perhaps,  the  best  general  idea  of  the  arterial  pres- 
sure, which  is  equal  to  about  five  feet  of  blood  (1.5  meters)  or  a  few  inches 
more  of  water.  The  oscillations  produced  by  the  contractions  of  the 
heart  are  not  very  extensive,  on  account  of  the  friction  in  so  long  a  tube  ; 
but  this  is  favorable  to  the  study  of  the  constant  pressure. 

The  experiments  of  Hales  were  made  with  a  view  of  calculating  the 
force  of  the  heart  and  were  not  directed  particularly  to  the  modifications 
and  variations  of  the  arterial  pressure.  It  is  only  since  the  experiments 
performed  by  Poiseuille  with  the  hemodynamometer,  in  1828,  that  physi- 
ologists have  had  reliable  data  on  this  latter  point.  Poiseuille's  instru- 
ment for  measuring  the  force  of  the  blood  is  a  graduated  U-tube,  half 
filled  with  mercury,  with  one  arm  bent  at  a  right  angle,  so  that  it  can 
easily  be  connected  with  the  artery.  The  pressure  of  blood  is  indicated 
by  a  depression  in  the  level  of  the  mercury  on  one  side  and  a  correspond- 
ing elevation  on  the  other.  This  instrument  possesses  certain  advan- 
tages over  the  long  glass  tube ;  but  for  estimating  simply  the  arterial 
pressure,  it  is  much  less  useful,  as  it  is  more  sensitive  to  the  impulses  of 
the  heart.  For  the  study  of  the  cardiac  pressure,  it  has  the  disadvan- 
tage, in  the  first  place,  of  considerable  friction,  and  again,  the  weight  of 
the  column  of  mercury  produces  an  extent  of  oscillation  by  mere  impe- 
tus, greater  than  that  which  would  actually  represent  the  alternation  of 
systole  and  diastole  of  the  heart. 

An  important  improvement  in  the  hemodynamometer  was  made  by 
Magendie.  This  apparatus,  the  cardiometer,  in  which  Bernard  made 
some  modifications,  is  the  one  now  commonly  used.  It  consists  of  a  small 
but  thick  glass  bottle,  with  a  fine  graduated  tube  about  twelve  inches 
(30.5  centimeters)  in  length,  communicating  with  it,  either  through  the 
stopper  or  an  orifice  in  the  side.  The  stopper  is  pierced  with  a  bent 
tube  which  is  to  be  connected  with  the  bloodvessel.  The  bottle  is  filled 
with  mercury  so  that  it  will  rise  in  the  tube  to  a  point  which  is  marked 
zero.  It  is  evident  that  the  pressure  on  the  mercury  in  the  bottle  will  be 
indicated  by  an  elevation  in  the  graduated  tube  ;  and,  moreover,  from 


58  CIRCULATION    OF   THE    BLOOD 

the  fineness  of  the  column  in  the  tube,  some  of  the  inconveniences  due 
to  the  weight  of  mercury  in  the  hemodynamometer  are  avoided,  and  there 
is,  also,  less  friction.  This  instrument  is  appropriately  called  the  cardi- 
ometer,  as  it  indicates  accurately,  by  the  extreme  elevation  of  the  mercury, 
the  force  of  the  heart ;  but  it  is  not  so  useful  in  measuring  the  mean 
arterial  pressure,  for  in  the  abrupt  descent  of  the  mercury  during  the 
diastole  of  the  heart,  the  impetus  causes  the  level  to  fall  below  the  real 
standard  of  the  constant  pressure.  Marey  corrected  this  difficulty  in  the 
"compensating  "  instrument,  which  is  constructed  on  the  following  prin- 
ciple :  Instead  of  a  simple  glass  tube  which  communicates  with  the  mer- 
cury in  the  bottle,  as  in  Magendie's  cardiometer,  there  are  two  tubes ; 
one  is  like  the  tube  already  described  and  represents  oscillations  pro- 
duced by  the  heart,  while  the  other  is  larger,  and  has,  at  the  lower  part, 
a  constriction  of  its  calibre,  which  is  here  reduced  to  capillary  fineness. 
The  latter  tube  is  designed  to  give  the  mean  arterial  pressure ;  the  con- 
stricted portion  offering  such  an  obstacle  to  the  rise  of  the  mercury  that 
the  intermittent  action  of  the  heart  is  not  felt,  the  mercury  rising  slowly 
to  a  certain  level,  which  is  constant  and  varies  only  with  the  constant 
pressure  in  the  vessels. 

The  instruments  in  use  in  physiological  laboratories  at  the  pres- 
ent day  are  modifications  of  the  "kymograph"  devised  by  Ludwig. 
Ludwig's  instrument  consists  of  a  U-tube  containing  mercury,  one 
arm  of  which  is  connected  with  an  artery.  The  mercury  in  the  distal 
arm  carries  a  float  to  which  is  attached  a  wire  terminating  in  a  writing- 
point  by  means  of  which  the  oscillations  may  be  recorded  in  the  usual 
way.  The  principle,  however,  is  the  same  as  that  of  the  instrument 
constructed  by  Poiseuille. 

Pressure  in  Differeitt  Arteries.  —  The  experiments  of  Hales,  Poi- 
seuille, Bernard  and  others  seem  to  show  that  the  constant  arterial 
pressure  does  not  vary  much  in  arteries  of  different  sizes.  These 
physiologists  experimented  particularly  on  the  carotid  and  crural,  and 
found  the  pressure  in  these  two  vessels  about  the  same.  From  their 
experiments  they  concluded  that  the  force  is  nearly  equal  in  all  parts 
of  the  arterial  system.  The  experiments  of  Volkmann,  however,  have 
shown  that  this  conclusion  is  not  correct.  With  the  registering  ap- 
paratus of  Ludwig,  he  took  the  pressure  in  the  carotid  and  the  meta- 
tarsal arteries  and  always  found  a  considerable  difference  in  favor  of 
the  former.  In  an  experiment  on  a  dog,  he  found  the  pressure  equal 
to  about  seven  inches  (172  millimeters)  in  the  carotid,  and  6.6  inches 
(165  millimeters)  in  the  metatarsal.  In  an  experiment  on  a  calf,  the 
pressure  was  4.64  inches  (116  millimeters)  in  the  carotid,  and  3.56 
inches  (89  millimeters)  in  the  metatarsal;  and  in  a  rabbit,  3.64  inches 


PRESSURE    OF   BLOOD    IN    THE   ARTERIES  59 

(91  millimeters)  in  the  carotid,  and  3.44  inches  (86  millimeters)  in  the 
crural.  These  experiments  show  that  the  pressure  is  not  the  same 
in  all  parts  of  the  arterial  system,  that  it  is  greatest  in  the  arteries 
nearest  the  heart  and  that  it  gradually  diminishes  toward  the  capil- 
laries. The  difference  is  slight,  almost  inappreciable,  except  in  vessels 
of  small  size  ;  but  here  the  pressure  is  directly  influenced  by  the  dis- 
charge of  blood  into  the  capillaries.  The  cause  of  this  diminution  of 
pressure  in  the  smallest  vessels  is  the  proximity  of  the  great  outlet  of 
the  arteries,  the  capillary  system  ;  for,  as  will  be  seen  farther  on,  the 
flow  into  the  capillaries  has  a  constant  tendency  to  diminish  the  pres- 
sure in  the  arteries. 

Influence  of  Respiration.  —  It  is  easy  to  see,  in  studying  the  arterial 
pressure,  that  there  is  a  marked  increase  with  expiration  and  a  diminu- 
tion with  inspiration.  In  tranquil  respiration  the  influence  on  the  flow 
of  blood  is  due  simply  to  the  mechanical  action  of  the  thorax.  With 
every  inspiration  the  air-cells  are  enlarged,  as  well  as  the  bloodvessels 
of  the  lungs,  the  air  rushes  in  through  the  trachea  and  the  movement 
of  the  blood  in  the  veins  near  the  chest  is  accelerated.  At  the  same 
time  the  blood  in  the  arteries  is  somewhat  retarded  in  its  flow  from  the 
thorax,  or  at  least  does  not  feel  the  expulsive  influence  which  follows 
with  the  act  of  expiration.  The  arterial  pressure  at  that  time  is  at 
its  minimum.  '  With  the  expiratory  act  the  air  is  expelled  by  com- 
pression of  the  lungs,  the  flow  of  blood  into  the  thorax  by  the  veins 
is  retarded  to  a  certain  extent,  while  the  flow  into  the  arteries  is 
favored.  This  is  shown  in  the  increased  force,  with  expiration,  in  the 
jet  from  a  divided  artery.  Under  these  conditions,  the  arterial  pres- 
sure is  at  its  maximum.  In  perfectly  tranquil  respiration,  the  changes 
due  to  inspiration  and  expiration  are  slight,  presenting  a  difference  of 
not  more  than  half  an  inch  or  an  inch  (12.7  or  25.4  millimeters)  in  the 
cardiometer.  When  the  respiratory  movements  are  exaggerated,  the 
oscillations  are  more  extensive. 

Interruption  of  respiration  is  followed  immediately  by  a  great  in- 
crease in  the  arterial  pressure.  This  is  due,  not  to  causes  within  the 
chest,  but  to  obstruction  to  the  circulation  in  the  capillaries.  With  an 
interruption  of  the  respiratory  movetnents,  the  non-aerated  blood  passes 
into  the  arteries  but  can  not  flow  readily  through  the  capillaries ;  and 
as  a  consequence  the  arteries  are  abnormally  distended  and  the  pres- 
sure is  increased.  If  respiration  is  permanently  arrested,  the  arterial 
pressure  becomes,  after  a  time,  diminished  below  the  normal  standard, 
and  is  finally  abolished  on  account  of  the  stoppage  of  the  action  of  the 
heart.  When  respiration  is  resumed  before  the  action  of  the  heart  has 
become  arrested,  the  pressure  soon  returns  to  the  normal  standard. 


6o  CIRCULATION    OF   THE    BLOOD 

biflucnce  of  Muscular  Action,  etc.  —  Muscular  effort  considerably 
increases  the  arterial  pressure.  This  is  due  to  two  causes.  In  the 
first  place,  the  chest  is  compressed,  and  this  favors  the  flow  of  blood 
into  the  great  -vessels.  In  the  second  place,  muscular  exertion  pro- 
duces a  certain  degree  of  obstruction  to  the  discharge  of  blood  from  the 
arteries  into  the  capillaries.  Experiments  on  the  inferior  animals 
show  a  great  increase  in  pressure  in  the  struggles  that  occur  during 
severe  operations.  It  has  been  shown  that  stimulation  of  the  sympa- 
thetic in  the  neck  and  of  certain  of  the  cerebro-spinal  nerves  increases 
the  arterial  pressure,  probably  from  an  influence  on  the  muscular  coats 
of  some  of  the  arteries,  causing  them  to  contract  and  thereby  dimin- 
ishing the  total  capacity  of  the  arterial  system. 

Effects  of  Hemorrhage,  etc.  —  Diminution  in  the  quantity  of  blood 
has  a  remarkable  effect  on  arterial  pressure.  If,  in  connecting  the 
instrument  with  the  arteries,  even  one  or  two  jets  of  blood  are  allowed 
to  escape,  the  pressure  will  be  found  diminished  perhaps  one-half  or 
even  more.  It  is  hardly  necessary  to  discuss  the  mechanism  of  the 
effect  of  the  loss  of  blood  on  the  tension  in  the  vessels,  but  it  is  re- 
markable how  soon  the  pressure  in  the  arteries  regains  the  normal 
standard  after  it  has  been  lowered  by  hemorrhage.  As  the  pressure 
depends  largely  on  the  quantity  of  blood,  so  soon  as  the  vessels  absorb 
serosities  in  sufficient  quantity  to  repair  the  loss,  the  pressure  is  in- 
creased. •  This  takes  place  in  a  short  time,  if  the  loss  of  blood  is  not 
too  great. 

Experiments  on  arterial  pressure  with  the  cardiometer  have  verified 
the  fact  mentioned  in  treating  of  the  form  of  the  pulse  ;  namely,  that 
the  pressure  in  the  vessels  bears  an  inverse  ratio  to  the  distention  pro- 
duced by  the  contractions  of  the  heart.  In  the  cardiometer,  the  mean 
height  of  the  mercury  indicates  the  constant,  or  arterial  pressure ;  and 
the  oscillations,  the  distention  produced  by  the  heart.  It  is  found  that 
when  the  pressure  is  great,  the  extent  of  oscillation  is  small,  and  vice 
versa.  It  will  be  remembered  that  the  researches  of  Marey  demon- 
strated that  an  increase  in  arterial  pressure  diminishes  the  amplitude 
of  the  pulsations,  as  indicated  by  the  sphygmograph,  and  that  the 
amplitude  is  great  when  the  pressure  is  slight.  It  is  also  true,  as  a 
general  rule,  that  the  force  of  the  heart,  as  indicated  by  the  cardi- 
ometer, bears  an  inverse  ratio  to  the  frequency  of  its  pulsations. 

An  instrument  called  the  sphygmomanometer  has  been  devised  for 
measuring  the  arterial  pressure  in  the  human  subject.  This  is  for  use 
chiefly  in  clinical  work  and  its  description  here  would  be  out  of  place. 
The  principle  on  which  it  is  constructed  is  to  measure  by  means  of 
a  column  of  mercury  the  pressure  required  to  arrest  the  pulse  at  the 


RAPIDITY  OF  THE  CURRENT  OF    BLOOD   IN  THE  ARTERIES       6l 

wrist,  the  pressure  being  applied  to  the  brachial  artery  just  above  the 
elbow. 

The  following  is  a  summary  of  the  conditions  that  influence  the 
arterial  pressure :  — 

The  pressure  is  increased  by  — 

1.  Increase  in  the  power  of  the  ventricular  systole. 

2.  Increase  in  the  total  quantity  of  blood. 

3.  Increased  contraction  of  the  small  vessels  that  supply  the  capil- 

lary system. 
The  pressure  is  decreased  by  — 

1.  Decrease  in  the  power  of  the  ventricular  systole. 

2.  Decrease  in  the  total  quantity  of  blood. 

3.  Decreased  contraction,  or  relaxation  of  the  small  vessels  that 

supply  the  capillary  system. 

Rapidity  of  the  Current  of  Blood  in  the  Arteries 

The  question  of  the  rapidity  of  the  flow  of  blood  in  the  arteries  has 
long  engaged  the  attention  of  physiologists ;  but  the  experiments  of 
Volkmann  with  the  hemodrometer,  and  of  Vierordt  with  a  peculiar  in- 
strument which  he  devised  for  the  purpose,  did  not  lead  to  results  that 
were  entirely  satisfactory.  The  apparatus  devised  by  Chauveau,  how- 
ever, is  more  reliable.  This  will  give,  by  calculation,  the  actual  rapidity 
of  the  current,  and  it  also  indicates  the  variations  in  velocity  that  occur 
at  different  stages  of  the  heart's  action. 

The  instrument  to  be  applied  to  the  carotid  of  the  horse  consists  of  a 
thin  brass  tube,  about  an  inch  and  a  half  (38.1  millimeters)  in  length 
and  of  the  diameter  of  the  artery  (about  three-eighths  of  an  inch,  or 
9.5  milUmeters),  which  is  provided  with  an  oblong  longitudinal  opening, 
or  window,  near  the  middle,  about  two  lines  (4.2  millimeters)  long  and 
one  line  (2.1  millimeters)  wide.  A  piece  of  thin  vulcanized  rubber  is 
wound  around  the  tube  and  firmly  tied  so  as  to  cover  this  opening. 
Through  a  transverse  slit  in  the  rubber  is  introduced  a  very  light  metal- 
lic needle,  an  inch  and  a  half  (38.1  millimeters)  in  length  and  flattened 
at  its  lower  part.  This  is  made  to  project  about  halfway  into  the  calibre 
of  the  tube.  A  flat  semicircular  piece  of  metal,  divided  into  an  arbi- 
trary scale,  is  attached  to  the  tube,  to  indicate  the  deviations  of  the  point 
of  the  needle. 

The  apparatus  is  introduced  into  the  carotid  of  a  horse,  by  making  a 
slit  in  the  vessel,  introducing  first  one  end  of  the  tube  directed  toward 
the  heart,  then  allowing  a  little  blood  to  enter  the  instrument,  so  as  to 
expel  the  air,  and,  when  full,  introducing  the  other  end,  securing  the 
whole  by  ligatures  above  and  below. 


62  CIRCULATION   OF   THE    BLOOD 

When  the  circulation  is  arrested,  the  needle  should  be  vertical  and 
mark  zero  on  the  scale.  When  the  flow  is  established,  a  deviation  of 
the  needle  occurs,  which  varies  in  extent  with  the  rapidity  of  the  current. 
Having  removed  all  pressure  from  the  vessel  so  as  to  allow  the  current 
to  resume  its  normal  character,*  the  deviations  of  the  needle  are  carefully 
noted,  as  they  occur  with  the  systole  and  with  the  diastole  of  the  heart. 
After  withdrawing  the  instrument,  it  is  appUed  to  a  tube  of  the  same 
size  of  the  artery,  in  which  a  current  of  water  is  made  to  pass  with  a 
rapidity  that  will  produce  the  same  deviations  as  occurred  when  the 
instrument  was  connected  with  the  bloodvessel.  The  rapidity  of  the 
current  in  this  tube  may  be  easily  calculated  by  receiving  the  water  in  a 
graduated  vessel  and  noting  the  time  occupied  in  discharging  a  given 
quantity.  By  this  means  the  rapidity  of  the  current  of  blood  is  as- 
certained. 

It  has  been  found  that  three  currents,  with  different  degrees  of  rapid- 
ity, may  be  distinguished  in  the  carotid  :  — 

1.  With  each  ventricular  systole,  as  the  average  of  the  experiments 
of  Chauveau,  the  blood  moves  in  the  carotids  at  the  rate  of  about  20.4 
inches  (510  millimeters)  per  second.  After  this,  the  rapidity  quickly 
diminishes  and  the  needle  returns  quite  or  nearly  to  zero,  which  would 
indicate  complete  arrest. 

2.  Immediately  succeeding  the  ventricular  systole,  a  second  impulse 
is  given  to  the  blood,  which  is  synchronous  with  the  closure  of  the  semi- 
lunar valves,  the  blood  moving  at  the  rate  of  about  8.6  inches  (215  milli- 
meters) per  second.     This  is  the  dicrotic  impulse. 

3.  After  the  dicrotic  impulse,  the  rapidity  of  the  current  gradually 
diminishes  until  just  before  the  systole  of  the  heart,  when  the  needle  is 
nearly  at  zero.  The  average  rate,  after  the  dicrotic  impulse,  is  about 
5.9  inches  (147.5  millimeters)  per  second. 

The  experiments  of  Chauveau  correspond  with  the  experiments  of 
Marey  on  the  form  of  the  pulse.  Marey  showed  that  there  is  a  marked 
oscillation  of  the  blood  in  the  vessels,  due  to  a  reaction  of  their  elastic 
walls  following  the  first  distention  by  the  heart ;  that  at  the  time  of 
closure  of  the  semilunar  valves,  the  arteries  present  a  second,  or  dicrotic 
distention,  much  less  than  the  first ;  and  following  this,  there  is  a 
gradual  decline  in  the  distention  until  the  minimum  is  reached.  Accord- 
ing to  the  observations  of  Chauveau,  corresponding  with  the  first  dilata- 
tion of  the  vessels,  the  blood  moves  with  great  rapidity  ;  following  this, 
the  current  suddenly  becomes  nearly  arrested  ;  this  is  followed  by  a 
second  acceleration  in  the  current,  less  than  the  first ;  and  following  this, 
there  is  a  gradual  decline  in  the  rapidity,  to  the  time  of  the  next 
pulsation. 


PHYSIOLOGICAL   ANATOMY    OF    THE  CAPILLARIES  63 

From  the  fact  that  the  arterial  system  progressively  increases  in 
capacity,  there  should  be  found  a  corresponding  diminution  in  the 
rapidity  of  the  flow  of  blood.  There  are,  however,  many  conditions, 
aside  from  simple  increase  in  the  capacity  of  the  vessels,  which  modify 
the  blood-current  and  render  inexact  calculations  made  on  purely  physical 
principles.  These  are  the  tension  of  the  blood  and  the  conditions  of 
contraction  or  relaxation  of  the  smallest  arteries.  It  is  necessary,  there- 
fore, to  have  recourse  to  actual  experiments  to  arrive  at  definite  results 
on  this  point.  Volkmann  found  a  great  difference  in  the  rapidity  of  the 
current  in  the  carotid  and  metatarsal  arteries,  the  averages  being  about 
10  inches  (254  millimeters)  per  second  in  the  carotid,  and  about  2.2 
inches  (56  miUimeters) 'in  the  metatarsal.  The  same  difference,  al- 
though not  quite  so  marked,  was  found  by  Chauveau,  between  the 
carotid  and  the  facial.  As  the  vessels  are  farther  and  farther  removed 
from  the  heart,  the  systolic  impulse  rapidly  diminishes,  being  reduced 
in  one  experiment  by  about  two-thirds;  the  dicrotic  impulse  becomes 
feeble  or  may  even  disappear ;  but  the  constant  flow  is  much  increased 
in  rapidity.  The  rapidity  of  the  flow  in  any  given  artery  must  be  sub- 
ject to  modifications  due  to  the  condition  of  the  arterioles  \vhich  are  sup- 
plied by  it.  When  these  little  vessels  are  dilated,  the  artery,  of  course, 
supplies  blood  with  greater  facility  and  the  rapidity  of  the  flow  is 
increased. 

Circulation  of  Blood  in  the  Capillaries 

Before  beginning  the  study  of  the  capillary  circulation,  it  should 
be  understood  what  is  meant  by  capillary  vessels  as  distinguished  from 
the  smallest  arteries  and  veins.  From  a  physiological  point  of  view,  the 
capillaries  are  to  be  regarded  as  beginning  where  the  blood  is  brought 
near  enough  to  the  tissues  to  enable  them  to  separate  the  matters  neces- 
sary for  their  regeneration  and  to  give  up  the  products  of  their  physio- 
logical wear;  but  at  present  it  is  impossible  to  assign  any  limit  where 
the  vessels  cease  to  be  simple  carriers  of  blood,  and  it  is  not  known  to 
what  part  of  the  vascular  system  the  processes  of  nutrition  are  exclu- 
sively confined.  The  divisions  of  the  bloodvessels  must  be,  to  a  certain 
extent,  arbitrarily  defined.  The  most  simple  view  is  to  regard  as  capil- 
laries vessels  that  have  but  a  single  coat ;  for  in  these,  the  blood  is  brought 
in  closest  proximity  to  the  tissues.  Vessels  that  are  provided,  in  addi- 
tion, with  a  muscular  or  with  muscular  and  fibrous  coats  may  be  con- 
sidered as  either  small  arteries  or  veins. 

Physiological  Anatomy  of  the  Capillaries.  —  If  the  arteries  are  fol- 
lowed out  to  their  minutest  ramifications,  they  will  be  found  progressively 
diminishing  in  size  as  they  branch,  and  their  coats,  especially  the  mus- 


64  CIRCULATION   OF   THE   BLOOD 

cular  coat,  becoming  thinner  and  thinner,  until  at  last  they  present 
an  internal  structureless  coat  lined  by  endothelium  with  oval  longitudi- 
nal nuclei,  a  middle  coat  formed  of  but  a  single  layer  of  circular  muscular 
fibres,  and  an  external  coat  composed  of  a  thin  layer  of  longitudinal 
bundles  of  fibrous  tissue.  These  vessels  are  ^-J-q  to  ^to  ^^  ^^  ^^^^ 
(62.5  to  125  /x)  in  diameter.  They  undoubtedly  possess  contractility, 
which  is  particularly  marked  in  the  arterial  system.  Following 
the  course  of  the  vessels,  when  they  are  reduced  in  size  to  about 
g-^  of  an  inch  (31  /x),  the  fibrous  coat  is  lost,  and  the  vessel  then 
presents  only  the  internal  coat  and  a  single  layer  of  muscular  fibres. 
The  vessels  become  smaller  as  they  branch,  finally  lose  the  muscular 
fibres  and  have  then  but  a  single  coat.  These  last  may  be  regarded 
as  the  true  capillary  vessels. 

The  single  coat  of  the  capillaries  consists  of  a  layer  of  fusiform  or 
polygonal  nucleated  endothelium  of  excessive  tenuity.  The  borders  of 
the  endothelial  cells  may  be  seen  after  staining  the  vessels  with  silver 
nitrate.  In  the  smallest  capillaries  the  cells  are  narrow  and  elon- 
gated or  fusiform  ;  and  in  the  larger  vessels  they  are  more  polygonal, 
with  irregular  borders.  In  staining  with  silver  nitrate,  irregular  non- 
nucleated  areas  frequently  are  brought  into  view ;  and  it  has  been  sup- 
posed by  some  that  these  indicate  the  presence  of  stomata,  or  orifices 
in  the  walls  of  the  vessels. 

The  diameter  of  the  capillaries  usually  is  as  small  as  that  of  the 
blood-corpuscles  ;  or  it  may  be  smaller,  so  that  these  bodies  move  in  a 
single  line  and  must  become  deformed  in  passing  through  the  smallest 
vessels,  recovering  their  normal  shape,  however,  when  they  pass  into 
vessels  of  larger  size.  The  capillaries  are  smallest  in  the  nervous  and 
muscular  tissue,  retina,  and  patches  of  Peyer,  where  they  have  a  diameter 
of  eoV^  ^o  4  0^07  of  ^^  ^^^^  (4-25  to  6.25  fx).  In  the  papillary  layer  of 
the  skin  and  in  the  mucous  membranes  they  are  4-500  ^^  24V0  of  an 
inch  (6.25  to  10  fx)  in  diameter.  They  are  largest  in  the  glands  and 
bones,  where  they  are  3o\)'o  ^o  2W0  of  an  inch  (8.3  to  12.5  fx)  in  diame- 
ter. It  is  only  the  largest  vessels  that  allow  the  passage  of  blood-disks 
without  change  in  form.  The  average  length  of  the  capillary  vessels  is 
about  -g^Q-  of  an  inch  (0.5  millimeter). 

Unlike  the  arteries,  which  grow  smaller  as  they  branch,  and  the  veins, 
which  become  larger  in  following  the  course  of  the  blood,  by  union  with 
each  other,  the  capillaries  form  a  true  plexus  of  vessels  of  nearly  uniform 
diameter,  branching  and  inosculating  in  every  direction  and  distributing 
blood  to  the  parts  as  their  physiological  necessities  demand.  This  mode 
of  inosculation  is  peculiar  to  these  vessels,  and  the  plexus  is  rich  in  the 
tissues,  as  a  general  rule,  in  proportion  to  the  activity  of  their  nutrition. 


PHYSIOLOGICAL   ANATOMY    OF    THE   CAPILLARIES 


65 


Although  their  arrangement  presents  certain  differences  in  different 
organs,  the  capillary  vessels  have  everywhere  the  same  general  charac- 
ters, the  most  prominent  of  which  are  a  nearly  uniform  diameter  and  an 
apparent  absence  of  any  definite  direction  in  their  branchings.  The 
network  thus  formed  is  rich  in  the  parenchyma  of  the  glands  and  in 
the  organs  of  absorption.  In  the  walls  of  the  pulmonary  alveoli  the 
meshes  are  particularly  close.  In  other  parts  the  vessels  are  not 
so  abundant,  presenting  great  variations  in  different  tissues.  In  the 
muscles  and  nerves,  in  which  nutrition  is  very  active,  the  supply  of 
blood  is  greater  than   in  other 

parts,    like    fibro-serous     mem-  ^.  -  ^  -  ^ 

branes,  tendons,  etc.  In  none 
of  the  tissues  do  the  capillaries 
penetrate  the  true  anatomical 
elements  of  the  parts,  as  the 
ultimate  muscular  or  nervous 
fibres.  Some  tissues  receive  no 
blood  —  at  least  they  contain 
no  vessels  that  are  capable  of 
carrying  red  blood  —  and  are 
nourished  by  imbibition  of  nu- 
trient matters  from  the  blood- 
plasma. 

The  capacity  of  the  capillary 
system  is  very  large.  It  is  neces- 
sary only  to  consider  the  great 
vascularity  of  the  skin,  mucous 
membrane  or  muscles,  to  appre- 
ciate this  fact.  In  injections  of 
these  parts,  it  seems,  on  microscopical  examination,  as  though  they 
contained  nothing  but  capillaries  ;  but  in  preparations  of  this  kind, 
the  coats  of  the  capillaries  are  distended  to  their  utmost  limit.  Under 
some  conditions  in  health,  they  are  largely  distended  with  blood,  as  in 
the  mucous  lining  of  the  alimentary  canal  during  digestion,  the  whole 
surface  presenting  a  vivid  red  color,  indicating  the  richness  of  the  capil- 
lary plexus.  Estimates  of  the  capacity  of  the  capillary  system,  as  com.- 
pared  with  the  arterial  system,  have  been  made,  but  they  are  simply 
approximative.  The  various  estimates  given  are  founded  on  calcula- 
tions from  microscopical  examinations  of  the  rapidity  of  the  capillary 
circulation  as  compared  with  the  circulation  in  the  arteries.  In  this  way, 
it  has  been  calculated  that  the  capacity  of  the  capillary  system  is  be- 
tween five  hundred  and  eight  hundred  times  that  of  the  arterial  system. 


^^- 1^:^- 


Fig.  25.  —  Small  arterv  and  capillaries  from  the 
muscular  coat  of  the  urinary  bladder  of  a  frog,  x  400 
(from  a  photograph  taken  at  the  United  States  Army 
Medical  Museum). 

This  preparation  shows  the  endothelium  of  the 
vessels.  It  is  injected  with  silver  nitrate  and  mounted 
in  Canada  balsam. 


^  CIRCULATION    OF    THE    BLOOD 

The  most  convenient  part  for  direct  observation  of  the  capillary 
circulation  is  the  tongue  or  the  web  of  the  frog.  Here  may  be  studied, 
not  only  the  movement  of  the  blood  in  the  capillaries,  but  the  circula- 
tion in  the  smallest  arteries  and  veins,  the  variations  in  calibre  of  these 
vessels,  especially  the  arterioles,  by  the  action  of  their  muscular  coat, 
and,  indeed,  the  action  of  vessels  of  considerable  size.  This  has  been 
a  valuable  means  of  studying  the  circulation  in  the  capillaries  as  con- 
trasted with  the  flow  in  the  small  arteries  and  veins. 

In  studying  the  circulation  under  the  microscope,  the  anatomical 
division  of  the  blood  into  corpuscles  and  a  clear  plasma  is  observed. 
This  is  peculiarly  evident  in  cold-blooded  animals,  the  corpuscles  being 
comparatively  large  and  floating  in  a  plasma  that  forms  a  distinct 
layer  next  the  walls  of  the  vessel.  The  leucocytes,  which  are  much 
fewer  than  the  red  corpuscles,  are  found  usually  in  the  layer  of 
plasma. 

In  vessels  of  considerable  size,  as  well  as  in  some  capillaries,  the 
corpuscles,  occupying  the  central  portion,  move  with  greater  rapidity 
than  the  rest  of  the  blood,  leaving  a  comparatively  still  layer  of  plasma 
at  the  sides.  A  red  corpuscle  occasionally  becomes  involved  in  the 
"  still  layer,"  when  it  moves  slowly,  turning  over  and  over,  or  even  may 
remain  stationary  for  a  time,  until  it  is  taken  up  again  and  carried 
along  with  the  central  current.  A  few  leucocytes  are  constantly  seen 
in  this  layer.  They  move  along  slowly  and  apparently  have  a  ten- 
dency to  adhere  to  the  walls  of  the  vessel.  This  is  due  to  the  adhesive 
character  of  the  surface  of  the  white  corpuscles  as  compared  with  the 
red,  which  can  easily  be  observed  in  examining  a  drop  of  blood  be- 
tween glass  surfaces,  the  red  corpuscles  moving  about  freely,  while  the 
white  corpuscles  have  a  tendency  to  adhere  to  the  glass. 

Great  differences  exist  in  the  character  of  the  flow  of  blood  in  the 
three  varieties  of  vessels  under  observation.  In  the  arterioles,  which 
may  be  distinguished  from  the  capillaries  by  their  size  and  the 
presence  of  the  muscular  and  fibrous  coats,  the  movement  is  distinctly 
pulsatile,  even  in  their  most  minute  ramifications.  The  blood  moves 
in  them  with  greater  rapidity  than  in  either  the  capillaries  or  veins. 
They  become  smaller  as  they  branch,  and  carry  the  blood  always  in 
the  direction  of  the  capillaries.  The  veins,  which  are  relatively 
larger  than  the  arteries,  carry  the  blood  more  slowly  and  in  a 
continuous  stream  from  the  capillaries  toward  the  heart.  In  both 
the  arteries  and  veins,  the  current  is  frequently  so  rapid  that  the 
form  of  the  corpuscles  can  not  be  distinguished.  Only  a  few  of  the 
leucocytes  occupy  the  still  layer,  the  others  being  carried  on  in  the 
central  current. 


RELATIONS   OF    CAPILLARY    CIRCULATION    TO   RESPIRATION       6/ 

In  the  true  capillaries,  the  blood  is  distributed  in  every  direction, 
in  vessels  of  nearly  uniform  diameter.  The  vessels  usually  are  so 
small  as  to  admit  but  a  single  row  of  corpuscles.  In  a  single  vessel, 
a  line  of  corpuscles  may  be  seen  moving  in  one  direction  at  one  mo- 
ment, and  a  few  moments  after,  taking  an  opposite  course.  When  the 
•circulation  is  normal,  the  movement  in  the  capillaries  is  always  quite 
slow  as  compared  with  the  current  in  the  arterioles,  and  is  continuous. 
Here,  at  last,  the  intermittent  impulse  of  the  heart  is  lost.  The 
corpuscles  do  not  necessarily  circulate  in  all  the  capillaries  that  are 
in  the  field  of  view.  Certain  vessels  may  not  receive  a  corpuscle  for 
some  time,  but  afterward,  one  or  two  corpuscles  become  engaged  in 
them  and  a  current  is  established.  In  some  of  the  vessels  of  smallest 
size,  the  corpuscles  are  slightly  deformed  as  they  pass  through.  The 
scene  is  changed  with  every  different  part  that  is  examined.  In  the 
tongue,  in  addition  to  the  arterioles  and  venules  and  the  rich  network 
of  capillaries,  dark-bordered  nerve-fibres,  striated  muscular  fibres, 
and  epithelium  can  be  distinguished.  In  the  lungs  large  polygonal 
air-cells  are  observed,  bounded  by  capillary  vessels  in  which  the  cor- 
puscles move  with  great  rapidity.  It  has  been  observed,  also,  that  the 
larger  vessels  in  the  lungs  are  crowded  to  their  utmost  capacity  with  red 
corpuscles. 

Pressure  of  Blood  in  the  Capillaries.  —  There  is,  apparently,  no  way 
of  directly  estimating  the  pressure  of  blood  in  the  capillaries.  If,  how- 
ever, a  glass  plate  is  placed  on  a  part  in  which  the  capillary  circulation 
is  active  and  is  weighted  until  the  subjacent  capillaries  are  emptied,  an 
approximate  idea  of  the  blood-pressure  in  the  vessels  may  be  obtained. 
Experiments  made  in  this  way,  by  Von  Kries,  show  that  the  pressure 
in  the  capillaries  of  the  hand  raised  above  the  head  is  equal  to  a  little 
less  than  one  inch  (24  millimeters)  of  mercury;  in  the  hand  hanging 
down,  a  little  more  than  two  inches  (54  millimeters) ;  and  in  the  ear, 
about  0.8  of  an  inch  (20  millimeters.) 

Rapidity  of  the  Capillaiy  Circulation.  —  The  current  in  the  capillaries 
of  a  part  is  subject  to  such  variations,  and  the  differences  in  different 
situations  are  so  considerable,  that  it  is  impossible  to  give  a  definite  rate 
that  will  represent  the  general  rapidity  of  the  capillary  circulation  ;  and 
in  view  of  the  uncertainty  of  the  methods  employed,  it  seems  unnecessary 
to  discuss  this  question  fully.  Volkmann  calculated  the  rapidity  in  the 
mesentery  of  the  dog  and  found  it  to  be  0.02  to  0.03  of  an  inch  (0.5  to 
0.75  millimeters)  per  second. 

Relations  of  the  Capillary  Circ?ilation  to  Respiration.  —  The  immediate 
effects  of  asphyxia  on  the  circulation  are  referable  to  the  general  capil- 
lary system.     In  a  series  of  experiments  made  on  frogs,  in  1857  (Flint), 


68  CIRCULATION    OF   THE    BLOOD 

the  buib  was  broken  up  and  the  web  of  the  foot  was  submitted  to  micro- 
scopical examination.  The  cutaneous  surface  was  then  coated  with  col- 
lodion, care  only  being  taken  to  avoid  the  web  under  observation.  The 
effect  on  the  circulation  was  immediate.  It  instantly  became  less  rapid, 
until,  at  the  expiration  of  twenty  minutes,  it  had  entirely  ceased.  The 
entire  coating  of  collodion  was  then  instantly  peeled  off.  Quite  a  rapid- 
circulation  immediately  began,  but  it  soon  declined  and  in  twenty  min- 
utes had  nearly  ceased.  In  another  observation,  the  coating  of  collodion 
was  applied  without  destroying  the  bulb.  The  circulation  was  affected 
in  the  same  manner  as  before  and  ceased  in  twenty-five  minutes.  These 
experiments,  taken  in  connection  with  observations  on  the  influence  of 
asphyxia  on  the  arterial  pressure,  show  that  non-aerated  blood  can  not 
circulate  freely  in  the  systemic  capillaries,  probably  on  account  of  con- 
traction of  the  muscular  coat  of  the  small  arteries,  due  to  irritation  from 
an  excess  of  carbon  dioxide  in  the  blood. 

Causes  of  the  Capillary  CirciLlation.  —  The  pressure  in  the  arteries, 
which  forces  the  blood  toward  the  capillaries,  is  competent,  unless 
opposed  by  contraction  of  the  arterioles,  not  only  to  send  the  blood 
through  the  capillaries  but  to  return  it  to  the  heart  by  the  veins.  A 
distinct  impulse,  following  each  ventricular  systole,  is  observed  in  the 
smallest  arteries ;  the  blood  flows  from  them  directly  and  freely  into  the 
capillaries ;  and  there  is  no  ground  for  the  supposition  that  the  force  is 
not  propagated  to  this  system  of  vessels.  There  is,  therefore,  a  force  — 
the  action  of  the  heart  —  that  is  capable  of  producing  the  capillary  circu- 
lation ;  and  there  is  nothing  in  the  phenomena  of  the  circulation  in  these 
vessels  inconsistent  with  its  full  operation. 

Influence  of  Temperature  on  the  Capillary  Circulation.  —  Within  mod- 
erate limits,  a  low  temperature,  produced  by  local  applications,  has  been 
found  to  diminish  the  quantity  of  blood  sent  to  the  capillaries  and  retard 
the  circulation,  while  a  high  temperature  increases  the  supply  of  blood 
and  accelerates  its  current.  Poiseuille  found  that  when  a  piece  of  ice 
was  applied  to  the  web  of  a  frog's  foot,  the  mesentery  of  a  small  warm- 
blooded animal  or  to  any  part  in  which  the  capillary  circulation  could 
be  observed,  the  number  of  corpuscles  circulating  in  the  arterioles 
was  much  diminished,  "  those  which  carried  two  or  three  rows  of  cor- 
puscles giving  passage  to  but  a  single  row."  The  circulation  in  the 
capillaries  first  became  slower  and  then  entirely  ceased  in  parts.  On 
removing  the  ice,  in  a  very  few  minutes  the  circulation  regained  its 
former  characters.  When,  on  the  other  hand,  the  part  was  covered 
with  water  at  104°  Fahr.  (40°  C),  the  rapidity  of  the  current  in  the 
capillaries  was  so  much  increased  that  the  form  of  the  corpuscles  could 
with  difificulty  be  distinguished. 


CIRCULATION    OF    BLOOD    IN    THE   VEINS 


69 


Circulation  of  Blood  in  the  Veins 

The  blood,  distributed  to  the  capillaries  of  all  the  tissues  and  organs 
by  the  arteries,  is  collected  from  these  parts  in  the  veins  and  carried 
to  the  right  side  of  the  heart.  In  studying  the  anatomy  of  the  capil- 
laries or  in  observing  the  passage  of  the  blood  from  the  capillaries  to 
larger  vessels  in  parts  of  the  living  organism  that  can  be  submitted  to 
microscopical  examination,  it  is  seen  that  the  capillaries  —  vessels  of 
nearly  uniform  diameter  and  anastomosing  in  every  direction  —  empty 
into  a  system  of  vessels,  which, 


i'Mr^ij 


by  union  with  others,  become 
larger  and  larger,  and  carry  the 
blood  away  in  a  continuous  cur- 
rent, in  which  the  intermittent 
impulse  derived  from  the  left 
ventricle  is  not  manifest.  These 
vessels  are  called  venules,  or 
venous  radicles.  They  are  the 
peripheral  radicles  of  the  vessels 
that  carry  the  blood  to  the  heart. 
The  venous  system  may  be 
considered  as  divided  into  two 
sets  of  vessels :  one,  which  is 
deep-seated   and  is   situated    in       „.      ,      ,^  .■  ,        ,      .    --  „ 

xj.v.,v.j_>  vjv,ij.i.v.^     c4.i  V4.  ^  Fig.  26.  —  Venous  raJu-ZcS  uniting  to  form  a  stnall 

proximity    to      the  arteries,     and  vein,  from  the  muscular  coat  0/ the  urinary  bladder  0/ 

,,  ,1  ,  .    ,  .  n    •    -t  a  frop,  X  400  (from  a  photOOTaph  taken  at  the  United 

the    other,    which  is     superficial  statef  Army  Medical  Museum) 

and  receives  the  greatest  part  This  preparation  shows  the  endothelium  of  the 
of  the  blood  from  the  cutaneous    ^^^sels.     it  is  injected  with  silver  nitrate  and  mounted 

in  Canada  balsam. 

surface.     The  entire  capacity  of 

the  venous  system,  as  compared  with  that  of  the  arteries,  is  very  great. 
As  a  rule,  each  vein,  when  fully  distended,  is  larger  than  its  adjacent 
artery.  Many  arteries  are  accompanied  by  two  veins,  as  the  arteries 
of  the  extremities ;  while  certain  of  them,  hke  the  brachial  or  spermatic, 
have  more  than  two.  Added  to  these,  are  the  superficial  veins,  which 
have  no  corresponding  arteries.  It  is  true  that  some  arteries  have  no 
corresponding  veins,  but  examples  of  this  kind  are  not  sufficient  in 
number  to  diminish,  in  any  marked  degree,  the  great  preponderance  of 
the  veins,  both  in  number  and  volume.  It  is  impossible  to  give  any- 
thing like  an  accurate  estimate  of  the  extreme  capacity  of  the  veins  as 
compared  with  the  arteries,  but  it  must  be  much  greater.  Borelli 
estimated  that  the  capacity  of  the  veins  was  to  the  capacity  of  the 
arteries,  as  4  to  i  ;  and  Haller,  as  2^  to  i.     The  proportion  is  variable 


JO  CIRCULATION   OF   THE    BLOOD 

in  different  parts  of  the  body.  In  some  situations  the  capacity  of  the 
veins  and  arteries  is  about  equal ;  while  in  others,  as  in  the  pia  mater, 
the  veins  contain,  when  fully  distended,  six  times  as  much  blood  as  the 
arteries. 

In  attempting  to  compare  the  quantity  of  blood  normally  circulating 
in  the  veins  with  that  contained  in  the  arteries,  such  variations  are  found 
at  different  times  and  in  different  parts,  both  in  the  quantity  of  blood, 
rapidity  of  circulation,  pressure  etc.,  that  a  definite  estimate  is  impos- 
sible. It  would  be  unprofitable  to  attempt  even  an  approximate  com- 
parison, as  the  variations  in  the  venous  circulation  constitute  one  of 
its  most  important  physiological  peculiarities,  which  must  be  fully 
appreciated  in  order  to  form  a  just  idea  of  the  uses  of  the  veins. 
The  arteries  are  always  full,  and  their  tension  is  subject  to  com- 
paratively slight  changes.  Following  the  blood  into  the  capillaries, 
important  modifications  in  the  circulation  are  observed  under  varying 
physiological  conditions  of  the  parts.  As  would  naturally  be  expected, 
the  condition  of  the  veins  varies  with  the  changes  in  the  capillaries 
from  which  the  blood  is  received. 

Following  the  veins  in  their  course,  it  is  observed  that  anastomoses 
with  each  other  form  the  rule,  and  not  the  exception,  as  in  the  arteries. 
There  is  always  a  number  of  channels  by  which  the  blood  may  be  re- 
turned from  a  part ;  and  if  one  vessel  is  obstructed  from  any  cause, 
the  current  is  diverted  into  another.  The  veins  do  not  present  a  true 
anastomosing  plexus,  such  as  exists  in  the  capillary  system,  but  simply 
an  arrangement  by  which  the  blood  may  readily  find  its  way  back  to 
the  heart,  and  by  which  the  vessels  can  accommodate  themselves  to 
variations  in  the  quantity  of  their  contents. 

Structure  and  Properties  of  the  Veins.  —  The  structure  of  the  veins 
is  more  complex  than  that  of  the  arteries.  Their  walls,  which  are  always 
much  thinner  than  the  walls  of  the  arteries,  may  be  divided  into  a  num- 
ber of  layers ;  but  for  convenience  of  physiological  description,  they 
may  be  regarded  as  presenting  three  coats. 

The  internal  coat  of  the  veins  is  a  continuation  of  the  single  coat  of 
the  capillaries  and  of  the  internal  coat  of  the  arteries.  It  is  in  the  form 
of  a  fenestrated  membrane,  somewhat  thinner  than  in  the  arteries,  lined 
with  a  delicate  layer  of  polygonal  endothelium,  the  cells  of  which  are 
shorter  and  broader  than  the  endothelial  cells  lining  the  arteries. 

The  middle  coat  is  divided  by  some  anatomists  into  two  layers ;  an 
internal  layer,  composed  chiefly  of  longitudinal  fibres,  and  an  external 
layer,  in  which  the  fibres  have  a  circular  direction.  These  two  layers 
are  intimately  adherent  and  are  quite  closely  attached  to  the  internal 
coat.     The  longitudinal  fibres  are  composed  of  connective-tissue  fibres 


STRUCTURE  AND  PROPERTIES  OF  THE  VEINS        /I 

with  a  large  number  of  the  smallest  variety  of  the  elastic  fibres.  This 
layer  contains  capillary  vessels  (vasa  vasorum).  The  circular  fibres 
are  composed  of  elastic  tissue,  some  of  the  fibres  of  the  same  variety  as 
is  found  in  the  longitudinal  layer,  some  of  medium  size,  and  some  in  the 
form  of  a  "  fenestrated  membrane."  In  addition,  there  are  inelastic 
fibres  interlacing  in  every  direction  and  mingled  with  capillary  blood- 
vessels and  non-striated  muscular  fibres.  In  the  human  subject,  in  the 
veins  of  the  central  portion  of  the  nervous  system,  the  dura  mater,  the 
pia  mater,  the  bones,  the  retina,  the  vena  cava  descendens,  the  thoracic 
portion  of  the  vena  cava  ascendens,  the  external  and  internal  jugulars 
and  the  subclavian  veins,  there  are  no  muscular  fibres  in  the  middle 
coat.  In  the  larger  veins,  such  as  the  abdominal  vena  cava,  the  iliac, 
crural,  popliteal,  mesenteric  and  axillary  veins,  there  are  both  longitu- 
dinal and  circular  fibres.  In  the  smaller  veins  the  fibres  are  circular. 
In  the  smallest  veins  the  middle  coat  is  composed  of  fine  fibres  of  con- 
nective tissue  with  a  very  few  muscular  fibres. 

The  external  coat  of  the  veins  is  composed  of  ordinary  fibrous  tissue, 
like  that  of  the  corresponding  coat  of  the  arteries.  In  the  largest  veins, 
particularly  those  of  the  abdominal  cavity,  this  coat  contains  a  layer  of 
longitudinal  non-striated  muscular  fibres.  In  the  veins  near  the  heart 
are  found  a  few  striated  fibres,  which  are  continued  on  to  the  veins 
from  the  auricle  (see  Plate  III,  Fig.  i). 

The  venous  sinuses  and  the  veins  that  pass  through  bony  tissue 
have  only  the  internal  coat,  to  which  are  added  a  few  longitudinal  fibres, 
the  vessels  being  closely  attached  to  the  surrounding  parts.  As  exam- 
ples may  be  mentioned  the  sinuses  of  the  dura  mater  and  the  veins  of 
the  large  bones  of  the  skull.  In  the  first  instance,  there  is  little  more 
than  the  internal  coat  of  the  vein  firmly  attached  to  the  surrounding 
layers  of  the  dura  mater.  In  the  second  instance,  the  same  thin  mem- 
brane is  adherent  to  canals  formed  by  a  layer  of  compact  bony  tissue. 
The  veins  are  more  closely  adherent  to  the  surrounding  tissues  than  the 
arteries,  particularly  when  they  pass  between  layers  of  aponeurosis. 
When  a  vein  is  cut  across,  its  walls  fall  together,  if  not  supported  by 
adhesions  to  surrounding  tissues,  so  that  its  calibre  is  nearly  or  quite 
obliterated.  The  elastic  tissue,  which  gives  to  the  larger  arteries  their 
great  thickness,  is  scanty  in  the  veins,  and  the  thin  walls  collapse  when 
not  sustained  by  liquid  in  the  interior  of  the  vessels. 

Although  with  much  thinner  walls,  the  veins,  as  a  rule,  will  resist  a 
greater  pressure  than  the  arteries.  Wintringham  (1740)  showed  that 
the  inferior  vena  cava  of  a  sheep,  just  above  the  opening  of  the  renal 
veins,  was  ruptured  by  a  pressure  of  one  hundred  and  seventy-six  pounds 
(79.8   kilos),  while  the    aorta,  at  a  corresponding  point,   yielded  to  a 


72  CIRCULATION    OF   THE    BLOOD 

pressure  of  one  hundred  and  fifty-eight  pounds  (71.7  kilos).  The 
strength  of  the  portal  vein  was  even  greater,  supporting  a  pressure  of 
nearly  five  atmospheres,  bearing  a  relation  to  the  vena  cava  of  six  to 
five ;  yet  these  vessels  had  hardly  one-fifth  the  thickness  of  the  arteries. 
In  the  lower  extremities  in  the  human  subject,  the  veins  are  thicker 
and  stronger  than  in  other  situations,  a  provision  against  the  increased 
pressure  to  which  they  are  habitually  subjected  in  the  upright  posture. 
Wintringham  noticed  a  singular  exception  to  the  general  rule  just  given. 
In  the  vessels  of  the  glands  and  of  the  spleen,  the  strength  of  the  arter- 
ies was  greater  than  that  of  the  veins.  The  splenic  vein  gave  way 
under  a  pressure  of  little  more  than  one  atmosphere,  while  the  artery 
supported  a  pressure  of  more  than  six  atmospheres. 

The  veins  possess  a  considerable  degree  of  elasticity,  although  this 
property  is  not  so  marked  as  it  is  in  the  arteries.  If  a  portion  of  a  vein 
distended  with  blood  is  included  between  two  ligatures  and  a  small  open- 
ing is  made  in  the  vessel,  the  blood  will  be  ejected  with  some  force,  and 
the  vessel  becomes  much  reduced  in  calibre. 

It  has  been  shown  by  direct  experiment  that  the  veins  are  endowed 
with  the  peculiar  contractility  characteristic  of  the  action  of  the  non- 
striated  muscular  fibres.  On  electric  or  mechanical  stimulation,  they 
contract  slowly  and  gradually,  the  contraction  being  followed  with  a 
correspondingly  gradual  relaxation.  There  is  never  any  rhythmical  or 
peristaltic  movement  in  the  veins  sufficient  to  assist  the  circulation.  The 
only  regular  movements  that  occur  are  seen  in  vessels  in  immediate 
proximity  to  the  right  auricle,  which  are  provided  with  a  few  fibres  simi- 
lar to  those  which  exist  in  the  walls  of  the  heart. 

Nerves  from  the  vasomotor  system  have  been  demonstrated  in  the 
walls  of  the  larger  veins  but  have  not  been  followed  out  to  the  smaller 
ramifications. 

Valves  of  the  Veins.  —  In  all  parts  of  the  venous  system,  except,  in 
general  terms,  in  the  abdominal,  thoracic  and  cerebral  cavities,  there  exist 
little  membranous  semilunar  folds,  resembling  the  aortic  and  pulmonic 
valves  of  the  heart.  When  the  valves  are  closed,  their  convexities  look 
toward  the  periphery.  In  the  great  majority  of  instances,  the  valves 
exist  in  pairs ;  but  they  are  occasionally,  although  very  rarely  in  the 
human  subject,  found  in  groups  of  three.  They  are  seldom  if  ever  found 
in  veins  of  a  less  diameter  than  one  Hne  (2.1  millimeters).  The  valves 
are  formed  in  part  of  the  lining  membrane  of  the  veins,  with  fine  fibres 
of  connective  tissue,  elastic  fibres  and  non-striated  muscular  fibres. 
There  exists,  also,  a  fibrous  ring  following  the  line  of  attachment  of  the 
valvular  curtains  to  the  vein,  which  renders  the  vessel  stronger  and  less 
dilatable  here  than  in  the  portions  between  the  valves.     The  valves  are 


VALVES   OF    THE    VEINS  73 

most  abundant  in  the  veins  of  the  lower  extremities.  They  usually  are  sit- 
uated just  below  the  point  where  a  small  vein  empties  into  one  of  larger 
size,  so  that  the  blood  as  it  enters  finds  an  immediate  obstacle  to  passage 
in  the  wrong  direction.  The  situation  of  the  valves  may  be  readily  ob- 
served in  any  of  the  superficial  veins.  If  the  flow  of  blood  is  obstructed, 
little  knots  will  be  formed  in  the  congested  vessels,  which  indicate  the 
position  and  action  of  the  valves.  When  the  vein  is  thus  congested  and 
knotted,  if  the  finger  is  pressed  along  the  vessel  in  the  direction  of  the 
blood-current,  a  portion  situated  between  two  valves  may  be  emptied  of 
blood ;  but  it  is  impossible  to  empty  any  part  of  the  vessel  by  pressing 
the  blood  in  the  opposite  direction  (Harvey).  On  slitting  open  a  vein, 
it  is  easy  to  observe  the  shape,  attachment  and  delicacy  of  structure  of 
the  valves.  When  the  vessel  is  empty  or  when  the  blood  moves  toward 
the  heart,  the  valves  are  closely  applied  to  the  walls ;  but  if  liquid  or 
air  is  forced  in  the  opposite  direction,  they  project  into  its  calibre, 
and  by  the  application  of  their  free  edges  to  each  other,  effectually 
prevent  any  backward  current.  When  closed,  the  application  of 
their  free  edges  forms  a  line  which  runs  across  the  vessel.  It  is 
found  that  in  successive  sets  of  valves  these  lines  are  at  right  angles 
to  each  other,  so  that  if  in  one  set  this  line  has  a  direction  from  before 
backward,  in  the  sets  above  and  below,  the  lines  run  from  side  to  side 
(Fabricius). 

There  are  exceptions  to  the  general  proposition  that  the  veins  of  the 
great  cavities  are  not  provided  with  valves.  Valves  are  found  in  the 
portal  system  of  some  of  the  inferior  animals,  as  in  the  horse.  They  do  not 
exist,  however,  in  this  situation  in  the  human  subject.  Usually,  in  fol- 
lowing out  the  branches  of  the  inferior  vena  cava,  no  valves  are  found 
until  the  crural  vein  is  reached ;  but  occasionally  there  is  a  double  valve 
at  the  opening  of  the  external  iliac.  In  some  of  the  inferior  animals, 
there  exists  constantly  a  single  valvular  fold  in  the  vena  cava  at  the 
openings  of  the  hepatic,  and  one  at  the  opening  of  the  renal  vein.  These 
are  not  constant  in  the  human  subject.  Valves  are  found  in  the  spermatic, 
but  not  in  the  ovarian  veins.  A  single  valvular  fold  has  been  described 
at  the  opening  of  the  right  spermatic  into  the  vena  cava.  There  are 
two  valves  in  the  azygos  vein  near  its  opening  into  the  superior  vena 
cava.  There  is  a  single  valve  at  the  opening  of  the  coronary  vein. 
There  are  no  valves  at  the  opening  of  the  brachio-cephalic  into  the 
superior  vena  cava;  but  there  is  a  strong  double  valve  at  the  point 
where  the  internal  jugular  opens  into  the  brachio-cephalic.  Between 
this  point  and  the  capillaries  of  the  brain,  the  vessels  have  no  valves, 
except  in  rare  instances,  when  one  or  two  are  found  in  the  course  of  the 
jugular. 


74  CIRCULATION    OF   THE    BLOOD 

In  addition  to  the  double,  or  more  rarely  triple  valves  just  described, 
there  is  another  variety,  found  in  certain  parts,  at  the  point  where  a 
tributary  vein  opens  into  a  main  trunk.  This  consists  of  a  single  fold, 
which  is  attached  to  the  smaller  vessel  but  projects  into  the  larger.  The 
veins  are  adapted  to  the  return  of  blood  to  the  heart  in  a  comparatively 
slow  and  unequal  current.  Distention  of  certain  portions  is  provided 
for  ;  and  the  vessels  are  so  protected  with  valves,  that  whatever  influences 
the  current  must  favor  its  flow  in  the  direction  of  the  heart. 

The  experiments  of  Hales  and  Sharpey,  showing  that  defibrinated 
blood  can  be  made  to  pass  from  the  arteries  into  the  capillaries  and  out 
at  the  veins  by  a  pressure  less  than  that  which  exists  in  the  arterial 
system,  and  the  observations  of  Magendie  on  the  circulation  in  the  leg 
of  a  living  dog,  showing  that  ligation  of  the  artery  arrests  the  flow  in 
the  vein,  have  established  the  fact  that  the  force  exerted  by  the  left 
ventricle  is  sufficient  to  account  for  the  venous  circulation.  The  force 
of  the  heart,  therefore,  must  be  regarded  as  the  prime  cause  of  the 
movement  of  blood  in  the  veins. 

As  a  rule,  in  the  normal  circulation,  the  flow  of  blood  in  the  veins 
is  continuous  and  uniform.  The  intermittent  impulse  of  the  heart, 
which  progressively  diminishes  toward  the  periphery,  but  is  still  felt 
even  in  the  smallest  arteries,  is  lost  in  the  capillaries.  Here,  for  the 
first  time,  the  blood  moves  in  a  constant  current ;  and  as  the  pressure 
in  the  arteries  is  continually  supplying  fresh  blood,  that  which  has 
circulated  in  the  capillaries  is  forced  into  the  venous  radicles  in  a 
steady  stream.  As  the  supply  to  the  capillaries  of  different  parts  is 
regulated  by  the  action  of  the  small  arteries,  and  as  this  supply  is  sub- 
ject to  great  variations,  there  must  necessarily  be  corresponding  varia- 
tions in  the  current  in  the  veins  and  in  the  quantity  of  blood  which 
these  vessels  receive. 

It  often  occurs  that  a  vein  becomes  obstructed  from  some  cause  that 
is  entirely  physiological,  such  as  the  action  of  muscles.  The  great 
number  of  veins,  as  compared  with  the  arteries,  and  their  free  com- 
munications with  each  other,  provide  that  the  current,  under  these 
conditions,  simply  is  diverted,  passing  to  the  heart  by  another  channel. 
When  any  part  of  the  venous  system  is  distended,  the  vessels  react 
on  the  blood  and  exert  a  certain  influence  on  the  current,  always  press- 
ing it  toward  the  heart,  for  the  valves  oppose  a  flow  in  the  opposite 
direction. 

Pressure  of  Blood  in  the  Veins 

The  pressure  in  the  veins  is  always  much  less  than  in  the  arteries,  and 
is  variable  in  different  parts  of  the  venous  system  and  in  the  same  part 


RAPIDITY   OF    THE    CURRENT    OF    BLOOD    LN    THE   VEINS         75 

at  different  times.  As  a  rule,  it  is  in  an  inverse  ratio  to  the  arterial  pres- 
sure. Whatever  favors  the  passage  of  blood  from  the  arteries  into  the 
capillaries  has  a  tendency  to  diminish  the  arterial  pressure,  and  as  it 
increases  the  quantity  of  blood  passing  into  the  veins,  it  must  increase 
the  venous  pressure.  The  great  capacity  of  the  venous  system,  its 
frequent  anastomoses  and  the  presence  of  valves  which  may  shut  off  a 
portion  from  the  rest,  are  conditions  that  involve  considerable  varia- 
tions in  pressure  in  different  vessels.  Muscular  effort  has  a  decided 
influence  on  the  force  of  the  circulation  in  certain  veins  and  produces 
an  elevation  in  the  pressure.  As  the  reduced  pressure  in  the  veins  is 
due  in  a  measure  to  the  great  relative  capacity  of  the  venous  system 
and  the  free  communications  between  the  vessels,  it  would  seem  that 
if  it  were  possible  to  reduce  the  capacity  of  the  veins  in  a  part  and 
force  all  the  blood  to  pass  to  the  heart  by  a  single  vessel  corresponding 
to  the  artery,  the  pressure  in  this  vessel  would  be  greatly  increased. 
Poiseuille  has  shown  this  to  be  the  fact  by  the  experiment  of  tying  all 
the  veins  coming  from  a  part,  except  one  which  had  the  volume  of  the 
artery  by  which  the  blood  was  supplied,  forcing  all  the  blood  to  return 
by  this  single  channel.  This  being  done,  he  found  that  the  pressure  in 
the  vein  was  much  increased,  becoming  nearly  equal  to  the  pressure  in 
the  artery. 

Rapidity  of  the  Current  of  Blood  in  thp  Veins 

It  is  impossible  to  fix  on  any  definite  rate  as  representing  the  ra- 
pidity of  the  current  of  blood  in  the  veins.  It  will  be  seen  that  various 
conditions  are  capable  of  increasing  very  considerably  the  rapidity  of 
the  flow  in  certain  veins,  and  that  the  current  in  some  parts  of  the 
venous  system  may  be  much  retarded.  Undoubtedly,  the  general 
movement  of  blood  in  the  veins  is  much  slower  than  in  the  arteries, 
from  the  fact  that  the  quantity  of  blood  is  greater.  If  it  is  assumed 
that  the  quantity  of  blood  in  the  veins  is  double  that  contained  in  the 
arteries,  the  general  average  of  the  current  would  be  diminished  one- 
half.  Near  the  heart,  however,  the  flow  becomes  more  uniform  and 
progressively  increases  in  rapidity,  as  the  quantity  of  blood  received  by 
the  heart  is  equal  to  the  quantity  discharged  into  the  arteries. 

As  the  effect  of  the  heart's  action  on  the  venous  circulation  is  subject 
to  many  modifying  influences  through  the  small  arteries  and  capillaries, 
and  as  there  are  other  forces  influencing  the  current,  that  are  by  no 
means  uniform  in  their  operation,  estimates  of  the  general  rapidity  of 
the  venous  circulation  or  of  the  variations  in  different  vessels  must 
necessarily  be  indefinite. 


>j^  CIRCULATION   OF   THE    BLOOD 

Causes  of  the  Venous  Circulation 

In  the  veins,  the  blood  is  farthest  removed  from  the  influence  of 
the  contractions  of  the  left  ventricle  ;  and  although  these  are  felt,  there 
are  many  other  causes  that  combine  to  carry  on  the  venous  circulation, 
and  many  influences  by  which  it  is  retarded  or  obstructed.  The  prin- 
cipal and  uniform  force  operating  on  the  circulation  in  these  vessels  is 
the  vis  a  tcrgo.  Reference  has  been  made  to  the  adequacy  of  the 
arterial  pressure,  extending  through  the  capillaries,  to  account  for  the 
movement  of  blood  in  the  veins,  provided  there  be  no  great  obstacles 
to  the  current.  The  other  forces  which  concur  to  produce  movement 
of  blood  in  the  veins  are  the  following  :  — 

1.  Muscular  action,  by  which  many  of  the  veins  are  at  times  com- 
pressed, thus  forcing  the  blood  toward  the  heart,  regurgitation  being 
prevented  by  the  action  of  the  valves. 

2.  A  suction  force  exerted  by  the  action  of  the  thorax  in  inspiration, 
operating,  however,  only  on  veins  in  the  immediate  neighborhood  of 
the  chest. 

3.  A  possible  influence  from  contraction  of  the  coats  of  the  vessels 
themselves.  This  is  marked  in  the  veins  near  the  heart,  in  some  of 
the  inferior  animals. 

4.  The  force  of  gravity,  which  operates  only  on  vessels  that  carry 
blood  from  above  downward  to  the  heart,  and  a  slight  suction  force 
which  may  be  eJcerted  on  the  blood  in  a  small  vein  as  it  passes  into  a 
larger  vessel  in  which  the  current  is  more  rapid. 

The  obstacles  to  the  venous  circulation  are  :  pressure  sufficient  to 
obliterate  the  calibre  of  a  vessel,  when,  from  the  free  communications 
with  other  vessels,  the  current  is  diverted  into  another  channel ;  ex- 
piratory efforts ;  the  contractions  of  the  right  side  of  the  heart ;  and 
the  force  of  gravity,  which  operates,  in  the  erect  posture,  on  the  cur- 
rent in  all  excepting  the  veins  of  the  head,  neck  and  parts  of  the  trunk 
above  the  heart. 

hifluence  of  Muscular  Contraction.  —  That  the  action  of  muscles  has 
considerable  influence  on  the  current  of  blood  in  the  veins  situated  be- 
tween them  and  in  their  substance,  has  long  been  recognized ;  and  this 
action  is  so  marked,  that  the  vessels  distributed  to  muscular  tissue  have 
been  compared  by  Chassaignac  to  a  sponge  full  of  liquid,  \dgorously 
pressed  by  the  hand.  It  must  be  remembered,  however,  that  although 
the  muscles  are  capable  of  acting  on  the  blood  contained  in  veins  in 
their  substance  with  great  vigor,  the  heart  is  fully  competent  to  carry  on 
the  venous  circulation  without  their  aid  ;  a  fact  exemplified  in  the  venous 
circulation  in  paralyzed  parts. 


CAUSES    OF   THE   VENOUS    CIRCULATION  JJ 

It  has  been  shown  by  actual  observations  with  the  hemodynamometer, 
that  muscular  action  is  capable  of  increasing  the  pressure  in  certain 
veins.  Bernard  found  that  the  pressure  in  the  jugular  of  a  horse,  in  re- 
pose, was  1.4  inch  (31.8  miUimeters) ;  but  the  action  of  the  muscles  in 
raising  the  head  increased  it  to  a  little  more  than  five  inches  (127  milli- 
meters), or  nearly  four  times.  Such  observations  show  at  once  the  great 
variations  in  the  current  and  the  important  influence  of  muscular  contrac- 
tion on  the  venous  circulation. 

In  order  that  contractions  of  muscles  shall  assist  the  venous  circula- 
tion, two  conditions  are  necessary  :  — 

1.  The  contractions  must  be  intermittent.  This  is  always  the 
case  in  the  voluntary  muscles.  It  is  a  view  entertained  by  many  physi- 
ologists that  each  muscular  fibre  relaxes  immediately  after  its  contrac- 
tion, which  is  instantaneous,  and  that  a  certain  period  of  rest  is  necessary 
before  it  can  contract  again.  However  this  may  be,  it  is  well  known 
that  all  active  muscular  contraction,  as  distinguished  from  the  efforts 
necessary  to  maintain  the  body  in  certain  ordinary  positions,  is  intermit- 
tent and  not  very  prolonged.  Thus  the  veins,  which  are  partly  emptied 
by  the  compression,  are  filled  again  during  the  repose  of  the  muscle. 

2.  There  should  be  no  possibihty  of  a  retrograde  movement  of  the 
blood.  This  condition  is  fulfilled  by  the  action  of  the  valves.  Ana- 
tomical researches  have  shown,  also,  that  these  valves  are  most  abundant 
in  veins  situated  in  the  substance  of  or  between  the  muscles  ;  and  they 
do  not  exist  in  the  veins  of  the  cavities,  which  are  not  subject  to  the 
same  kind  of  compression. 

Force  of  Aspiration  from  the  TJiorax. —  During  the  act  of  inspiration, 
the  enlargement  of  the  thorax,  by  depression  of  the  diaphragm  and  eleva- 
tion of  the  ribs,  affects  the  movements  of  fluids  in  all  the  tubes  in  its 
vicinity.  The  air  enters  by  the  trachea  and  expands  the  lungs  so  that 
they  follow  the  movements  of  the  thoracic  walls.  The  flow  of  blood  into 
the  great  arteries  is  somewhat  retarded,  as  is  indicated  by  a  diminution 
in  the  arterial  pressure ;  and  finally,  the  blood  in  the  great  veins  passes 
to  the  heart  with  greater  facility  and  in  increased  quantity.  This  last- 
mentioned  phenomenon  can  be  readily  observed,  when  the  veins  are 
prominent,  in  profound  or  violent  inspiration.  The  veins  at  the  lower 
part  of  the  neck  are  then  seen  to  empty  themselves  of  blood  during  in- 
spiration, and  they  become  distended  during  expiration,  producing  a  sort 
of  pulsation  that  is  synchronous  with  respiration.  This  can  always  be 
observed  after  exposure  of  the  jugular  in  the  lower  part  of  the  neck. 
Direct  observations  on  the  jugulars,  however,  show  that  the  influence  of 
inspiration  can  not  be  felt  much  beyond  these  vessels.  They  are  seen 
to  collapse  with  each  inspiratory  act,  a  condition  which  Hmits  this  influence 


78  CIRCULATION    OF   THE    BLOOD 

to  the  veins  near  the  heart.  The  flaccidity  of  the  wall  of  the  veins  will 
not  permit  the  extended  action  of  any  suction  force.  In  the  circulation, 
the  veins  are  moderately  distended  with  blood  by  the  vis  a  tergo,  and, 
to  a  certain  extent,  they  are  supported  by  connections  with  surrounding 
tissues,  so  that  the  force  of  aspiration  is  felt  farther  than  in  experiments 
on  vessels  removed  from  the  body.  The  blood,  as  it  approaches  the 
thorax,  impelled  by  other  forces,  is  considerably  accelerated  in  its  flow ; 
but  it  is  evident  that  beyond  a  certain  distance,  and  that  very  near  the 
chest,  ordinary  aspiration  has  no  influence,  and  violent  efforts  rather  retard 
than  favor  the  venous  current. 

In  the  Uver  the  influence  of  inspiration  becomes  an  important  element 
in  the  mechanism  of  the  circulation.  This  organ  presents  a  vascular 
arrangement  that  is  exceptional.  The  blood,  distributed  by  the  arteries 
in  a  capillary  plexus  in  the  mucous  membrane  of  the  alimentary  canal 
and  in  the  spleen,  instead  of  being  returned  directly  to  the  heart  by  the 
veins,  is  collected  into  the  portal  vein,  carried  to  the  liver  and  is  there 
distributed  in  a  second  set  of  capillary  vessels.  It  is  then  collected  in 
the  hepatic  veins  and  carried  by  the  vena  cava  to  the  heart.  The  three 
hepatic  veins  open  into  the  inferior  vena  cava  near  the  diaphragm,  where 
the  force  of  aspiration  from  the  thorax  would  materially  assist  the  current 
of  blood.  On  following  these  vessels  into  the  substance  of  the  liver,  it  is 
found  that  their  walls  are  so  firmly  adherent  to  the  hepatic  tissue,  that 
when  cut  across,  they  remain  patulous  ;  and  it  is  evident  that  they  must 
remain  open  under  all  conditions.  The  thorax  can  therefore  exert  a 
powerful  influence  on  the  hepatic  circulation  ;  for  it  is  only  the  flaccidity 
of  the  walls  of  the  vessels  which  prevents  this  influence  from  operating 
throughout  the  venous  system.  Although  this  must  be  an  important 
element  in  the  circulation  in  the  liver,  the  fact  that  the  blood  circu- 
lates in  this  organ  in  the  foetus  before  any  movements  of  the  thorax 
take  place  shows  that  it  is  not  essential. 

Aside  from  the  pressure  exerted  by  the  contraction  of  muscles  and 
the  force  of  aspiration  from  the  thorax,  the  influences  that  assist  the 
venous  circulation  are  insignificant.  There  is  a  slight  contraction  in 
the  venae  cavae  in  the  immediate  proximity  of  the  heart,  which  is  more 
extended  in  many  of  the  lower  vetebrate  animals  and  may  be  mentioned 
as  having  an  influence  —  very  small  it  is  true  —  on  the  flow  of  blood 
from  the  great  veins. 

In  the  veins  that  pass  from  above  downward,  the  force  of  gravity 
favors  the  flow  of  blood.  This  is  shown  by  the  turgescence  of  the  veins 
of  the  neck  and  face  when  the  head  is  kept  for  a  short  time  below  the 
level  of  the  heart.  If  the  arm  is  elevated  above  the  head,  the  veins  of 
the  back  of  the  hand  are  reduced  in  size,  from  the  greater  facility  with 


USES    OF   THE   VALVES    OF   THE    VEINS  79 

which  the  blood  passes  to  the  heart,  while  they  are  distended  when  the 
hand  is  allowed  to  hang  by  the  side  and  the  blood  has  to  rise  against 
the  force  of  gravity. 

Some  physiologists  are  of  the  opinion  that  the  right  ventricle  exerts 
an  active  suction  force  during  its  diastole ;  but  experiments  on  animals 
do  not  sustain  this  view,  and  if  such  a  force  be  exerted,  its  effect  on  the 
circulation,  even  in  the  veins  near  the  heart,  must  be  very  slight.  In  the 
great  irregularity  in  the  rapidity  of  the  circulation  in  different  veins,  it 
must  frequently  happen  that  a  vessel  empties  its  blood  into  another  of 
larger  size  in  which  the  current  is  more  rapid.  In  such  an  instance,  as 
a  physical  necessity,  the  more  rapid  current  in  the  large  vein  exerts  a 
certain  suction  force  on  the  blood  in  the  smaller  vessel. 


Uses  of  the  Valves  of  the  Veins 

There  are  two  distinct  conditions  under  which  the  valves  of  the  veins 
may  be  closed.  One  is  the  arrest  of  circulation,  from  any  cause,  in  veins 
in  which  the  blood  has  to  rise  against  the  force  of  gravity  ;  and  the 
other,  compression  of  veins,  from  any  cause  —  usually  from  muscular 
contraction  —  which  tends  to  force  the  blood  from  the  vessels  com- 
pressed, into  others,  when  the  valves  offer  an  obstruction  to  a  flow  toward 
the  capillaries  and  necessitate  a  current  in  the  direction  of  the  heart.  In 
the  first  of  these  conditions,  the  valves  are  antagonistic  to  the  force  of 
gravity;  and  when  a  vessel  is  temporarily  obstructed,  they  aid  in  directing 
the  current  into  anastomosing  vessels.  It  is  but  rarely,  however,  that 
they  act  thus  in  opposition  to  the  force  of  gravity ;  and  it  is  only  when 
many  of  the  veins  of  a  part  are  simultaneously  compressed  that  they  aid 
in  diverting  the  current.  When  a  single  vein  is  obstructed,  it  is  not  prob- 
able that  the  valves  are  necessary  to  divert  the  current  into  other  vessels, 
for  this  would  take  place  in  obedience  to  the  vis  a  tergo  ;  but  when  many 
veins  are  obstructed  in  a  dependent  part  and  the  avenues  to  the  heart 
become  insufficient,  the  valves  divide  the  columns  of  blood,  so  that  the 
pressure  is  equally  distributed  throughout  the  extent  of  the  vessels. 
This  is,  however,  but  an  occasional  action  of  the  valves  ;  and  it  is  evi- 
dent that  their  influence  is  only  to  prevent  the  weight  of  the  entire  col- 
umn of  blood  from  operating  on  the  smallest  veins  and  the  capillaries. 

It  is  in  connection  with  the  intermittent  compression  of  the  veins 
that  the  valves  have  their  principal  use.  Their  situation  alone  leads  to 
this  supposition.  They  are  found  in  greatest  numbers  throughout  the 
muscular  system,  having  been  demonstrated  in  vessels  one  line  (2.1  milli- 
meters) in  diameter.  They  are  also  found  in  the  upper  parts  of  the  body, 
where  they  certainly  do  not  operate  against  the  force  of  gravity,  while 


8o  CIRCULATION    OF   THE    BLOOD 

they  do  not  exist  in  the  cavities,  where  the  venous  trunks  are  not  sub- 
ject to  compression.  In  the  action  of  muscles,  the  skin  frequently  is 
stretched  over  the  part,  and  the  cutaneous  veins  are  somewhat  com- 
pressed. This  may  be  seen  in  the  hand,  by  letting  it  hang  by  the  side 
until  the  veins  become  swollen,  and  then  contracting  the  muscles,  when 
the  skin  will  become  tense  and  the  veins  much  less  prominent.  Here 
the  valves  have  an  important  action.  The  compression  of  the  veins  is 
greater  in  the  substance  of  and  between  the  muscles  than  in  the  skin ; 
but  the  blood  is  forced  from  the  muscles  into  the  skin,  and  the  valves 
act  to  prevent  it  from  taking  a  retrograde  course. 

Co7iditions  that  impede  Venous  Circulation.  —  Expiration,  in  its  influ- 
ence on  the  circulation  in  veins  near  the  thorax  is  directly  opposed  to 
inspiration.  As  inspiration  has  a  tendency  to  draw  the  blood  from  these 
vessels  into  the  chest,  expiration  assists  in  forcing  the  blood  out  from 
the  vessels  of  the  thorax  and  opposes  a  flow  in  the  opposite  direction. 
The  effect  of  prolonged  and  violent  expiratory  efforts  is  quite  marked, 
being  followed  by  congestion  of  the  veins  of  the  face  and  neck  and  a 
sense  of  fulness  in  the  head,  which  may  become  distressing.  The  op- 
position to  the  venous  current  usually  extends  only  to  vessels  in  the 
immediate  vicinity  of  the  thorax,  or  it  may  be  stated  in  general  terms, 
to  those  veins  in  which  the  flow  of  blood  is  assisted  by  the  movements 
of  inspiration ;  but  while  the  inspiratory  influence  is  confined  to  a  very 
restricted  circuit  of  vessels,  the  obstructive  influence  of  violent  and 
prolonged  expiration  may  be  extended  much  farther,  as  is  seen  when 
the  vessels  of  the  neck,  face  and  conjunctiva  become  congested  in  pro- 
longed vocal  efforts,  blowing  etc.  This  is  not  simply  a  reflux  from  the 
large  trunks  of  the  thoracic  cavity ;  for  in  this  case,  it  would  be 
necessary  to  assume  an  insufficiency  of  certain  valves,  which  does  not 
exist. 

It  is  in  the  internal  jugular  that  the  influence  of  expiration  is  most 
important,  both  on  account  of  its  great  size  in  the  human  subject,  as 
compared  with  the  other  vessels,  and  the  importance  and  delicacy  of  the 
parts  from  which  it  collects  the  blood.  At  the  opening  of  this  vessel 
into  the  innominate  vein,  is  a  pair  of  strong  and  perfect  valves,  which 
effectually  close  the  orifice  when  there  is  a  tendency  to  regurgitation. 
When  the  act  of  expiration  arrests  the  onward  flow  in  the  veins  near  the 
thorax,  these  valves  are  closed  and  protect  the  brain  from  congestion 
by  regurgitation.  The  blood  accumulates  behind  the  valves,  but  the 
free  communication  of  the  internal  jugular  with  the  other  veins  of  the 
neck  relieves  the  brain  from  congestion,  unless  the  effort  is  extraordi- 
narily violent  and  prolonged. 

It  is  evident  that  there  are  other  conditions  that  may  impede  the 


CIRCULATION    IN    THE   CRANIAL    CAVITY  8 1 

venous  circulation.  Accidental  compression  may  temporarily  arrest 
the  flow  in  some  one  vein.  When  the  volume  of  blood  is  materially 
increased,  as  after  a  full  meal  with  copious  ingestion  of  liquids,  the 
additional  quantity  of  blood  accumulates  mainly  in  the  venous  system 
and  proportionally  diminishes  the  rapidity  of  the  venous  circulation. 

The  force  of  gravity  also  has  an  important  influence.  It  is  more 
difflcult  for  the  blood  to  pass  from  below  upward  to  the  heart  than  to 
flow  downward  from  the  head  and  neck.  The  action  of  this  is  seen  if 
comparison  is  made  between  the  circulation  in  the  arm  elevated  above 
the  head  and  hanging  by  the  side.  In  the  one  case  the  veins  are 
readily  emptied  and  contain  but  little  blood,  and  in  the  other,  the  circu- 
lation is  more  difficult  and  the  vessels  are  moderately  distended.  The 
walls  of  the  veins  are  thickest  and  the  valves  are  most  abundant  in 
parts  of  the  body  that  are  habitually  dependent. 

Circulation  in  Special  Parts 

Circulation  in  the  Cranial  Cavity.  —  In  the  encephalic  cavity  there 
are  certain  peculiarities  in  the  anatomy  of  some  of  the  vessels,  with 
exceptional  conditions  of  the  blood  as  regards  atmospheric  pressure, 
that  have  been  regarded  as  capable  of  considerably  modifying  the  circu- 
lation. In  the  adult  the  cranium  is  a  closed  air-tight  box,  containing 
the  incompressible  cerebral  substance,  blood,  lymph  and  the  cephalo- 
rachidian  fluid ;  and  the  blood  is  here  under  conditions  quite  different 
from  those  presented  in  other  parts.  The  venous  passages  in  the  brain, 
which  correspond  to  the  great  veins  in  other  situations,  are  in  the  form 
of  sinuses  between  the  layers  of  the  dura  mater  and  are  but  slightly  dilat- 
able. In  the  perfectly  consolidated  adult  head,  the  blood  is  not  sub- 
jected to  atmospheric  pressure,  as  in  other  parts,  and  the  semisolids 
and  liquids  which  make  up  the  encephalic  mass  can  not  increase  in  size 
in  congestion  and  diminish  in  anemia.  Nothwithstanding  these  con- 
ditions, the  fact  remains  that  examinations  of  the  vessels  of  the  brain 
after  death  show  differences  in  the  quantity  of  blood.  The  question 
then  arises  as  to  what  is  displaced  to  make  room  for  the  blood  in  con- 
gestion, and  what  supplies  the  place  of  the  blood  in  anemia.  An 
anatomical  peculiarity  not  yet  considered  offers  an  explanation  of 
these  conditions.  Between  the  pia  mater  and  the  arachnoid  of  the 
brain  and  spinal  cord  there  exists  a  liquid,  the  cephalo-rachidian  fluid, 
that  may  pass  from  the  surface  of  the  brain  to  the  spinal  canal  and 
communicates  with  the  contents  of  the  ventricles  (Magendie).  The 
communication  between  the  cranial  cavity  and  the  spinal  canal  is  quite 
free.     It  is  easy  to   see  one  of  the  physiological  uses  of  this  liquid. 


82  CIRCULATION    OF   THE    BLOOD 

When  the  pressure  of  blood  in  the  arteries  going  to  the  brain  is  in- 
creased or  when  there  is  an  obstacle  to  the  return  of  blood  by  the  veins, 
more  or  less  congestion  takes  place,  and  the  blood  forces  the  liquid 
from  the  cranial  cavity  into  the  spinal  canal.  The  reverse  takes  place 
when  the  supply  of  blood  to  the  brain  is  diminished. 

The  influence  of  gravity  on  the  cerebral  circulation  may  be  consider- 
able, as  is  shown  by  the  following  experiment :  If  an  ordinary  "  hutch  " 
rabbit  is  held  by  the  ears  with  the  body  dependent,  the  supply  of  blood 
to  the  brain  becomes  so  far  reduced  that  the  animal  soon  becomes  un- 
conscious and  will  die  if  kept  in  this  position  for  half  an  hour ;  but  if 
placed  in  the  horizontal  position,  it  is  soon  restored  to  consciousness. 
This  is  due  to  large  accumulation  of  blood  in  the  pendulous  abdominal 
cavity  and  a  consequent  deficient  supply  to  the  encephalon. 

Cimilatioji  in  Erectile  Tiss?ies.  —  In  the  organs  of  generation  of  both 
sexes,  there  exists  a  tissue  that  is  subject  to  increase  in  volume  and  hard- 
ness when  in  a  condition  of  what  is  called  erection.  The  parts  in  which 
the  erectile  tissue  exists  are,  in  the  male,  the  corpora  cavernosa  of  the 
penis,  the  corpus  spongiosum  and  the  glans  penis;  and  in  the  female, 
the  corpora  cavernosa  of  the  clitoris,  the  gland  of  the  clitoris  and  the 
bulb  of  the  vestibule. 

The  vascular  arrangement  in  erectile  organs  is  peculiar  and  is  not 
found  in  any  other  part  of  the  circulatory  system.  Taking  the  penis  as 
an  example,  the  arteries,  which  have  an  unusually  thick  muscular  layer, 
after  they  have  entered  the  organ,  do  not  simply  branch  and  subdivide, 
as  in  most  other  parts,  but  send  off  large  numbers  of  arborescent  branches, 
which  immediately  become  tortuous  and  are  distributed  in  the  cavernous 
and  spongy  bodies  in  anastomosing  vessels,  which  have  but  a  single  thin 
homogeneous  coat.  These  vessels  are  larger,  even,  than  the  arterioles 
which  supply  them  with  blood,  some  having  a  diameter  of  0^5  to  -^j  of  an 
inch  ( I  to  1.5  millimeters).  The  cavernous  bodies  have  an  external  invest- 
ment of  strong  fibrous  tissue  of  considerable  elasticity,  which  sends  bands, 
or  trabeculae,  into  the  interior,  by  which  they  are  divided  up  into  cells. 
The  trabeculae  are  composed  of  fibrous  tissue  mixed  with  a  large  number  of 
non-striated  muscular  fibres.  These  cells  lodge  the  bloodvessels,  which 
ramify  in  the  tortuous  manner  already  indicated  and  finally  terminate  in 
the  veins.  The  anatomy  of  the  corpora  spongiosa  is  essentially  the  same, 
the  only  difference  being  that  the  fibrous  envelope  and  the  trabeculae  are 
more  delicate  and  the  cells  are  smaller. 

During  sexual  excitement,  or  when  erection  occurs  from  any  cause,  the 
thick  muscular  walls  of  the  arteries  of  supply  relax  and  allow  the  arterial 
pressure  to  distend  the  capacious  vessels  lodged  in  the  cells  of  the  cav- 
ernous and  spongy  bodies.     This  produces  the  characteristic  change  in 


PULMONARY    CIRCULATION  83 

the  volume  and  position  of  the  organ.  It  is  evident  that  erection  de- 
pends on  the  peculiar  arrangement  of  the  bloodvessels,  and  is  not  simply 
a  congestion,  such  as  might  occur  in  any  vascular  part.  During  erection 
there  is  not  a  stasis  of  blood ;  but  if  it  continues  for  a  certain  time,  the 
quantity  passing  out  by  the  veins  must  be  equal  to  that  which  passes  in 
by  the  arteries. 

Denvative  Circjilation.  —  In  some  parts  of  the  circulatory  system, 
there  exists  a  direct  communication  between  the  arteries  and  the  veins, 
so  that  all  the  blood  does  not  necessarily  pass  through  the  true  capillaries. 
This  peculiarity,  which  had  been  noted  by  Todd  and  Bowman,  Paget  and 
others,  has  been  closely  studied  by  Sucquet.  By  using  a  black  solidifi- 
able  injection,  he  found  certain  parts  of  the  upper  and  lower  extremities 
and  the  head,  which  became  colored  by  the  injection  while  other  parts 
were  not  penetrated.  Following  the  vessels  by  dissection,  he  showed 
that  in  the  upper  extremity,  the  skin  of  the  fingers  and  part  of  the  palm 
of  the  hand  and  the  skin  over  the  olecranon  were  provided  with  vessels  of 
considerable  size,  which  allowed  the  fluid  injected  by  the  axillary  artery 
to  pass  directly  into  some  of  the  veins,  while  in  other  parts  the  veins  were 
entirely  empty.  Extending  his  researches  to  the  lower  extremity,  he 
found  analogous  communications  between  the  vessels  in  the  knee,  toes 
and  parts  of  the  sole  of  the  foot.  He  also  found  communications  in  the 
nose,  cheeks,  lips,  forehead  and  tips  of  the  ears,  parts  that  are  peculiarly 
liable  to  changes  in  color  from  congestion  of  vessels.  These  observa- 
tions have  been  in  the  main  confirmed  by  the  more  recent  researches  of 
Hoyer.  It  is  evident  that  under  certain  conditions  a  larger  quantity  of 
blood  than  usual  may  pass  through  these  parts  without  necessarily  pene- 
trating the  capillaries. 

Pulmonary  Circulation.  —  The  vascular  system  of  the  lungs  merits 
the  name,  which  is  frequently  applied  to  it,  of  the  lesser  circulation. 
The  right  side  of  the  heart  acts  simultaneously  with  the  left,  but  is 
anatomically  distinct  from  it,  and  its  muscular  walls  are  less  powerful. 
The  pulmonary  artery  has  thinner  and  more  distensible  walls  than  the 
aorta  and  distributes  its  blood  to  a  single  system  of  capillaries,  situated 
but  a  short  distance  from  the  heart.  In  the  lungs,  the  pulmonary  artery  is 
broken  up  into  capillaries,  most  of  them  just  large  enough  to  allow  the  pas- 
sage of  blood-corpuscles  in  a  single  row.  These  vessels  are  provided  with 
a  single  coat  and  form  a  close  network  surrounding  the  air-cells.  From 
the  capillaries  the  blood  is  collected  in  the  pulmonary  veins  and  is  carried 
to  the  left  auricle.  There  is  no  great  disparity  between  the  arteries  and 
veins  of  the  pulmonary  system  as  regards  capacity.  The  pulmonary 
veins  in  the  human  subject  have  no  valves. 

The  blood  in  its  passage  through  the  lungs  does  not  meet  with  the 


84 


CIRCULATION    OF    THE    BLOOD 


resistance  that  is  presented  in  the  systemic  circulation  ;  and  the 
anatomy  of  the  pulmonary  vessels  and  of  the  right  side  of  the  heart 
shows  that  the  blood  must  circulate  in  the  lungs  with  comparative 
facility.  The  right  ventricle  has  about  one-third  the  force  of  the 
left,  and  the  pulmonary  artery  will  sustain  a  much  less  pressure  than 
the  aorta. 

The  pressure  of  blood  in  the  pulmonary  artery,  measured  by  con- 
necting a  cardiometer  with  a  trocar  introduced  into  the  pulmonary 
artery  of  a  living  horse  through  one  of  the  intercostal  spaces,  was 
found  to  be  about  one-third  as  great  as  the  pressure  in  the  aorta,  which 
nearly  corresponds  with  an  estimate  of  the  comparative  power  of  the 
two  ventricles,  judging  from  'the  thickness  of  their  muscular  walls 
(Chauveau  and  Faivre). 

On  microscopical  examination  of  the  circulation  in  the  lower  animals, 
as  in  the  frog,  the  movement  of  blood  in  the  capillaries  of  the  lungs 
does  not  present  any  differences  from  the  capillary  circulation  in  other 
parts,  except  that  the  vessels  seem  more  crowded  with  corpuscles  and 
there  is  no  "  still  layer  "  next  their  walls. 

Circulation  in  the  Walls  of  the  Heart.  —  The  circulation  in  the  walls 
of  the  heart  does  not   present  important    peculiarities.       It   has  been 

^,-'  shown  that  the  pressure 

of  blood  in  the  coronary 
arteries  in  the  dog,  dur- 
ing the  ventricular  sys- 
tole, is  sufficient  to  supply 
the  arterioles  in  the  sub- 
stance of  the  heart  with 
blood,  precisely  as  it  is 
supplied  to  the  general 
arterial  system.  In  a 
number  of  experiments 
in  which  simultaneous 
traces  of  the  pulse-beats 
were  obtained,  it  was 
found  that  the  coronary 
and  carotid  pulses  were 
practically  synchronous 
(Martin). 

Passage  of  Blood-Cor- 
puscles through  the  Walls  of  the  Vessels  {Migration  and  Diapedesis').  — 
In  the  frog  it  has  been  observed  that  leucocytes  sometimes  pass  through 
the  walls  of  the  bloodvessels,  either  by  means  of   small  orifices  (stro- 


Fig.  27.  —  Migration  of  leucocytes  and  diapedesis  of  red  cor- 
puscles (Councilman). 

This  figure  represents  a  portion  of  the  mesentery  of  a  frog 
two  hours  after  exposure,  a,  a,  small  arteries;  b,b,  small  veins; 
c,  a  few  leucocytes  in  connective  tissue ;  d,  d,  diapedesis  of  red 
corpuscles;  e,  e,  emigration  of  leucocytes. 


RAPIDITY   OF   THE    CIRCULATION  85 

mata)  or  by  a  kind  of  filtration  tlirough  the  substance  which  unites  the 
borders  of  the  endothelial  cells.  This  phenomenon  was  described  by 
Waller,  in  1841,  but  has  attracted  much  attention  since  the  more  recent 
researches  of  Cohnheim.  In  this  process  it  is  observed  that  the  leuco- 
cytes, which  first  adhere  to  the  vascular  walls,  send  out  little  projections 
which  penetrate  the  membrane,  so  that  a  point  appears  outside  of  the 
vessel.  This  point  becomes  larger  and  larger,  until  the  corpuscle  has 
passed  through.  The  corpuscles  then  migrate  a  certain  distance  by 
means  of  the  movements  known  as  ameboid,  which  have  already  been 
described.  It  was  supposed  by  Cohnheim  that  this  was  one  of  the  early 
phenomena  of  inflammation,  the  migrating  corpuscles  afterward  multi- 
plying by  division,  constituting  the  so-called  pus-corpuscles.  Following 
stasis  of  blood  in  the  small  vessels,  the  red  corpuscles,  it  is  supposed, 
may  pass  out  in  the  same  way.  It  is  not  certain  that  these  are  normal 
processes  or  that  they  take  place  in  the  human  subject.  According  to 
Hering,  red  corpuscles  pass  through  the  walls  of  the  vessels  (diapedesis), 
only  when  the  blood-pressure  is  sufficient  to  produce  transudation  of 
the  plasma. 

Rapidity  of  the  Circulation 

Questions  of  considerable  physiological  importance  arise  in  connec- 
tion with  the  general  rapidity  of  the  circulation  :  — 

1.  What  length  of  time  is  occupied  in  the  passage  of  the  blood 
through  both  the  lesser  and  the  greater  circulations  ? 

2.  What  is  the  time  required  for  the  passage  of  the  entire  mass  of 
blood  through  the  heart  ? 

3.  What  influence  has  the  number  of  pulsations  of  the  heart  on  the 
general  rapidity  of  the  circulation  ? 

The  first  of  these  questions  is  the  one  that  has  been  most  satis- 
factorily answered  by  experiments  on  living  animals.  In  1827  Hering 
made  the  experiment  of  injecting  into  the  jugular  vein  of  a  living  ani- 
mal a  solution  of  potassium  ferrocyanide,  noting  the  time  which  elapsed 
before  it  could  be  detected  in  the  blood  of  the  vein  of  the  opposite 
side.  This  gave  the  first  correct  idea  of  the  rapidity  of  the  circulation. 
He  drew  the  blood  at  intervals  of  five  seconds  after  beginning  the 
injection,  and  thus,  by  repeated  observations,  ascertained  pretty  nearly 
the  rapidity  of  a  circuit  of  blood  in  the  animals  on  which  he  experi- 
mented. Vierordt  (1858)  collected  the  blood  as  it  flowed,  in  little 
vessels  fixed  on  a  disk  revolving  at  a  known  rate,  which  gave  more 
exactness  to  the  observations.  The  results  obtained  in  these  two  ex- 
periments were  nearly  identical. 

The  only  reasonable  objection  to  these  experiments  is  that  a  saline 


86  CIRCULATION    OF   THE    BLOOD 

solution,  introduced  into  the  circulation,  would  have  a  tendency  to 
diffuse  itself  throughout  the  whole  mass  of  blood,  it  might  be,  with 
considerable  rapidity.  This  certainly  is  an  element  that  should  be 
taken  into  account ;  but  from  the  definite  data  obtained  concerning 
the  rapidity  of  the  arterial  circulation  and  the  inferences  that  are  un- 
avoidable in  regard  to  the  rapidity  of  the  venous  circulation,  it  would 
seem  that  the  saline  solution  must  be  carried  on  by  the  mere  rapidity 
of  the  arterial  flow  to  the  capillaries,  which  are  very  short,  taken  up 
from  them,  and  carried  on  by  the  veins,  and  thus  through  the  entire 
circuit,  before  it  has  had  time  to  diffuse  itself  to  any  considerable  ex- 
tent. It  is  not  apparent  how  this  objection  can  be  overcome;  for  a 
substance  must  be  used  that  will  mix  with  the  blood,  as  otherwise  it 
could  not  pass  through  the  capillaries. 

There  seems  no  reason  why,  with  the  above  restrictions,  the  results 
obtained  by  Hering  and  Vierordt  should  not  be  accepted  and  their 
application  be  made  to  the  human  subject. 

Hering  found  that  the  rapidity  of  the  circulation  in  different  ani- 
mals had  an  inverse  ratio  to  their  size  and  a  direct  ratio  to  the  rapidity 
of  the  action  of  the  heart. 

The  following  are  the  mean  results  in  certain  of  the  domestic  ani- 
mals, taking  the  course  from  jugular  to  jugular,  when  the  blood  passes 
through  the  lungs  and  through  the  capillaries  of  the  head  :  — 

In  the  Horse,  the  circulation  is  accomplished  in  27.3  seconds. 
In  the  Dog,  the  circulation  is  accomplished  in  15.2  seconds. 
In  the  Goat,  the  circulation  is  accomplished  in  12.8  seconds. 
In  the  Rabbit,  the  circulation  is  accomplished  in    6.9  seconds. 

Applying  these  results  to  the  human  subject  and  taking  into  ac- 
count the  size  of  the  body  and  the  rapidity  of  the  heart's  action,  the 
duration  of  the  circuit  from  one  jugular  to  the  other  may  be  estimated 
at  21.4  seconds,  and  the  general  average  through  the  entire  system,  at 
23  seconds.  This  estimate  is  simply  approximate  ;  but  the  results  in 
the  inferior  animals  may  be  received  as  nearly  accurate. 

Estimates  of  the  time  required  for  the  passage  of  the  whole  mass  of 
blood  through  the  heart  are  even  less  definite  than  the  estimate  of  the 
general  rapidity  of  the  circulation.  To  arrive  at  a  satisfactory  result, 
it  is  necessary  to  know  the  entire  quantity  of  blood  in  the  body  and 
the  exact  quantity  which  passes  through  the  heart  at  each  pulsation. 
If  the  entire  mass  of  blood  is  divided  by  the  quantity  discharged  from 
the  heart  with  each  ventricular  systole,  the  result  will  be  the  number 
of  pulsations  required  for  the  passage  of  the  blood  through  the  heart ; 
and  knowing  the  number  of  beats  per  minute,  the  length  of  time  thus 


RAPIDITY    OF    THE    CIRCULATION  87 

occupied  is  ascertained.  The  objection  to  this  kind  of  estimate  is  the 
inaccuracy  of  the  data  respecting  the  quantity  of  blood  in  the  system 
as  well  as  the  quantity  which  passes  through  the  heart  with  each  pulsa- 
tion. Nevertheless,  an  estimate  can  be  made,  which,  if  not  entirely 
accurate,  can  not  be  far  from  the  truth. 

The  entire  quantity  of  blood,  according  to  estimates  based  on  the 
most  reliable  data,  is  about  one-twentieth  the  weight  of  the  body,  or 
seven  pounds  {2). 7  kilograms),  in  a  man  weighing  one  hundred  and  forty 
pounds  (63.5  kilograms).  The  quantity  discharged  at  each  ventricular 
systole  is  estimated  at  three  ounces  (90  cubic  centimeters).  It  would 
require,  therefore,  forty-five  pulsations  for  the  passage  through  the 
heart  of  the  entire  mass  of  blood.  Assuming  the  pulsations  to  be 
seventy-two  per  minute,  this  would  occupy  a  little  more  than  thirty-one 
seconds. 

The  relation  of  the  rapidity  of  the  circulation  to  the  frequency  of 
the  heart's  action  is  a  question  not  neglected  in  the  experiments  of 
Hering.  It  is  evident  that  if  the  charge  of  blood  sent  into  the  arteries 
is  the  same,  or  nearly  the  same,  under  all  conditions,  an  increase  in  the 
number  of  pulsations  of  the  heart  would  produce  a  corresponding  accel- 
eration of  the  general  current  of  blood.  This  is  a  proposition,  how- 
ever, which  can  not  be  taken  for  granted ;  and  there  are  many  facts 
that  favor  a  contrary  opinion.  It  may  be  stated  as  a  general  rule, 
that  when  the  acts  of  the  heart  increase  in  frequency  they  diminish  in 
force ;  and  this  renders  it  probable  that  the  ventricle  is  most  com- 
pletely distended  and  emptied  when  its  action  is  moderately  slow. 
When,  however,  the  pulse  is  much  accelerated,  the  increased  number 
of  pulsations  of  the  heart  might  be  sufficient  to  overbalance  the  di- 
minished force  of  each  act  and  would  increase  the  rapidity  of  the  cir- 
culation. In  regard  to  the  relations  between  the  rapidity  of  the  heart's 
action  and  the  general  rapidity  of  the  circulation,  the  following  con- 
clusions may  be  accepted  as  the  results  of  experimental  inquiry  :  — 

1.  In  physiological  increase  in  the  number  of  beats  of  the  heart,  as 
the  result  of  exercise,  for  example,  the  general  circulation  is  somewhat 
increased  in  rapidity,  though  not  in  proportion  to  the  increase  in  the 
rapidity  of  the  pulse. 

2.  In  pathological  acceleration  of  the  heart's  action,  as  in  febrile 
conditions,  the  rapidity  of  the  general  circulation  usually  is  diminished, 
it  may  be  to  a  considerable  extent. 

3.  Whenever  the  number  of  beats  of  the  heart  is  considerably  in- 
creased from  any  cause,  the  quantity  of  blood  discharged  at  each  ven- 
tricular systole  is  much  diminished,  either  from  lack  of  complete  distention 
or  from  imperfect  emptying  of  the  cavities. 


88  CIRCULATION    OF    THE   BLOOD 

PJienomeiia  in  the  Circulatory  System  after  Death.  —  Nearly  every 
autopsy  shows  that  after  death  the  blood  does  not  remain  equally  dis- 
tributed in  the  arteries,  capillaries  and  veins.  Influenced  by  gravitation, 
it  accumulates  in  and  discolors  the  most  dependent  parts  of  the  body. 
The  arteries  are  always  found  empty,  and  blood  accumulates  in  the 
venous  system  and  capillaries  ;  a  fact  which  was  observed  by  the  ancients 
and  gave  rise  to  the  belief  that  the  arteries  were  air-bearing  tubes.  This 
is  readily  explained  by  the  post-mortem  contraction  of  the  muscular 
coat  of  the  arteries.  If  the  artery  and  vein  of  a  limb  are  exposed  in  a 
living  animal  and  all  the  other  vessels  are  tied,  compression  of  the  artery 
does  not  immediately  arrest  the  current  in  the  vein,  but  the  blood  will 
continue  to  flow  until  the  artery  is  emptied  ( Magendie).  The  artery, 
when  relieved  from  the  distending  force  of  the  heart,  reacts  on  its  con- 
tents by  virtue  of  its  contractile  coat  and  completely  empties  itself  of 
blood.  An  action  similar  to  this  takes  place  throughout  the  arterial 
system  after  death.  The  vessels  react  on  their  contents  and  gradually 
force  the  blood  into  and  through  the  capillaries,  which  are  very  short,  to 
the  veins,  which  are  capacious,  distensible  and  but  slightly  contractile. 
This  begins  immediately  after  death,  while  the  contractility  of  the  muscu- 
lar coat  of  the  arteries  remains,  and  is  seconded  by  subsequent  cadaveric 
rigidity,  which  affects  involuntary  as  well  as  voluntary  muscular  fibres. 
Once  in  the  venous  system,  the  blood  can  not  return  on  account  of  the 
valves.     Thus,  after  death,  the  blood  is  found  in  the  veins  and  capillaries. 


CHAPTER   IV 

RESPIRATORY   MOVEMENTS 

Physiological  anatomy  of  the  respiratory  organs  —  Movements  of  respiration  —  Action  of  the 
diaphragm  —  Action  of  the  muscles  which  raise  the  ribs  —  Scalene  muscles  —  Intercostal 
muscles  —  Levatores  costarum  —  Auxiliary  muscles  of  inspiration  —  Expiration  —  Influence 
of  the  elasticity  of  the  pulmonary  structure  and  walls  of  the  chest  —  Action  of  muscles 
in  expiration  —  Internal  intercostals  —  Infracostales  —  Triangularis  sterni  —  Obliquus  ex- 
ternus — Obliquus  internus  —  Types  of  respiration  —  Frequency  of  the  respiratory  move- 
ments—  Respiratory  sounds  —  Coughing,  sneezing,  sighing,  yawning,  laughing,  sobbing 
and  hiccough  —  Quantity  of  air  changed  m  the  respiratory  acts  —  Diffusion  of  air  in  the 
lungs. 

The  tide  of  air  in  the  lungs  does  not  strictly  constitute  respiration, 
these  organs  serving  merely  to  facilitate  the  introduction  of  oxygen 
into  the  blood  and  the  exhalation  of  carbon  dioxide.  When  the  system 
is  drained  of  blood  or  if  the  blood  is  rendered  incapable  of  interchanging 
its  gases  with  the  air,  respiration  ceases  and  all  the  phenomena  of  as- 
phyxia are  presented,  although  air  may  be  introduced  into  the  lungs 
with  perfect  regularity.  As  in  the  nutrition  of  tissue  the  nitrogenous 
constituents  of  the  blood,  united  with  inorganic  substances,  are  transformed 
into  the  tissue  itself,  finally  changed  into  excrementitious  products,  such 
as  the  urinary  matters,  and  discharged  from  the  body,  so  the  oxygen  of 
the  blood  is  appropriated,  and  carbon  dioxide,  which  is  an  excrementi- 
tious substance,  is  produced  and  is  discharged  in  the  expired  air. 

The  essential  conditions  for  respiration  in  animals  that  have  a  circu- 
lating nutritive  liquid  are  air  and  blood  separated  by  a  membrane  that 
will  allow  the  passage  of  gases.  The  effete  products  of  respiration 
contained  in  the  blood,  the  most  important  of  which  is  carbon  dioxide, 
pass  out  and  vitiate  the  air.  The  air  is  deprived  of  a  certain  proportion 
of  its  oxygen,  which  passes  into  the  blood,  to  be  conveyed  to  the  tissues. 
Thus  the  air  must  be  changed  to  supply  fresh  oxygen  and  get  rid  of  car- 
bon dioxide. 

Physiological    Anatomy   of    the    Respiratory    Organs 

Passing  from  the  mouth  to  the  pharynx,  two  openings  are  observed; 
a  posterior  opening,  which  leads  to  the  oesophagus,  and  anteriorly  the 
opening  of  the  larynx,  which  is  the  beginning  of  the  passages  concerned 
exclusively  in  respiration. 


90 


RESPIRATION 


Beginning  with  the  larynx,  it  is  seen  that  the  cartilages  of  which  it 
is  composed  are  sufficiently  rigid  and  unyielding  to  resist  the  pressure 
produced  by  any  inspiratory  effort.  Across  its  opening  are  the  vocal 
chords,  which  are  four  in  number  and  have  a  direction  from  before 
backward.  The  two  superior  are  called  the  false  vocal  chords,  because 
they  are  not  concerned  in  the  production  of  the  voice.     The  two  inferior 


Fig.  28. —  Trachea  ayid  bronchial  tubes  (Sappey). 

I,  2,  larynx ;  3,  3,  trachea  ;  4,  bifurcation  of  the  trachea ;  5,  right  bronchus  ;  6,  left  bronchus  ;  7,  bron- 
chial division  to  the  upper  lobe  of  the  right  lung;  8,  division  to  the  middle  lobe;  9,  division  to  the 
lower  lobe;  10,  division  to  the  upper  lobe  of  the  left  lung;  11,  division  to  the  lower  lobe;  12,  12,  12, 
12,  ultimate  ramifications  of  the  bronchia;  13,  13,  13,  13,  lungs,  represented  in  contour;  14,  14,  summit 
of  the  lungs;   15,  15,  base  of  the  lungs. 

are  the  true  vocal  chords.  They  are  ligamentous  bands  covered  with 
folds  of  mucous  membrane,  which  is  quite  thick  on  the  superior  chords 
and  very  thin  and  delicate  on  the  true  vocal  chords.  These  bands  are 
attached  anteriorly  to  a  fixed  point  between  the  thyroid  cartilages,  and 
posteriorly,  to  the  movable  arytenoid  cartilages.  Air  is  admitted  to  the 
trachea  through  an  opening  between  the  chords,  which  is  called  the  rima 
glottidis.     Little  muscles,  arising  from  the  thyroid  and  cricoid  and  at- 


PHYSIOLOGICAL    ANATOMY    OF    THE    RESPIRATORY   ORGANS      91 

tached  to  the  arytenoid  cartilages,  are  capable  of  separating  and  approxi- 
mating the  points  to  which  the  vocal  chords  are  attached  posteriorly,  so 
as  to  open  and  close  the  rima  glottidis. 

In  man,  the  respiratory  movements  of  the  glottis  have  been  studied 
by  means  of  the  laryngoscope.  In  tranquil  respiration,  the  rima  glottidis 
is  opened  to  a  certain  extent  in  inspiration,  by  the  tonic  contraction  of 
the  posterior  crico-arytenoid  muscles,  and  its  form  is  triangular ;  it  is  a 
little  narrower  in  expiration ;  but  in  forced,  rapid  or  difficult  breathing, 
the  crico-arytenoids  act  vigorously  and  the  glottis  is  widely  opened  with 
each  inspiration,  the  opening  being  somewhat  elliptical.  In  the  cadaver, 
the  width  of  the  opening  of  the  glottis  is  reduced  about  one-half.  The 
muscles  concerned  in  the  respiratory  movements  of  the  glottis  are  ani- 
mated by  the  recurrent  laryngeal  nerves,  but  the  filaments  going  to  these 
muscles  are  not  derived  from  the  spinal  accessory.  While  the  recurrents 
also  contain  filaments,  derived  from  the  accessories,  that  preside  over  the 
vocal  movements  of  the  glottis,  these  movements  are  quite  distinct  from 
those  connected  with  the  act  of  inspiration.  The  true  vocal  sounds  are 
expiratory. 

Attached  to  the  anterior  portion  of  the  larynx,  is  the  epiglottis,  a  leaf- 
shaped  lamella  of  elastic  cartilage,  which,  during  ordinary  respiration,  pro- 
jects upward  and  lies  against  the  base  of  the  tongue.  During  deglutition, 
respiration  is  momentarily  interrupted,  and  the  air-passages  are  protected 
by  the  muscles  that  approximate  the  vocal  chords  and  by  the  tongue, 
which  presses  backward,  carrying  the  epiglottis  before  it  and  completely 
closing  the  glottis.  Physiologists  have  questioned  whether  the  epiglottis 
be  necessary  to  the  complete  protection  of  the  air-passages ;  and  it  has  fre- 
quently been  removed  from  the  lower  animals,  apparently  without  inter- 
fering with  the  deglutition  of  solids  or  liquids.  It  is  a  question,  however, 
whether  the  results  of  this  experiment  can  be  absolutely  applied  to  the 
buman  subject.  In  a  case  of  loss  of  the  entire  epiglottis,  observed  in 
Bellevue  Hospital,  the  patient  experienced  slight  difficulty  in  swallowing, 
from  the  passage  of  little  particles  into  the  larynx,  which  produced  cough. 
This  case  and  others  of  a  similar  character  show  that  the  presence  of  the 
epiglottis,  in  the  human  subject  at  least,  is  necessary  to  the  complete  pro- 
tection of  the  air-passages  in  deglutition. 

Passing  down  the  neck  from  the  larynx  toward  the  lungs,  is  the  tra- 
chea, which  is  four  to  four  and  a  half  inches  (10.16  to  1 1.43  centimeters) 
in  length  and  about  three-quarters  of  an  inch  ( 19.  i  millimeters)  in  diameter. 
It  is  provided  with  cartilaginous  rings,  sixteen  to  twenty  in  number, 
which  partly  surround  the  tube,  leaving  one-third  of  its  posterior  portion 
occupied  by  fibrous  tissue  mixed  with  non-striated  muscular  fibres.  Pass- 
ing into  the  chest,  the  trachea  divides  into  the  two  primitive  bronchia. 


92 


RESPIRATION 


the  right  being  shorter,  larger  and  more  nearly  horizontal  than  the  left. 
These  tubes,  provided,  like  the  trachea,  with  imperfect  cartilaginous 
rings,  enter  the  lungs,  divide  and  subdivide,  until  the  minute  ramifica- 
tions of  the  bronchial  tree  open  directly  into  the  air-cells.  After  pene- 
trating the  lungs,  the  cartilages  become  irregular  and  are  in  the  form 


Fip-   29  —  Lungs,  anterior  vteiu  (,Sappey). 

T,  Upper  lobe  of  the  left  lung ;  2,  lower  lobe ;  2,  fissure ;  4,  notch  corresponding  to  the  apex  of  the 
heart;  5,  pericardium  ;  6,  upper  lobe  of  the  right  lung ;  7,  middle  lobe;  ^,  lower  lobe  ;  g,  fissure  ;  10, 
fissure ;  11,  diaphragm  ;  12,  anterior  mediastinum  ;  13,  tliyroid  gland  ;  14,  middle  cervical  aponeurosis; 
15,  process  of  attachment  of  the  mediastinum  to  the  pericardium  ;  16,  16,  seventh  ribs;  17,  17,  trans- 

versales  muscles  ;   18,  linea  alba. 


of  oblong  angular  plates,  which  are  so  disposed  as  to  completely  en- 
circle the  tubes.  In  tubes  of  very  small  size,  these  plates  are  fewer 
than  in  the  larger  bronchia,  until  in  tubes  of  a  diameter  less  than  -^^  of 
an  inch  (0.5  millimeter),  they  are  lost. 

The  walls  of  the  trachea  and  bronchial  tubes  are  composed  of  twa 
distinct  membranes ;  an  external  membrane,  between  the  layers  of  which 


PHYSIOLOGICAL   ANATOMY    OF   THE    RESPIRATORY    ORGANS      93 

the  cartilages  are  situated,  and  a  mucous  membrane.  The  external  mem- 
brane is  composed  of  inelastic  and  elastic  fibrous  tissue.  Posteriorly,  in 
the  space  not  covered  with  cartilaginous  rings,  these  fibres  are  mixed 
with  a  certain  number  of  non-striated  muscular  fibres,  which  exist  in  two 
layers ;  a  thick,  internal  layer,  in  which  the  fibres  are  transverse,  and  a 
thinner,  longitudinal  layer,  which  is  external.  The  collection  of  mus- 
cular fibres  in  the  posterior  part  of  the  trachea  is  sometimes  called  the 
trachealis  muscle.     Throughout  the  bronchial  tubes,  there  are  circular 


131 


Fig.  30.  —  Bronchia  and  lungs ,  posterior  vien)  (Sappey). 

1,  I,  summit  of  the  hcngs  ;  2,  2,  base  of  the  lungs ;  3,  trachea;  4,  right  bronchus ;  5,  division  to  the 
upper  lobe  of  the  lung  ;  6,  division  to  the  lower  lobe  ;  7,  left  bronchus  ;  8,  division  to  the  upper  lobe  ;  9, 
division  to  the  lower  lobe ;  10,  left  branch  of  the  pulmonary  artery;  11,  right  branch;  12,  left  auricle 
of  the  heart;  13,  left  superior  pulmonary  vein;  14,  left  inferior  pulmonary  vein;  15,  right  superior 
pulmonary  vein;  16,  right  inferior  pulmonary  vein;  17,  inferior  vena  cava;  18,  left  ventricle  of  the 
heart;   19,  right  ventricle. 

fasciculi  of  non-striated  muscular  fibres  lying  just  beneath  the  mucous 
membrane,  with  a  number  of  longitudinal  elastic  fibres.  The  character 
of  the  bronchia  abruptly  changes  in  tubes  less  than  -J-^-  of  an  inch  (0.5  milli- 
meter) in  diameter.  They  then  lose  the  cartilaginous  rings,  and  the 
external  and  the  mucous  membranes  become  so  closely  united  that  they 
can  no  longer  be  separated  by  dissection.  The  circular  muscular  fibres 
continue  as  far  as  the  air-cells.  The  mucous  membrane  is  smooth, 
covered  with  ciliated  epithelium,  the  movements  of  the  cilia  being  from 
within  outward,  and  is  provided  with  mucous  glands.  These  glands  are 
of  the  racemose  variety,  and  in  the  larynx  they  are  of  considerable  size. 


94  RESPIRATION 

In  the  trachea  and  bronchia,  racemose  glands  exist  in  the  membrane  on 
the  posterior  portion  of  the  tubes ;  but  anteriorly  are  small  folUcles,  ter- 
minating in  a  single,  and  sometimes  a  double,  blind  extremity.  These 
follicles  are  lost  in  tubes  measuring  less  than  ^^  of  an  inch  (0.5  milli- 
meter) in  diameter  (see  Plate  II,  Fig.  4). 

When  moderately  inflated,  the  lungs  have  the  appearance  of  irregular 
cones,  with  rounded  apices,  and  concave  bases  resting  upon  the  diaphragm. 
They  fill  that  part  of  the  cavity  of  the  thorax  which  is  not  occupied  by 
the  heart  and  great  vessels,  and  are  completely  separated  from  each  other 
by  the  mediastinum.  The  lungs  are  in  contact  with  the  thoracic  walls, 
each  lung  being  covered  with  a  reflection  of  the  serous  membrane  that  lines 
the  cavity  of  the  corresponding  side.  Thus  they  necessarily  follow  the 
movements  of  expansion  and  contraction  of  the  thorax.  Deep  fissures 
divide  the  right  lung  into  three  lobes  and  the  left  lung  into  two.  The 
surface  of  the  lungs  is  divided  into  irregularly  polygonal  spaces,  \  of  an 
inch  to  an  inch  (6.4  to  25.4  millimeters)  in  diameter,  which  mark  what 
are  sometimes  called  the  pulmonary  lobules ;  but  this  term  is  incorrect, 
as  each  of  these  divisions  includes  a  number  of  the  true  lobules. 

Following  out  the  bronchial  tubes  from  the  diameter  of  -^^  of  an  inch 
(0.5  millimeter),  the  smallest,  which  are  ^|^  to  y"^  of  an  inch  (0.21  to  0.33 
millimeter)  in  diameter,  open  into  a  collection  of  oblong  vesicles,  which  are 
the  air-cells.  Each  collection  of  vesicles  constitutes  one  of  the  true  pul- 
monary lobules  and  is  -^^  to  -^.^  of  an  inch  (0.5  to  2.1  millimeters)  in 
diameter.  After  entering  the  lobule,  the  tube  forms  a  tortuous  central 
canal,  sending  off  branches  which  terminate  in  groups  of  eight  to  fifteen 
pulmonary  cells,  or  alveoli.  The  cells  are  a  little  deeper  than  they  are 
wide  and  have  each  a  rounded  blind  extremity.  Some  are  smooth,  but 
many  are  marked  by  little  circular  constrictions.  In  the  normal  lung  of 
the  adult,  after  death,  they  measure  2^  to  ^2*0  °^  yV  *^f  ^^  ^^^^  (0.125  to 
0.21  or  0.36  millimeter)  in  diameter,  but  are  capable  of  great  distention. 
The  smallest  cells  are  in  the  deep  portions  of  the  lungs,  and  the  largest 
are  near  the  surface.  There  are  considerable  variations  in  the  size  of  the 
cells  at  different  periods  of  life.  The  smallest  cells  are  found  in  young 
children,  and  they  progressively  increase  in  size  with  age.  The  walls 
of  the  air-cells  contain  abundant  small  elastic  fibres,  which  do  not  form 
distinct  bundles  for  each  air-cell,  but  anastomose  freely  with  each  other, 
so  that  the  same  fibres  belong  to  two  or  more  cells.  This  structure  is 
peculiar  to  the  lungs  and  gives  to  these  organs  their  great  distensibility 
and  elasticity,  properties  which  play  an  important  part  in  expelling  the 
air  from  the  chest,  as  a  consequence  simply  of  cessation  of  the  action  of 
the  inspiratory  muscles.  Interwoven  with  these  elastic  fibres,  is  the 
richest  plexus  of   capillary  bloodvessels  found  in  the  economy.      The 


INSPIRATION  95 

vessels  are  larger  than  the  capillaries  in  other  situations,  and  the  plexus 
is  so  close  that  the  spaces  between  them  are  narrower  than  the  vessels 
themselves.  When  distended,  the  bloodvessels  form  the  greatest  part 
of  the  walls  of  the  cells. 

Lining  the  air-cells,  are  thin  cells  of  flattened  epithelium,  o-gVo"  ^^ 
2-qVo  of  ^^  i^ch  (lo  to  12.5  /x)  in  diameter,  which  are  applied  directly 
to  the  walls  of  the  bloodvessels.  The  epithelium  here  does  not  seem  to 
be  regularly  desquamated  as  in  other  situations.  Examination  of  in- 
jected specimens  shows  that  the  bloodvessels  are  so  situated  between 
the  cells  that  the  blood  in  the  greater  part  of  their  circumference  is 
exposed  to  the  air  (see  Plate  II,  Fig.  5). 

The  entire  mass  of  venous  blood  is  distributed  in  the  lungs  by  the 
pulmonary  artery.  Arterial  blood  is  conveyed  to  the  lungs  by  the  bron- 
chial arteries,  which  ramify  and  subdivide  on  the  bronchial  tubes  and 
follow  their  course  into  the  lungs,  for  the  nourishment  of  these  parts. 
It  is  possible  that  the  tissue  of  the  lungs  may  receive  some  nourishment 
from  the  blood  of  the  pulmonary  artery ;  but  as  this  vessel  does  not 
send  branches  to  the  bronchial  tubes,  the  bronchial  arteries  supply  the 
matters  for  their  nutrition  and  for  the  secretion  by  the  mucous  glands 
(see  Plate  II,  Fig.  4). 

Movements  of  Respiration 

In  man  and  in  the  warm-blooded  animals  generally,  inspiration  takes 
place  as  a  consequence  of  enlargement  of  the  thoracic  cavity  and  the 
entrance  of  air  through  the  respiratory  passages,  corresponding  with  the 
increased  capacity  of  the  lungs.  In  the  mammalia,  the  chest  is  en- 
larged by  the  action  of  muscles  ;  and  in  ordinary  respiration,  inspiration 
is  an  active  process,  while  ordinary  expiration  is  mainly  passive. 

The  walls  of  the  thorax  are  formed  by  the  dorsal  vertebras  and  ribs 
posteriorly,  by  the  upper  ten  ribs  laterally,  and  by  the  sternum  and 
costal  cartilages  anteriorly.  The  direction  of  the  ribs,  their  mode  of 
connection  with  the  sternum  by  the  costal  cartilages,  and  their  articula- 
tion with  the  vertebral  column  are  such  that  by  their  movements,  the 
antero-posterior  and  transverse  diameters  of  the  chest  may  be  consider- 
ably modified. 

Inspiration.  —  The  ribs  are  somewhat  twisted  upon  themselves  and 
have  a  general  direction  forward  and  downward.  The  first  rib  is  nearlv 
horizontal,  but  the  obliquity  of  the  ribs  progressively  increases  from  the 
upper  to  the  lower  part  of  the  chest.  They  are  articulated  with  the 
bodies  of  the  vertebrae  so  as  to  allow  of  considerable  motion.  The 
upper  seven  ribs  are  attached  by  the  costal  cartilages  to  the  sternum, 


96 


RESPIRATION 


these  cartilages  running  upward  and  inward.  The  cartilages  of  the 
eighth,  ninth  and  tenth  ribs  are  joined  to  the  cartilage  of  the  seventh. 
The  eleventh  and  twelfth  are  floating  ribs  and  are  attached  only  to  the 
vertebras. 

It  may  be  stated  in  general  terms  that  inspiration  is  effected  by 
descent  of  the  diaphragm  and  elevation  of  the  ribs ;  and  expiration,  by 
elevation  of  the  diaphragm  and  descent  of  the  ribs. 

Arising  severally  from  the  lower  border  of  each  rib  and  attached  to 
the  upper  border  of  the  rib  below,  are  the  eleven  external  intercostal 
muscles,  the  fibres  of  which  have  an  oblique  direction  from  above  down- 


Fig.  31.  —  Thorax,  anterior  vieiv  (Sappey). 

I,  2, 3,  sternum  ;  4,  circumference  of  the  upper 
portion  of  the  thorax;  5,  circumference  of  the  base 
of  the  thorax  ;  6,  first  rib  ;  7,  second  rib  ;  8,  8,  last 
five  sternal  ribs  ;  9,  upper  three  false  ribs;  10,  last 
two,  or  floating  ribs;  11,  costal  cartilages. 


Fig.  32. —  Thorax,  posterior  view  (Sappey). 

I,  I,  spinous  processes  of  the  dorsal  verte- 
brae; 2,  2,  laminae  of  the  vertebrae;  3,  3,  trans- 
verse processes  ;  4,  4,  dorsal  portions  of  the  ribs  ; 
5,  5,  angles  of  the  ribs. 


ward  and  forward.  Attached  to  the  inner  borders  of  the  ribs,  are  the 
internal  intercostals,  which  have  a  direction  from  above  downward  and 
backward,  nearly  at  right  angles  to  the  fibres  of  the  external  intercos- 
tals. There  are  also  certain  muscles  attached  to  the  thorax  and  spine, 
thorax  and  head,  upper  part  of  humerus  etc.,  that  are  capable  of  ele- 
vating either  the  entire  chest  or  the  ribs.  These  act  as  muscles  of  inspi- 
ration when  the  attachments  to  the  thorax  become  the  movable  points. 
Some  of  them  are  called  into  action  during  ordinary  respiration  ;  others 
act  as  auxiliaries  when  respiration  is  moderately  exaggerated,  as  after 
exercise,  and  are  called  ordinary  auxiliaries ;  while  others,  which  ordi- 


MUSCLES    OF    INSPIRATION  97 

narily  have  different  uses,  act  only  when  respiration  is  difficult,  and  are 
called  extraordinary  auxiliaries. 

The  following  are  the  principal  muscles  concerned  in  inspiration :  — 

MUSCLES   OF   INSPIRATION 
Ordinary  Respiration 

MUSCLE  ATTACHMENTS 

Diaphragm Circumference  of  lower  border  of  thorax. 

Scalenus  antieus Transverse  processes  of  third,  fourth,  fifth  and  sixth 

cervical  vertebrse  —  tubercle  of  first  rib. 
Scalenus  medius Transverse  processes  of  lower  six  cervical  vertebrse 

—  upper  surface  of  first  rib. 

Scalenus  posticus Transverse  processes  of  lower  two  or  three  cervical 

vertebrse — outer  surface  of  second  rib. 

External  intercostals Outer  borders  of  the  ribs. 

Sternal  portion  of  internal  intercostals  .     .     Borders  of  the  costal  cartilages. 

Twelve  levatores  costarum Transverse  processes  of  dorsal  vertebrse  —  ribs,  be- 
tween the  tubercles  and  angles. 

Ordinary  Auxiliaries 

Serratus  posticus  superior Ligamentum  nuchse,  spinous  processes  of  last  cer- 
vical and  upper  two  or  three  dorsal  vertebras  — 
upper  borders  of  second,  third,  fourth  and  fifth 
ribs,  just  beyond  the  angles. 

Sterno-mastoideus Upper  part  of  sternum  —  mastoid  process  of  tem- 
poral bone. 

Extraordinary  Auxiliaries 

Levator  anguli  scapula Transverse  processes  of  upper  three  or  four  cer- 
vical vertebrse  —  posterior  border  of  superior 
angle  of  scapula. 

Trapezius  (superior  portion) Ligamentum  nuchas  and  seventh  cervical  vertebra 

—  upper  border  of  spine  of  scapula. 
Pectoralis  minor     . Coracoid  process  of  scapula  —  anterior  surface  and 

upper  margins  of  third,  fourth  and  fifth  ribs,  near 
the  cartilages. 

Pectoralis  major  (inferior  portion)     .     .     .     Bicipital  groove  of  humerus  —  costal  cartilages  and 

lower  part  of  sternum. 

Serratus  magnus Inner  margin  of  posterior  border  of  scapula  —  exter- 
nal surface  and  upper  border  of  upper  eight  ribs. 

Action  of  the  Diaphragm.  —  The  descriptive  and  general  anatomy  of 
the  diaphragm  gives  an  idea  of  its  uses  in  respiration.  It  arises  from 
the  border  of  the  lower  circumference  of  the  thorax  and  mounts  into  the 
cavity  of  the  chest,  forming  a  vaulted  arch,  or  dome,  with  its  concavity 
toward  the  abdomen  and  its  convexity  toward  the  lungs.  In  the  central 
portion,  there  is  a  tendon  of  considerable  size  and  shaped  something 
like  the  club  on  a  playing-card,  with  middle,  right  and  left  leaflets.  The 
rest  of  the  diaphragm  is  composed  of  radiating  fibres  of  striated  muscular 
tissue.  The  oesophagus,  aorta  and  inferior  vena  cava  pass  through  the 
diaphragm  from  the  thoracic  to  the  abdominal  cavity,  by  three  openings. 


98 


RESPIRATION 


The  opening  for  the  oesophagus  is  surrounded  with  muscular  fibres, 
by  which  it  is  partly  closed  when  the  diaphragm  contracts  in  inspiration, 
as  the  fibres  simply  surround  the  tube  and  are  not  attached  to  its  walls. 

The  opening  for  the  aorta  is  bounded  by  the  bone  and  aponeurosis 
posteriorly,  and  in  front,  by  a  fibrous  band  to  which  the  muscular  fibres 
are  attached,  so  that  their  contraction  has  a  tendency  rather  to  increase 
than  to  diminish  the  calibre  of  the  vessel. 

The  opening  for  the  vena  cava  is  surrounded  by  tendinous  structure, 
and  contraction  of  the  diaphragm,  although  it  may  render  the  form  of 
the  opening  more  nearly  circular,  can  have  no  effect  on  its  size. 


Fig.  33.  —  DiapAra^m  (Sappey). 

I,  2,  3,  central  tendon;  4,  right  pillar;  5,  left  pillar;  6,  7,  processes  between  the  pillars;  8,  8, 
openings  for  the  splanchnic  nerves;  9,  fibrous  arch  passing  over  the  psoas  magnus;  10,  fibrous  arch 
passing  over  the  quadratus  lumborum  ;  11,  muscular  fibres  arising  from  these  two  arches ;  12,  12,  mus- 
cular fibres  arising  from  the  lower  six  ribs ;  13,  fibres  from  the  ensiform  cartilage ;  14,  opening  for  the 
vena  cava;  15,  opening  for  the  oesophagus;  16,  opening  for  the  aorta;  17,  17,  part  of  the  transversaiis 
muscle;  18,  18,  aponeurosis;  19,  19,  quadratus  lumborum;  20,  20,  psoas  magnus;  21,  fourth  lumbar 
vertebra. 

In  ordinary  inspiration,  the  descent  of  the  diaphragm  and  its  ap- 
proximation to  a  plane  are  the  chief  phenomena  observed  ;  but  as  there 
is  some  resistance  to  the  depression  of  the  central  tendon,  it  is  probable 
that  there  is  also  a  slight  elevation  of  the  inferior  ribs. 

The  phenomena  referable  to  the  abdomen  which  coincide  with  the 
descent  of  the  diaphragm  can  easily  be  observed  in  the  human  subject. 
As  the  diaphragm  is  depressed,  it  necessarily  pushes  the  viscera  before 
it,  and  inspiration  is  therefore  accompanied  with  protrusion  of  the 
abdomen. 


MUSCLES    WHICH    RAISE    THE    RIBS  99 

The  effects  of  the  action  of  the  diaphragm  on  the  size  of  its  openings 
are  limited  chiefly  to  the  oesophageal  opening.  The  anatomy  of  the 
parts  is  such  that  contraction  of  the  muscular  fibres  has  a  tendency  to 
constrict  this  opening.  The  contraction  of  the  diaphragm  is  auxiliary 
to  the  action  of  the  muscular  walls  of  the  oesophagus  itself,  by  which  the 
cardiac  opening  of  the  stomach  is  regularly  closed  during  inspiration. 
This  may  become  important  when  the  stomach  is  much  distended;  for 
descent  of  the  diaphragm  compresses  all  the  abdominal  organs  and 
might  otherwise  cause  regurgitation  of  food. 

The  contractions  of  the  diaphragm  are  animated  by  the  phrenic 
nerve  ;  a  nerve  which,  having  the  office  of  supplying  the  most  important 
respiratory  muscle,  derives  its  filaments  from  a  number  of  sources.  It 
arises  from  the  third  and  fourth  cervical  nerves,  receiving  a  branch  from 
the  fifth  and  sometimes  from  the  sixth.  It  then  passes  through  the  chest, 
penetrates  the  diaphragm  and  is  distributed  on  its  under  surface.  Stimu- 
lation of  this  nerve  produces  convulsive  contractions  of  the  diaphragm, 
and  its  section  paralyzes  the  muscle  almost  completely. 

From  the  great  increase  in  the  capacity  of  the  chest  produced  by  the 
action  of  the  diaphragm  and  its  constant  and  universal  action  in  respira- 
tion, it  must  be  regarded  as  by  far  the  most  important  and  efficient  of  the 
muscles  of  inspiration. 

Hiccough,  sobbing,  laughing  and  crying  are  due  mainly  to  the  action 
of  the  diaphragm,  particularly  hiccough  and  sobbing,  which  are  produced 
by  spasmodic  contractions  of  this  muscle,  usually  not  under  the  control 
of  the  w^ill. 

Action  of  the  Muscles  which  raise  the  Ribs.  —  Scalene  Muscles.  —  In 
ordinary  respiration,  the  ribs  and  the  entire  chest  are  elevated  by  the 
combined  action  of  a  number  of  muscles.  The  three  scalene  muscles  are 
attached  to  the  cervical  vertebras  and  the  first  and  second  ribs.  These 
muscles,  which  act  particularly  on  the  first  rib,  must  elevate  with  it,  in 
inspiration,  the  rest  of  the  thorax.  The  articulation  of  the  first  rib  with 
the  vertebral  column  is  very  movable,  but  it  is  joined  to  the  sternum  by 
a  short  cartilage,  which  allows  of  very  little  movement,  so  that  its  eleva- 
tion necessarily  carries  with  it  the  sternum.  This  movement  increases 
both  the  transverse  and  antero-posterior  diameters  of  the  thorax,  on  ac- 
count of  the  mode  of  articulation  and  direction  of  the  ribs,  which  are 
somewhat  rotated  as  well  as  rendered  more  nearly  horizontal. 

Intercostal  Muscles.  —  Concerning  the  mechanism  of  the  action  of  these 
muscles,  there  is  considerable  difference  of  opinion  among  physiologists  ; 
so  much,  indeed,  that  the  question  is  still  left  in  some  uncertainty.  The 
most  extended  researches  on  this  point  are  those  of  Beau  and  Maissiat 
(1843),  and  of  Sibson  (1846).     The  latter  seem  to  settle  the  question  of 


lOO  RESPIRATIOiN 

the  mode  of  action  of  the  intercostals  and  explain  satisfactorily  certain 
points  which  even  now  are  not  commonly  appreciated.  Onimus  and, 
more  recently,  Laborde  have  shown  by  experiments  on  decapitated 
criminals  that  the  external  intercostals  raise  and  the  internal  intercostals 
depress  the  ribs,  confirming  the  views  of  Sibson. 

In  the  dorsal  region,  the  spinal  column  forms  an  arch,  with  its  con- 
cavity looking  toward  the  chest,  and  the  ribs  increase  in  length  progres- 
sively, from  above  downward,  to  the  deepest  portion  of  the  arch,  where 
they  are  longest,  and  then  progressively  become  shorter.  "  During  in- 
spiration the  ribs  approach  to  or  recede  from  each  other  according  to 
the  part  of  the  arch  with  which  they  articulate  ;  the  four  superior  ribs 
approach  each  other  anteriorly  and  recede  from  each  other  posteriorly ; 
the  fourth  and  fifth  ribs,  and  the  intermediate  set  (sixth,  seventh  and 
eighth),  move  farther  apart  to  a  moderate,  the  diaphragmatic  set  (four 
inferior),  to  a  great  extent.  The  upper  edge  of  each  of  these  ribs  glides 
toward  the  vertebrae  in  relation  to  the  lower  edge  of  the  rib  above,  with 
the  exception  of  the  lowest  rib,  which  is  stationary"  (Sibson).  These 
movements  increase  the  antero-posterior  and  transverse  diameters  of  the 
thorax.  As  the  ribs  are  elevated  and  become  more  nearly  horizontal, 
they  push  forward  the  lower  portion  of  the  sternum.  Their  configuration 
and  mode  of  articulation  with  the  vertebrae  are  such  that  they  can  not  be 
elevated  without  undergoing  a  considerable  rotation,  by  which  the  con- 
cavity looking  directly  toward  the  lungs  is  increased,  and  with  it  the 
bilateral  diameter  of  the  chest.  All  the  intercostal  spaces  posteriorly 
are  widened  in  inspiration. 

The  ribs  are  elevated  by  the  action  of  the  external  intercostals,  the 
sternal  portion  of  the  internal  intercostals  and  the  levatores  costarum. 
The  external  intercostals  are  situated  between  the  ribs  only  and  are  want- 
ing in  the  region  of  the  costal  cartilages.  As  the  vertebral  extremities 
of  the  ribs  are  the  pivots  on  which  these  levers  move,  and  as  the  sternal 
extremities  are  movable,  the  direction  of  the  fibres  of  the  intercostals  from 
above  downward  and  forward  renders  elevation  of  the  ribs  a  necessary 
consequence  of  their  contraction,  if  it  can  be  assumed  that  the  first  rib 
is  fixed  or  at  least  does  not  move  downward.  The  scalene  muscles  ele- 
vate the  first  rib  in  ordinary  inspiration  ;  and  in  deep  inspiration,  this 
takes  place  to  such  an  extent  as  palpably  to  carry  with  it  the  sternum 
and  the  lower  ribs.  Theoretically,  then,  the  external  intercostals  can  do 
nothing  but  render  the  ribs  more  nearly  horizontal. 

If  the  external  intercostals  are  exposed  in  the  dog  —  in  which  the 
costal  type  of  respiration  is  quite  prominent  —  close  observation  can 
hardly  fail  to  show  that  these  muscles  enter  into  action  with  inspiration. 
If  attention  is  directed  to  the  sternal  portion  of  the  internal  intercostals, 


MUSCLES    WHICH    RAISE    THE    RIBS  lOI 

situated  between  the  costal  cartilages,  their  fibres  having  a  direction  from 
above  downward  and  backward,  it  is  equally  evident  that  they  enter 
into  action  with  inspiration.  By  artificially  inflating  the  lungs  after 
death,  it  is  seen  that  when  the  lungs  are  filled  with  air,  the  fibres  of 
these  muscles  are  shortened  (Sibson).  In  inspiration  the  ribs  are  all 
separated  posteriorly ;  but  laterally  and  anteriorly,  some  are  separated 
(all  below  the  fourth),  and  some  are  approximated  (all  above  the  fourth). 
Thus  all  the  interspaces,  except  the  anterior  portion  of  the  upper  three, 
are  widened  in  inspiration.  Sibson  has  shown  by  inflation  of  the  chest, 
that  although  the  ribs  are  separated  from  each  other,  the  attachments 
of  the  intercostals  are  approximated.  The  ribs,  from  an  oblique  posi- 
tion, are  rendered  nearly  horizontal ;  and  consequently  the  inferior 
attachments  of  the  intercostals  are  brought  nearer  the  spinal  column, 
while  the  superior  attachments  to  the  upper  borders  of  the  ribs  are 
slightly  removed  from  it.  Thus  these  muscles  are  shortened.  If,  by 
separating  and  elevating  the  ribs,  the  muscles  are  shortened,  it  follows 
that  shortening  of  the  muscles  will  necessarily  elevate  and  separate  the 
'ribs.  In  the  three  superior  interspaces,  the  constant  direction  of  the 
ribs  is  nearly  horizontal,  and  the  course  of  the  intercostal  fibres  is  not  so 
oblique  as  in  those  situated  between  the  lower  ribs.  These  spaces  are 
narrowed  in  inspiration.  The  muscles  between  the  costal  cartilages 
have  a  direction  opposite  to  that  of  the  external  intercostals  and  act 
on  the  ribs  from  the  sternum,  as  the  others  act  from  the  spinal  column. 
The  superior  interspace  is  narrowed,  and  the  others  are  widened  in 
inspiration. 

Levatores  Costaricm.  —  The  action  of  these  muscles  can  not  be  mis- 
taken. They  have  immovable  points  of  origin,  the  transverse  processes 
of  twelve  vertebrae  from  the  last  cervical  to  the  eleventh  dorsal,  and 
spreading  out  like  a  fan,  are  attached  to  the  upper  edges  of  the  ribs 
between  the  tubercles  and  the  angles.  In  inspiration  they  contract 
and  assist  in  the  elevation  of  the  ribs. 

Auxiliary  Muscles  of  Inspiration. — The  muscles  which  have  just 
been  considered  are  competent  to  increase  the  capacity  of  the  thorax 
sufficiently  in  ordinary  respiration ;  but  there  are  certain  muscles  at- 
tached to  the  chest  and  the  upper  part  of  the  spinal  column  or  the 
upper  extremities,  which  may  act  in  inspiration,  although  ordinarily  the 
chest  is  the  fixed  point  and  they  move  the  head,  neck  or  arms.  These 
muscles  are  brought  into  action  when  the  movements  of  respiration  are 
exaggerated.  When  this  exaggeration  is  but  slight  and  is  physiological, 
as  after  exercise,  certain  of  the  ordinary  auxiliaries  act  for  a  time,  until 
the  tranquillity  of  the  movements  is  restored ;  but  when  there  is  obstruc- 
tion in  the  respiratory  passages  or  when  respiration  is  difficult  from  any 


102  RESPIRATION 

cause,  threatening  suffocation,  all  the  muscles  that  can  by  any  possi- 
bility raise  the  chest  are  brought  into  action.  These  are  classed  in  the 
table  as  extraordinary  auxiliaries.  Most  of  these  muscles  can  volunta- 
rily be  brought  into  play  to  raise  the  chest,  and  the  mechanism  of  their 
action  may  in  this  way  be  demonstrated. 

Scrratiis  Posticus  Stiperior.  —  This  muscle,  by  reversing  its  ordinary 
action,  is  capable  of  increasing  the  capacity  of  the  thorax. 

Stefuo-mastoideiis.  —  That  portion  of  the  muscle  which  is  attached 
to  the  mastoid  process  of  the  temporal  bone  and  the  sternum,  when  the 
head  is  fixed,  is  capable  of  acting  as  a  muscle  of  inspiration.  It  does 
not  act  in  ordinary  respiration,  but  its  contractions  may  be  observed 
whenever  respiration  is  hurried  or  exaggerated. 

The  following  muscles  as  a  rule  act  as  muscles  of  inspiration  only 
when  respiration  is  difficult  or  labored  :  — 

Levator  Angiili  Scapiilce  and  Superior  Portion  of  the  Trapezius. — 
Movements  of  the  scapula  have  often  been  observed  in  labored  res- 
piration. Its  elevation  during  inspiration  is  effected  chiefly  by  the 
levator  anguli  scapulae  and  the  upper  portion  of  the  trapezius. 

Pectoralis  Minor  mid  Inferior  Portion  of  the  Pcctoralis  Major.  — 
These  muscles  act  together  to  raise  the  ribs  in  difficult  respiration. 
The  pectoralis  minor  is  the  more  efficient.  With  the  coracoid  process 
as  the  fixed  point,  this  muscle  is  capable  of  powerfully  assisting  in  the 
elevation  of  the  ribs.  That  portion  of  the  pectoralis  major  which  is 
attached  to  the  lower  part  of  the  sternum  and  costal  cartilages  is  capa- 
ble of  acting  from  its  insertion  into  the  bicipital  groove  of  the  humerus, 
when  the  shoulders  are  fixed,  in  concert  with  the  pectoralis  minor. 

Serratus  Magnns. —  Acting  from  the  scapula  as  the  fixed  point,  this 
muscle  is  capable  of  assisting  the  pectorals  in  raising  the  ribs  and  be- 
comes a  powerful  auxiliary  in  difficult  inspiration. 

The  division  into  muscles  of  ordinary  inspiration,  ordinary  auxiliaries 
and  extraordinary  auxiliaries,  must  not  be  taken  as  absolute.  In  the 
male,  in  ordinary  respiration,  the  diaphragm,  intercostals  and  levatores 
costarum  are  the  principal  inspiratory  muscles,  and  the  action  of  the 
scaleni,  with  the  consequent  elevation  of  the  sternum,  is  commonly  very 
slight  or  it  may  be  wanting.  In  the  female,  the  movements  of  the 
upper  parts  of  the  chest  are  more  prominent,  and  the  scaleni,  the  ser- 
ratus posticus  superior,  and  sometimes  the  sterno-mastoid,  are  brought 
into  action  in  ordinary  respiration.  In  the  different  types  of  respiration, 
the  action  of  the  muscles  necessarily  presents  considerable  variations. 

Expiration.  —  The  air  is  expelled  from  the  lungs,  in  ordinary  expira- 
tion, by  a  simple  and  comparatively  passive  process.  The  lungs  contain 
a  large  number  of  elastic  fibres  surrounding  the  air-cells  and  the  small- 


EXPIRATION  103 

est  ramifications  of  the  bronchial  tubes,  which  give  them  great  elas- 
ticity. The  thoracic  walls  are  also  very  elastic,  particularly  in  young 
persons.  After  the  muscles  which  increase  the  capacity  of  the  thorax 
cease  their  action,  the  elasticity  of  the  costal  cartilages  and  the  tonicity 
of  the  muscles  that  have  been  put  on  the  stretch  restore  the  chest  to 
what  may  be  called  its  passive  dimensions.  This  elasticity  is  likewise 
capable  of  acting  as  an  inspiratory  force  when  the  chest  has  been  com- 
pressed in  any  way.  There  are  also  certain  muscles,  the  action  of 
which  is  to  draw  the  ribs  downward  and  which,  in  tranquil  respiration, 
are  antagonistic  to  those  which  elevate  the  ribs.  Aside  from  this, 
many  operations,  such  as  speaking,  blowing,  singing  etc.,  require  power- 
ful, prolonged  or  complicated  acts  of  expiration,  in  which  many  muscles 
are  brought  into  play. 

Expiration  may  be  considered  as  depending  on  two  causes  :  — 

1.  The  passive  influence  of  the  elasticity  of  the  lungs  and  thoracic 
walls. 

2.  The  action  of  certain  muscles,  which  either  diminish  the  trans- 
verse and  antero-posterior  diameters  of  the  chest  by  depressing  the  ribs 
and  sternum,  or  the  vertical  diameter,  by  pressing  the  abdominal  viscera 
upward  against  the  diaphragm. 

Influence  of  the  Elasticity  of  tJie  Pulmonary  Structure  and  Walls  of 
the  Chest.  —  It  is  easy  to  understand  the  influence  of  the  elasticity  of 
the  pulmonary  structure  in  expiration.  From  the  collapse  of  the  lungs 
when  openings  are  made  in  the  chest,  it  is  seen  that  even  after  the  most 
complete  expiration,  these  organs  have  a  tendency  to  expel  part  of  their 
gaseous  contents,  which  can  not  be  fully  satisfied  until  the  chest  is 
opened.  They  remain  partially  distended,  on  account  of  the  impossi- 
bility of  retraction  of  the  thoracic  walls  beyond  a  certain  degree;  and  by 
virtue  of  their  elasticity,  they  exert  a  suction  force  on  the  diaphragm, 
causing  it  to  form  a  vaulted  arch,  or  dome,  above  the  level  of  the  lower 
circumference  of  the  chest.  When  the  lungs  are  collapsed,  the  dia- 
phragm hangs  loosely  between  the  abdominal  and  thoracic  cavities. 
In  inspiration  and  in  expiration,  then,  the  relations  between  the  lungs 
and  diaphragm  are  reversed.  In  inspiration,  the  descending  diaphragm 
exerts  a  suction  force  on  the  lungs,  drawing  them  downward  ;  in  expira- 
tion, the  elastic  lungs  exert  a  suction  force  on  the  diaphragm,  drawing 
it  upward.  This  antagonism  is  one  of  the  causes  of  the  great  power 
and  importance  of  the  diaphragm  as  an  inspiratory  muscle. 

The  elasticity  of  the  lungs  operates  chiefly  on  the  diaphragm  in 
reducing  the  capacity  of  the  chest ;  for  the  walls  of  the  thorax,  by  rea- 
son of  their  own  elasticity,  have  a  reaction  which  succeeds  the  move- 
ments produced  by  the  inspiratory  muscles.     Although  this  is  the  main 


I04  RESPIRATION 

action  of  the  lungs  themselves  in  expiration,  their  relations  to  the  walls 
of  the  thorax  are  important.  By  virtue  of  their  elasticity,  they  assist 
the  passive  retraction  of  the  chest.  When  they  lose  this  property  to  any 
considerable  extent,  as  in  vesicular  emphysema,  they  offer  a  notable  re- 
sistance to  the  contraction  of  the  thorax;  so  much,  indeed,  that  in  old 
cases  of  this  disease  the  thoracic  movements  are  restricted,  and  the  chest 
presents  a  characteristic  rounded  and  distended  appearance. 

Little  more  need  be  said  concerning  the  passive  movements  of  the 
thoracic  walls.  When  the  action  of  the  inspiratory  muscle  ceases,  the 
ribs  regain  their  oblique  direction,  the  intercostal  spaces  are  narrowed, 
and  the  sternum,  if  it  has  been  elevated  and  drawn  forward,  falls  back 
to  its  place,  simply  by  virtue  of  the  elasticity  of  the  parts. 

Action  of  Muscles  ifi  Expiration. — The  following  are  the  principal 
muscles  concerned  in  expiration  :  — 

MUSCLES   OF   EXPIRATION 

Ordinary  Respiration 

MUSCLE  ATTACHMENTS 

Osseous  portion  of  internal  intercostals    .     .     Inner  borders  of  the  ribs. 

Infracostales Inner  surfaces  of  the  ribs. 

Triangularis  sterni Ensiform    cartilage,    lower   borders    of    sternum, 

lower  three  or  four  costal  cartilages  —  carti- 
lages of  the  second,  third,  fourth  and  fifth  ribs. 

Auxiliaries 

Obliquus  externus External  surface  and  inferior  borders  of  eight  in- 
ferior ribs  —  anterior  half  of  the  crest  of  the 
ileum,  Poupart's  ligament,  linea  alba. 

Obliquus  internus Outer  half  of  Poupart's  ligament,  anterior  two- 
thirds  of  the  crest  of  the  ileum,  lumbar  fascia 
—  cartilages  of  four  inferior  ribs,  linea  alba, 
crest  of  the  pubis,  pectineal  line. 

Transversalis „  .  .  .  .  Outer  third  of  Poupart's  ligament,  anterior  two- 
thirds  of  the  crest  of  the  ileum,  lumbar  verte- 
brje,  inner  surface  of  cartilages  of  six  inferior 
ribs  —  crest  of  the  pubis,  pectineal  line,  linea 
alba. 

Sacro-lumbalis Sacrum  —  angles  of  six  inferior  ribs. 

Internal  Intercostals. — The  internal  intercostals  have  different  uses 
in  different  parts  of  the  thorax.  They  are  attached  to  the  inner  borders 
of  the  ribs  and  costal  cartilages.  Between  the  ribs  they  are  covered 
by  the  external  intercostals,  but  between  the  costal  cartilages  they  are 
covered  simply  by  aponeurosis.  Their  direction  is  from  above  down- 
ward and  backward,  nearly  at  right  angles  to  the  external  intercostals. 
The  action  of  that  portion  of  the  internal  intercostals  situated  between 
the  costal  cartilages  has  already  been  noted.     They  assist  the  external 


MUSCLES    OF    EXPIRATION  105 

intercostals  in  elevating  the  ribs  in  inspiration.  Between  the  ribs  these 
muscles  are  directly  antagonistic  to  the  external  intercostals.  Thev 
are  more  nearly  at  right  angles  to  the  ribs,  particularly  in  that  portion 
of  the  thorax  where  the  obliquity  of  the  ribs  is  greatest.  They  are 
elongated  when  the  chest  is  distended,  and  are  shortened  when  the 
chest  is  retracted.  This  fact,  taken  in  connection  with  experiments 
on  living  animals,  shows  that  they  are  muscles  of  expiration.  Their 
contraction  tends  to  depress  the  ribs  and  consequently  to  diminish  the 
capacity  of  the  chest. 

hifracostales. — These  muscles,  situated  at  the  posterior  part  of  the 
thorax,  are  variable  in  size  and  number.  They  are  most  common  at 
the  lower  part  of  the  chest.  Their  fibres  arise  from  the  inner  surface 
of  one  rib  to  be  inserted  into  the  inner  surface  of  the  first,  second  or 
third  rib  below.  The  fibres  follow  the  direction  of  the  internal  inter- 
costals, and  acting  from  their  lower  attachments,  their  contractions 
assist  these  muscles  in  drawing  the  ribs  downward. 

Triangularis  Sterni.  —  There  has  never  been  any  doubt  concerning 
the  expiratory  action  of  the  triangularis  sterni.  From  its  origin,  the 
ensiform  cartilage,  lower  borders  of  the  sternum,  and  lower  three  or 
four  costal  cartilages,  it  acts  on  the  cartilages  of  the  second,  third, 
fourth  and  fifth  ribs,  to  which  it  is  attached,  drawing  them  downward 
and  thus  diminishing  the  capacity  of  the  chest. 

The  above-mentioned  muscles  are  called  into  action  in  ordinary 
tranquil  respiration,  and  their  sole  office  is  to  diminish  the  capacity  of 
the  chest.  In  labored  or  difficult  expiration,  and  in  the  acts  of  blowing, 
phonation  etc.,  other  muscles,  called  auxiliaries,  play  a  more  or  less 
important  part.  These  muscles  all  enter  into  the  formation  of  the 
walls  of  the  abdomen,  and  their  general  action  in  expiration  is  to  press 
the  abdominal  viscera  and  diaphragm  into  the  thorax  and  diminish  its 
vertical  diameter.  Their  action  is  voluntary ;  and  by  an  effort  of  the 
will,  it  may  be  opposed  more  or  less  by  the  diaphragm,  by  which  means 
the  duration  or  extent  of  the  expiratory  act  is  regulated.  They  are 
also  attached  to  the  ribs  or  costal  cartilages,  and  while  they  press  the 
diaphragm  upward,  they  depress  the  ribs  and  thus  diminish  the  antero- 
posterior and  transverse  diameters  of  the  chest.  In  this  action,  they 
may  be  opposed  by  voluntary  contraction  of  the  muscles  that  raise  the 
ribs,  also  for  the  purpose  of  regulating  the  force  of  the  expiratory  act. 

In  labored  respiration  in  disease  and  in  the  hurried  respiration 
which  follows  \aolent  exercise,  the  auxiliary  muscles  of  expiration,  as 
well  as  of  inspiration,  are  called  into  action  to  a  considerable  extent. 

Obliqmis  Externus.  — This  muscle,  in  connection  with  the  obliquus 
internus  and  transversalis,  is  efficient  in  forced  or  labored  expiration,  by 


I06  RESPIRATIOxN 

pressing  the  abdominal  viscera  against  the  diaphragm.  Acting  from 
its  attachments  to  the  linea  alba,  the  crest  of  the  ileum  and  Poupart's 
ligament,  by  its  attachment  to  the  eight  inferior  ribs,  it  draws  the  ribs 
downward. 

Ob lig litis  Intcrnus.  —  This  muscle  also  acts  in  forced  expiration  by 
compressing  the  abdominal  viscera.  The  direction  of  its  fibres  is  from 
below  upward  and  forward.  Acting  from  its  attachments  to  the  crest 
of  the  ileum,  Poupart's  ligament  and  the  lumbar  fascia,  by  its  attach- 
ments to  the  cartilages  of  the  four  inferior  ribs,  it  draws  them  down- 
ward. The  direction  of  the  fibres  of  this  muscle  is  the  same  as  that  of 
the  internal  intercostals.  By  its  action  the  ribs  are  drawn  inward  as 
well  as  downward. 

Transversa/is.  —  The  expiratory  action  of  this  muscle  is  exerted 
mainly  in  compressing  the  abdominal  viscera. 

Sacro-lnvibalis.  —  This  muscle  is  situated  at  the  posterior  portion  of 
the  abdomen  and  thorax.  Its  fibres  pass  from  its  origin  at  the  sacrum, 
upward  and  a  little  outward,  to  be  inserted  into  the  six  inferior  ribs  at 
their  angles.  In  expiration  it  draws  the  ribs  downward,  acting  as  an 
antagonist  to  the  lower  levatores  costarum. 

There  are  other  muscles  that  may  be  used  in  forced  expiration, 
assisting  in  the  depression  of  the  ribs,  such  as  the  serratus  posticus 
inferior,  the  superior  fibres  of  the  serratus  magnus  and  the  inferior 
portion  of  the  trapezius  ;  but  their  action  in  respiration  is  unimportant. 

Types  of  Respiration.  —  In  the  movements  of  expansion  of  the  chest, 
although  all  the  muscles  that  have  been  classed  as  ordinary  inspiratory 
muscles  are  brought  into  action  to  a  greater  or  less  extent,  the  fact  that 
certain  sets  may  act  in  a  more  marked  manner  than  others  has  led 
physiologists  to  recognize  different  types  of  respiration.  Three  types 
usually  are  given  in  works  on  physiology :  — 

1.  TJie  Abdominal  Type.  —  In  this,  the  action  of  the  diaphragm, and 
the  consequent  movements  of  the  abdomen  are  most  prominent. 

2.  The  Inferior  Costal  Type.  —  In  this,  the  action  of  the  muscles 
that  expand  the  lower  part  of  the  thorax,  from  the  seventh  rib  inclusive, 
is  most  prominent. 

3.  The  Superior  Costal  Type.  —  In  this,  the  action  of  the  muscles 
that  dilate  the  thorax  above  the  seventh  rib  and  elevate  the  entire 
chest  is  most  prominent. 

The  abdominal  type  is  most  marked  in  children  less  than  three  years 
of  age,  irrespective  of  sex,  respiration  being  carried  on  almost  exclu- 
sively by  the  diaphragm. 

At  a  variable  period  after  birth,  a  difference  in  the  types  of  respira- 
tion in  the   sexes  is  observed.     In  the  male  the  abdominal  conjoined 


FREQUENCY   OF   THE    RESPIRATORY   MOVEMENTS 


107 


with  the  inferior  costal  type  is  predominant,  and  this  continues  through 
hfe.  In  the  female  the  inferior  costal  type  is  insignificant  and  the 
superior  costal  type  predominates.  The  cause  of  the  pronounced  move- 
ments of  the  upper  part  of  the  chest  in  the  female  has  been  the  subject 
of  much  discussion.  It  is  probably  due,  in  a  great  measure,  to  the 
mode  of  dress  now  so  common  in  civilized  countries,  which  confines  the 
lower  part  of  the  chest  and  renders  movements  of  expansion  somewhat 
difficult.  In  a  series  of  observations  by  Dr.  Thomas  J.  Mays  (1887), 
on  eighty-two  Indian  girls  at  the  Lincoln  Institution  in  Philadelphia, 
between  ten  and  twenty  years  of  age,  who  had  never  worn  tight  cloth- 
ing, the  abdominal  type  of  respiration  was  found  to  predominate,  the 
respiratory  tracings  hardly  differing  from  the  tracings  in  the  male. 
These  observations  seem  to  show,  in  opposition  to  the  views  of  Hutchin- 
son and  others,  that  the  predominance  of  the  superior  costal  type  in  the 
female  is  confined  to  civilized  races ;  but  it  is  certain  that  females 
accommodate  themselves  more  readily  than  the  male  to  the  superior 
costal  type ;  and  this  probably  is  a  provision  for  the  physiological  en- 
largement of  the  uterus  in  pregnancy,  which  nearly  arrests  respiratory 
movements  except  those  of  the  upper  part  of  the  chest. 

Frequejicy  of  the  Respiratory  Movements.  —  In  counting  the  respira- 
tory acts,  it  is  desirable  that  the  subject  be  unconscious  of  the  observa- 
tion, otherwise  their  normal  rhythm  is  hkely  to  be  disturbed.  Of  all 
who  have  written  on  this  subject,  Hutchinson  has  presented  the  largest 
and  most  reliable  collection  of  facts.  This  observer  ascertained  the 
number  of  respiratory  acts  per  minute,  in  the  sitting  posture,  in  1897 
males.  The  results  of  his  observations  as  to  frequency  are  given  in  the 
following  table : 


KESPIRATIONS  PER  NUMBER  OF 

MINUTE  CASES 

9  to  16 79 

16 239 

17 105 

18 195 

19 74 

20 561 


RESPIRATIONS  PER  NUMBER  OF 

MINUTE  CASES 

21 129 

22 143 

23 42 

24 243 

24  to  40 87 


Although  this  table  shows  considerable  variations  in  different  indi- 
viduals, the  great  majority  (173 1)  breathed  sixteen  to  twenty-four  times 
per  minute.  Nearly  a  third  breathed  twenty  times  per  minute,  a  number 
that  may  be  taken  as  the  average. 

The  relations  of  the  respiratory  acts  to  the  pulse  are  quite  constant 
in  health.  It  has  been  shown  by  Hutchinson  that  the  proportion  in  the 
great  majority  of  instances  is  one  respiratory  act  to  four  pulsations  of  the 


I08  RESPIRATION 

heart.  The  same  proportion  usually  obtains  when  the  pulse  is  accel- 
erated in  disease,  except  when  the  pulmonary  organs  are  involved. 

Age  has  an  influence  on  the  frequency  of  the  respiratory  acts,  corre- 
sponding with  what  has  already  been  noted  in  regard  to  the  pulsations  of 
the  heart. 

The  following  are  the  results  of  observations  on  three  hundred  males 
(Quetelet):  — 

Forty-four  respirations  per  minute,  soon  after  birth ; 

Twenty-six,  at  the  age  of  five  years ; 

Twenty,  between  fifteen  and  twenty  years ; 

Nineteen,  between  twenty  and  twenty-five  years ; 

Sixteen,  about  the  thirtieth  year ; 

Eighteen,  between  thirty  and  fifty  years. 

The  influence  of  sex  is  not  marked  in  very  young  children.  There 
is  no  difference  between  males  and  females  at  birth ;  but  in  young 
women,  the  respirations  are  a  little  less  frequent  than  in  young  men  of 
the  same  age. 

The  various  physiological  conditions  which  have  been  noted  as  affect- 
ing the  pulse  have  a  corresponding  influence  on  respiration.  In  sleep 
the  number  of  respiratory  acts  is  diminished  by  about  twenty  per  cent 
(Quetelet).  Muscular  effort  accelerates  the  respiratory  movements  pari 
passu,  with  the  movements  of  the  heart. 

Relatio7is  of  Inspiration  and  Expiration  to  each  other.  —  Respiratory 
Sounds.  —  In  ordinary  respiration,  inspiration  is  produced  by  the  action 
of  muscles,  and  expiration,  by  the  passive  reaction  of  the  lungs  and  of 
the  elastic  walls  of  the  thorax.  The  inspiratory  and  expiratory  acts  do 
not  follow  each  other  immediately.  Beginning  with  inspiration,  it  is 
found  that  this  act  maintains  about  the  same  intensity  throughout.  There 
is  then  a  very  brief  interval,  when  expiration  follows,  which  has  its  maxi- 
mum of  intensity  at  the  beginning  of  the  act  and  gradually  dies  away. 
Between  the  acts  of  expiration  and  inspiration  is  an  interval  somewhat 
longer  than  the  interval  between  inspiration  and  expiration. 

The  duration  of  expiration  usually  is  a  little  longer  than  that  of 
inspiration,  although  the  two  acts  may  be  nearly,  or  in  some  instances, 
quite  equal.  After  five  to  eight  ordinary  respiratory  acts,  an  effort 
commonly  is  made  which  is  rather  more  profound  than  usual,  by  which 
the  air  in  the  lungs  is  more  thoroughly  changed.  Temporary  arrest  of 
the  acts  of  respiration  in  violent  muscular  efforts,  in  straining,  in  partu- 
rition etc.,  is  sufficiently  familiar. 

Ordinarily  respiration  is  not  accompanied  with  any  sound  that  can  be 
heard  without  applying  the  ear  directly,  or  by  the  intervention  of  a  stetho- 
scope, to  the  chest,  except  when  the  mouth  is  closed  and  breathing  is 


RESPIRATORY    SOUNDS  109 

carried  on  exclusively  through  the  nasal  passages,  when  a  soft  breezy 
sound  accompanies  both  acts.  If  the  -mouth  is  opened  sufficiently  to 
admit  the  free  passage  of  air,  no  sound  is  to  be  heard  in  health.  In 
sleep  the  respirations  are  more  profound ;  and  if  the  mouth  is  closed 
the  sound  is  rather  more  intense. 

Snoring,  which  sometimes  accompanies  the  respiratory  acts  during 
sleep,  occurs  when  the  air  passes  through  both  the  mouth  and  the  nose.  It 
is  more  marked  in  inspiration,  sometimes  accompanying  both  acts,  and 
sometimes  it  is  not  heard  in  expiration.  It  is  not  necessary  to  describe 
the  character  of  a  sound  so  familiar.  Snoring  is  an  idiosyncrasy  in 
many  individuals,  although  those  who  do  not  snore  habitually  may  do  so 
when  the  system  is  unusually  exhausted  and  relaxed.  It  occurs  when 
the  mouth  is  open,  and  the  sound  is  produced  by  vibration  and  a  sort  of 
flapping  of  the  velum  pendulum  palati,  between  the  two  currents  of  air 
from  the  mouth  and  nose,  together  with  a  vibration  in  the  column  of  air 
itself. 

Applying  the  stethoscope  over  the  larynx  or  trachea,  a  sound  is 
heard,  of  a  distinctly  and  purely  tubular  character,  accompanying  both 
acts  of  respiration.  In  inspiration,  according  to  the  late  Dr.  Austin 
Flint,  "it  attains  its  maximum  of  intensity  quickly  after  the  develop- 
ment of  the  sound  and  maintains  the  same  intensity  to  the  close  of  the 
act,  when  the  sound  abruptly  ends,  as  if  suddenly  cut  off."  After  a 
brief  interval,  the  sound  of  expiration  follows.  This  also  is  tubular  in 
quality.  It  soon  attains  its  maximum  of  intensity,  but  unlike  the  sound 
of  inspiration,  it  gradually  dies  away  and  is  lost  imperceptibly.  It  is 
seen  that  these  phenomena  correspond  with  the  nature  of  the  two  acts 
of  respiration.  Sounds  approximating  in  character  the  foregoing  are 
heard  over  the  bronchial  tubes  before  they  penetrate  the  lungs. 

Over  the  lungs,  a  sound  may  be  heard  entirely  different  in  its  char- 
acter from  that  heard  over  the  larynx,  trachea  or  bronchial  tubes.  In 
inspiration  the  sound  is  much  less  intense  than  over  the  trachea  and 
has  a  breezy,  expansive,  or  what  is  called  in  auscultation,  a  vesicular 
character.  It  is  much  lower  in  pitch  than  the  tracheal  sound.  It  is 
continuous  and  rather  increases  in  intensity  from  its  beginning  to  its 
termination,  ending  abruptly,  like  the  tracheal  inspiratory  sound.  The 
sound  is  produced  in  part  by  the  movement  of  air  in  the  small  bronchial 
tubes,  but  chiefly  by  the  expansion  of  the  air-cells  of  the  lungs.  It  is 
followed,  without  an  interval,  by  the  sound  of  expiration,  which  is  shorter 
—  one-fifth  or  one-fourth  as  long  —  lower  in  pitch  and  much  less  intense. 
A  sound  is  not  always  heard  in  expiration. 

Variations  in  the  intensity  of  the  respiratory  sounds  in  different  indi- 
viduals are  considerable.     As  a  rule  they  are  more  intense  in  young  per- 


no  RESPIRATION 

sons ;  which  has  given  rise  to  the  term  "  puerile  respiration,"  when  the 
sounds  are  exaggerated  in  parts  of  the  lung  in  certain  cases  of  disease. 
The  sounds  usually  are  more  intense  in  females  than  in  males,  particu- 
larly in  the  upper  regions  of  the  thorax. 

It  is  difficult  by  any  description  or  comparison  to  convey  an  adequate 
idea  of  the  character  of  the  sounds  heard  over  the  lungs  and  air-passages, 
and  it  is  unnecessary  to  make  the  attempt,  when  they  can  be  so  easily 
studied  in  the  living  subject. 

Coughing,  Sneezing,  Sighing,  Yawning,  LajigJiing,  Sobbiiig  and  Hic- 
cough. —  These  peculiar  acts  demand  a  few  words  of  explanation.  Cough- 
ing and  sneezing  usually  are  involuntary  acts,  produced  by  irritation 
in  the  air-tubes  or  nasal  passages,  although  coughing  often  is  voluntary. 
In  both  these  acts,  there  is  first  a  deep  inspiration  followed  with  a 
convulsive  action  of  the  expiratory  muscles,  by  which  the  air  is  violently 
expelled  with  a  characteristic  sound,  in  the  one  case  by  the  mouth,  and 
in  the  other  by  the  mouth  and  nares.  Foreign  bodies  lodged  in  the  air- 
passages  frequently  are  expelled  in  violent  fits  of  coughing.  In  hyper- 
secretion of  the  bronchial  mucous  membrane,  the  accumulated  mucus  is 
carried  by  the  act  of  coughing  either  to  the  mouth  or  well  into  the  larynx, 
when  it  may  be  expelled  by  the  act  of  exspuition.  When  either  of  these 
acts  is  the  result  of  irritation  from  a  foreign  substance  or  from  secretions, 
it  may  be  modified  or  partly  smothered  by  the  will,  but  is  not  completely 
under  control.  The  sensibility  of  the  mucous  membrane  at  the  summit 
of  the  air-passages  usually  protects  them  from  the  entrance  of  foreign 
matters,  both  liquid  and  solid ;  for  the  sUghtest  impression  received  by 
the  membrane  gives  rise  to  a  violent  and  involuntary  cough,  by  which 
the  offending  substance  may  be  removed.  The  glottis,  also,  is  spasmodi- 
cally contracted. 

In  sighing,  a  prolonged  and  deep  inspiration  is  followed  with  a  rapid 
and  usually  an  audible  expiration.  This  occurs,  as  a  rule,  once  in  five 
to  eight  respiratory  acts,  for  the  purpose  of  changing  the  air  in  the  lungs 
more  completely,  and  it  is  due  to  an  exaggeration  of  the  cause  that 
gives  rise  to  the  ordinary  acts  of  respiration.  When  due  to  depressing 
emotions,  it  has  the  same  cause ;  for  at  such  times  respiration  is  less 
efificiently  performed.  Yawning  is  an  analogous  process,  but  it  differs 
from  sighing  in  the  fact  that  it  is  involuntary  and  can  not  be  produced 
by  an  effort  of  the  will.  It  is  characterized  by  a  wide  opening  of  the 
mouth  and  a  profound  inspiration.  Yawning  commonly  is  assumed  to 
be  an  evidence  of  fatigue,  but  it  often  occurs  from  a  sort  of  contagion. 
When  not  the  result  of  imitation,  it  has  the  same  exciting  cause  as  sigh- 
ing —  deficient  oxygenation  of  the  blood  —  and  it  is  followed  with  a  sense 
of  satisfaction,  which  shows  that  it  meets  some  decided  want  on  the  part 
of  the  system. 


AIR    CHANGED    IN    THE    RESPIRATORY   ACTS  III 

Laughing  and  sobbing,  although  expressing  opposite  conditions,  are 
produced  by  nearly  the  same  action.  The  characteristic  sounds  accom- 
panying these  acts  are  the  result  of  short,  rapid  and  convulsive  move- 
ments of  the  diaphragm,  attended  with  contractions  of  the  muscles  of 
the  face,  which  produce  the  expressions  characteristic  of  hilarity  or  grief. 
Although  to  a  certain  extent  under  the  control  of  the  will,  these  acts  are 
mainly  involuntary.  Violent  and  convulsive  laughter  may  be  excited  in 
many  individuals  by  titillation  of  certain  portions  of  the  surface  of  the 
body.  Laughter  and  sometimes  sobbing,  like  yawning,  may  be  the  re- 
sult of  involuntary  imitation. 

Hiccough  is  a  peculiar  modification  of  the  act  of  inspiration,  to  which 
it  is  exclusively  confined.  It  is  produced  by  a  sudden,  convulsive  and 
entirely  involuntary  contraction  of  the  diaphragm,  accompanied  with 
spasmodic  constriction  of  the  glottis.  The  contraction  of  the  diaphragm 
is  more  extensive  than  in  laughing  and  sobbing  and  occurs  only  once  in 
every  four  or  five  respiratory  acts. 


Capacity   of   the   Lungs,   and   the  Quantity  of   Air  changed  in 
THE   Respiratory   Acts 

The  volume  of  air  ordinarily  contained  in  the  lungs  is  about  two 
hundred  cubic  inches  (3277  cubic  centimeters);  but  it  is  e\'ident,  from 
the  simple  experiment  of  opening  the  chest,  when  the  elastic  lungs  col- 
lapse and  expel  a  certain  quantity  of  air  which  can  not  be  removed  while 
the  lungs  are  in  situ,  that  a  part  of  the  gaseous  contents  of  these  organs 
necessarily  remains  after  the  most  forcible  expiration.  After  an  ordinary 
act  there  is  a  certain  quantity  of  air  in  the  lungs,  which  can  be  expelled 
by  a  forced  expiration.  In  ordinary  respiration  a  comparatively  small 
volume  of  air  enters  with  inspiration,  and  a  nearly  equal  quantity  is  ex- 
pelled by  the  succeeding  expiration.  By  the  extreme  action  of  all  the 
inspiratory  muscles  in  a  forced  inspiration,  a  supplemental  quantity  of 
air  may  be  taken  into  the  lungs,  which  then  contain  much  more  than 
they  ever  do  in  ordinary  respiration.  For  convenience  of  description, 
physiologists  have  adopted  the  following  names,  which  are  applied  to 
these  various  volumes  of  air  :  — 

1.  Residual  Air ;  that  which  is  not  and  can  not  be  expelled  by  a 
forced  expiration. 

2.  Reserve  Air ;  that  which  remains  after  an  ordinary  expiration, 
deducting  the  residual  air. 

3.  Tidal,  or  Ordinary  Breathing  Air ;  that  which  is  changed  in  the 
ordinary  acts  of  inspiration  and  expiration. 


112  RESPIRATION 

4.  Complemental  Ah- ;  the  excess  over  the  ordinary  breathing  air, 
which  may  be  introduced  by  a  forcible  inspiration. 

In  measuring  the  air  changed  in  ordinary  breathing,  it  has  been  found 
that  the  acts  of  respiration  are  so  easily  influenced  and  it  is  so  difficult 
to  experiment  on  any  individual  without  his  knowledge,  that  the  results 
of  many  good  observers  are  not  entirely  reliable.  This  is  one  of  the 
most  important  of  the  questions  under  consideration.  The  difficulties  in 
the  way  of  estimating  with  accuracy  the  residual,  reserve  or  complemen- 
tal volumes,  will  readily  suggest  themselves.  The  observations  on  these 
points  which  may  be  taken  as  the  most  definite  and  exact  are  those  of 
Herbst  and  of  Hutchinson.  Those  of  the  last-named  observer  are  very 
elaborate  and  were  made  on  a  large  number  of  subjects  of  both  sexes 
and  of  all  ages  and  occupations.  They  are  commonly  accepted  by 
physiologists  as  the  most  extended  and  accurate. 

Residual  Air.  —  Perhaps  there  is  not  one  of  the  questions  under  con- 
sideration more  difficult  to  answer  definitely  than  that  of  the  quantity  of 
air  remaining  in  the  lungs  after  a  forced  expiration  ;  but  it  fortunately  is 
not  one  of  great  practical  importance.  The  residual  air  remains  in  the 
lungs  as  a  physical  necessity.  The  lungs  in  health  are  always  in  contact 
with  the  walls  of  the  thorax;  and  when  the  chest  is  reduced  to  its  small- 
est dimensions,  it  is  impossible  that  more  air  should  be  expelled.  The 
volume  which  thus  remains  has  been  variously  estimated.  The  residual 
volume  has  been  put  at  about  one  hundred  cubic  inches  (1639  cubic 
centimeters),  but  the  quantity  varies  very  considerably  in  different  indi- 
viduals (Hutchinson).  Taking  everything  into  consideration,  it  may  be 
assumed  that  this  estimate  is  as  nearly  correct  as  any. 

Reserve  Air.  — This  name  is  given  to  the  volume  of  air  that  may  be 
expelled  and  changed  by  a  voluntary  effort,  but  which  remains  in  the 
lungs,  added  to  the  residual  air,  after  an  ordinary  act  of  expiration.  It 
may  be  estimated,  without  reference  to  the  residual  air,  by  forcibly  ex- 
pelling air  from  the  lungs  after  an  ordinary  expiration.  The  average 
volume,  according  to  Hutchinson,  is  one  hundred  cubic  inches  (1639 
cubic  centimeters). 

More  or  less  of  the  reserve  air  is  changed  whenever  there  is  a  neces- 
sity for  more  complete  renovation  of  the  contents  of  the  lungs  than 
ordinary.  It  is  encroached  upon  in  the  unusually  profound  inspiration 
and  expiration  which  occur  once  in  every  five  to  eight  acts.  It  is  used  in 
certain  prolonged  vocal  efforts,  in  blowing  etc.  Added  to  the  residual  air, 
it  constitutes  the  minimum  capacity  of  the  lungs  in  ordinary  respiration. 
As  it  is  continually  receiving  watery  vapor  and  carbon  dioxide,  it  is 
always  more  or  less  vitiated,  and  when  reenforced  by  the  breathing  air, 
which  enters  with  inspiration,  is  continually  in  circulation,  in  obedience 


EXTREME    BREATHING    CAPACITY  II3 

to  the  law  of  the  diffusion  of  gases.  Those  who  are  in  the  habit  of 
arresting  respiration  for  a  time,  learn  to  change  the  reserve  air  as  com- 
pletely as  possible  by  several  forcible  acts  and  then  fill  the  lungs  with 
fresh  air.  In  this  way  they  are  enabled  to  suspend  the  respiratory  acts 
for  two  or  three  minutes  without  much  inconvenience.  The  introduc- 
tion of  fresh  air  with  each  inspiration  and  the  constant  diffusion  which 
is  going  on  and  by  which  the  proper  quantity  of  oxygen  finds  its  way  to 
the  air-cells  give,  in  ordinary  breathing,  a  composition  to  the  air  in  the 
deepest  portions  of  the  lungs,  which  insures  constant  aeration  of  the 
blood. 

Tidal,  or  Ordinary  Breathing  Air.  —  The  volume  of  air  changed  in 
the  ordinary  acts  of  respiration  is  subject  to  certain  physiological  varia- 
tions ;  and  the  respiratory  movements,  as  regards  their  extent,  are  so 
easily  influenced,  that  care  is  necessary  to  avoid  error  in  estimating  the 
volume  of  ordinary  breathing  air.  As  a  mean  of  the  results  obtained  by 
Herbst  and  by  Hutchinson,  the  average  volume  of  breathing  air,  in  a 
man  of  ordinary  stature,  is  twenty  cubic  inches  (327.7  cubic  centimeters). 
According  to  Hutchinson,  in  perfect  repose,  when  the  respiratory  move- 
ments are  hardly  perceptible,  not  more  than  seven  to  twelve  cubic  inches 
(i  14.7  to  196.6  cubic  centimeters)  are  changed  ;  while,  under  excitement, 
the  volume  may  be  increased  to  seventy-seven  cubic  inches  (126 1.8 
cubic  centimeters).  The  breathing  volume  progressively  increases  in 
proportion  to  the  stature  of  the  individual  and  bears  no  definite  relation 
to  the  apparent  capacity  of  the  chest  (Herbst). 

Complemental  Air.  —  The  thorax  may  be  so  enlarged  by  an  extreme 
inspiratory  effort  as  to  contain  a  quantity  of  air  much  larger  than  after 
an  ordinary  inspiration.  The  additional  volume  of  air  thus  taken  in  may 
be  estimated  by  measuring  all  the  air  that  can  be  expelled  from  the 
lungs  after  the  most  profound  inspiration,  and  deducting  the  sum  of  the 
reserve  air  and  breathing  air.  This  quantity  has  been  found  by  Hutch- 
inson to  vary  in  different  individuals,  bearing  a  close  relation  to  stature. 
The  mean  complemental  volume  is  one  hundred  and  ten  cubic  inches 
(1802.9  cubic  centimeters). 

The  complemental  air  is  drawn  upon  whenever  an  effort  is  made 
which  requires  a  temporary  arrest  of  respiration.  Brief  and  violent 
muscular  exertion  usually  is  preceded  by  a  profound  inspiration.  In 
sleep,  as  the  volume  of  breathing  air  is  somewhat  increased,  the  comple- 
mental air  is  encroached  upon.  A  part  or  all  of  the  complemental  air 
also  is  used  in  certain  vocal  efforts,  in  blowing,  in  yawning,  in  the  deep 
inspiration  which  precedes  sneezing,  in  straining  etc. 

Extreme  Breathing  Capacity.  —  By  the  extreme  breathing  capacity 
is  meant  the  volume  of  air  that  can  be  expelled  from  the  lungs  by  the 


114 


RESPIRATION 


most  forcible  expiration  after  the  most  profound  inspiration.  This  has 
been  called  by  Hutchinson,  the  vital  capacity,  as  signifying  "  the  volume 
of  air  which  can  be  displaced  by  living  movements."  Its  volume  is 
equal  to  the  sum  of  the  reserve  air,  the  breathing  air  and  the  comple- 
mental  air,  and  it  represents  the  extreme  capacity  of  the  chest,  less  the 
residual  air.  Its  physiological  importance  is  due  to  the  fact  that  it  can 
be  determined  by  an  appropriate  apparatus,  the  spirometer,  and  compari- 
sons may  thus  be  made  between  different  individuals,  both  healthy  and 
diseased.  The  number  of  observations  on  this  point  made  by  Hutchin- 
son amounts  in  all  to  a  little  less  than  five  thousand. 

The  extreme  breathing  capacity  in  health  is  subject  to  variations 
that  bear  a  close  relation  to  the  stature  of  the  individual.  Hutchinson 
begins  with  the  proposition  that  in  a  man  of  medium  height  (five  feet 
eight  inches,  or  170.2  centimeters),  it  is  equal  to  two  hundred  and  thirty 
cubic  inches  (3768.6  cubic  centimeters). 

The  most  striking  result  of  the  experiments  of  Hutchinson,  in  re- 
gard to  the  modifications  of  the  vital  capacity,  is  that  it  bears  a  definite 
relation  to  stature,  without  being  much  affected  by  weight  or  by  the 
circumference  of  the  chest.  This  is  especially  remarkable,  as  it  is  well 
known  that  height  does  not  depend  so  much  on  the  length  of  the  body 
as  on  the  length  of  the  lower  extremities.  He  ascertained  that  for 
every  inch  (2.5  centimeters)  in  height,  between  five  and  six  feet  (152.4 
and  182.9  centimeters),  the  extreme  breathing  capacity  is  increased  by 
eight  cubic  inches  (131.  i  cubic  centimeters). 

Age  has  an  influence,  though  less  marked  than  stature,  on  the 
extreme  breathing  capacity.  As  the  result  of  4800  observations  on 
males,  it  was  shown  that  the  volume  increased  with  age  up  to  the 
thirtieth  year,  and  progressively  decreased,  with  tolerable  regularity, 
from  the  thirtieth  to  the  sixtieth  year.  The  figures  given  above,  al- 
though subject  to  certain  individual  variations,  may  be  taken  as  a  basis 
for  examinations  of  the  extreme  breathing  capacity  in  disease. 

Relations  in  Volume  of  the  Expired  to  the  Inspired  Air.  —  A  certain 
proportion  of  the  inspired  air  is  lost  in  respiration,  so  that  the  air  ex- 
pired is  always  a  little  less  in  volume  than  that  taken  into  the  lungs. 
The  loss  was  put  by  Davy  at  one-seventieth,  and  by  Cuvier  at  one-fiftieth 
of  the  volume  of  air  introduced.  Observations  on  this  point,  to  be 
exact,  must  include  a  considerable  number  of  respiratory  acts ;  and 
from  the  difficulty  in  continuing  respiration  in  a  regular  and  normal 
manner  when  attention  is  directed  to  the  respiratory  movements,  the 
most  accurate  results  may  probably  be  obtained  from  experiments  on 
the  lower  animals.  Despretz  caused  six  young  rabbits  to  respire  for 
two    hours  in   a  confined  space  containing   2990  cubic  inches  (49,000 


DIFFUSION    OF   AIR    IN    THE    LUNGS  II5 

cubic  centimeters)  of  air,  and  ascertained  that  the  volume  had  dimin- 
ished by  sixty-one  cubic  inches  (1000  cubic  centimeters),  or  a  little 
more  than  one-fiftieth.  Adopting  the  approximations  of  Davy  and 
Cuvier,  applied  to  the  human  subject,  as  nearly  correct,  it  may  be 
assumed  that  in  the  lungs  one-seventieth  to  one-fiftieth  of  the  inspired 
air  is  lost. 

Diffusion  of  Air  in  the  Lungs.  —  When  it  is  remembered  that  with 
each  inspiration,  but  about  twenty  cubic  inches  (327.7  cubic  centimeters) 
of  fresh  air  are  introduced,  sufficient  only  to  fill  the  trachea  and  larger 
bronchial  tubes,  it  is  evident  that  some  forces  must  act  by  which  this 
fresh  air  finds  its  way  into  the  air-cells,  and  the  vitiated  air  is  brought 
into  the  larger  tubes,  to  be  expelled  with  the  succeeding  expiration. 

The  interchange  between  the  fresh  air  in  the  upper  portions  of  the 
respiratory  apparatus  and  the  air  in  the  deeper  parts  of  the  lungs  is 
constantly  going  on  by  diffusion  aided  by  the  active  currents  or  impulses 
produced  by  the  alternate  movements  of  the  chest.  In  the  respiratory 
apparatus,  at  the  end  of  an  inspiration,  the  atmospheric  air,  composed  of 
a  mixture  of  oxygen  and  nitrogen,  is  introduced  into  the  tubes  with  a 
considerable  impetus  and  is  brought  into  contact  with  the  gas  in  the 
lungs,  which  is  heavier,  as  it  contains  a  certain  quantity  of  carbon 
dioxide.  Diffusion  then  takes  place,  aided  by  the  elastic  lungs,  which 
are  gradually  forcing  the  gaseous  contents  out  of  the  cells,  until  a 
certain  portion  of  the  air  loaded  with  carbon  dioxide  finds  its  way  to 
the  larger  tubes,  to  be  thrown  off  in  expiration,  its  place  being  supplied 
with  fresh  air. 

In  accordance  with  the  law  that  the  diffusibility  of  gases  is  in 
inverse  ratio  to  the  square  root  of  their  densities,  the  penetration  of 
atmospheric  air,  which  is  the  lighter,  to  the  deep  portions  of  the  lungs 
would  take  place  with  greater  rapidity  than  the  ascent  of  air  charged 
with  carbon  dioxide ;  so  that  eighty-one  parts  of  carbon  dioxide  should 
be  replaced  with  ninety-five  parts  of  oxygen.  It  is  found,  indeed,  that 
the  volume  of  carbon  dioxide  exhaled  is  always  less  than  the  volume  of 
oxygen  absorbed.  This  diffusion  is  constantly  going  on,  so  that  the  air 
in  the  pulmonary  alveoli,  where  the  interchange  of  gases  with  the 
blood  takes  place,  maintains  a  nearly  uniform  composition.  The  pro- 
cess of  aeration  of  the  blood,  therefore,  has  little  of  that  intermittent 
character  which  attends  the  muscular  movements  of  respiration. 


CHAPTER   V 

CHANGES    WHICH    THE    AIR    AND    THE    BLOOD    UNDERGO    IN 

RESPIRATION 

Composition  of  the  air  —  Consumption  of  oxygen — Exhalation  of  carbon  dioxide —  Influence 
of  age  —  Influence  of  sex  —  Influence  of  digestion  —  Influence  of  diet — Influence  of 
muscular  activity  —  Influence  of  moisture  and  temperature  —  Influence  of  the  season  of 
the  year  —  Relations  between  the  oxygen  consumed  and  the  carbon  dioxide  exhaled  — 
Sources  of  carbon  dioxide  in  the  expired  air- — ^  Respiratory  quotient  —  Exhalation  of 
watery  vapor  —  Exhalation  of  ammonia,  organic  matter  etc.  —  Exhalation  of  nitrogen  — 
Changes  of  the  blood  in  respiration  —  Analysis  of  the  blood  for  gases  —  Nitrogen  of  the 
blood  —  Oxygen  of  the  blood- — ^ Carbon  dioxide  of  the  blood  —  Respiration  by  the  tissues 
—  Respiratory  efforts  before  birth — Asphy^xia. 

Changes  of  the  Air  in  Respiration 

Composition  of  the  Air.  —  Pure  atmospheric  air  is  a  mixture  of  79.05 
parts  of  nitrogen  with  20.95  parts  of  oxygen.  Dewar  and  others,  how- 
ever, have  discovered  in  the  air  a  small  quantity  of  hydrogen,  with  new 
elements  called  argon,  metargon,  neon,  xenon  and  helium,  all  to  be  in- 
cluded in  the  proportion  assigned  to  nitrogen.  The  air  usually  contains 
in  addition  about  one  part  in  two  thousand  of  carbon  dioxide.  The  air 
is  never  free  from  moisture,  which  is  variable  in  quantity,  being  usually 
more  abundant  at  a  high  than  at  a  low  temperature.  Floating  in  the 
atmosphere  are  large  numbers  of  minute  organic  bodies,  and  various 
odorous  and  other  gaseous  matters  are  accidental  constituents. 

It  is  necessary  to  the  regular  performance  of  respiration  that  the  air 
should  contain  about  four  parts  of  nitrogen  to  one  of  oxygen  and  should 
have  about  the  density  that  exists  on  the  surface  of  the  earth.  When 
the  density  is  much  increased,  as  in  mines,  respiration  is  more  or  less 
disturbed.  Under  great  pressure,  such  as  exists  in  caissons,  a  quantity 
of  nitrogen  —  which  is  sparingly  soluble  under  ordinary  conditions  — 
may  be  forced  into  the  blood.  Return  to  the  outer  air  should  be  gradual ; 
for  if  the  excessive  pressure  is  suddenly  removed,  bubbles  of  nitrogen 
may  be  rapidly  disengaged,  often  with  a  fatal  result.  Exposure  to  a 
rarefied  atmosphere,  as  in  the  ascent  of  high  mountains  or  in  aerial 
voyages,  may  seriously  disturb  respiration,  from  the  fact  that  less  oxygen 
than  usual  is  presented  to  the  respiratory  surface  and  the  reduced 
atmospheric  pressure  diminishes  the  capacity  of  the  blood  for  retaining 

116 


CONSUMPTION    OF    OXYGEN 


"7 


gases.  Allen  and  Pepys  confined  animals  for  twenty-four  hours  in  an 
atmosphere  of  pure  oxygen  without  any  notable  results ;  but  these 
experiments  do  not  show  that  it  would  be  possible  to  respire  unmixed 
oxygen  indefinitely  without  inconvenience.  The  only  gas  beside  oxygen, 
that  has  the  power  of  maintaining  respiration,  even  for  a  time,  is  nitro- 
gen monoxide.  This  is  appropriated  by  the  blood-corpuscles  with  great 
avidity;  and  for  a  time  it  produces  excitement  with  delirium  etc.,  which 
has  given  it  the  common  name  of  the  laughing  gas ;  but  this  condition 
is  followed  by  anesthesia,  and  finally  by  asphyxia,  probably  because  the 
gas  has  so  strong  an  affinity  for  the  blood-corpuscles  as  to  remain  to  a 
certain  extent  fixed,  interfering  with  the  interchange  of  gases  that  is 
essential  to  life.  Notwithstanding  this,  experimenters  have  confined 
rabbits  and  other  animals  in  an  atmosphere  of  nitrogen  monoxide  for  a 
number  of  hours  without  fatal  results.  In  all  cases  they  became  as- 
phyxiated, but  in  some  instances  they  were  restored  on  being  brought 
again  into  the  ordinary  atmosphere. 

Other  gases  that  may  be  introduced  into  the  lungs  either  produce 
asphyxia,  negatively,  from  the  fact  that  they  are  incapable  of  carrying 
on  respiration,  like  hydrogen  or  nitrogen,  or  positively,  by  a  poisonous 
effect  on  the  system.  The  most  important  of  the  gases  that  act  as 
poisons  are  carbon  monoxide,  hydrogen  monosulphide  and  arsenious 
hydride.  Carbon  monoxide  unites  with  the  red  corpuscles,  forming 
carbon-monoxide-hemoglobin.  This  union  is  so  stable  that  it  paralyzes 
the  corpuscles  as  oxygen-carriers  and  produces  death  by  asphyxia.  It 
is  probable  that  carbon  dioxide  is  not  in  itself  poisonous.  Regnault 
and  Reiset  exposed  animals  (dogs  and  rabbits)  for  many  hours,  to  an 
atmosphere  containing  twenty-three  per  cent  of  carbon  dioxide,  artifi- 
cially introduced,  with  between  thirty  and  forty  per  cent  of  oxygen, 
without  any  ill  effects. 

Consumption  of  Oxygen. — The  determination  of  the  quantity  of  oxy- 
gen removed  from  the  air  in  respiration  is  important ;  and  on  this  point, 
there  is  an  accumulated  mass  of  observations  that  are  comparatively 
unimportant  from  the  fact  that  they  were  made  before  the  methods  of 
analysis  of  gases  were  as  accurate  as  now.  In  the  observations  of 
Regnault  and  Reiset,  animals  were  placed  in  a  receiver  filled  with  air, 
a  measured  quantity  of  oxygen  was  introduced  as  fast  as  it  was  con- 
sumed in  respiration,  and  the  carbon  dioxide  was  constantly  removed 
and  carefully  estimated.  In  most  of  the  experiments,  the  confinement 
did  not  appear  to  interfere  with  the  functions  of  the  animal,  which  ate 
and  drank  in  the  apparatus  and  was  in  as  good  condition  at  the  end  as 
at  the  beginning  of  the  observation.  This  method  is  more  accurate 
than  that  of  simply  causing  an  animal  to  breathe  in  a  confined  space, 


Il8  RESPIRATION 

when  the  consumption  of  oxygen  and  accumulation  of  carbon  dioxide 
and  other  matters  interfere  more  or  less  with  the  respiratory  function. 
As  employed  by  Regnault  and  Reiset,  it  is  adapted  only  to  experiments 
on  animals  of  small  size.  These  give  an  approximate  idea,  however,  of 
the  processes  as  they  take  place  in  the  human  subject.  Pettenkofer 
constructed  a  chamber  large  enough  to  admit  a  man  and  allow  freedom 
of  motion,  eating,  sleeping  etc.,  into  which  air  could  be  introduced  in 
definite  quantity,  and  from  which  the  products  of  respiration  were 
removed  and  estimated.  This  method  had  been  adapted  to  the  human 
subject  on  a  small  scale  in  1843,  by  Scharling ;  but  there  was  no  arrange- 
ment for  estimating  the  quantity  of  oxygen  consumed. 

Estimates  of  the  quantities  of  oxygen  consumed  or  of  carbon  dioxide 
exhaled,  based  on  analyses  of  the  inspired  and  expired  air,  calculations 
from  the  average  quantity  of  air  changed  with  each  respiratory  act  and 
the  average  number  of  respirations  per  minute,  are  not  so  reliable  as 
analyses  showing  the  actual  changes  in  the  air,  like  those  of  Regnault 
and  Reiset.  Where  there  is  so  much  multiplication  and  calculation,  a 
slight  inaccuracy  in  the  estimates  of  the  quantities  consumed  or  pro- 
duced in  a  single  respiration  will  make  a  large  error  in  the  estimate  for 
a  day  or  even  for  an  hour.  Bearing  in  mind  these  sources  of  error,  from 
the  experiments  of  Valentin  and  Brunner,  Dumas,  Regnault  and  Reiset 
and  others,  a  sufficiently  accurate  approximation  of  the  proportion  of 
oxygen  consumed  by  the  human  subject  may  be  made.  The  air,  which 
contains,  when  inspired,  about  twenty-one  per  cent  of  oxygen,  is  found 
on  expiration  to  contain  but  about  sixteen  per  cent.  In  other  words, 
the  volume  of  oxygen  absorbed  in  the  lungs  is  about  five  per  cent  of 
the  volume  of  air  inspired. 

The  quantity  of  oxygen  consumed  in  respiration  is  subject  to  great 
variations,  depending  on  temperature,  the  condition  of  the  digestive  sys- 
tem, muscular  activity  etc.  The  following  conclusions,  the  results  of  the 
observations  of  Lavoisier  and  Seguin,  give  at  a  glance  the  variations 
from  the  above-mentioned  causes  :  — 

"I.  A  man,  in  repose  and  fasting,  with  an  external  temperature  of 
about  90°  Fahr.  (32.5°  C),  consumes  1465  cubic  inches  (24  liters)  of 
oxygen  per  hour. 

"  2.  The  same  man,  in  repose  and  fasting,  with  an  external  tempera- 
ture of  59°  Fahr.  (15°  C),  consumes  1627  cubic  inches  (26.66  liters)  of 
oxygen  per  hour. 

"  3.  The  same  man,  during  digestion,  consumes  2300  cubic  inches 
(37.69  liters)  of  oxygen  per  hour. 

"4.  The  same  man,  fasting,  accomplishing  the  labor  necessary  to 
raise,  in  fifteen  minutes,  a  weight  of  about  16  pounds  3  ounces  (7.343 


CONSUMPTION    OF    OXYGEN  II9 

kilograms)  to  the  height  of  656  feet  (200  meters),  consumes  3874  cubic 
inches  (63.48  liters)  of  oxygen  per  hour. 

"  5.  The  same  man,  during  digestion,  accomplishing  the  labor  neces- 
sary to  raise,  in  fifteen  minutes,  a  weight  of  about  16  pounds  3  ounces 
(7.343  kilograms)  to  the  height  of  692  feet  (2 11. 146  meters),  consumes 
5568  cubic  inches  (91.24  liters)  of  oxygen  per  hour." 

Immediately  after  birth  the  consumption  of  oxygen  in  warm-blooded 
animals  is  relatively  very  slight.  It  has  been  shown  that  just  after  birth, 
dogs  and  other  animals  will  live  for  half  an  hour  or  longer  under  water ; 
and  cases  are  on  record  in  which  life  has  been  restored  in  newborn  chil- 
dren after  seven,  and,  it  has  been  stated,  after  twenty-three,  hours  of 
asphyxia  (Milne-Edwards).  During  the  first  periods  of  extra-uterine  life, 
the  condition  of  the  newly  born  is  nearly  that  of  a  cold-blooded  animal. 
The  lungs  are  relatively  small,  and  it  is  some  time  before  they  fully 
assume  their  office.  There  is,  also,  very  little  power  of  resistance  to  a 
low  temperature.  Although  accurate  researches  regarding  the  compara- 
tive quantities  of  oxygen  in  the  venous  and  arterial  blood  of  the  foetus 
are  wanting,  it  has  frequently  been  observed  that  the  difference  in  color 
is  not  so  marked  as  it  is  after  pulmonary  respiration  has  become  estab- 
lished. The  direct  researches  of  W.  F.  Edwards  have  shown  that  the 
absolute  consumption  of  oxygen  by  very  young  animals  is  quite  small; 
and  the  observations  of  Legallois,  on  rabbits,  made  every  five  days  dur- 
ing the  first  month  of  life,  show  a  rapidly  increasing  demand  for  oxygen. 

The  consumption  of  oxygen  is  greater  in  lean  than  in  fat  animals, 
provided  they  are  in  perfect  health.  The  consumption  is  greater,  also, 
in  carnivorous  than  in  herbivorous  animals ;  and  in  animals  of  different 
sizes,  it  is  relatively  greater  in  those  which  are  very  small.  In  small 
birds,  such  as  the  sparrow,  the  relative  quantity  of  oxygen  absorbed  was 
ten  times  greater  than  in  the  fowl. 

During  sleep  the  quantity  of  oxygen  consumed  is  considerably  dimin- 
ished ;  and  in  hibernation  it  is  so  small,  that  Spallanzani  could  not  detect 
any  difference  in  the  composition  of  the  air  in  which  a  marmot  in  a 
state  of  torpor  had  remained  for  three  hours.  In  experiments  on  a  mar- 
mot in  hibernation,  Regnault  and  Reiset  observed  a  reduction  in  the 
oxygen  consumed  to  about  one-thirtieth  of  the  ordinary  quantity. 

It  has  been  shown  by  experiments  that  the  consumption  of  oxygen 
bears  a  nearly  constant  ratio  to  the  production  of  carbon  dioxide ;  and 
as  observations  on  the  influence  of  sex,  the  number  of  respiratory  acts 
etc.,  on  the  activity  of  the  respiratory  processes  have  been  made  chiefly 
with  reference  to  the  carbon  dioxide  exhaled,  these  influences  will  be 
considered  in  connection  with  the  products  of  respiration. 

Experiments  on  the  effect  of  increasing  the  proportion  of  oxygen  in. 


I20  RESPIRATION 

the  air  have  led  to  various  results  at  the  hands  of  different  observers. 
Regnault  and  Reiset  did  not  discover  any  increase  in  the  consumption 
of  oxygen  when  this  gas  was  largely  in  excess  in  the  atmosphere. 

The  results  of  confining  an  animal  in  an  atmosphere  composed  of 
twenty-one  parts  of  oxygen  and  seventy-nine  parts  of  hydrogen  are  re- 
markable. When  hydrogen  is  substituted  for  nitrogen,  the  consumption 
of  oxygen  is  largely  increased.  This  has  been  attributed  to  the  greater 
refrigerating  power  of  the  hydrogen  ;  but  a  more  rational  explanation  is 
in  its  greater  diffusibihty.  Hydrogen  is  the  most  diffusible  of  gases; 
and  when  introduced  into  the  lungs  in  place  of  nitrogen,  the  vitiated 
air,  charged  with  carbon  dioxide,  is  undoubtedly  more  readily  removed 
from  the  deep  portions  of  the  lungs,  giving  place  to  the  mixture  of 
hydrogen  and  oxygen.  It  is  probably  for  this  reason  that  the  quantity 
of  oxygen  consumed  is  increased.  It  is  probable  that  the  nitrogen  of 
the  air  plays  an  important  part  in  the  phenomena  of  respiration,  by 
virtue  of  its  degree  of  diffusibihty. 

In  view  of  the  great  variations  in  the  consumption  of  oxygen,  de- 
pendent on  different  physiological  conditions,  such  as  digestion,  exercise, 
temperature  etc.,  it  is  impossible  to  fix  on  any  number  that  will  represent, 
even  approximately,  the  average  quantity  consumed  per  hour.  The  esti- 
mate arrived  at  by  Longet,  from  a  comparison  of  the  results  obtained 
by  different  reliable  observers,  is  perhaps  as  near  the  truth  as  is  possible. 
This  estimate  puts  the  hourly  consumption  at  1220  to  1525  cubic  inches 
(20  to  25  liters),  "  in  an  adult  male,  during  repose  and  under  normal  con- 
ditions of  health  and  temperature." 

In  passing  through  the  lungs,  the  air,  in  addition  to  losing  a  certain 
proportion  of  its  oxygen,  undergoes  the  following  changes :  — 

1.  Elevation  in  temperature. 

2.  Gain  of  carbon  dio.xide. 

3.  Gain  of  watery  vapor. 

4.  Gain  of  ammonia. 

5.  Gain  of  a  small  quantity  of  organic  matter. 

6.  Gain,  and  occasionally  loss,  of  nitrogen. 

The  elevation  in  temperature  of  the  air  that  has  passed  through  the 
lungs  has  been  studied  by  Grehant.  He  found  that  with  an  external 
temperature  of  72°  Fahr.  (22.22°  C.),  respiring  seventeen  times  per  min- 
ute, the  air  taken  in  by  the  nares  and  expired  by  the  mouth  through  an 
apparatus  containing  a  thermometer  carefully  protected  from  external 
influences,  marked  a  temperature  of  95.4°  Fahr.  (35-22°  C.).  Taking  in 
the  air  by  the  mouth,  the  temperature  of  the  expired  air  was  93°  Fahr. 
(33.89°  C.).  At  the  beginning  of  the  expiration,  Grehant  noted  a  tem- 
perature of  94°  Fahr.  (34.44°  C.).     After  a  prolonged  expiration,  the  tem- 


EXHALATION    OF    CARBON    DIOXIDE  121 

perature  was  96°  Fahr.  (35.55°  C).  In  these  observations  the  temperature 
taken  beneath  the  tongue  was  98°  Fahr.  (36.67°  C). 

Exhalation  of  Carbon  Dioxide.  —  On  account  of  variations  in  the  quan- 
tities of  carbon  dioxide  exhaled  at  different  times  of  the  day,  and  par- 
ticularly the  influence  of  the  rapidity  of  the  respiratory  movements,  it  is 
difficult  to  fix  on  any  number  that  will  represent  the  average  proportion 
of  this  gas  contained  in  the  expired  air.  The  same  influences  have  been 
found  affecting  the  consumption  of  oxygen,  and  the  same  difficulties  are 
experienced  in  forming  an  estimate  of  the  proportion  of  this  gas  con- 
sumed. As  it  may  be  assumed,  after  a  comparison  of  the  results  obtained 
by  different  observers,  that  the  volume  of  oxygen  consumed  is  about  five 
per  cent  of  the  entire  volume  of  air,  it  may  be  stated,  as  an  approxima- 
tion, that  in  the  intervals  of  digestion,  in  repose  and  under  normal  condi- 
tions as  regards  the  frequency  of  the  pulse  and  respiration,  the  volume 
of  carbon  dioxide  exhaled  is  about  four  per  cent  of  the  volume  of  the 
expired  air.  As  the  volume  of  oxygen  that  enters  into  the  composition 
of  a  definite  quantity  of  carbon  dioxide  is  equal  to  the  volume  of  the 
carbon  dioxide,  it  is  seen  that  a  certain  quantity  of  oxygen  disappears  in 
respiration  and  is  not  represented  in  the  carbon  dioxide  exhaled. 

There  are  great  differences  in  the  proportion  of  carbon  dioxide  in  the 
expired  air,  depending  on  the  time  during  which  the  air  has  remained  in 
the  lungs.  This  point  was  studied  by  Vierordt,  in  a  series  of  ninety-four 
experiments  made  on  his  own  person,  with  the  following  results :  — 

"  When  the  respirations  are  frequent,  the  quantity  of  carbon  dioxide 
expelled  at  each  expiration  is  much  less  than  in  a  slow  expiration ;  but 
the  quantity  of  carbon  dioxide  produced  during  a  given  time  by  frequent 
respirations  is  greater  than  that  which  is  thrown  off  by  slow  expirations." 

The  air  that  escapes  during  the  first  part  of  an  expiration  is  less  rich 
in  carbon  dioxide  than  that  which  is  last  expelled  and  comes  directly 
from  the  deeper  portions  of  the  lungs.  Dividing,  as  nearly  as  possible, 
the  expiration  into  two  equal  parts,  Vierordt  found,  as  the  mean  of 
twenty-one  experiments,  a  percentage  of  3.72  in  the  first  part  of  the 
expiration  and  5.44  in  the  second  part. 

Temporary  arrest  of  respiratory  movements  has  a  marked  influence 
in  increasing  the  proportion  of  carbon  dioxide  in  the  expired  air,  although 
the  absolute  quantity  exhaled  in  a  given  time  is  diminished.  In  a  number 
of  experiments  on  his  own  person,  Vierordt  ascertained  that  the  per- 
centage of  carbon  dioxide  becomes  uniform  in  all  parts  of  the  respiratory 
organs  after  holding  the  breath  for  forty  seconds.  Holding  the  breath 
after  an  ordinary  inspiration,  for  twenty  seconds,  the  percentage  of  car- 
bon dioxide  in  the  expired  air  was  increased  by  1.73  per  cent  above  the 
normal  standard  ;  but  the  absolute  quantity  exhaled  was  diminished  by 


122  RESPIRATION 

2.642  cubic  inches  (43.3  cubic  centimeters).  After  taking  the  deepest 
possible  inspiration  and  holding  the  breath  for  a  hundred  seconds,  the 
percentage  was  increased  3.08  above  the  normal  standard  ;  but  the  ab- 
solute quantity  was  diminished  more  than  fourteen  cubic  inches  (229.4 
cubic  centimeters).  Allen  and  Pepys  noted  that  air  which  had  passed 
nine  or  ten  times  through  the  lungs  contained  9.5  per  cent  of  carbon 
dioxide. 

Vierordt  has  given  the  following  formula  representing  the  influence 
of  the  frequency  of  the  respirations  on  the  production  of  carbon  dioxide : 
Taking  2.5  parts  per  hundred  as  the  constant  value  of  the  gas  exhaled 
by  the  blood,  the  increase  over  this  proportion  in  the  expired  air  is  in 
exact  ratio  to  the  duration  of  the  contact  of  the  air  and  blood. 

Among  the  most  reliable  observations  on  the  quantity  of  carbon 
dioxide  exhaled  by  the  human  subject  in  a  definite  time  and  the  varia- 
tions to  which  it  is  subject,  are  those  of  Andral  and  Gavarret  and  of 
Edward  Smith.  The  observations  of  Lavoisier  and  Seguin,  Prout,  Davy, 
Dumas,  Allen  and  Pepys,  Scharling  and  others,  do  not  seem  to  have 
fulfilled  the  necessary  experimental  conditions  so  completely.  The  ob- 
servations of  Andral  and  Gavarret  were  made  on  sixty-two  persons  of 
either  sex  and  different  ages  and  under  identical  conditions  as  regards 
digestion,  time  of  the  day,  barometric  pressure  and  temperature;  and 
the  observations  on  males,  between  the  ages  of  sixteen  and  thirty,  be- 
tween I  and  2  P.M.,  under  identical  conditions  of  the  digestive  and  mus- 
cular systems,  each  experiment  lasting  eight  to  thirteen  minutes,  showed 
an  exhalation  of  about  1220  cubic  inches  (20  liters)  of  carbon  dioxide 
per  hour. 

Edward  Smith  employed  the  following  method  for  the  estimation  of 
the  carbon  dioxide  exhaled  :  He  used  a  mask,  fitting  closely  to  the  face, 
which  covered  only  the  air-passages.  The  air  was  admitted  after  having 
been  measured  by  an  ordinary  dry  gas-meter.  The  expired  air  was 
passed  through  a  drying  apparatus,  and  the  carbon  dioxide  was  absorbed 
by  a  solution  of  potassium  hydrate,  arranged  in  a  number  of  layers  so  as 
to  present  a  surface  of  about  seven  hundred  square  inches  (45  square 
decimeters),  and  was  carefully  weighed.  This  apparatus  was  capable  of 
collecting  all  the  carbon  dioxide  exhaled  in  an  hour.  The  estimates  were 
made  for  eighteen  waking  hours  and  six  hours  of  sleep.  The  observa- 
tions occupied  ten  minutes  each  and  were  made  every  hour  and  half- 
hour  for  eighteen  hours.  The  average  for  the  eighteen  hours  gave 
20,082  cubic  inches  (329  liters)  of  carbon  dioxide  for  the  whole  period. 
Observations  during  the  six  hours  of  sleep  showed  a  total  exhalation  of 
4126  cubic  inches  (7.145  liters).  This,  added  to  the  quantity  exhaled 
during  the  day,  gives  as  the  total  exhalation  in  the  twenty-four  hours. 


EXHALATION    OF    CARBON    DIOXIDE  1 23 

during  complete  repose,  24,208  cubic  inches  (about  14.24  cubic  feet,  or 
336.145  liters),  containing  7.144  ounces  (202.47  grams)  of  carbon.  In 
view  of  the  great  variations  in  the  exhalation  of  carbon  dioxide,  this 
estimate  can  be  nothing  more  than  an  approximation. 

One  of  the  important  modifying  influences  is  muscular  exertion,  by 
which  the  production  of  carbon  dioxide  is  largely  increased.  This  would 
indicate  a  large  quantity  during  ordinary  conditions  of  exercise,  and  a 
much  larger  quantity  in  the  laboring  classes.  Dr.  Smith  has  given  the 
following  approximate  estimates  of  these  differences:  — 

Inquietude 7.144  ounces  (202.47  grams)  of  carbon. 

Non-laborious  class 8.68    ounces  (246.04  grams)  of  carbon. 

Laborious  class 11. 7       ounces  (331.61  grams)  of  carbon. 

Influence  of  Age.  —  During  the  first  few  days  of  life,  the  infant  does 
little  more  than  sleep  and  take  the  small  quantity  of  colostrum  furnished 
by  the  mammary  glands  of  the  mother.  While  the  animal  functions 
are  so  imperfectly  developed  and  until  alimentation  becomes  more  abun- 
dant and  the  infant  begins  to  increase  rapidly  in  weight,  the  quantity  of 
carbon  dioxide  exhaled  is  very  small.  After  the  respiratory  function  has 
become  fully  established,  it  is  probable,  from  the  greater  number  of  respi- 
ratory movements  in  early  life,  that  the  production  of  carbon  dioxide,  in 
proportion  to  the  weight  of  the  body,  is  greater  in  infancy  and  childhood 
than  in  adult  life.  Direct  observations,  however,  are  wanting  on  this 
point. 

The  observations  of  Andral  and  Gavarret  show  the  comparative  ex- 
halation of  carbon  dioxide  in  the  male,  between  the  ages  of  twelve  and 
eighty-two,  and  give  the  results  of  a  single  observation  at  the  age  of  one 
hundred  and  two  years.  They  show  an  increase  in  the  absolute  quantity 
exhaled,  from  the  age  of  twelve  to  thirty-two ;  a  slight  diminution,  from 
thirty-two  to  sixty ;  and  a  considerable  diminution,  from  sixty  to  eighty- 
two.  Taking  into  consideration  the  increase  in  the  weight  of  the  body 
with  age,  it  is  evident  that  the  respiratory  activity  is  much  greater  in 
youth  than  in  adult  life,  and  there  can  be  no  doubt  that  there  is  a  rapid 
diminution  in  the  relative  quantity  of  carbon  dioxide  produced  in  old  age. 
Scharling,  in  a  series  of  observations  on  a  boy  nine  years  of  age,  an  adult 
of  twenty-eight  and  one  of  thirty-five  years,  showed  that  the  respiratory 
activity  in  the  child  was  nearly  twice  as  great,  in  proportion  to  his  weight, 
as  the  average  in  the  adults. 

Influence  of  Sex.  —  All  observers  have  found  a  notable  difference  be- 
tween the  sexes,  in  favor  of  the  male,  in  the  proportion  of  carbon  dioxide 
exhaled.  Andral  and  Gavarret  noted  an  absolute  difference  of  about 
forty-five  cubic  inches  (737.4  cubic  centimeters)  per  hour,  but  did  not 


124  RESPIRATION 

take  into  consideration  differences  in  the  weight  of  the  body.  Scharling, 
taking  the  proportion  exhaled  to  the  weight  of  the  body,  noted  a  marked 
difference  in  favor  of  the  male.  The  difference  in  muscular  activity  in 
the  sexes  is  sufficient  to  account  for  the  greater  elimination  of  carbon 
dioxide  in  the  male,  for  this  substance  is  exhaled  in  proportion 
to  the  muscular  development  of  the  individual ;  but  there  is  an  im- 
portant difference  connected  with  the  variations  with  age,  which  de- 
pends on  the  condition  of  the  generative  system  of  the  female.  The 
absolute  increase  in  the  exhalation  of  carbon  dioxide  with  age  in  the 
female  is  arrested  at  the  time  of  puberty  and  remains  stationary  until 
the  cessation  of  the  menses,  provided  the  menstrual  flow  occurs  with 
regularity.  During  this  time  the  average  exhalation  per  hour  is  714 
cubic  inches  (11.69  liters).  After  the  cessation  of  the  menses  the 
quantity  gradually  increases,  until,  at  the  age  of  sixty,  it  amounts  to  91 5 
cubic  inches  (15  liters)  per  hour.  From  the  age  of  sixty  to  eighty-two 
the  quantity  diminishes  to  793  (13  liters),  and  finally  to  670  cubic  inches 
(about  1 1  liters).  When  the  menses  are  suppressed,  there  is  an  increase 
in  the  exhalation  of  carbon  dioxide,  which  continues  until  the  flow  be- 
comes reestablished.  In  a  case  of  pregnancy  observed  by  Scharling  the 
exhalation  was  increased  to  about  885  cubic  inches  (14.5  liters). 

Influence  of  Digestion.  —  Lavoisier  and  Seguin  found  that  in  repose 
and  fasting,  the  quantity  of  carbon  dioxide  exhaled  per  hour  was  12 10 
cubic  inches  (19.82  liters),  which  was  raised  to  1800  and  1900  (29.5  and 
31.14  liters)  during  digestion.  A  series  of  observations  on  this  point 
was  made  by  Vierordt  upon  his  own  person.  Taking  his  dinner  between 
12.30  and  I  p.:m.,  having  noted  the  frequency  of  the  pulse  and  respirations 
and  the  exhalation  of  carbon  dioxide  at  12  m.,  he  found  at  2  p.m.,  the 
pulse  and  respirations  increased  in  frequency,  the  volume  of  expired  air 
augmented,  and  the  carbon  dioxide  exhaled  increased  from  15.77  to 
18.22  cubic  inches  (258.43  to  298.6  cubic  centimeters)  per  minute.  In 
order  to  ascertain  that  this  variation  did  not  depend  on  the  time  of  day, 
independently  of  the  digestive  process,  he  made  a  comparison  at  12  m., 
at  I  and  at  2  p.m.  without  taking  food,  which  showed  no  notable  varia- 
tion, either  in  the  pulse,  number  of  respirations,  volume  of  expired  air 
or  quantity  of  carbon  dioxide  exhaled. 

The  effect  of  inanition  is  to  diminish  the  exhalation  of  carbon  dioxide. 
Bidder  and  Schmidt  noted  the  daily  production  in  a  cat  subjected  to 
eighteen  days  of  inanition,  at  the  end  of  which  time  it  died.  The 
quantity  diminished  gradually  from  day  to  day,  until  just  before  death 
it  was  reduced  by  a  little  more  than  one-half.  Edward  Smith  noted  in 
his  own  person  the  influence  of  a  fast  of  twenty-seven  hours.  There 
was  a  marked  diminution  in  the  quantity  of  air  respired,  in  the  quantity 


EXHALATION    OF    CARBON    DIOXIDE  125 

of  vapor  exhaled,  in  the  number  of  respirations  and  in  the  rapidity  of 
the  pulse.  The  exhalation  of  carbon  dioxide  was  diminished  by  one- 
fourth.  An  important  point  in  this  observation  was  that  the  quantity 
was  as  small  four  and  a  half  hours  after  eating  as  at  the  end  of  the 
twenty-seven  hours. 

Influence  of  Diet.  —  The  most  extended  series  of  investigations  on 
the  influence  of  diet  upon  the  absolute  quantity  of  carbon  dioxide  ex- 
haled are  those  of  Edward  Smith.  This  observer  made  a  large  number 
of  experiments  on  the  influence  of  various  kinds  of  food  and  extended 
his  inquiries  into  the  influence  of  certain  beverages,  such  as  tea,  coffee, 
cocoa,  malt  liquors  and  fermented  liquors.  He  divided  food  into  two 
classes :  one  which  increased  the  exhalation  of  carbon  dioxide,  which 
he  called  respiratory  excitants,  and  the  other,  which  diminished  the 
exhalation,  he  called  non-exciters.  The  following  are  the  results  of  a 
large  number  of  observations  upon  four  persons :  — 

"The  excito-respiratory  are  nitrogenous  food,  milk  and  its  compo- 
nents, sugars,  rum,  beer,  stout,  the  cereals,  and  potato. 

"The  non-exciters  are  starch,  fat,  certain  alcoholic  compounds,  the 
volatile  elements  of  wines  and  spirits,  and  coffee-leaves. 

"  Respiratory  excitants  have  a  temporary  action ;  but  the  action  of 
most  of  them  commences  very  quickly,  and  attains  its  maximum  within 
one  hour. 

"The  most  powerful  respiratory  excitants  are  tea  and  sugar;  then 
coffee,  rum,  milk,  cocoa,  ales,  and  chiccory ;  then  casein  and  gluten, 
and  lastly,  gelatin  and  albumen.  The  amount  of  action  was  not  in  uni- 
form proportion  to  their  quantity.  Compound  ailments,  as  the  cereals, 
containing  several  of  these  substances,  have  an  action  greater  than  that 
of  any  of  their  elements. 

"  Most  respiratory  excitants,  as  tea,  coffee,  gluten,  and  casein,  cause 
an  increase  in  the  evolution  of  carbon  greater  than  the  quantity  which 
they  supply,  while  others,  as  sugar,  supply  more  than  they  evolve  in 
this  excess,  that  is,  above  the  basis.  No  substance  containing  a  large 
amount  of  carbon  evolves  more  than  a  small  portion  of  that  carbon  in 
the  temporary  action  occurring  above  the  basis-line,  and  hence  a  large 
portion  remains  unaccounted  for  by  these  experiments." 

The  comparative  observations  on  the  four  subjects  of  experiment 
demonstrated  one  important  fact ;  namely,  that  the  action  of  different 
kinds  of  food  on  respiration  is  modified  by  idiosyncrasies  and  the  tastes 
of  different  individuals. 

The  following  are  the  results  of  observations  on  the  effects  of  differ- 
ent alcoholic  beverages  taken  during  the  intervals  of  digestion:  — 

"  Brandy,  whiskey,  and  gin,  and  particularly  the  latter,  almost  always 


126  RESPIRATION 

lessened  the  respiratory  changes  recorded,  while  rum  as  commonly  in- 
creased them.  Rum-and-milk  had  a  very  pronounced  and  persistent 
action,  and  there  was  no  effect  on  the  sensorium.  Ale  and  porter 
always  increased  them,  while  sherry  wine  lessened  the  quantity  of  air 
inspired,  but  slightly  increased  the  carbonic  acid  evolved. 

"  The  volatile  elements  of  alcohol,  gin,  rum,  sherry,  and  port-wine, 
when  inhaled,  lessened  the  quantity  of  carbonic  acid  exhaled,  and 
usually  lessened  the  quantity  of  air  inhaled.  The  effect  of  fine  old 
port-wine  was  very  decided  and  uniform  ;  and  it  is  known  that  wines 
and  spirits  improve  in  aroma  and  become  weaker  in  alcohol  by  age. 
The  excito-respiratory  action  of  rum  is  probably  not  due  to  its  volatile 
elements." 

From  these  facts  it  would  seem  that  the  most  constant  effect  of 
alcohol  and  of  alcoholic  liquors,  such  as  wines  and  spirits,  is  to  diminish 
the  exhalation  of  carbon  dioxide.  This  effect  is  almost  instantaneous, 
when  the  articles  are  taken  into  the  stomach  fasting ;  and  when  taken 
with  the  meals,  the  increase  in  carbon  dioxide,  which  habitually  accom- 
panies the  process  of  digestion,  is  materially  lessened.  Rum,  which 
was  found  to  be  a  respiratory  excitant,  is  an  exception.  Malt  liquors 
seem  to  increase  the  exhalation  of  carbon  dioxide.  "  The  action  of 
pure  alcohol  was  much  more  to  increase  than  to  lessen  the  respiratory 
changes,  and  sometimes  the  former  effect  was  well  pronounced." 

Influence  of  Sleep. — All  who  have  directed  attention  to  the  influence 
of  sleep  on  the  respiratory  products  have  noted  a  marked  diminution 
in  the  exhalation  of  carbon  dioxide.  According  to  Edward  Smith,  the 
quantity  during  the  night  is  to  the  quantity  during  the  day,  in  complete 
repose,  as  ten  to  eighteen.  It  has  already  been  stated  that  there  is 
great  diminution  in  the  quantity  of  oxygen  consumed  in  hibernating 
animals.  Regnault  and  Reiset  found  that  a  marmot  in  hibernation 
consumed  only  one-thirtieth  of  the  oxygen  ordinarily  appropriated  in  the 
active  condition.  In  the  same  animal,  they  noted  an  exhalation  of  carbon 
dioxide  equal  to  but  little  more  than  half  the  weight  of  oxygen  absorbed. 

Influence  of  Miiscular  Activity.  —  The  results  of  the  experiments  of 
Dr.  Edward  Smith  on  the  influence  of  exercise  are  as  follows :  — 

In  walking  at  the  rate  of  two  miles  (3.22  kilometers)  per  hour,  the 
exhalation  of  carbon  dioxide  during  one  hour  was  equal  to  the  quantity 
produced  during  i|  hour  of  repose  with  food  or  2\  hours  of  repose 
without  food. 

Walking  at  the  rate  of  three  miles  (4.828  kilometers)  per  hour,  one 
hour  was  equal  to  2|  hours  with  food  or  i\  hours  without  food. 

One  hour's  labor  at  the  tread-wheel,  while  actually  working  the 
wheel,  was  equal  to  4^  hours  of  rest  with  food  or  6  hours  without  food. 


EXHALATION    OF   CARBON    DIOXIDE  12/ 

It  has  been  observed,  however,  that  when  muscular  exertion  is 
carried  so  far  as  to  produce  great  fatigue  and  exhaustion,  the  exhalation 
of  carbon  dioxide  is  notably  diminished. 

Influence  of  Moisture  and  Te^nperatiire.  —  It  has  been  shown  that 
the  exhalation  of  carbon  dioxide  is  greater  in  a  moist  than  in  a  dry 
atmosphere.  It  has  also  been  ascertained  that  the  exhalation  is  much 
greater  at  low  than  at  high  temperatures,  within  the  limits  of  heat  and 
cold  that  are  easily  endured,  amounting,  according  to  the  experiments 
of  Vierordt  on  the  human  object,  to  an  increase  of  about  one-sixth, 
under  the  influence  of  a  moderate  diminution  in  temperature.  It  was 
found,  also,  that  the  quantity  of  air  taken  into  the  lungs  was  slightly 
increased  at  low  temperatures. 

Influence  of  the  Season  of  the  Year,  etc.  —  It  has  been  shown  by  the 
researches  of  Edward  Smith,  that  spring  is  the  season  of  the  greatest, 
and  fall  the  season  of  the  least  activity  of  the  respiratory  function. 

The  months  of  maximum  are  January,  February,  March  and  April. 

The  months  of  minimum  are  July,  August  and  a  part  of  September. 

The  months  of  decrease  are  June  and  July. 

The  months  of  increase  are  October,  November  and  December. 

Observations  on  the  influence  of  barometric  pressure  have  not  been 
sufficiently  definite  in  their  results  to  warrant  any  exact  conclusions. 

Some  physiologists  have  attempted  to  fix  certain  hours  of  the  day 
when  the  exhalation  of  carbon  dioxide  is  at  its  maximum  and  at  its 
minimum  ;  but  the  respiratory  activity  is  influenced  by  such  a  variety  of 
conditions  that  it  is  impossible  to  do  this  with  any  degree  of  accuracy. 

Relations  between  the  Oxygen  consumed  and  the  Carbon  Diox- 
ide  EXHALED 

Oxygen  unites  with  carbon  in  a  certain  proportion  to  form  carbon 
dioxide,  the  volume  of  which  is  equal  to  the  volume  of  the  oxygen  that 
enters  into  its  composition.  It  is  possible,  therefore,  to  study  the  rela- 
tions of  the  volumes  of  these  gases  in  respiration,  by  simply  comparing 
the  volumes  of  the  inspired  and  expired  air.  It  is  now  commonly  recog- 
nized that  the  volume  of  air  expired  is  less,  at  a  given  temperature, 
than  the  volume  of  air  inspired.  Assuming,  then,  that  the  changes  in 
the  expired  air,  as  regards  nitrogen  and  all  gases  except  oxygen  and 
carbon  dioxide,  are  insignificant,  it  must  be  admitted  that  a  certain 
quantity  of  the  oxygen  consumed  is  unaccounted  for  by  the  oxygen  that 
enters  into  the  composition  of  the  carbon  dioxide  exhaled.  It  has 
already  been  noted  that  -^-^  to  -g^,  (1.4  to  2  per  cent)  of  the  inspired  air 
is  lost  in  the  lungs  ;  or  it  may  be  said  in  general  terms  that  the  oxygen 


128  RESPIRATION 

absorbed  is  equal  to  about  five  per  cent  of  the  volume  of  air  inspired, 
and  the  carbon  dioxide  exhaled,  only  about  four  per  cent.  A  part  of 
the  deficiency  in  volume  of  the  expired  air  is  to  be  accounted  for,  then, 
by  a  deficiency  in  the  exhalation  of  carbon  dioxide. 

The  experiments  of  Regnault  and  Reiset  have  an  important  bearing 
on  the  question  under  consideration.  As  these  observers  were  able  to 
measure  accurately  the  quantities  of  oxygen  consumed  and  carbon 
dioxide  produced  in  a  given  time,  the  relation  between  the  two  gases 
was  kept  constantly  in  view.  They  found  great  variations  in  this  rela- 
tion, dependent  mainly  on  the  regimen  of  the  animal.  The  total  loss 
of  oxygen  was  found  to  be  greater  in  carnivorous  than  in  herbivorous 
animals ;  and  in  animals  that  could  be  subjected  to  a  mixed  diet,  by 
regulating  the  food  this  was  made  to  vary  between  the  two  extremes. 
The  mean  of  seven  experiments  on  dogs  showed  that  for  every  looo 
parts  of  oxygen  consumed,  745  parts  were  exhaled  in  the  form  of  carbon 
dioxide.  In  six  experiments  on  rabbits,  the  mean  was  919  for  every 
1000  parts  of  oxygen. 

In  animals  fed  on  grains,  the  proportion  of  carbon  dioxide  exhaled 
was  greatest,  sometimes  passing  a  little  beyond  the  volume  of  oxygen 
consumed. 

"The  relation  is  nearly  constant  for  animals  of  the  same  species 
when  subjected  to  a  uniform  alimentation,  as  is  easy  to  realize  as  re- 
gards dogs ;  but  it  varies  notably  in  animals  of  the  same  species,  and 
in  the  same  animal,  submitted  to  the  same  regimen,  but  in  which  we 
can  not  regulate  the  alimentation,  as  in  fowls." 

When  herbivorous  animals  were  deprived  of  food,  the  relation  be- 
tween the  gases  was  the  same  as  in  carnivorous  animals. 

The  final  result  of  the  experiments  of  Regnault  and  Reiset  was  that 
the  "  relation  between  the  oxygen  contained  in  the  carbon  dioxide  and 
the  total  oxygen  consumed,  varies,  in  the  same  animal,  between  0.62 
and  1.04,  according  to  the  regimen  to  which  it  is  subjected."  These 
observations  on  animals  have  been  confirmed  in  the  human  subject  by 
Doyere,  who  found  great  differences  in  the  relations  of  the  two  gases  in 
respiration ;  the  volume  of  carbon  dioxide  exhaled  varying  between 
0.862  and  1.087  for  i  P^-^t  of  oxygen  consumed. 

As  regards  the  destination  of  the  oxygen  that  is  not  represented  in 
the  carbon  dioxide  exhaled,  it  is  certain  that  a  part  of  it,  at  least,  unites 
with  hydrogen  to  form  water,  this  contributing  to  the  production  of 
animal  heat,  a  question  that  will  be  fully  discussed  in  another  connec- 
tion. 

The  variations  in  the  relative  volumes  of  oxygen  consumed  and 
carbon  dioxide  produced  in  respiration  are  not  favorable  to  the  hypothe- 


RESPIRATORY    QUOTIENT  129 

sis  that  the  carbon  dioxide  is  always  a  result  of  the  direct  action  of 
oxygen  upon  carbohydrates  and  fats.  Such  a  definite  relation  between 
these  two  gases  can  not  be  assumed  to  exist,  in  view  of  the  fact  that 
carbon  dioxide  may  be  given  off  by  the  tissues  in  the  absence  of 
oxygen. 

Many  of  the  points  that  have  been  considered  in  relation  to  the 
variations  in  the  exhalation  of  carbon  dioxide  have  been  investigated  in 
Pettenkofer's  chamber,  and  the  results  very  nearly  correspond  with  the 
observations  quoted  from  Scharling,  Edward  Smith  and  others. 

Sources  of  Carbon  Dioxide  in  the  Expired  Air. — All  the  carbon 
dioxide  in  the  expired  air  comes  from  the  venous  blood,  where  it  exists 
in  two  forms;  in  a  condition  either  of  simple  solution  or  of  association 
with  certain  of  the  constituents  of  the  plasma,  and  in  union  with  bases, 
forming  the  carbonates  and  bicarbonates.  The  fact  that  carbon  dioxide, 
as  regards  the  quantity  absorbed  by  the  blood,  does  not  obey,  in  all 
regards,  the  laws  which  regulate  the  absorption  of  gases  by  liquids 
under  different  conditions  of  pressure,  has  led  some  physiologists  to 
regard  all  this  gas  as  existing  in  the  blood  in  combination ;  the  greater 
part  being  loosely  united  with  certain  other  substances,  and  a  small 
quantity  of  that  which  is  thrown  off  in  the  expired  air  being  in  a  condi- 
tion of  union  much  more  stable. 

The  greater  part  of  the  carbon  dioxide  exhaled  comes  from  the 
plasma,  where  it  is  in  a  condition  of  what  is  known  as  association.  An- 
other and  a  smaller  part  probably  is  set  free  by  the  action  of  the 
oxyhemoglobin,  which  is  distinctly  acid.  It  has  been  shown  that  more 
carbon  dioxide  can  be  extracted  by  means  of  a  vacuum  from  the  entire 
blood  than  from  the  serum  ;  and  it  is  more  readily  extracted  from  arterial 
than  from  venous  blood.  The  mechanism  by  which  carbon  dioxide  is 
discharged  from  the  venous  blood  is  probably  the  following :  — 

Carbon  dioxide  is  carried  from  the  tissues  to  the  lungs,  in  the  venous 
blood.  Here  it  exists  mainly  in  the  plasma,  a  small  quantity,  only, 
existing  in  the  corpuscles.  As  the  venous  blood  passes  through  the 
lungs,  the  greater  part  of  the  carbon  dioxide  of  the  plasma  either  simply 
diffuses  from  the  blood  into  the  air-cells  or  passes  out  by  a  process 
known  as  dissociation.  It  is  certain  that  the  oxyhemoglobin,  which  is 
constantly  forming  in  the  lungs,  assists  materially  in  this  process,  pos- 
sibly acting  as  an  acid. 

Respiratory  Quotient.  —  The  result  of  the  division  of  the  carbon 
dioxide  exhaled  by  the  oxygen  taken  up  by  the  blood  is  called  the 
respiratory  quotient.  Under  ordinary  conditions  of  respiration,  this  is 
equal  to  about  ninety  (4.5  -^  5).  The  greater  the  proportion  of  oxygen 
consumed  to  the  carbon  dioxide  exhaled,  the  less  is  the  respiratory  quo- 


I30  RESPIRATION 

tient ;  and  the  less  the  proportion  of  oxygen  to  carbon  dioxide,  the 
greater  is  the  quotient.  It  is  evident  from  this  that  the  observations  of 
physiologists  on  the  consumption  of  oxygen  and  the  elimination  of 
carbon  dioxide,  when  applied  to  the  respiratory  quotient,  must  undergo 
some  revision. 

The  respiratory  quotient  is  lowered  by  animal  food  and  increased  by 
a  vegetable  diet.     It  is  much  lowered  by  fasting. 

The  quotient  is  lower  in  children  than  in  adults. 

The  quotient  is  higher  during  the  day  than  during  the  night. 

The  quotient  is  much  diminished  during  sleep. 

The  quotient  is  much  increased  by  muscular  work. 

The  quotient  is  much  diminished  by  low  external  temperature. 

The  quotient  is  much  increased  by  breathing  a  mixture  containing 
twenty-one  parts  of  oxygen  and  seventy-nine  parts  of  hydrogen. 

Exhalation  of  Watery  Vapor.  —  From  a  large  number  of  observations 
on  his  own  person  and  on  eight  others,  collecting  the  water  by  sulphuric 
acid,  Valentin  made  the  following  estimates  of  the  quantities  of  water 
exhaled  from  the  lungs  in  twenty-four  hours  :  — 

In  his  own  person  the  exhalation  in  twenty-four  hours  was  5934 
grains  (384.48  grams). 

In  a  young  man  of  small  size  the  quantity  was  5401  grains  (350 
grams). 

In  a  student  rather  above  the  ordinary  height  the  quantity  was  1 1,929 
grains  (773  grams). 

The  mean  of  his  observations  gave  a  daily  exhalation  of  8333  grains 
(540  grams),  or  about  a  pound  and  a  half. 

The  extent  of  respiratory  surface  has  a  marked  influence  on  the 
quantity  of  watery  vapor  exhaled.  This  fact  is  well  shown  by  a  com- 
parison of  the  exhalation  in  the  adult  and  in  old  age,  as  in  advanced  life 
the  extent  of  respiratory  surface  is  much  diminished.  Barral  found  the 
exhalation  in  an  old  man  less  than  half  that  of  the  adult.  It  is  evident 
that  the  quantity  of  vapor  exhaled  is  increased  when  respiration  is  ac- 
celerated. The  quantity  of  water  in  the  blood  also  exerts  an  important 
influence.  Valentin  found  that  the  pulmonary  transpiration  was  more 
than  doubled  in  a  man  immediately  after  drinking  a  large  quantity  of 
water. 

The  vapor  in  the  expired  air  is  derived  from  the  entire  surface  over 
which  the  air  passes  in  respiration,  and  not  exclusively  from  the  air-cells. 
The  air  that  passes  into  the  lungs  derives  a  certain  quantity  of  moisture 
from  the  mouth,  nares  and  trachea.  The  great  vascularity  of  the  mucous 
membranes  in  these  situations,  as  well  as  of  the  air-cells,  and  the  great 
number  of  mucous  glands  which  they  contain,  serve  to  keep  the  respira- 


EXHALATION    OF   NITROGEN  131 

tory  surfaces  constantly  moist.  This  is  important,  for  only  moist  mem- 
branes allow  the  free  passage  of  gases,  which  is  of  course  essential  to 
the  process  of  respiration. 

Exhalation  of  Ammonia,  Organic  Matter,  etc.  — A  small  quantity  of 
ammonia  is  exhaled  by  the  lungs  in  health,  and  this  is  increased  in  cer- 
tain diseases,  particularly  in  uremia.  Its  characters  in  the  expired  air 
are  frequently  so  marked  that  patients,  who  presumably  are  unacquainted 
with  the  pathology  of  uremia,  sometimes  recognize  an  ammoniacal  odor 
in  their  own  breath. 

The  pulmonary  surface  exhales  a  small  quantity  of  organic  matter. 
This  has  not  been  collected  in  sufficient  quantity  for  analysis,  but  its 
presence  may  be  demonstrated  by  the  fact  that  a  sponge  saturated  with 
the  exhalations  from  the  lungs,  or  the  vapor  from  the  lungs  condensed 
in  a  glass  vessel,  will  undergo  putrefaction,  which  is  a  property  distinc- 
tive of  organic  substances. 

It  is  well  known  that  certain  substances  which  are  but  occasionally 
found  in  the  blood  may  be  eliminated  by  the  lungs.  Certain  odorous 
matters  in  the  breath  are  constant  in  those  who  take  liquors  habitually 
in  considerable  quantity.  The  odor  of  garlics,  onions,  turpentine  and 
of  many  other  articles  taken  into  the  stomach  may  be  recognized  in  the 
expired  air. 

The  lungs  eliminate  certain  gases  that  are  poisonous  in  small  quan- 
tities when  absorbed  in  the  lungs  and  carried  to  the  general  system  in 
the  arterial  blood.  Hydrogen  monosulphide,  which  produces  death  in  a 
bird  when  it  exists  in  the  atmosphere  in  the  proportion  of  one  to  eight 
hundred,  may  be  taken  in  solution  into  the  stomach  with  impunity  and 
even  be  injected  into  the  venous  system  ;  in  both  instances  being  elimi- 
nated by  the  lungs  with  great  promptness  and  rapidity.  The  lungs, 
while  they  present  an  immense  and  rapidly  absorbing  surface  for 
volatile  poisonous  substances,  are  capable  of  relieving  the  system  of  some 
of  these  by  exhalation  when  they  find  their  way  into  the  veins. 

Exhalation  of  Nitrogen.  —  The  most  accurate  direct  experiments, 
particularly  those  of  Regnault  and  Reiset,  show  that  the  exhalation  of 
a  small  quantity  of  nitrogen  by  the  lungs  is  nearly  constant.  As  the 
result  of  a  large  number  of  experiments,  these  observers  came  to  the  con- 
clusion that  when  animals  are  subjected  to  their  habitual  regimen,  they 
exhale  a  quantity  of  nitrogen  equal  in  weight  to  -^-^  or  -gig-  of  the 
weight  of  oxygen  consumed.  In  birds,  during  inanition,  they  sometimes 
observed  an  absorption  of  nitrogen,  but  this  was  rarely  seen  in  mam- 
mals. Boussingault,  estimating  the  nitrogen  taken  into  the  body  and 
comparing  it  with  the  entire  quantity  discharged,  arrived  at  the  same 
results  in  experiments  upon  a  cow.     Barral,  by  the  same  method,  con- 


132 


RESPIRATION 


firmed  these  observations  by  experiments  on  the  human  subject.  Not- 
withstanding the  conflicting  testimony  of  physiologists,  there  can  be  Httle 
doubt  that  under  ordinary  physiological  conditions  there  is  an  exhalation 
of  a  small  quantity  of  nitrogen  by  the  lungs. 

Changes    of   the    Blood    in    Respiration   (Hematosis) 

There  is  a  marked  difference  in  color,  composition  and  properties, 
between  the  blood  in  the  arteries  and  in  the  veins,  the  change  from 
venous  to  arterial  blood  being  effected  almost  instantaneously  in  its 
passage  through  the  lungs.  The  blood  which  goes  to  the  lungs  is  col- 
lected from  all  parts  of  the  body  and  presents  great  differences  in  its 
composition  in  different  veins.  In  some  veins  it  is  almost  black,  and  in 
some  it  is  nearly  as  red  as  in  the  arteries.  In  the  hepatic  vein  it  con- 
tains sugar,  and  its  nitrogenous  constituents  and  the  corpuscles  are 
diminished  ;  in  the  portal  vein,  during  digestion,  it  contains  matters 
absorbed  from  the  alimentary  canal  ;  and  finally,  there  is  every  reason 
to  suppose  that  parts  which  require  different  substances  for  their  nutri- 
tion and  produce  different  excrementitious  matters  exert  different 
influences  on  the  constitution  of  the  blood  which  passes  through  them. 
After  this  mixture  of  different  kinds  of  blood  has  been  collected  in  the 
right  side  of  the  heart  and  passed  through  the  lungs,  it  is  returned  to 
the  left  side  and  sent  to  the  system,  and  as  arterial  blood,  it  has  a  nearly 
uniform  composition.  The  change,  therefore,  which  the  blood  under- 
goes in  its  passage  through  the  lungs,  is  the  transformation  of  the  mixture 
of  venous  blood  from  all  parts  of  the  organism  into  a  liquid  of  uniform 
character,  which  is  capable  of  nourishing  every  tissue  and  organ  of  the 
body. 

The  capital  phenomena  of  respiration,  as  regards  the  air  in  the  lungs, 
are  loss  of  oxygen  and  gain  of  carbon  dioxide,  the  other  phenomena 
being  comparatively  unimportant.  As  the  blood  is  capable  of  absorb- 
ing gases,  the  essential  changes  which  it  undergoes  in  respiration  are  to 
be  looked  for  in  connection  with  the  proportions  of  oxygen  and  carbon 
dioxide  before  and  after  it  has  passed  through  the  lungs. 

The  elements  of  the  blood  which  absorb  the  greatest  part  of  the 
oxygen  are  the  red  corpuscles.  While  the  plasma  will  absorb,  perhaps, 
twice  as  much  gas  as  pure  water,  it  has  been  shown  that  the  volume  of 
oxygen  fixed  by  the  corpuscles  is  about  twenty-five  times  that  which  is 
dissolved  in  the  plasma  (Fernet,  Lothar  Meyer). 

Aiialysis  of  the  Blood  for  Gases.  —  In  disengaging  and  estimating  the 
gases  of  the  blood,  it  is  necessary  to  complete  the  analysis  as  soon  as 
possible  after  the  blood  has  been  drawn,  for  the  reason  that  delay  in- 


ANALYSIS    OF    THE    BLOOD    FOR   GASES  1 33 

volves  a  disappearance  of  a  considerable  quantity  of  oxygen,  which  is 
replaced  by  carbon  dioxide.  This  accounts  for  the  indefinite  results  ob- 
tained by  the  earlier  observers.  Modern  experimenters  make  use  of  the 
mercurial  gas-pumps,  either  of  Ludwig  or  of  Pfliiger,  in  which  all  the 
gases  of  the  bload  are  disengaged  by  removing  atmospheric  pressure. 
By  means  of  a  "  froth-chamber,"  the  gases  can  be  collected  and  analyzed 
with  but  little  loss  of  time ;  but  it  is  probable  that  there  is  always  a  slight 
error  in  estimates,  made  in  this  way,  of  the  relative  proportions  of  oxygen 
and  carbon  dioxide,  the  proportion  of  oxygen  being  too  small,  and  of 
carbon  dioxide,  too  large.  Nevertheless,  the  results  obtained  by  this 
method  correspond  pretty  closely  with  what  is  known  of  the  nature  of 
the  respiratory  process ;  and  analyses  of  the  blood  taken  at  different 
times  show  variations  in  the  quantities  of  oxygen  in  the  arterial  blood 
and  of  carbon  dioxide  in  the  venous  blood,  corresponding  with  some  of 
the  variations  that  have  been  noted  in  the  loss  of  oxygen  and  gain  of 
carbon  dioxide  in  the  air  in  respiration.  Nearly  all  the  gases  contained 
in  the  blood  may  be  disengaged  by  means  of  the  gas-pump,  but  accord- 
ing to  most  observers,  a  small  quantity  of  carbon  dioxide  remains  in  the 
blood  in  combination.  This  may  be  removed  by  the  introduction  into 
the  apparatus  of  a  small  quantity  of  tartaric  acid.  It  was  justly  remarked 
by  Bert,  that  as  the  apparatus  for  the  exhaustion  of  air  has  been  made 
more  and  more  nearly  perfect,  the  quantity  of  carbon  dioxide  in  combi- 
nation has  seemed  less  and  less.  By  far  the  greatest  quantity  of  the 
excrementitious  carbon  dioxide  in  the  blood  is  extracted  by  the  removal 
of  atmospheric  pressure  in  the  most  carefully  prepared  apparatus. 

The  quantity  of  carbon  dioxide  varies  considerably  in  different  parts 
of  the  venous  system.  It  is  well  known  that  the  venous  blood  coming 
from  certain  glands  is  dark  during  the  intervals  of  secretion  and  is  nearly 
as  red  as  arterial  blood  during  secretion.  In  the  venous  blood  from  the 
submaxillary  gland  of  a  dog,  Bernard  found  18.07  P^r  cent  of  carbon 
dioxide  during  repose  and  10.14  per  cent  during  secretion.  The  blood 
coming  from  the  muscles  is  the  darkest  in  the  body  and  contains  the 
greatest  quantity  of  carbon  dioxide.  The  quantity  of  carbon  dioxide, 
also,  is  increased  in  the  venous  blood  during  digestion. 

These  facts  coincide  with  the  views  now  held  regarding  the  essential 
processes  of  respiration.  The  blood  going  to  the  lungs  contains  carbon 
dioxide  and  but  a  small  proportion  of  oxygen.  In  the  lungs  carbon 
dioxide  is  given  off,  appearing  in  the  expired  air,  and  the  oxygen  which 
disappears  from  the  air  is  carried  away  by  the  arterial  blood. 

Nitrogen  of  the  Blood.  —  So  far  as  is  known,  nitrogen  has  no  impor- 
tant office  connected  with  respiration.  There  is  sometimes  a  slight  ex- 
halation of  this  gas  by  the  lungs,  and  analyses  have  demonstrated  its 


134  RESPIRATION 

existence  in  solution  in  the  blood.  There  is  no  evidence  that  nitrogen 
enters  into  combination  with  the  blood-corpuscles.  It  exists  simply  in 
solution  in  the  blood,  which  is  capable  of  absorbing  about  ten  times  as 
much  as  water.  Nothing  is  known  in  regard  to  the  relations  of  the  free 
nitrogen  of  the  blood  to  the  processes  of  nutrition. 

Using  the  mercurial  gas-pump,  it  is  possible  to  extract  about  sixty- 
volumes  of  gas  from  one  hundred  parts  of  blood.  In  experiments  on 
the  blood  of  the  dog,  the  average  percentage  volumes  of  oxygen,  carbon 
dioxide  and  nitrogen  in  arterial  and  venous  blood  were  as  follows 
(Kirkes):  — 


Oxygen 
Carbon  dioxide 
Nitrogen 


ARTERIAL    BLOOD 

VENOUS    BLOOD 

20 

8  to  12 

40 

46 

I   to  2 

I  to  2 

Oxygeti  of  the  Blood.  — When  oxygen  exists  in  a  condition  of  simple 
solution  in  any  liquid,  the  quantity  dissolved  is  in  direct  ratio  to  the 
pressure;  and  when  the  pressure  is  increased,  the  amount  held  in 
solution  is  increased  in  exact  proportion.  This  law,  however,  is  not 
operative  in  the.  case  of  the  oxygen  of  the  blood.  When  the  condition 
is  one  of  saturation,  the  amount  does  not  vary  with  the  pressure.  In 
the  case  of  a  mechanical  mixture  of  gases,  what  is  known  as  the 
"  partial  pressure  "  of  each  gas  is  the  force  which  leads  to  its  diffusion, 
and  this  may  be  measured  by  means  of  a  column  of  mercury. 

The  following  application  of  this  law  may  be  made  to  the  oxygen 
of  the  inspired  air :  The  partial  pressure  of  oxygen  in  the  atmosphere, 
expressed  in  percentages  of  the  pressure  of  one  atmosphere  =  20.96  ; 
the  pressure  of  oxygen  in  the  air  contained  in  the  air-cells  =18;  the 
tension  of  oxygen  in  the  arterial  blood  =14;  in  the  tissues,  the  tension 
of  the  oxygen  is  zero  (Fredericq). 

This  reduction  in  pressure,  from  20.96  to  zero,  indicates  the  direc- 
tion of  diffusion  of  oxygen.  The  oxygen  of  the  inspired  air  is  diffused 
into  the  air-cells  because  the  pressure  is  18  instead  of  20.96;  it  is  dif- 
fused into  the  blood  because  the  tension  is  here  reduced  to  14;  it  passes 
into  the  tissues  because  the  pressure  in  the  tissues  is  zero.  The  ten- 
sion of  gases  held  in  solution  in  liquids  is  the  force  which  holds  them 
in  solution,  or  which  prevents  their  escape  by  diffusion.  The  oxygen 
contained  in  the  blood  is  "  associated  "  with  hemoglobin,  a  condition  of 
union  that  has  already  been  considered  in  treating  of  the  composition 
of  the  blood. 

Carbon  Dioxide  of  the  Blood.  —  The  relations  of  carbon  dioxide  to 
the  tissues,  the  blood  and  the  contents  of  the  air-cells  are  rather  more 
complex  than  in  the  case  of  oxygen,  especially  as  regards  the  blood. 


RESPIRATORY    PROCESSES    BEFORE    BIRTH  1 35 

The  tension  of  carbon  dioxide  in  the  tissues  =  5  to  9 ;  in  the  venous 
blood  it  =  3.8  to  5.4  ;  in  the  air-cells  it  =  2.8;  in  the  external  air  it  = 
0.03.  For  the  same  reason  that  oxygen  diffuses  from  the  external  air, 
where  the  pressure  is  20.96,  to  the  tissues,  where  the  tension  is  zero, 
carbon  dioxide  passes  from  the  tissues,  where  the  tension  is  5  to  9,  to 
the  external  air,  where  it  is  0.03   (Fredericq). 

The  carbon  dioxide  of  the  blood  is  contained  chiefly  in  the  plasma, 
but  a  small  quantity  exists  in  the  red  corpuscles,  in  which  this  gas  is 
shghtly  more  soluble  than  in  pure  water.  It  is  somewhat  difficult  to 
determine  the  exact  condition  of  carbon  dioxide  in  the  plasma.  It  is 
estimated  that  about  five  per  cent  exists  in  simple  solution,  seventy-five 
to  eighty-five  per  cent  in  a  condition  of  loose  combination  and  ten  to 
twenty  per  cent  in  firmer  combination.  These  conditions  render  it 
difficult  to  determine  the  exact  tension  of  the  gas  in  the  plasma ;  and, 
indeed,  the  estimates  of  the  tension  of  carbon  dioxide  are  much  less 
exact  than  of  oxygen. 

Respiration  in  the  Tissues.  —  Nearly  all  tissues  contain  coloring 
matters  known  as  histohematins.  The  most  important  of  these  is  found 
in  the  muscles  and  is  called  myohematin.  It  is  thought  that  the  oxygen 
of  the  blood  combines  with  these  histohematins,  the  process  involving 
true  tissue-respiration.  At  all  events,  the  interchange  of  gases  between 
the  tissues  and  the  blood  are  exactly  opposite  to  the  changes  that  take 
place  in  the  lungs.  In  the  lungs,  the  blood  loses  carbon  dioxide  and 
gains  oxygen ;  in  the  tissues,  the  blood  loses  oxygen  and  gains  carbon 
dioxide.     The  real  seat  of  respiration  is  in  the  tissues. 

Respiratory  Processes  before  Birth 

It  is  commonly  admitted  that  one  of  the  most  important  uses  of  the 
placenta  —  the  one,  indeed,  most  immediately  connected  with  the  life 
of  the  foetus  —  is  a  respiratory  interchange  of  gases,  analogous  to  that 
which  takes  place  in  the  gills  of  aquatic  animals.  The  placental  villi 
are  bathed  in  the  blood  of  the  uterine  sinuses,  and  this  is  the  only  way 
in  which  the  foetal  blood  can  receive  oxygen.  Legallois  observed  a 
bright  red  color  in  the  blood  of  the  umbilical  vein  ;  and  on  alternately 
compressing  and  releasing  the  vessel,  he  saw  the  blood  change  in  color 
successively  from  red  to  dark  and  from  dark  to  red.  Zweifel  has 
demonstrated  the  presence  of  oxyhemoglobin  in  the  blood  of  the  um- 
bilical vessels  by  means  of  the  spectroscope,  showing  that  it  contains 
oxygen.  As  oxygen  is  thus  adequately  supplied  to  the  system,  the 
foetus  is  in  a  condition  similar  to  that  of  animals  in  which  artificial 
respiration  is  maintained.     The  want  of  oxygen  is  fully  met,  and  there- 


136  RESPIRATION 

fore  no  respiratory  efforts  take  place.  Respiratory  movements  occur, 
however,  even  in  very  young  foetuses,  when  there  is  a  deficient  supply 
of  oxygen. 

Cutaneous  Respiration 

Respiration  by  the  skin,  although  important  in  many  of  the  lower 
orders  of  animals,  is  inconsiderable  in  the  human  subject  and  is  even 
more  insignificant  in  animals  covered  with  hair  or  feathers ;  still,  an  appre- 
ciable quantity  of  oxygen  is  absorbed  by  the  skin  of  the  human  sub- 
ject, and  a  quantity  of  carbon  dioxide,  which  is  relatively  larger,  is 
exhaled.  Carbon  dioxide  is  given  off  with  the  general  emanations  from 
the  surface,  being  found,  also,  in  solution  in  the  urine  and  in  most  of 
the  secretions. 

An  estimate  of  the  extent  of  the  cutaneous,  as  compared  with  pul- 
monary respiration,  has  been  made  by  Scharling,  by  comparing  the 
relative  quantities  of  carbon  dioxide  exhaled  in  the  twenty-four  hours. 
According  to  this  observer,  the  skin  performs  5V  to  ^^o  of  the  respiratory 
office.  It  is  difficult,  however,  to  collect  all  the  carbon  dioxide  given 
off  by  the  skin  under  normal  conditions.  In  the  observations  by  Aubert, 
the  estimate  is  much  lower  than  that  given  by  Scharling. 

Asphyxia 

A  remarkable  power  of  resisting  asphyxia  exists  in  newborn  ani- 
mals that  have  never  breathed.  Legallois  found  that  young  rabbits  will 
live  for  fifteen  minutes  deprived  of  air  by  submersion,  but  that  this 
power  of  resistance  diminished  rapidly  with  age.  W.  F.  Edwards  has 
shown  that  there  exists  a  great  difference  in  this  regard  in  different 
species.  Dogs  and  cats,  which  are  born  with  the  eyes  shut  and  in 
which  there  is  at  first  a  very  small  development  of  animal  heat,  will 
show  signs  of  life  after  submersion  for  more  than  half  an  hour ;  while 
Guinea  pigs,  which  are  born  with  the  eyes  open,  are  much  more  active 
and  produce  a  greater  amount  of  heat,  will  not  live  for  more  than  seven 
minutes.  The  explanation  of  this  is  that  in  most  warm-blooded  animals, 
during  the  first  periods  of  extra-uterine  life,  the  demands  on  the  part  of 
the  system  for  oxygen  are  comparatively  slight.  At  this  time  there  is 
very  little  activity  in  the  general  processes  of  nutrition  and  in  the  con- 
sumption of  oxygen  and  the  exhalation  of  carbon  dioxide.  The  actual 
difference  between  the  consumption  of  oxygen  immediately  after  birth 
and  at  the  age  of  a  few  days  is  sufficient  to  explain  the  remarkable 
power  of  resisting  asphyxia  just  after  birth. 

Breathing  in  a  Confined  Space.  —  An  important  question  connected 
with  the  physiology  of  asphyxia  is  the  effect  on  the  system  of  air  vitiated 


ASPHYXL-^ 


^>7 


by  breathing  in  a  confined  space.  There  are  here  several  points  that 
present  themselves  for  consideration.  The  effect  of  respiration  on  the 
air  is  to  take  away  a  certain  proportion  of  oxygen  and  to  add  certain 
matters  regarded  as  deleterious.  The  emanation  which  commonly  has 
been  considered  as  having  the  most  decided  influence  on  the  svstem  is 
carbon  dioxide ;  but  this  has  been  much  overestimated.  In  death  from 
charcoal-fumes,  carbon  monoxide  is  the  poisonous  agent.  Regnault  and 
Reiset  exposed  dogs  and  rabbits  for  many  hours  to  an  atmosphere  con- 
taining twenty-three  per  cent  of  carbon  dioxide  artificially  introduced, 
and  between  thirty  and  forty  per  cent  of  oxygen,  without  ill  effects. 
They  took  care,  however,  to  keep  up  a  free  supply  of  oxvgen. 

These  experiments  are  at  variance  with  results  obtained  by  others  ; 
but  Regnault  and  Reiset  explained  this  difference  by  the  supposition 
that  the  gases  in  other  observations  were  impure,  containing  chlorin  or 
carbon  monoxide.  This  view  is  sustained  by  the  experiments  of  Bernard 
with  carbon  monoxide.  In  animals  killed  by  this  gas,  the  blood,  both 
venous  and  arterial,  is  of  a  bright  red  color,  which  is  due  to  the  fixation 
of  the  gas  by  the  blood-corpuscles.  In  this  way,  the  red  corpuscles  are 
paralyzed  and  the  animal  dies  from  asphyxia. 

In  breathing  in  a  confined  space,  the  distress  and  the  fatal  results 
are  produced,  in  all  probability,  more  by  animal  emanations  and  a  defi- 
ciency of  oxygen  than  by  carbon  dioxide.  When  the  latter  gas  is 
removed  as  fast  as  it  is  produced,  the  effects  of  diminution  in  the  pro- 
portion of  oxygen  are  soon  very  marked,  and  they  progressively  increase 
until  death  occurs.  The  influence  of  emanations  from  the  lungs  and 
general  surface  is  considerable;  and  this  fact,  which  almost  all  have 
experienced  more  or  less,  has  been  illustrated  in  instances  of  large  num- 
bers of  persons  confined  without  proper  change  of  air. 

In  crowded  assemblages,  the  slight  diminution  of  oxygen,  the  eleva- 
tion of  temperature,  increase  in  moisture,  and  particularly  the  presence 
of  organic  emanations  combine  to  produce  unpleasant  sensations.  The 
effects  of  this  carried  to  an  extreme  degree  were  exemplified  in  the 
confinement  of  the  one  hundred  and  forty-six  English  prisoners,  for 
eight  hours  only,  in  the  "  Black  Hole  of  Calcutta,"  a  chamber  eighteen 
feet  (5.486  meters)  square,  with  only  two  small  windows,  and  these 
obstructed  by  a  veranda.  Out  of  this  number,  ninety-six  died  in  six 
hours,  and  one  hundred  and  twenty-three,  at  the  end  of  the  eight  hours. 
Many  of  those  who  immediately  survived  died  afterward  of  putrid 
fever  {Annual  Register,  1758).  The  incident  of  the  "Black  Hole  of 
Calcutta "  has  frequently  been  repeated  on  emigrant  and  slave  ships, 
by  confining  great  numbers  in  the  hold  of  the  vessel,  where  they  were 
entirely  shut  off  from  the  fresh  air. 


CHAPTER   VI 

ALIMExXTATlON 

Hunger  and  thirst  —  Nitrogenous  alimentary  substances  —  Non-nitrogenous  alimentary  sub- 
stances —  Carbohydrates  —  Dextrose  —  Levulose  —  Galactose  —  Saccharose  —  Lactose  — 
Maltose — Starch  —  Glycogen — Cellulose,  inosite  and  gums — The  fats:  triolein;  tri- 
palmitin ;  tristearin  —  Saponification  — .  Emulsification  —  Inorganic  alimentary  substances  — 
Water  —  Sodium  chloride  —  Calcium  phosphate  —  Iron  —  Alcohol  —  Coffee  —  Tea  — 
Chocolate  —  Condiments  and  flavoring  articles  —  The  daily  ration  —  Necessity  of  a  varied 
diet  —  Meats  —  Bread  —  Potatoes  —  Milk  —  Eggs. 

In  the  organism  of  animals  every  part  is  continually  undergoing 
what  may  be  called  physiological  wear,  or  katabolism ;  the  nitrogenous 
constituents  of  the  body  are  being  constantly  transformed  into  effete 
matter ;  and  as  these  constituents  never  exist  without  inorganic  matters, 
with  which  they  are  closely  and  inseparably  associated,  it  is  found  that 
the  products  of  their  katabolism  are  always  discharged  from  the  body 
in  connection  with  inorganic  substances.  This  process  of  molecular 
change  is  a  necessary  condition  of  life.  Its  activity  may  be  increased 
or  retarded  by  various  means,  but  it  can  not  be  arrested.  The  excre- 
mentitious  matters  thus  formed  are  produced  constantly  by  the  tissues 
and  must  be  as  constantly  eliminated.  It  is  evident,  from  the  amount 
of  matter  that  is  daily  discharged,  that  the  process  of  katabolism  must 
be  very  active.  Its  constant  operation  necessitates  a  constant  appropria- 
tion of  new  matter  by  the  parts,  in  order  that  they  may  maintain  their 
integrity  of  composition  and  be  always  ready  to  perform  their  offices  in 
the  economy.  The  blood  contains  all  the  materials  necessary  for  the 
regeneration  of  the  organism.  Its  inorganic  constituents  are  found 
usually  in  the  form  in  which  they  exist  in  the  substance  of  the  tissues ; 
but  the  organic  constituents  of  the  parts  are  formed  in  the  substance  of 
the  tissues  themselves,  by  a  transformation  of  matters  furnished  by  the 
blood.  The  physiological  wear  of  the  organism  is,  therefore,  being  con- 
stantly repaired  by  the  blood ;  but  in  order  to  keep  the  great  nutritive 
fluid  from  becoming  impoverished,  the  matters  which  it  is  constantly 
losing  must  be  supplied  from  some  source  out  of  the  body,  and  this 
necessitates  the  ingestion  of  articles  known  as  food.  Food  is  taken 
into  the  body  in  obedience  to  a  want  on  the  part  of  the  system,  which  is 

I -.8 


HUNGER    AND    THIRST  1 39 

expressed  by  the  sensation  of  hunger,  when  it  relates  to  solid  or  semi- 
solid matters,  and  of  thirst,  when  it  relates  to  water. 


Hunger  and  Thirst 

The  term  hunger  may  be  applied  to  all  degrees  of  that  peculiar  want 
felt  by  the  system,  that  leads  to  the  ingestion  of  nutritive  substances. 
Its  first  manifestations  are,  perhaps,  best  expressed  by  the  term  "appetite  " ; 
a  sensation  by  no  means  disagreeable,  and  one  that  may  be  excited  by 
the  sight,  smell,  or  even  the  recollection  of  savory  articles,  at  times  when 
it  does  not  depend  on  a  want  in  the  system.  In  the  ordinary  and  moder- 
ate development  of  appetite  for  food,  it  is  impossible  to  say  that  the 
sensation  is  referable  to  any  distinct  part  or  organ.  It  is  influenced  in 
some  degree  by  habit ;  in  many  persons,  the  feeling  being  experienced 
at  or  near  the  hours  when  food  ordinarily  is  taken.  If  not  gratified,  the 
appetite  is  rapidly  intensified  until  it  becomes  actual  hunger.  Except 
when  the  quantity  of  food  taken  is  unnecessarily  large,  the  appetite 
simply  disappears  on  the  introduction  of  food  into  the  stomach,  and  gives 
place  to  the  sense  of  satisfaction  that  accompanies  the  undisturbed  and 
normal  action  of  the  digestive  organs. 

It  has  been  observed  that  children  and  old  persons  do  not  endure 
deprivation  of  food  so  well  as  adults.  This  was  noted  in  the  case  of  the 
wreck  of  the  frigate  Medusa.  After  the  wreck,  one  hundred  and  fifty 
persons,  of  all  ages,  were  exposed  on  a  raft  for  thirteen  days,  with  hardly 
any  food.  Out  of  this  number  only  fifteen  survived;  and  the  children, 
the  young  persons  and  the  aged  were  the  first  to  succumb. 

In  cold  cUmates  and  during  the  winter  season  in  temperate  climates, 
the  desire  for  food  is  notably  increased  and  the  tastes  are  somewhat  modi- 
fied. Animal  food,  particularly  fats,  are  more  agreeable  at  that  time, 
and  the  quantity  of  nutriment  demanded  by  the  system  is  considerably 
increased.  In  many  persons  the  difference  in  the  appetite  in  warm  and 
in  cold  seasons  is  very  marked. 

If  food  is  not  taken  in  obedience  to  the  demands  of  the  system  as 
expressed  by  the  appetite,  the  sensation  of  hunger  becomes  most  distress- 
ing. It  is  then  manifested  by  a  peculiar  and  indescribable  sensation  in 
the  stomach,  which  soon  becomes  developed  into  actual  pain.  This 
usually  is  accompanied  with  intense  pain  in  the  head  and  a  feeling  of 
general  distress,  which  soon  render  the  satisfaction  of  this  imperative  de- 
mand on  the  part  of  the  system  the  absorbing  idea  of  existence.  Furious 
delirium  frequently  supervenes  after  a  few  days  of  complete  abstinence ; 
and  this  usually  is  the  immediate  precursor  of  death.  It  is  unnecessary 
to  cite  the  many  instances  in  which  murder  and  cannibalism  have  been 


I40  ALIMENTATION 

resorted  to  when  starvation  had  become  imminent;  suffice  it  to  say  that 
the  extremity  of  hunger  or  of  thirst,  Hke  the  sense  of  impending  suffoca- 
tion, is  a  demand  on  the  part  of  the  system  so  imperative  that  it  must 
be  satisfied  if  within  the  range  of  possibiHty. 

When  the  system  is  suffering  from  defective  nutrition,  as  after  pro- 
longed abstinence  or  during  convalescence  from  diseases  attended  with 
defective  assimilation,  the  mere  filHng  of  the  stomach  produces  a  sen- 
sation of  repletion  of  this  organ,  but  the  sense  of  hunger  is  not  re- 
lieved ;  but  if,  on  the  other  hand,  the  nutrition  is  active  and  sufficient, 
the  stomach  frequently  is  entirely  empty  for  a  considerable  time  without 
the  development  of  the  sense  of  hunger.  The  appetite  is  preserved  and 
hunger  is  felt  by  persons  who  suffer  from  extensive  organic  disease  of 
the  stomach,  and  the  sensation  occasionally  has  been  relieved  by  nutri- 
tious enemata  or  by  injections  into  the  veins.  It  is  certain  that  appetite 
and  the  sense  of  hunger  are  expressions  of  a  want  on  the  part  of  the 
organism,  referred  by  the  sensations  to  the  stomach,  but  really  existing 
in  the  general  system.  This  can  be  completely  satisfied  only  by  the 
absorption  of  digested  alimentary  matters  by  the  blood  and  their  assimi- 
lation by  the  tissues. 

The  sense  of  hunger  undoubtedly  is  appreciated  by  the  cerebrum, 
and  it  has  been  a  question  whether  there  be  any  special  nerves  that 
convey  this  impression  to  the  encephalon.  The  nerve  which  naturally 
would  be  supposed  to  have  this  office  is  the  pneumogastric ;  but  not- 
withstanding certain  observations  to  the  contrary,  it  has  been  shown 
that  section  of  both  these  nerves  by  no  means  abolishes  the  desire  for 
food.  It  has  been  observed  that  dogs  eat,  apparently  with  satisfaction, 
after  section  of  the  glosso-pharyngeal  and  lingual  nerves.  It  has  been 
thought,  also,  that  the  sensation  of  hunger  is  conveyed  to  the  brain 
through  the  sympathetic  system.  Although  there  are  various  consid- 
erations that  render  this  somewhat  probable,  it  is  not  apparent  how  it 
can  be  demonstrated  experimentally.  It  is  undoubtedly  the  sympathetic 
system  of  nerves  that  presides  specially  over  nutrition ;  and  hunger, 
which  depends  upon  deficiency  of  nutrition,  is  certainly  not  conveyed  to 
the  brain  by  any  of  the  cerebro-spinal  nerves. 

Thirst  is  the  peculiar  sensation  that  leads  to  the  ingestion  of  water. 
In  its  moderate  development,  this  usually  is  an  indefinite  feeling,  accom- 
panied by  more  or  less  dryness  and  heat  of  the  throat  and  fauces,  and 
sometimes,  after  the  ingestion  of  a  quantity  of  very  dry  food,  by  a 
sensation  referred  to  the  stomach.  When  the  sensation  of  thirst  has 
become  intense,  the  immediate  satisfaction  following  the  ingestion  of  a 
liquid,  particularly  water,  is  very  great.  Thirst  is  very  much  under  the 
influence  of  habit ;  some  persons  experiencing  a  desire  to  take  liquids 


HUNGER    AND    THIRST  I4I 

only  two  or  three  times  daily,  while  others  do  so  much  more  frequently. 
The  sensation  is  also  sensibly  influenced  by  the  condition  of  the  atmos- 
phere as  regards  moisture,  by  exercise  and  by  other  conditions  that 
influence  the  discharge  of  water  from  the  body,  particularly  by  the  skin. 
A  copious  loss  of  blood  is  always  followed  by  intense  thirst ;  and  in 
diseases  characterized  by  increased  discharge  of  liquids,  thirst  usually  is 
excessive. 

The  demand  on  the  part  of  the  system  for  water  is  much  more  im- 
perative than  for  solids ;  and  in  this  respect  it  is  second  only  to  the  demand 
for  oxygen.  Animals  live  much  longer  when  deprived  of  solid  food  but 
allowed  to  drink  freely  than  if  deprived  of  both  food  and  drink.  A  man, 
supplied  with  dry  food  but  deprived  of  water,  will  not  survive  more 
than  a  few  days.  Water  is  necessary  to  the  processes  of  nutrition,  and 
acts,  moreover,  as  a  solvent  in  removing  from  the  system  the  products 
of  katabolism. 

After  deprivation  of  water  for  a  considerable  time,  the  intense  thirst 
becomes  most  distressing.  The  dryness  and  heat  of  the  throat  and 
fauces  are  increased  and  accompanied  with  a  sense  of  constriction.  A 
general  febrile  condition  supervenes,  the  blood  is  diminished  in  quan- 
tity and  becomes  thickened,  the  urine  is  scanty  and  scalding,  and 
there  seems  to  be  a  condition  of  the  principal  viscera  approaching 
inflammation.  Death  takes  place  in  a  few  days,  usually  preceded  by 
delirium. 

The  sensation  of  thirst  is  instinctively  referred  to  the  mouth,  throat 
and  fauces ;  but  it  is  not  appeased  necessarily  by  the  passage  of  water 
over  these  parts,  and  it  may  be  effectually  relieved  by  the  introduction 
of  water  into  the  system  by  other  channels,  as  by  injecting  it  into  the 
veins.  Bernard  has  demonstrated,  by  the  following  experiment,  that 
water  must  be  absorbed  before  the  demands  of  the  system  can  be  satis- 
fied :  He  made  a  section  of  the  oesophagus  in  a  horse,  tied  the  lower 
opening  and  allowed  the  animal  to  drink  after  he  had  been  deprived  of 
water  for  a  number  of  hours.  The  animal  drank  an  immense  quantity, 
but  the  water  did  not  pass  into  the  stomach  and  the  thirst  was  not  re- 
lieved. He  modified  this  experiment  by  causing  dogs  to  drink,  with  a 
fistulous  opening  into  the  stomach  by  which  the  water  was  immediately 
discharged.  They  continued  to  drink  without  being  satisfied,  until  the 
fistula  was  closed  and  the  water  could  be  absorbed.  In  a  case  reported 
by  Gairdner  (1820),  in  the  human  subject,  all  the  liquids  swallowed 
passed  out  at  a  wound  in  the  neck,  by  which  the  oesophagus  had 
been  cut  across.  The  thirst  in  this  case  was  insatiable,  although 
buckets  of  water  were  taken  in  the  day  ;  but  on  injecting  water  into 
the  stomach,  the  sensation  was  soon  relieved. 


142 


ALIMENTATION 


Although  the  sensation  of  thirst  is  referred  to  special  parts,  it  is  an 
expression  of  the  want  of  liquids  in  the  system  and  is  to  be  effectually 
reUeved  only  by  their  absorption  by  the  blood.  There  are  no  nerves 
belonging  to  the  cerebro-spinal  system  that  have  the  office  of  conveying 
this  sensation  to  the  brain,  division  of  which  will  aboUsh  the  desire  for 
liquids.  Experiments  show  that  no  effectual  relief  of  the  sensation  is 
afforded  by  simply  moistening  the  parts  to  which  the  heat  and  dryness 
are  referred.  As  a  demand  on  the  part  of  the  system,  it  is  analogous 
to  the  sense  of  want  of  air  and  of  hunger,  differing  only  in  the  manner 
in  which  it  is  manifested. 

The  duration  of  life  after  complete  deprivation  of  food  and  drink  is 
variable.  The  influence  of  age  has  already  been  referred  to.  Taking 
no  account  of  certain  remarkable  individual  instances  of  starvation  in 
the  human  subject  that  have  been  reported,  it  may  be  stated,  in  general 
terms,  that  death  occurs  within  five  to  eight  days  after  total  deprivation 
of  food.  In  the  instance  of  the  one  hundred  and  fifty  persons  wrecked 
on  the  frigate  Medusa,  in  1816,  who  were  exposed  on  a  raft  in  the  open  sea 
for  thirteen  days,  only  fifteen  were  found  alive.  Dr.  Savigny,  one  of 
the  survivors,  gave,  in  an  inaugural  thesis,  an  instructive  and  accurate 
account  of  this  occurrence,  which  has  often  been  quoted  in  works  on 
physiology.  Authentic  instances  are  on  record  in  which  hfe  has  been 
prolonged  much  beyond  the  period  above  mentioned ;  but  they  usually 
occurred  in  persons  who  were  so  situated  as  not  to  suffer  from  cold, 
which  the  system,  under  this  condition,  has  but  little  power  to  resist.  In 
these  cases,  also,  there  was  no  muscular  exertion,  and  water  was  taken 
in  abundance. 

Berard  quoted  the  example  of  a  convict  who  died  of  starvation  after 
sixty-three  days,  but  in  this  case  water  was  taken.  An  instance  of  eight 
miners  who  survived  after  five  days  and  sixteen  hours  of  almost  com- 
plete deprivation  of  food  is  referred  to  in  works  on  physiology.  Berard 
has  also  quoted  from  various  authors  instances  of  deprivation  of  food 
for  periods  varying  between  four  months  and  sixteen  years ;  but  these 
accounts  have  been  discredited  by  physiologists.  They  occurred  usually 
in  hysterical  females ;  and  their  consideration  belongs  to  psychology 
rather  than  to  physiology.  According  to  the  observations  of  Chossat, 
death  from  starvation  occurs  after  a  loss  of  four-tenths  of  the  weight 
of  the  body,  the  time  of  death,  however,  being  very  variable  in  different 
classes  of  animals. 

Thirty  to  thirty-five  days  may  be  taken  as  the  average  duration  *of 
life  in  dogs  deprived  entirely  of  food  and  water.  It  is  important  to  bear 
in  mind  this  fact  in  connection  with  observations  on  the  nutritive  value 
of  different  articles  of  food. 


NITROGENOUS  ALIMENTARY  SUBSTANCES         143 

Alimentation 

Under  the  name  of  aliment,  in  its  widest  signification,  it  is  proposed 
to  include  all  articles  composed  of  or  containing  substances  in  a  form 
in  which  they  can  be  used  for  the  nourishment  of  the  body,  either  by 
being  themselves  appropriated  by  the  organism,  by  influencing  favorably 
the  processes  of  nutrition  or  by  retarding  katabolism.  The  substances 
that  are  themselves  appropriated  may  be  called  direct  aliments ;  and 
those  which  simply  assist  nutrition  without  contributing  reparative  mate- 
rial, together  with  those  which  retard  katabolism,  may  be  termed  indi- 
rect aliments.  In  this  definition  of  aliment,  nothing  is  excluded  that 
contributes  to  nutrition.  Oxygen  must  be  considered  in  this  light,  as 
well  as  water  and  all  articles  commonly  called  drinks. 

In  the  various  articles  used  as  food,  nutritious  substances  frequently 
are  combined  with  each  other  and  with  indigestible  and  innutritions 
matters.  The  constituents  of  the  food  directly  used  in  nutrition  are  the 
true  alimentary  substances,  embracing,  thus,  only  those  capable  of  ab- 
sorption and  assimilation.  The  ordinary  food  of  warm-blooded  animals 
contains  alimentary  matters  united  with  innutritions  substances  from 
which  they  are  separated  in  digestion.  This  necessitates  a  complicated 
digestive  apparatus.  In  some  of  the  inferior  animals,  the  quantity  of 
nutritious  matter  forms  so  small  a  part  of  the  ingesta  that  the  digestive 
apparatus  is  more  complicated  than  in  the  human  subject.  This  is 
specially  marked  in  the  herbivora,  the  flesh  of  which  is  an  important 
part  of  the  diet  of  man.  In  addition  to  what  are  distinctly  recognized 
as  alimentary  substances,  food  has  many  constituents  that  exert  an  im- 
portant influence  on  nutrition,  which  have  never  been  isolated  and 
analyzed,  but  which  render  it  agreeable.  Many  of  these  are  developed 
in  the  process  of  cooking. 

Alimentary  substances  belong  to  the  inorganic,  vegetable  and 
animal  kingdoms.     They  may  be  divided  into  the  following  classes  :  — 

1.  Organic  nitrogenous  substances  (albumin,  fibrin,  casein,  myosin 
etc.),  belonging  to  the  animal  kingdom,  and  vegetable  nitrogenous  sub- 
stances, such  as  gluten  and  legumin. 

2.  Organic  non-nitrogenous  substances  (sugars,  starch  and  fats). 

3.  Inorganic  substances. 

Nitrogenous  Alimentary  Substances.  —  In  the  nutrition  of  certain 
classes  of  animals,  these  substances  are  derived  exclusively  from  the 
animal  kingdom,  and  in  others,  exclusively  from  the  vegetable  kingdom; 
but  in  man,  both  animals  and  vegetables  contribute  nitrogenous  matters. 
In  both  animal  and  vegetable  food,  nitrogenous  substances  are  always 
found   associated  with  inorganic  matters   (water,  sodium  chloride,  the 


144  ALIMENTATION 

phosphates,  sulphates  etc.),  and  frequently  with  non-nitrogenous  matters, 
especially  the  carbohydrates. 

The  most  important  nitrogenous  alimentary  constituents  of  food 
are  contained  in  muscular  tissue,  eggs,  milk,  the  juices  of  vegetables, 
cereal  grains  etc.  Among  the  most  important  are  the  following : 
myosin,  the  chief  proteid  constituent  of  muscle,  the  various  albumins 
found  in  eggs  and  in  animal  liquids,  analogous  substances  existing  in 
vegetables,  casein  in  milk,  a  substance  sometimes  called  vegetable 
casein,  vitellin  in  yolk  of  egg,  fibrin,  gelatin,  and  gluten,  an  important 
alimentary  substance  found  in  the  cereal  grains.  A  distinctive 
character  of  these  substances  is  that  they  contain  nitrogen,  being  com- 
posed of  carbon,  oxygen,  hydrogen  and  nitrogen,  probably  with  a  small 
quantity  of  sulphur.  They  are  either  liquid  or  semisolid  in  consistence 
and  are  coagulable  by  various  reagents.  The  type  of  substances  of 
this  class  is  albumin,  which  has  the  empirical  formula,  C72Hji2022NigS. 
Certain  of  these  are  called  proteids,  after  a  hypothetical  substance  de- 
scribed by  Mulder,  under  the  name  of  protein. 

Nitrogenous  substances  are  found  in  animal  bodies,  as  has  already 
been  stated.  They  originate  in  vegetables  by  a  union  of  nitrogen, 
derived  chiefly  from  saline  matters,  with  carbohydrates,  the  carbohy- 
drates in  vegetables  being  produced  from  carbon  dioxide  and  water. 

A  distinctive  character  of  nitrogenous  matters  is  that  under  favor- 
able conditions  of  heat  and  moisture  they  undergo  a  peculiar  form  of 
decomposition  called  putrefaction.  In  the  processes  of  digestion,  these 
substances  are  converted  into  peptones,  and  afterward,  it  is  thought, 
a  part  may  be  changed  into  leucin,  tyrosin  and  other  substances 
not  well  defined.  An  analogous  decomposition  is  said  to  take  place 
under  the  influence  of  dilute  hydrochloric  acid,  at  a  temperature  of 
104°  Fahr.  (40°  C),  and  of  dilute  sulphuric  acid,  at  a  temperature  of 
212°  Fahr.  (100°  C).  The  chemical  history  of  these  substances  would 
require  an  elaborate  description  such  as  properly  belongs  only  to  special 
works  on  physiological  chemistry. 

Non-nitrogenous  Alimentary  Substances.  —  The  important  non-nitrog- 
enous alimentary  matters  are  sugars,  starch  and  fats.  These  are  com- 
posed of  carbon,  hydrogen  and  oxygen.  In  sugars  and  starch,  the 
hydrogen  and  oxygen  exist  in  the  proportion  to  form  water,  and  these 
matters  are  therefore  called  carbohydrates. 

Sugars.  —  Many  varieties  of  sugar  occur  in  food,  and  this  substance 
may  be  derived  from  both  the  animal  and  vegetable  kingdoms.  The 
most  common  varieties  derived  from  animals  are  sugar  of  milk,  and 
honey,  beside  a  small  quantity  of  liver-sugar,  which  is  taken  whenever 
the  liver    is  used  as  food.     Only  a   few  of  the  carbohydrates  are  of 


CARBOHYDRATES  145 

physiological  interest.  The  formulae  given  are  merely  empirical,  and 
the  molecular  weights  in  many  instances  are  indefinite.  In  the  group 
of  amyloses  (starch-groups)  the  molecules  are  very  large  —  20,000 
to  30,000  (Brown  and  Morris).  The  various  changes  which  substances 
belonging  to  this  group  undergo  are  very  complex,  and  it  will  be  more 
convenient  to  discuss  these  in  connection  with  the  physiology  of  diges- 
tion. Here  little  more  than  an  enumeration  of  some  of  the  carbohydrates 
will  be  given.  The  following  is  the  usual  classification.  The  sign  + 
indicates  that  the  substance  is  dextro-rotatory  and  the  sign  — ,  that  it  is 
levo-rotatory. 

I.  Gbicoses  2.   Saccharoses  3.    Amyloses 

(QHj.O,)  (Ci^H^Pu)  (« C.HiA) 

-I-  Dextrose  -H  Saccharose  +  Starch 

—  Levulose  +  Lactose  +  Glycogen 

-f  Galactose  +  Maltose  -f  Dextrin 

Cellulose 
Gums 

Dextrose.  —  This  carbohydrate  —  often  called  grape-sugar  —  is  found 
in  fruits,  honey,  and  sometimes  in  small  quantity  in  the  blood  and  in 
various  tissues.  Its  empirical  formula  is  CgH^206-  •'■^  ^^  soluble  in  hot 
and  cold  water  and  in  alcohol.  It  reduces  the  copper  salts  and  is 
fermentible. 

LeviUose.  —  This  carbohydrate  is  obtained  by  treating  saccharose 
with  a  dilute  mineral  acid.  The  saccharose  then  undergoes  what  is 
known  as  inversion,  appropriating  water  and  changing  into  a  mixture 
of  equal  parts  of  levulose  and  dextrose.  This  mixture  is  levo-rotatory, 
the  levo-rotatory  power  being  greater  than  the  dextro-rotatory.  It  has 
the  same  general  reactions  as  dextrose.  It  crystalhzes  with  difficulty. 
Its  empirical  formula  is  the  same  as  the  formula  for  dextrose  (CgHigOg). 

Galactose.  —  This  carbohydrate  is  formed  by  the  action  of  dilute 
mineral  acids  on  lactose.  It  is  dextro-rotatory  and  has  the  same  gen- 
eral reactions  as  dextrose.     Its  empirical  formula  is  CgH^206- 

Saccharose.  —  This  carbohydrate  is  derived  from  the  vegetable  king- 
dom. It  crystallizes  readily  and  is  dextro-rotatory.  It  does  not  reduce 
the  salts  of  copper.  On  the  addition  of  yeast,  it  first  undergoes  change 
into  invert-sugar  and  then  ferments.  It  is  by  far  the  most  important 
of  the  sugars  used  as  food.  By  boiling  with  a  dilute  mineral  acid,  it 
undergoes  inversion  into  equal  parts  of  dextrose  and  levulose.  It  is 
inverted,  also,  in  the  processes  of  digestion.     Its  empirical  formula  is 

^12      22^11" 

Lactose. — This  is  the  sugar  found  in  milk.  It  assumes  water  under 
the  same  conditions  as  saccharose  and  splits  into  dextrose  and  galac- 


146        '  ALIMENTATION 

tose  by  the  following  process:  Lactose  (C12H22OJ1  +  H^O  =  dextrose, 
CgHj20g  +  galactose,  CgHj20g).  It  does  not  of  itself  undergo  fermen- 
tation, but  when  it  has  been  inverted  by  the  action  of  yeast,  it  slowly 
ferments. 

Maltose.  —  This  carbohydrate  is  the  product  of  the  action  of  malt- 
diastase  on  starch.  It  is  strongly  dextro-rotatory.  Boiled  with  dilute 
mineral  acids  or  exposed  to  the  action  of  inverting  ferments,  it  assumes 
water  and  is  converted  into  dextrose.  It  undergoes  this  change  in 
digestion.  It  reduces  the  salts  of  copper  and  promptly  undergoes 
alcoholic  fermentation  when  mixed  with  yeast.     Its  empirical  formula 

Starch.  —  This  carbohydrate  is  of  vegetable  origin.  It  is  composed 
of  hard  granules  that  are  insoluble  in  cold  water.  Treated  with  boiling 
water,  the  granules  swell,  press  together  and  gelatinize  on  cooling. 
Under  the  influence  of  the  diastatic  ferments,  it  is  first  converted  into 
soluble  starch,  then  into  dextrin,  and  finally  into  dextrose.  The  em- 
pirical formula  of  soluble  starch  is  (CgHi(,O5)20  (?)•  Starch  gives  an 
intense  blue  reaction  with  iodine,  even  in  very  small  quantity.  This 
color  is  discharged  by  heat  but  reappears  on  cooling. 

Glycogen.  —  Glycogen,  or  animal  starch,  is  found  in  the  liver,  mus- 
cular tissue,  leucocytes  and  the  blood  of  the  hepatic  veins.  In  the 
liver  the  products  of  digestion  of  the  carbohydrates  of  food  are  stored 
up  in  the  form  of  glycogen.  Treated  with  iodine,  glycogen  gives  a 
reddish  reaction.     It  is  dextro-rotatory. 

Cellulose,  Inosite  and  Gums.  —  The  hard  covering  of  starch-granules 
is  composed  of  cellulose.  By  boiling  starch,  these  coverings  are  rup- 
tured, the  starch  is  set  free  and  it  may  be  acted  on  slightly  by 
the  digestive  secretions.  It  exists  in  vegetable  food,  but  on  account 
of  its  difficult  solubility  it  is  not  readily  digested.  Treated  with  dilute 
mineral  acids  for  a  long  time,  like  starch,  it  is  converted  into  glucose. 

Inosite,  or  the  sugar  of  muscular  tissue,  exists  in  muscle,  the  liver, 
the  kidney  and  in  various  other  parts  in  small  quantity. 

The  gums  exist  in  food  and  in  the  blood  in  very  small  quantity. 
They  are  unimportant  in  the  processes  of  nutrition. 

The  Fats.  —  Fats  exist  in  the  body  either  in  the  form  of  adipose 
tissue  or  in  granules  and  in  some  instances  in  molecular  union  with 
nitrogenous  matters.  They  present  three  forms,  or  varieties :  triolein, 
liquid  at  a  temperature  of  23°  Fahr.  (-5°  C);  tripalmitin,  liquid  at  115° 
Fahr.  (45°  C);  tristearin,  liquid  at  128°  Fahr.  (53.66°  C).  Fats  are 
regarded  by  chemists  as  compounds  of  fatty  acids  with  glycerin,  and 
on  this  account  they  are  sometimes  called  glycerids.  It  is  incorrect  to 
call  them  hydrocarbons,  a  name  by  which  they  were  formerly  known. 


INORGANIC   ALIMENTARY    SUBSTANCES  147 

The  fatty  acids,  with  the  exception  of  oleic  acid,  are  derived  by 
oxidation  from  the  monatomic  alcohols.  Oleic  acid,  however,  belongs 
to  the  acrylic  series.  Glycerin  is  a  triatomic  alcohol,  being  formed  of 
three  atoms  of  hydroxyl  with  glyceril.  The  type  of  the  neutral  fats 
is  triacetin;  and  the  fats  should  be  called  triolein,  tripalmitin  and 
tristearin,  for  the  reason  that  in  the  glycerin  which  enters  into  their 
composition,  the  three  atoms  of  hydrogen  of  the  hydroxyls  are  replaced 
by  the  acid  radicles. 

The  following  are  the  empirical  formulae  for  the  fats  found  in  the 
body;  triolein,  CgHj  (OCjyHggCOjg ;  tripalmitin,  C3H5  (OC-i5Hg5CO)g ; 
tristearin,  CgH^  (OC^yHgjCOjg.  At  the  temperature  of  the  body, 
triolein  holds  the  two  other  fats  in  solution  ;  and  the  fats  of  the  body, 
therefore,  are  composed  of  the  three  varieties  and  are  not  solid. 

Boiled  with  an  alkali  in  the  presence  of  water,  fats  are  decomposed 
into  glycerin,  which  remains  free,  and  the  fatty  acid,  which  latter  unites 
with  the  alkali  to  form  a  soap.  The  following  is  an  example  of  this 
decomposition :  — 

CgH^  ( OCisHgiCOjg  +  3  KHO  =  CgH,5  (OH)g  +  3  Ci-HgiCO.OK. 

A  similar  decomposition  takes  place  under  the  influence  of  superheated 
steam.  When  a  soap  is  formed,  the  decomposition  is  called  saponifica- 
tion ;  when  no  soap  is  formed,  it  is  called  acidification.  The  pancreatic 
juice  has  the  property  of  acidifying  fats. 

Shaken  up  with  gummy  or  mucilaginous  mixtures,  liquid  fats  are 
subdivided  into  small  granules  or  globules  and  held  permanently  in  sus- 
pension. This  is  called  emulsification  ;  and  the  form  of  the  fats  is 
changed  in  this  way  in  digestion.  Examples  of  fatty  emulsions  in  the 
body  are  milk  and  chyle. 

The  lecithins  are  very  complex  fats,  the  formula  of  which  is 
C^gHg^NPOg.  By  decomposition  they  yield  glycerin,  phosphoric  acid, 
a  fatty  acid  and  cholin.     These  have  been  called  phosphorized  fats. 

Cholesterin  is  a  crystallizable  monatomic  alcohol  with  the  formula 
CgyH^gO.  It  is  found  in  large  quantity  in  nervous  tissue  and  also  exists 
in  the  bile,  crystalline  lens,  spleen,  protoplasm  of  cells  and  in  some 
other  situations.  It  is  taken  up  from  the  nervous  tissue  by  the  blood, 
separated  from  the  blood  by  the  liver,  discharged  into  the  small  intestine 
with  the  bile  and  is  eliminated  in  the  form  of  stercorin(C27H4gO).  Ster- 
corin  is  to  be  regarded  as  a  product  of  katabolism,  particularly  of  the 
nervous  tissue.  Cholesterin  will  be  treated  of  more  fully  in  connection 
with  the  bile. 

Inorganic  Aliine7itary  Substances.  —  It  has  been  shown  that  all  the 
organs,  tissues    and   liquids  of   the  body  contain    inorganic  matter  in 


148  ALIMENTATION 

greater  or  less  quantity.  The  same  is  true  of  vegetable  products.  All 
the  organic  nitrogenous  matters  contain  mineral  substances  which  can 
not  be  separated  without  incineration.  When  new  organic  matter  is 
appropriated  by  the  tissues  to  supply  the  place  of  that  which  has 
become  effete,  mineral  substances  are  deposited  with  them  ;  and  the 
organic  matters,  as  they  are  transformed  into  excrementitious  sub- 
stances and  discharged  from  the  body,  are  always  thrown  off  in  con- 
nection with  the  mineral  substances  with  which  they  are  associated. 
This  constant  discharge  of  inorganic  matters,  forming,  as  they  do,  an 
essential  part  of  the  organism,  necessitates  their  introduction  with  the 
food  in  order  to  maintain  the  normal  constitution  of  the  parts.  As 
these  matters  are  necessary  to  the  proper  constitution  of  the  body, 
they  must  be  regarded  as  alimentary  substances. 

Wafer.  —  This  is  one  of  the  most  important  of  the  constituents  of 
the  organism,  is  found  in  every  tissue  and  part  without  exception,  is 
introduced  with  all  kinds  of  food  and  is  the  basis  of  all  drinks.  As  a 
rule  it  is  taken  in  greater  or  less  quantity  in  a  nearly  pure  state. 
Although,  as  a  drink,  water  should  be  colorless,  odorless  and  tasteless, 
it  always  contains  more  or  less  saline  and  other  matters  in  solution,  with 
a  certain  quantity  of  air.  The  air  and  gases  may  be  driven  off  by 
boiUng  or  by  reducing  the  atmospheric  pressure.  The  demand  on  the 
part  of  the  system  for  water  is  regulated  to  a  certain  extent  by  the 
quantity  discharged  from  the  organism,  and  this  is  subject  to  great 
variations.  The  quantity  taken  as  drink  also  depends  on  the  constitu- 
tion of  the  food  as  regards  the  water  that  enters  into  its  composition. 

Water  is  beyond  comparison  the  most  important  compound  in 
Nature.  It  is  essential  to  all  chemical  changes  that  occur  out  of  the 
body  and  to  all  processes  of  digestion,  anabolism  and  katabolism.  It 
is  the  most  powerful  dissocient  known.  According  to  modern  views, 
molecules  have  no  chemical  activity  and  chemical  combinations  occur 
only  when  they  are  dissociated  into  ions.  Anhydrous  hydrochloric  acid 
will  not  decompose  carbonates;  pure  sulphuric  acid  has  no  action  on 
dry  litmus ;  dried  ammonia  and  hydrochloric  acid  will  not  combine  if 
brought  together ;  and  other  illustrations  might  be  given  of  the  action 
of  water  in  chemical  combinations.^ 

Although  organic  compounds  dissociate  into  ions  slowly  and  feebly, 
water  is  the  most  important  agent  in  their  chemical  changes.  The 
subject,  however,  of  the  possible  and  probable  reactions  between  pro- 
teids  and  water  is  so  vast,  and  as  yet  the  results  of  experiments  have 

1  According  to  Dewar,  a  chemical  combination  can  occur,  in  the  absence  of  water,  at  very 
low  temperatures,  such  as  that  of  liquid  air  ;  but  at  present,  this  is  the  only  exception  to  the 
general  proposition  stated  above. 


INORGANIC   ALIMENTARY    SUBSTANCES  149 

been  so  indefinite  in  their  applications  to  physiology,  that  its  discussion 
would  be  out  of  place  in  this  work.  It  is  sufficient  to  say  that  these 
reactions  involve  hydrolytic  cleavages  accelerated  by  various  condi- 
tions—  such  as  elevation  of  temperature  and  the  presence  of  acids  and 
enzymes  —  and  retarded  by  others.  These  changes  are  thought  to  be 
due  to  the  dissociation  of  water  and  the  action  of  the  hydrogen  ion.^ 
Applications  of  these  ideas  to  what  may  be  called  general  metabolic 
changes  in  the  living  body  are  evident ;  and  theoretical  considerations 
of  this  kind  might  be  extended  to  the  digestion  of  proteids.  The 
hydrolytic  changes  in  carbohydrates  have  been  closely  studied  and  many 
of  them  accurately  described.  It  is  not  too  much  to  say  that  the  most 
efficient  agent  in  the  most  important  of  the  digestive,  nutritive  and 
katabolic  processes  probably  is  dissociated  water,  its  action  being 
favored  or  retarded  by  varying  conditions. 

Sodiufn  Chloride.  —  Of  all  saline  substances,  sodium  chloride  is  the 
one  most  widely  distributed  in  the  animal  and  the  vegetable  kingdoms. 
It  exists  in  all  varieties  of  food ;  but  the  quantity  taken  in  combination 
with  other  matters  usually  is  insufficient  for  the  purposes  of  the  economy, 
and  common  salt  is  added  to  certain  articles  of  food  as  a  condiment, 
when  it  improves  their  flavor,  promotes  the  secretion  of  certain  of  the 
digestive  fluids  and  meets  a  nutritive  demand.  Experiments  and  obser- 
vations have  shown  that  a  deficiency  of  sodium  chloride  in  food  has  an 
unfavorable  influence  on  the  general  processes  of  nutrition. 

Calcunn  Phosphate. — This  is  almost  as  common  a  constituent  of 
vegetable  and  animal  food  as  sodium  chloride.  It  is  seldom  taken  except 
in  combination,  particularly  with  nitrogenous  alimentary  matters.  Its 
importance  in  alimentation  has  been  experimentally  demonstrated,  it 
having  been  shown  that  in  animals  deprived  as  completely  as  possible 
of  this  salt,  the  nutrition  of  the  body,  particularly  in  parts  that  contain 
it  in  considerable  quantity,  as  the  bones,  is  seriously  affected. 

Iron.  —  Hemoglobin,  the  coloring  matter  of  the  blood,  contains,  inti- 
mately united  with  organic  matters,  a  certain  proportion  of  iron.  Ex- 
amples of  simple  anemia,  which  are  frequently  met  with  in  practice  and 
are  almost  always  relieved  in  a  short  time  by  the  administration  of  iron, 
are  evidences  of  the  importance  of  this  substance  in  alimentation. 
The  quantity  of  iron  discharged  from  the  body  is  slight,  only  a  trace 
being  discoverable  in  the  urine.  A  small  quantity  of  iron  frequently  is 
introduced  in  solution  in  the  water  taken  as  drink,  and  it  is  a  constant 
constituent  of  milk  and  eggs.  When  its  supply  in  the  food  is  insufficient, 
it  is  necessary,  in  order  to  restore  the  normal  processes  of  nutrition,  to 

^  A  very  lucid  exposition  of  the  action  of  the  hydrogen  ion  in  catalysis  is  given  by  Jones,  in 
"The  Elements  of  Physical  Chemistry,"  New  York,  1902,  p.  456. 


150  ALIMENTATION 

administer  it  in  some  form,  until  its  proportion  in  the  organism  shall 
have  reached  the  proper  standard. 

It  is  hardly  necessary  even  to  enumerate  the  other  inorganic  ali- 
mentary substances,  as  nearly  all  are  in  such  intimate  association  with 
nitrogenous  matters  that  they  may  be  regarded  as  part  of  their  substance. 
Suffice  it  to  say,  that  all  inorganic  matters  existing  in  the  organism  are 
found  in  food.  That  these  are  essential  to  nutrition  can  not  be  doubted; 
but  it  is  evident  that  by  themselves  they  are  incapable  of  supporting 
life,  as  they  can  not  be  converted  into  either  nitrogenous  or  non-nitroge- 
nous organic  matters. 

Alcohol.  —  All  distilled  and  fermented  liquors  and  wines  contain  a 
greater  or  less  proportion  of  alcohol.  As  these  are  so  commonly  used 
as  beverages  and  as  the  effects  of  their  excessive  use  are  so  serious,  the 
influence  of  alcohol  on  the  organism  must  be  regarded  as  one  of  the 
most  important  questions  connected  with  alimentation.  Some  alcohoHc 
beverages  influence  the  functions  solely  through  the  alcohol  which  they 
contain ;  while  others,  as  beer  and  porter,  with  a  comparatively  small 
proportion  of  alcohol,  contain  a  considerable  quantity  of  solid  matter. 

Alcohol  (CgHgO),  from  its  composition,  is  to  be  classed  with  the  non- 
nitrogenous  substances.  It  has  already  been  stated  that  sugar  and  fat 
are  essential  to  proper  nutrition  and  that  they  undergo  important 
changes  in  the  organism.  Alcohol  is  absorbed  and  taken  into  the 
blood ;  and  it  becomes  a  question  of  importance  to  determine  whether 
it  be  consumed  in  the  economy  or  discharged  unchanged  by  the  various 
emunctories. 

Alcohol  has  long  since  been  recognized  in  the  expired  air  after  it  has 
been  taken  into  the  stomach ;  and  late  researches  have  confirmed  the 
earlier  observations  in  regard  to  its  elimination  in  its  original  form,  and 
have  shown,  also,  that  after  it  has  been  taken  in  quantity,  it  exists  in  the 
blood  and  all  the  tissues  and  organs,  particularly  the  liver  and  nervous 
system.  Lallemand  and  Perrin  and  Duroy  have  stated,  also,  that  there 
is  a  considerable  elimination  of  alcohol  by  the  lungs,  skin  and  kidneys ; 
but  the  accuracy  of  the  experiments  by  which  these  results  were  arrived 
at  has  been  questioned.  The  observations  of  Anstie  and  of  Dupre 
have,  indeed,  thrown  doubt  on  the  chromic-acid  test  for  alcohol,  which 
was  employed  by  the  French  observers  above  mentioned.  Neverthe- 
less, when  alcohol  has  been  taken  in  narcotic  doses,  there  is  some 
alcoholic  elimination  in  the  urine,  as  was  shown  long  ago  by  Percy.  It 
is  certain  that  most  of  the  alcohol  taken  in  quantities  not  sufficient  to 
produce  alcoholic  intoxication  is  consumed  in  the  organism,  and  but  a 
trivial  quantity  is  thrown  off,  either  in  the  urine,  the  feces,  the  breath 
or  the  cutaneous  transpiration.     This  question  is  of  importance  in  regard 


ALCOHOL  151 

to  the  moderate  use  of  alcohol  under  normal  conditions,  and  especially 
in  its  bearing  on  the  therapeutical  action  of  the  various  alcoholic  drinks 
administered  in  cases  of  disease. 

Taken  in  moderate  quantity,  alcohol  usually  produces  a  certain  de- 
gree of  nervous  exaltation  which  gradually  passes  off.  In  some  individ- 
uals the  mental  faculties  are  sharpened  by  alcohol,  while  in  others  they 
are  blunted.  There  is  nothing,  indeed,  more  variable  than  the  immediate 
effects  of  alcohol  on  different  persons.  In  large  doses  the  effects  are 
the  well-known  phenomena  of  intoxication,  delirium,  more  or  less  anes- 
thesia, coma,  and  sometimes,  if  the  quantity  is  excessive,  death.  As  a 
rule,  the  mental  exaltation  produced  by  alcohol  is  followed  by  reaction 
and  depression,  except  in  debilitated  or  exhausted  conditions  of  the 
system,  when  alcohol  seems  to  supply  a  decided  want. 

The  views  of  physiologists  concerning  the  influence  of  a  moderate 
quantity  of  alcohol  on  the  nervous  system  are  somewhat  conflicting. 
That  it  may  temporarily  give  tone  and  vigor  to  the  system  when  the 
energies  are  unusually  taxed,  can  not  be  doubted  ;  but  this  effect  is  not 
produced  in  all  individuals.  The  constant  use  of  alcohol  may  create  an 
apparent  necessity  for  it,  producing  a  condition  of  the  system  that  must 
be  regarded  as  pathological. 

The  immediate  effects  of  the  ingestion  of  a  moderate  quantity  of 
alcohol,  continued  for  a  few  days,  are  decided.  It  notably  diminishes 
the  exhalation  of  carbon  dioxide  and  the  discharge  of  other  excrementi- 
tious  matters,  particularly  urea.  These  facts  have  long  since  been  ex- 
perimentally demonstrated.  Proper  mental  and  physical  exercise, 
tranquillity  of  the  nervous  system,  and  all  conditions  that  favor  vigorous 
nutrition  and  development  of  the  organism  physiologically  increase, 
rather  than  diminish,  the  quantity  of  the  excretions,  correspondingly 
increase  the  demand  for  food,  and  if  continued,  are  of  permanent  benefit. 
Alcohol,  on  the  other  hand,  diminishes  the  activity  of  nutrition.  If  its 
use  is  long  continued,  the  assimilative  powers  become  so  weakened  that 
the  proper  quantity  of  food  can  not  be  appropriated,  and  alcohol  is  craved 
to  supply  a  self-engendered  want.  The  organism  may,  in  many  in- 
stances, be  restored  to  its  physiological  condition  by  discontinuing  the 
use  of  alcohol ;  but  it  usually  is  some  time  before  the  nutritive  powers 
become  active,  and  alcohol,  meanwhile,  seems  absolutely  necessary  to 
existence. 

Under  ordinary  conditions,  when  the  organism  can  be  adequately 
supplied  with  food,  alcohol  is  injurious.  When  the  quantity  of  food  is 
insufficient,  alcohol  may  supply  the  want  for  a  time  and  temporarily 
restore  the  powers  of  the  body ;  but  the  effects  of  its  continued  use, 
conjoined  with  insufficient  nourishment,  show  that  it  can  not  take  the 


152  ALIMENTATION 

place  of  assimilable  matters.  These  effects  are  too  well  known  to  the 
physician,  particularly  in  hospital-practice,  to  need  further  comment. 
Notwithstanding  these  undoubted  physiological  facts,  alcohol,  in  some 
form,  is  used  by  almost  every  people  on  the  face  of  the  earth,  civilized 
or  savage.  Whether  this  be  in  order  to  meet  some  want  occasionally 
felt  by  and  peculiar  to  the  human  organism,  is  a  question  on  which 
physiologists  have  found  it  impossible  to  agree.  That  alcohol,  at  certain 
times,  taken  in  moderation,  soothes  and  tranquillizes  the  nervous  system 
and  relieves  exhaustion  dependent  on  unusually  severe  mental  or  physical 
exertion,  can  not  be  doubted.  It  is  by  far  too  material  a  view  to  take  of 
existence,  to  suppose  that  the  highest  condition  of  man  is  that  in  which 
the  functions,  possessed  in  common  with  the  lower  animals,  are  perfectly 
performed.  Inasmuch  as  temporary  insufficiency  of  food,  great  exhaus- 
tion of  the  nervous  system,  and  various  conditions  in  which  alcohol 
seems  to  be  useful,  must  of  necessity  often  occur,  it  is  hardly  proper 
that  this  agent  should  be  absolutely  condemned ;  but  it  is  the  article, 
par  excellence,  which  is  liable  to  abuse;  and  its  effects  on  the  mind  and 
body,  when  habitually  taken  in  excess,  are  most  serious. 

Although  alcohol  imparts  a  certain  warmth  when  the  system  is 
suffering  from  excessive  cold,  it  is  not  proved  that  it  enables  men  to 
endure  a  very  low  temperature  for  a  great  length  of  time.  This  end 
can  be  effectually  attained  only  by  an  increased  quantity  of  food. 
The  testimony  of  Dr.  Hayes,  the  Arctic  explorer,  is  very  strong  upon 
this  point.  He  says :  "  While  fresh  animal  food,  and  especially  fat,  is 
absolutely  essential  to  the  inhabitants  and  travellers  in  Arctic  countries, 
alcohol  is,  in  almost  any  shape,  not  only  completely  useless  but  positively 
injurious.  .  .  .  Circumstances  may  occur  under  which  its  administra- 
tion seems  necessary ;  such,  for  instance,  as  great  prostration  from 
long-continued  exposure  and  exertion,  or  from  getting  wet ;  but  then  it 
should  be  avoided,  if  possible,  for  the  succeeding  reaction  is  always  to  be 
dreaded ;  and,  if  a  place  of  safety  is  not  near  at  hand,  the  immediate 
danger  is  only  temporarily  guarded  against,  and  becomes,  finally,  greatly 
augmented  by  reason  of  decreased  vitality.  If  given  at  all,  it  should  be 
in  very  small  quantities  frequently  repeated,  and  continued  until  a  place 
of  safety  is  reached.  I  have  known  the  most  unpleasant  consequences 
to  result  from  the  injudicious  use  of  whiskey  for  the  purpose  of  tempo- 
rary stimulation,  and  have  also  known  strong  able-bodied  men  to  have 
become  utterly  incapable  of  resisting  cold  in  consequence  of  the  long- 
continued  use  of  alcoholic  drinks."  In  a  paper  by  General  Greely 
(1887)  is  the  following,  which  confirms  the  results  of  the  experience  of 
Hayes :  "  It  seems  to  me  to  follow  from  these  Arctic  experiences  that 
the  regular  use  of  spirits,  even  in  moderation,  under  conditions  of  great 


COFFEE  153 

physical  hardship,  continued  and  exhausting  labor,  or  exposure  to  severe 
cold  can  not  be  too  strongly  deprecated,  and  that  when  used  as  a  mental 
stimulus  or  as  a  physical  luxury  they  should  be  taken  in  moderation. 
When  habit  or  inclination  induces  the  use  of  alcohol  in  the  field,  under 
conditions  noted  above,  it  should  be  taken  only  after  the  day's  work  is 
done,  as  a  momentary  stimulus  while  waiting  for  the  preferable  hot  tea 
and  food ;  or  better,  after  the  food,  when  going  to  bed,  for  then  it  may 
quickly  induce  sleep  and  its  reaction  pass  unfelt." 

It  is  not  demonstrated  that  alcohol  increases  the  capacity  to  endure 
severe  and  protracted  bodily  exertion.  Its  influence  as  a  therapeutic 
agent,  in  promoting  assimilation  in  certain  conditions  of  defective  nutri- 
tion, in  relieving  shock  and  nervous  exhaustion,  in  sustaining  the  powers 
of  life  in  acute  diseases  attended  with  rapid  emaciation  and  abnormally 
active  disassimilation,  etc.,  can  hardly  be  doubted  ;  but  the  considera- 
tion of  these  questions  does  not  belong  to  physiology.^ 

Coffee.  —  Coffee  is  an  article  consumed  daily  by  many  millions  of 
human  beings  in  all  quarters  of  the  globe.  In  armies  it  has  been  found 
almost  indispensable,  enabling  men  on  moderate  rations  to  perform  an 
amount  of  labor  which  would  otherwise  be  impossible.  After  exhaust- 
ing efforts  of  any  kind,  there  is  no  article  that  relieves  the  overpowering 
sense  of  fatigue  so  completely  as  coffee.  Army-surgeons  say  that  at 
night,  after  a  severe  march,  the  first  desire  of  the  soldier  is  for  coffee, 
hot  or  cold,  with  or  without  sugar,  the  only  essential  being  a  sufficient 
quantity  of  the  pure  article.  Almost  every  one  can  bear  testimony 
from  personal  experience  to  the  effects  of  coffee  in  relieving  the  sense 
of  fatigue  after  mental  or  bodily  exertion  and  in  increasing  the  capacity 
for  labor,  especially  mental  work,  by  producing  wakefulness  and  clear- 
ness of  intellect.  From  these  facts,  the  importance  of  coffee,  either  as 
an  alimentary  substance  or  as  taking  the  place,  to  a  certain  extent,  of 
aliment,  is  apparent. 

Except  in  persons  who,  from  idiosyncrasies,  are  unpleasantly 
affected  by  it,  coffee,  taken  in  moderate  quantity  and  at  proper  times, 
produces  an  agreeable  sense  of  tranquillity  and  comfort,  with,  however, 
no  disinclination  to  exertion,  either  mental  or  physical.  Its  immediate 
influence  on  the  system,  which  undoubtedly  is   stimulant,  is   peculiar 

1  Inasmuch  as  my  views  in  regard  to  the  physiological  effects  of  alcohol  have  undergone  no 
material  change,  I  repeat  here  what  has  appeared  in  my  "Text-book  of  Human  Physiology" 
(1888).  Recent  observations  have  shown  that  when  alcohol  is  taken  in  moderate  quantity, 
about  ninety  per  cent  is  consumed  in  the  organism  (Strassmann).  The  observations  of  Rose- 
mann  have  shown  that  alcohol  may  be  substituted  isodynamically  for  fats  and  carbohydrates, 
when  it  acts  as  an  alimentary  substance.  These  observations,  however,  are  not  opposed  to 
the  fact  that  alcohol  in  large  doses  acts  as  a  poison  and  that  its  use,  in  perfect  health,  is 
unnecessary  and  likely  to  be  deleterious. 


154  ALIMENTATION 

and  is  not  followed  by  reaction  or  unpleasant  after-effects.  Habitual 
use  renders  coffee  almost  a  necessity,  even  in  those  who  are  otherwise 
well  nourished  and  subjected  to  no  extraordinary  mental  or  bodily 
strain.  Taken  in  excessive  quantity,  or  in  those  unaccustomed  to  its 
use,  particularly  at  night,  it  may  produce  persistent  wakefulness.  These 
effects  are  so  well  known  that  it  is  often  taken  for  the  purpose  of 
preventing  sleep. 

It  has  been  shown  that  the  use  of  coffee  permits  a  reduction  in  the 
quantity  of  food,  in  workingmen  especially,  much  below  the  standard 
that  would  otherwise  be  necessary  to  maintain  the  organism  in  proper 
condition.  In  the  observations  of  De  Gasparin  on  the  regimen  of  the 
Belgian  miners,  it  was  found  that  the  addition  of  a  quantity  of  coffee  to 
the  daily  ration  enabled  them  to  perform  their  arduous  labors  on  a  diet 
which  was  even  below  that  found  necessary  in  prisons  where  this  article 
was  not  used.  Experiments  have  shown,  also,  that  coffee  diminishes 
the  absolute  quantity  of  urea  discharged  by  the  kidneys.  In  this  respect, 
so  far  as  has  been  ascertained,  the  action  of  coffee  is  like  that  of  alco- 
hol; and  it  may  reasonably  be  supposed  to  retard  katabolism,  with  the 
important  difference  that  it  is  followed  by  no  unfavorable  after-effects 
and  can  be  used  in  moderation  for  an  indefinite  time  with  advantage. 

Coffee  usually  is  roasted  before  an  infusion  is  made.  During  this 
process,  the  grains  are  considerably  swollen,  but  they  lose  sixteen  or 
seventeen  per  cent  in  weight.  A  peculiar  aromatic  substance  also  is 
developed  by  roasting.  If  torrefaction  is  pushed  too  far,  much  of 
the  agreeable  flavor  of  coffee  is  lost,  and  an  acrid  empyreumatic  sub- 
stance is  produced  that  is  disagreeable  to  the  taste. 

Tea.  —  An  infusion  of  the  dried  and  prepared  leaves  of  the  tea-plant 
is  perhaps  as  common  a  beverage  as  coffee ;  and  taking  into  considera- 
tion its  large  consumption  in  China  and  Japan,  it  actually  is  used  by  a 
greater  number  of  persons.  Its  effects  on  the  system  are  similar  to 
those  of  coffee,  but  they  usually  are  not  so  marked.  Ordinary  tea, 
taken  in  moderate  quantity,  like  coffee,  relieves  fatigue  and  increases 
mental  activity,  but  does  not  usually  produce  such  persistent  wake- 
fulness. 

Both  tea  and  coffee  contain  peculiar  organic  substances.  The  active 
principle  of  tea  is  called  thein,and  the  active  principle  of  coffee,  caffein. 
As  they  are  supposed  to  be  particularly  efficient  in  producing  the  pecul- 
iar effects  on  the  nervous  system  characteristic  of  both  tea  and  coffee, 
there  is  good  reason  to  suppose  that  they  are  nearly  identical  in  their 
physiological  action.  Analyses  have  shown  that  thein,  or  caffein 
(CgHj^N^Oa  +  H2O),  exists  in  greater  proportion  in  tea  than  in  coffee ; 
but  as  a  rule,  a  greater  quantity  of  soluble  matter  is  extracted  in  the 


NECESSARY    QUANTITY   AND    VARIETY    OF   FOOD  155 

preparation  of  coffee,  which  may  account  for  its  more  marked  effects  on 
the  system. 

Chocolate.  —  Chocolate  is  made  from  the  seeds  of  the  cocoa-tree, 
roasted,  deprived  of  their  husks  and  ground  with  warm  rollers  into  a 
pasty  mass  with  sugar,  flavoring  substances  being  sometimes  added. 
It  is  then  made  into  cakes,  cut  into  small  pieces  or  scraped  to  a  powder, 
and  boiled  with  milk  or  milk  and  water,  when  it  forms  a  thick,  gruel- 
like drink,  which  is  highly  nutritive  and  has  some  of  the  exhilarating 
properties  of  coffee  or  tea.  Beside  containing  a  large  proportion  of 
nitrogenous  matter  resembling  albumin,  the  cocoa-seed  is  rich  in  fatty 
matter  and  contains  a  peculiar  substance,  theobromin  (C7HgN403),  analo- 
gous to  caffein  and  thein,  which  is  supposed  to  possess  similar  physio- 
logical properties. 

Condiments  and  Flavoring  Articles. — The  refinements  of  cookery 
involve  the  use  of  many  articles  that  can  not  be  classed  as  alimentary 
substances.  Pepper,  capsicum,  vinegar,  mustard,  spices  and  other 
articles  of  this  class,  so  commonly  used,  have  no  decided  influence  on 
nutrition,  except  in  so  far  as  they  promote  the  secretion  of  the  digestive 
juices.  Common  salt,  however,  is  very  important,  and  this  has  been 
considered  in  connection  with  inorganic  alimentary  substances.  The 
various  flavoring  seeds  and  leaves,  truifles,  mushrooms  etc.  have  no 
physiological  importance  except  as  they  render  articles  of  food  more 
palatable. 

Quantity  and  Variety  of  Food  necessary  to  Nutrition.  —  The  inferior 
animals,  especially  those  not  subjected  to  the  influence  of  man,  regu- 
late by  instinct  the  quantity  and  kind  of  food.  The  same  is  true  of 
man  during  the  earliest  periods  of  his  existence  ;  but  later  in  life,  the  diet 
is  variously  modified  by  taste,  habit,  climate  and  what  may  be  termed 
artificial  wants.  It  is  usually  a  safe  rule  to  follow  the  appetite  in  re- 
gard to  quantity,  and  the  tastes,  when  they  are  not  manifestly  vitiated 
or  morbid,  in  regard  to  variety.  The  cravings  of  nature  indicate  when 
to  change  the  form  in  which  nutriment  is  taken ;  and  that  a  sufficient 
quantity  has  been  taken  is  manifested  by  a  sense,  not  exactly  of  satiety, 
but  of  evident  satisfaction  of  the  demands  of  the  system.  During  early 
life,  the  supply  must  be  a  little  in  excess  of  the  actual  loss,  in  order  to 
furnish  materials  for  growth  ;  during  the  later  periods,  the  quantity  of 
nitrogenous  matter  assimilated  is  somewhat  less  than  the  loss ;  but  in 
adult  age,  the  system  is  maintained  at  a  tolerably  definite  standard  by 
the  assimilation  of  matter  about  equal  in  quantity  to  that  discharged  in 
the  form  of  excretions. 

Although  the  loss  of  substance  by  katabolism  creates  and  regulates 
the  demand  for  food,  it  is  an  important  fact,  never  to  be  lost  sight  of. 


136  ALIMENTATION 

that  the  supply  of  food  has  a  great  influence  on  the  quantity  of  the 
excretions.  An  illustration  of  this  is  the  influence  of  food  on  the  ex- 
halation of  carbon  dioxide ;  and  this  is  but  an  example  of  what  takes 
place  in  regard  to  other  excretions.  The  quantity  of  the  excretions  is 
even  more  strikingly  modified  by  exercise,  which,  within  physiological 
limits,  increases  the  vigor  of  the  system,  provided  the  increased  quantity 
of  food  required  be  supplied. 

TJie  Daily  Ration.  —  The  daily  loss  of  substance  which  must  be 
supplied  by  matters  introduced  from  without  is  considerable.  A  large 
portion  of  this  discharge  takes  place  by  the  lungs,  and  a  consideration 
of  the  mode  of  introduction  of  gases  to  supply  part  of  this  waste  belongs 
to  the  subject  of  respiration.  The  most  abundant  discharge  which  is 
compensated  by  absorption  from  the  alimentary  canal  is  that  of  water 
both  in  a  liquid  and  vaporous  condition.  The  entire  quantity  of  water 
ehminated  daily  has  been  estimated  at  about  four  and  a  half  pounds 
(2041  grams),  and  it  is  probable  that  about  the  same  quantity  is  intro- 
duced in  the  form  of  drink  and  as  a  constituent  of  the  so-called  solid 
articles  of  food.  The  quantity  taken  in  the  form  of  drink  varies  with 
the  character  of  the  food.  When  the  solid  articles  contain  a  large 
proportion  of  water,  the  quantity  of  drink  may  be  diminished ;  and  it 
is  possible,  by  taking  a  large  quantity  of  the  watery  vegetables,  to  exist 
entirely  without  drink.  There  is  no  article  more  frequently  taken  than 
water,  merely  as  a  matter  of  habit,  any  excess  being  readily  removed 
by  the  kidneys,  skin  and  lungs.  Dalton  estimates  the  daily  quantity 
necessary  for  a  full-grown  healthy  male,  at  fifty-four  fluidounces  (1530 
grams),  or  3.38  pounds. 

The  quantity  of  solid  food  necessary  to  nutrition  is  shown  by  esti- 
mating the  soUd  matter  in  the  excretions;  and  the  facts  thus  ascer- 
tained correspond  closely  with  the  quantity  of  material  which  the 
system  has  been  found  to  actually  demand.  The  following  are  the 
estimated  daily  losses  of  the  organism  :  — 

Carbon   (or  its  j  Respiration,  8.825  ounces  (250  grams))  ^^^^^  ^^^^^^  ^^^^  grams). 

equivalent).    /Excretions,    2. 116  ounces   (  60  grams)  i 
Nitrogenous  substances   (containing  308.64  grains,  or 

20  grams  of  nitrogen) 4-586  ounces  (130  grams). 

15.527  ounces  (440  grams). 

From  this  it  is  estimated  that  the  normal  ration,  supposing  the  food 
to  consist  of  lean  meat  and  bread,  is  as  follows :  — 

Bread 35.300  ounces  (1000  grams). 

Meat  (without  bones) 10.088  ounces    (286  grams). 

45.388  ounces  (1286  grams). 


THE    DAILY   RATION  1 57 

NITROGENOUS   SUBSTANCES  CARBON 

Bread  contains  .     2.469  ounces    (70.00  grams)  and  10.582  ounces  (300.00  grams)  . 

Meat  contains  .         .     2.125  ounces     (60.26  grams)  and    1. 109  ounces     (31.46  grams). 

4.594  ounces  (130.26  grams)  and  11. 691  ounces  (331.46  grams). 

This  daily  ration,  which  is  purely  theoretical,  is  shown  by  actual 
observation  to  be  nearly  correct.  Dalton  says  :  "  According  to  our 
own  observations,  a  man  in  full  health,  taking  active  exercise  in  the 
open  air,  and  restricted  to  a  diet  of  bread,  fresh  meat,  and  butter,  with 
water  and  coffee  for  drink,  consumes  the  following  quantities  per  day :  — • 

Meat  ........  453  grams,  or  about   16  ounces. 

Bread  .......  540  grams,  or  about   19  ounces. 

Butter  or  fat 100  grams,  or  about  3.5  ounces. 

Water         .......  1530  grams,  or  about  54  ounces." 

Bearing  in  mind  variations  in  the  nutritive  demands  of  the  system 
in  different  persons,  it  may  be  stated,  in  general  terms,  that  in  an 
adult  male,  ten  to  twelve  ounces  (282  to  340  grams)  of  carbon  and 
four  to  five  ounces  (113  to  142  grams)  of  nitrogenous  matters,  estimated 
dry,  are  discharged  from  the  organism  and  must  be  replaced  by  the 
ingesta  ;  and  this  demands  a  daily  consumption  of  between  two  and 
three  pounds  (907  and  1361  grams)  of  solid  food,  the  quantity  of  food 
depending,  of  course,  greatly  on  its  proportion  of  nutritive  constituents. 

It  is  true  that  the  daily  ration  frequently  is  diminished  consider- 
ably below  the  physiological  standard  in  charitable  institutions,  prisons 
and  elsewhere ;  but  when  there  is  complete  inactivity  of  body  and 
mind,  this  produces  no  other  effect  than  that  of  slightly  diminishing  the 
weight  and  strength.  The  system  then  becomes  reduced  without  any 
actual  disease,  and  there  is  simply  a  diminished  capacity  for  labor ; 
but  in  the  alimentation  of  large  bodies  of  men  subjected  to  exposure 
and  frequently  called  upon  to  perform  severe  labor,  the  question  of 
food  is  of  great  importance,  and  the  men  collectively  are  like  a  machine 
in  which  a  certain  quantity  of  materia]  must  be  furnished  in  order  to 
produce  the  required  amount  of  force.  This  important  fact  is  strikingly 
exemplified  in  armies  ;  and  the  history  of  the  world  presents  few  ex- 
amples of  warlike  operations  in  which  the  efficiency  of  the  men  has  not 
been  impaired  by  insufficient  food. 

The  influence  of  diet  on  the  capacity  for  labor  was  well  illustrated 
by  a  comparison  of  the  amount  of  work  accomplished  by  English  and 
French  laborers,  in  1841,  on  a  railway  from  Paris  to  Rouen.  The 
French  laborers  engaged  on  this  work  were  able  at  first  to  perform 
only  about  two-thirds  of  the  labor  accomplished  by  the  English.  It 
was  suspected  that  this  was  due  to  the  more  substantial  diet  of  the 


158  ALIMENTATION 

English,  which  proved  to  be  the  fact ;  for  when  the  French  laborers 
were  subjected  to  a  similar  regimen,  they  were  able  to  accompHsh  an 
equal  amount  of  work.  In  all  observations  of  this  kind,  it  has  been 
shown  that  an  animal  diet  is  more  favorable  to  the  development  of  the 
physical  forces  than  one  consisting  mainly  of  vegetables. 

It  is  commonly  acknowledged  that  the  consumption  of  all  kinds  of 
food  is  greater  in  cold  than  in  warm  chmates,  and  almost  every  one  has 
experienced  in  his  own  person  a  considerable  difference  in  the  appetite 
at  different  seasons  of  the  year.  Travellers'  accounts  of  the  quantity  of 
food  taken  by  the  inhabitants  of  the  frigid  zone  seem  almost  incredible. 
They  speak  of  men  consuming  more  than  a  hundred  pounds  (45.36  kilo- 
grams) of  meat  in  a  day ;  and  a  Russian  admiral,  Saritcheff,  gave  an 
instance  of  a  man  who,  in  his  presence,  ate  at  a  single  meal  a  mess  of 
boiled  rice  and  butter  weighing  twenty-eight  pounds  (12.7  kilograms). 
Although  it  is  difficult  to  regard  these  statements  with  entire  confidence, 
the  common  opinion  that  the  appetite  is  greater  in  cold  than  in  warm 
climates  undoubtedly  is  well  founded.  Hayes  stated,  from  his  personal 
observation,  that  the  daily  ration  of  the  Esquimaux  is  twelve  to  fifteen 
pounds  (5.443  to  6.804  kilograms)  of  meat,  about  one-third  of  which  is 
fat.  On  one  occasion  he  saw  an  Esquimau  consume  ten  pounds  (4.536 
kilograms)  of  walrus-flesh  and  blubber  at  a  single  meal,  which  lasted, 
however,  several  hours.  The  continued  low  temperature  he  found  had 
a  remarkable  effect  on  the  tastes  of  his  own  party.  With  the  thermom- 
eter ranging  from  —60°  to  —70°  Fahr.  (-51°  to  —57°  C),  there  was 
a  persistent  craving  for  a  strong  animal  diet,  particularly  fatty  substances. 
Some  members  of  the  party  were  in  the  habit  of  drinking  the  contents 
of  the  oil-kettle  with  evident  relish. 

Necessity  of  a  Varied  Diet.  —  In  considering  the  nutritive  value  of 
the  various  alimentary  substances,  the  fact  that  no  single  article  is 
capable  of  supplying  all  the  material  for  the  regeneration  of  the  organ- 
ism has  frequently  been  mentioned.  The  normal  appetite  —  which  is 
the  best  guide  as  regards  the  quantity  and  the  selection  of  food  —  indi- 
cates that  a  varied  diet  is  necessary  to  proper  nutrition.  This  fact  is 
exemplified  in  a  marked  degree  in  long  voyages  and  in  the  alimentation 
of  armies,  when,  from  necessity  or  otherwise,  the  necessary  variety  of 
aliment  is  not  presented.  Analytical  chemistry  fails  to  show  why  this 
change  in  ahmentation  is  necessary  or  in  what  the  deficiency  in  a  single 
kind  of  diet  consists;  but  it  is  nevertheless  true  that  after  the  organic 
constituents  of  the  organism  have  appropriated  the  nutritious  elements 
of  particular  kinds  of  food  for  a  certain  time,  they  lose  the  power  of 
effecting  the  changes  necessary  to  proper  nutrition.  This  fact  is  par- 
ticularly well  marked  when  the  diet  consists  in  great  part  of  salted  meats, 


MEATS  159 

although  it  sometimes  occurs  when  a  single  kind  of  fresh  meat  is  con- 
stantly used.  After  long  confinement  to  a  diet  restricted  as  regards 
variety,  a  supply  of  other  matters,  such  as  fresh  vegetables,  the  organic 
acids,  and  articles  which  are  usually  called  antiscorbutics,  becomes 
indispensable ;  otherwise,  the  modifications  in  nutrition  and  in  the  con- 
stitution of  the  blood  incident  to  the  scorbutic  condition  are  almost  always 
developed. 

It  is  thus  apparent  that  adequate  quantity  and  proper  quality  of  food 
are  not  all  that  is  required  in  alimentation ;  and  those  who  have  the 
responsibihty  of  regulating  the  diet  of  large  numbers  of  persons  must 
bear  in  mind  the  fact  that  the  organism  demands  considerable  variety. 
Fresh  vegetables,  fruits  etc.  should  be  taken  at  the  proper  seasons.  It 
is  almost  always  found,  when  there  is  of  necessity  some  sameness  in  diet, 
that  there  is  a  craving  for  particular  articles,  and  these,  if  possible,  should 
be  supplied.  This  was  frequently  exemplified  in  the  civil  war.  At 
times  when  the  diet  was  necessarily  somewhat  monotonous,  there  was 
an  almost  universal  craving  for  onions  and  raw  potatoes,  which  were 
found  by  army-surgeons  to  be  excellent  antiscorbutics. 

With  those  who  supply  their  own  food,  the  question  of  variety  in 
diet  usually  regulates  itself ;  and  in  institutions,  it  is  a  good  rule  to 
follow  as  far  as  possible  the  reasonable  tastes  of  the  inmates.  In  indi- 
viduals, particularly  females,  it  is  not  uncommon  to  observe  marked  dis- 
orders in  nutrition  attributable  to  want  of  variety  in  the  diet  as  well  as 
to  an  insufficient  quantity  of  food  as  a  matter  of  education  or  habit. 

A  full  consideration  of  the  varieties  of  food  and  of  the  different 
methods  employed  in  its  preparation  belongs  properly  to  special  works 
on  dietetics.  Among  the  ordinary  articles  of  diet,  the  most  important 
are  meats,  bread,  potatoes,  milk,  butter  and  eggs ;  and  it  is  necessary 
only  to  treat  of  these  very  briefly. 

Meats.  —  Among  the  various  kinds  of  muscular  tissue,  beef  has  been 
found  to  possess  the  greatest  nutritive  value.  Other  varieties  of  flesh, 
even  that  of  birds,  fishes  and  animals  in  a  wild  state,  do  not  present  an 
appreciable  difference,  so  far  as  can  be  ascertained  by  chemical  analysis  ; 
but  when  taken  daily  for  a  long  time,  they  become  distasteful,  the  appe- 
tite fails  and  the  system  seems  to  demand  a  change.  The  flesh  of  car- 
nivorous animals  is  rarely  used  as  food ;  and  animals  that  eat  animal  as 
well  as  vegetable  food,  such  as  pigs  or  ducks,  acquire  a  disagreeable 
flavor  when  they  are  not  fed  on  vegetables.  Soups,  broths,  and  most  of 
the  liquid  extracts  of  meat  really  possess  but  little  nutritive  value  and 
they  can  not  replace  the  ordinary  cooked  meats.  The  following  is  the 
composition  of  roasted  meat,  no  dripping  being  lost,  according  to  the 
analysis  of  Ranke,  quoted  by  Pavy  :  — 


i6o 


ALIMENTATION 


Nitrogenous  matters      ..........     27.60 

Fat 15.45 

Saline  matters       ...........       2.95 

Water 54.00 

100.00 

Bread.  —  Bread  presents  a  considerable  variety  of  alimentary  con- 
stituents and  is  a  very  important  article  of  diet.  The  constituents  of 
flour  undergo  peculiar  changes  in  panification,  which  give  to  good  bread 
its  characteristic  flavor.  Bread,  especially  coarse  brown  bread, 'as  a 
single  article  of  food,  is  capable  of  sustaining  life  for  a  long  time.  It 
contains  a  large  proportion  of  starch,  but  its  important  nitrogenous 
constituent  is  gluten,  which  is  not  a  simple  substance  but  contains  vege- 
table fibrin,  vegetable  albumins,  a  peculiar  substance  soluble  in  alcohol, 
called  glutin,  with  fatty  and  inorganic  matters.  The  following  is  the 
composition  of  bread  (Letheby):  — 


Nitrogenous  matters 
Carbohydrates  (chiefly  starch) 
Fatty  matters     .         .         .         . 
Saline  matters  .         .         .         . 
Water 


8.1 

51.0 
1.6 
2-3 

37-0 


Potatoes.  —  Potatoes  are  very  useful  as  an  article  of  diet,  especially 
on  account  of  the  agreeable  form  in  which  starchy  matter  is  presented ; 
but  they  contain  a  small  proportion  of  nitrogenous  matter  and  do  not 
possess  so  much  nutritive  value  as  bread.  They  are  selected  from  the 
vegetable  foods  for  description  because  they  are  almost  universally  used 
in  civilized  countries  throughout  the  year.  They  usually  are  thoroughly 
cooked,  but  the  raw  potato  is  a  valuable  antiscorbutic.  The  following 
is  the  composition  of  potato  (Letheby):  — 


Nitrogenous  matters 

Starchy  matters 

Sugar 

Fat    . 

Saline  matters  . 

Water 


2.1 
18.8 

3-2 

0.2 

0.7 

75-0 

1 00.0 


Milk.  —  Milk,  and  articles  prepared  from  milk,  such  as  butter  and 
cheese,  are  important  articles  of  food.  In  the  treatment  of  disease, 
milk  frequently  is  used  as  a  single  article  of  diet.  On  account  of  the 
variety  of  alimentary  matters  which  it  contains,  including  a  great  num- 
ber of  inorganic  salts  and  even  a  small  quantity  of  iron,  milk  will  meet 
all  the  nutritive  demands,  probably  for  an  indefinite  time.     It  is  largely 


EGGS  l6l 

used  in  the  preparation  of  other  articles  of  food  by  cooTcing.  Pure 
butter,  which  represents  the  fatty  constituents  of  milk,  contains,  in  lOO 
parts,  30  parts  of  olein,  68  parts  of  palmitin,  and  2  parts  of  other  fats 
peculiar  to  milk.  The  following  is  the  composition  of  cow's  milk 
(Letheby) :  — 

Nitrogenous  matters  .         .         . 4-i 

Fatty  matters °         •         •       3-9 

Sugar 5-2 

Inorganic  matters 0.8 

Water 86.0 

100.0 

In  connection  with  the  composition  of  human  milk,  to  be  given 
farther  on,  the  great  variety  of  its  constituents  will  be  more  fully 
considered. 

E£-£:s.  —  As  regards  nutrition,  the  analogy  between  eggs  and  milk 
is  evident  when  it  is  remembered  that  the  constituents  of  eggs  furnish 
materials  for  the  growth  of  the  chick,  to  which  must  be  added  certain 
saline  matters  absorbed  from  the  shell  during  the  process  of  incubation. 
Among  the  inorganic  constituents  of  eggs,  there  is  always  a  small 
quantity  of  iron.  The  following  is  the  composition  of  the  entire 
contents  of  the  egg  (Pavy)  :  — 

Nitrogenous  matters       ..........     14.0 

Fatty  matters  .  .         .  .         .         .         «         .         .         .  .10.5 

Inorganic  matters  .         ,         .         .         .         .         .         .         .         .1.5 

Water   .         .         .       • 74.0 

100. o 

A  number  of  different  nitrogenous  and  fatty  matters,  a  small  quantity 
of  saccharine  matter,  as  well  as  a  great  variety  of  inorganic  salts,  exist  in 
eggs. 

The  physiological  effects  of  a  diet  restricted  to  a  single  constituent 
of  food  or  to  a  few  articles  have  been  closely  studied  both  in  the  human 
subject  and  in  the  inferior  animals.  Animals  subjected  to  a  diet  com- 
posed exclusively  of  non-nitrogenous  matters  die  in  a  short  time  with 
symptoms  of  inanition.  The  same  result  follows  when  dogs  are  con- 
fined to  white  bread  and  water ;  but  these  animals  live  very  well  on  the 
mihtary  brown  bread,  as  this  contains  a  greater  variety  of  alimentary  mat- 
ters (Magendie).  Facts  of  this  nature  were  multiplied  by  the  "gelatin 
commission,"  and  the  experiments  were  extended  to  nitrogenous  sub- 
stances and  articles  containing  a  considerable  variety  of  alimentary 
matters.  In  these  experiments,  it  was  shown  that  dogs  could  not  live 
on  a  diet  of  pure  myosin,  the  appetite  entirely  failing  at  the  forty-third 
to  the  fifty-fifth  day.     They  were  nourished  perfectly  well  by  gluten, 


1 62  ALIMENTATION 

which  is  composed  of  a  number  of  different  alimentary  substances 
Among  the  conclusions  arrived  at  by  this  commission,  which  bear  par- 
ticularly on  the  questions  under  consideration,  were  the  following :  — 

"  Gelatin,  albumin,  fibrin,  talcen  separately,  do  not  nourish  animals 
except  for  a  very  limited  period  and  in  a  very  incomplete  manner.  In 
ofeneral,  these  substances  soon  excite  an  insurmountable  disgust,  to  the 
point  that  animals  prefer  to  die  of  hunger  rather  than  touch  them. 

"  The  same  substances  artificially  combined  and  rendered  agreeably 
sapid  by  seasoning  are  accepted  more  readily  and  longer  than  if  they 
were  isolated,  but  ultimately  they  have  no  better  influence  on  nutrition, 
for  animals  that  take  them,  even  in  considerable  quantity,  finally  die 
with  all  the  signs  of  complete  inanition. 

"  Muscular  flesh,  in  which  gelatin,  albumin  and  fibrin  are  united 
according  to  the  laws  of  organic  nature,  and  when  they  are  associated 
with  other  matters,  such  as  fat,  salts  etc.,  suffices,  even  in  very  small 
quantity,  for  complete  and  prolonged  nutrition  "  (Paris,  1841). 

In  1769  Dr.  Stark,  a  young  English  physiologist,  fell  a  victim  at  an 
early  age  to  experiments  on  his  own  person  on  the  physiological  effects 
of  different  kinds  of  food.  He  lived  for  forty-four  days  on  bread  and 
water,  for  twenty-nine  days  on  bread,  sugar  and  water,  and  for  twenty- 
four  days  on  bread,  water  and  olive-oil.  He  finally  died  from  the  effects 
of  his  experiments. 


CHAPTER   VII 
MASTICATION,    INSALIVATIOX    AND    DEGLUTITION 

Physiological  anatomy  of  the  organs  of  mastication  —  The  teeth  —  Enamel  of  the  teeth  — 
Dentin  —  Cement  —  Pulp-cavity — Superior  maxillary  bones  —  Inferior  maxilla  —  Tem- 
poro-maxillary  articulation  —  Muscles  of  mastication —  Saliva  —  Parotid  saliva  —  Sub- 
maxillary saliva  —  Sublingual  saliva  —  Secretions  from  the  smaller  glands  of  the  mouth, 
tongue  and  pharynx  —  Mixed  saliva  —  General  properties  and  composition  of  the  saliva  — 
Uses  of  the  saliva  —  Deglutition — Mechanism  of  deglutition  —  Protection  of  the  poste- 
rior nares  during  the  second  period  of  deglutition — Protection  of  the  opening  of  the 
larynx  and  uses  of  the  epiglottis  in  deglutition. 

Inorganic  alimentary  substances,  with  few  exceptions,  are  introduced 
in  the  form  in  which  they  exist  in  the  blood  and  .require  no  preparation 
or  change  before  they  are  absorbed ;  but  organic  nitrogenous  substances 
are  always  associated  with  more  or  less  matter  possessing  no  nutritive 
properties,  from  which  they  must  be  separated ;  and  even  when  pure, 
they  undergo  certain  changes  before  they  are  taken  up  by  the  blood. 
The  non-nitrogenous  matters  also  undergo  changes  in  constitution  or 
in  form  preparatory  to  absorption. 

Mastication 

In  order  that  digestion  may  take  place  in  a  perfectly  natural  manner, 
it  is  necessary  that  the  food,  as  it  is  received  into  the  stomach,  should 
be  so  far  comminuted  and  incorporated  with  the  liquids  of  the  mouth 
as  to  be  readily  acted  on  by  the  gastric  juice;  otherwise,  gastric  diges- 
tion is  prolonged  and  difficult. 

Physiological  Ajiatomy  of  the  Organs  of  Mastication.  — In  the  adult, 
each  jaw  is  provided  with  sixteen  teeth,  all  being  about  equally 
developed.  The  canines,  so  largely  developed  in  the  carnivora  but 
rudimentary  in  the  herbivora,  and  the  incisors  and  molars,  so  fully 
developed  in  the  herbivora,  are,  in  man,  of  nearly  the  same  length. 
Each  tooth  presents  for  anatomical  description  a  crown,  a  neck  and  a 
root.  The  crown  is  the  portion  not  covered  by  the  gums ;  the  root  is 
the  portion  embedded  in  the  alveolar  cavities  of  the  maxillary  bones  ; 
and  the  neck  is  the  portion,  sometimes  slightly  constricted,  between  the 
crown  and  the  root  and  covered  by  the  edge  of  the  gum.  Each  tooth 
presents  on  section  several  distinct  structures. 

163 


164 


DIGESTION 


Enamel  of  the  Teeth.  —  The  crown  is  covered  with  the  enamel, 
which  is  by  far  the  hardest  structure  in  the  economy.  This  is  white 
and  glistening  and  is  thickest  on  the  lower  portion  of  the  tooth,  espe- 
cially over  the  surfaces  which,  from  being  opposed  to  each  other  on 
either  jaw,  are  most  exposed  to  wear.  It  here  exists  in  several  con- 
centric layers.     The  incrustation  of  enamel  gradually  becomes  thinner 

toward  the  neck,  where  it  ceases.  The 
enamel  is  made  up  of  pentagonal  or 
hexagonal  rods,  one  end  resting  on  the 
subjacent  structure,  and  the  other,  when 
there  exists  but  a  single  layer  of  enamel, 
terminating  just  beneath  the  cuticle  of 
the  teeth. 

The  exposed  surfaces  of   the  teeth 
are  still  further  protected  by  a  mem- 


brane, 3  oioo  to  15^  00  of  an  inch  (0.8  to 
1.7  /a)  in  thickness,  closely  adherent  to 
the  enamel,  called  the  cuticle  of  the 
enamel  (Nasmyth's  membrane).  The 
cuticle  presents  a  strong  resistance  to 
reagents  and  is  useful  in  protecting  the 
teeth  from  the  action  of  acids  that  may 
find  their  way  into  the  mouth. 

Dentin.  —  The  largest  portion  of 
the  teeth  is  composed  of  dentin.  In 
many  respects,  particularly  in  its  com- 
position, this  resembles  bone ;  but  it  is 
much  harder  and  does  not  present  the 
lacunae  and  canaliculi,  which  are  charac- 
teristic of  true  osseous  structure.  The 
dentin  bounds  and  encloses  the  central 
cavity  of  the  tooth,  extending  in  the 
crown  to  the  enamel,  and  in  the  root,  to 
the  cement.  It  is  formed  of  a  hopio- 
geneous  fundamental  substance,  which 
is  penetrated  by  a  large  number  of  canals  radiating  from  the  pulp-cavity 
toward  the  exterior.  These  are  called  the  dentinal  tubules  or  canals. 
They  are  2  5^o"o  ^^  12000"  of  an  inch  (i  to  2  yu.)  in  diameter,  with  walls 
of  a  thickness  a  little  less  than  their  calibre.  Their  course  is  slightly 
wavy  or  spiral.  Beginning  at  the  pulp-cavity,  into  which  these  canals 
open,  they  are  found  to  branch  and  occasionally  anastomose,  their  com- 
munications and  branches  becoming  more  frequent  as  they  approach 


Fig.  34.  —  Longitudinal  section  of  a 
molar  tooth  of  man,  X  4  —  reduced  one- 
half  (Sobotta). 

This  figure  gives  a  general  view  of 
the  structure  of  the  tooth.  The  pulp- 
cavity  is  not  cut  its  whole  length  in  the 
two  roots  seen  in  the  section.  We  recog- 
nize tiie  three  main  elements  of  the  tooth 
—  dentin,  enamel  and  cementum  —  and 
their  division  into  crown  and  root.  On 
account  of  the  low  magnification,  the  in- 
terglobular spaces  appear  only  as  a  dark 
zone  on  the  surface  of  the  dentin. 
C,  cementum ;  D,  dentin ;  P,  pulp- 
cavity;    S,  enamel. 


THE   TEETH  165 

the  external  surface  of  the  tooth.  The  canals  of  largest  diameter  are 
found  next  the  pulp-cavity,  and  they  become  smaller  as  they  branch. 
The  structure  forming  the  walls  of  these  tubules  is  somewhat  denser 
than  the  intermediate  portion,  which  is  sometimes  called  the  intertubu- 
lar  substance  of  the  dentin  ;  but  in  some  portions  of  the  tooth,  the 
tubules  are  so  abundant  that  their  walls  touch  each  other.  Near  the 
origin  and  near  the  peripheral  ends  of  the  dentinal  tubules,  are  some- 
times found  solid  globular  masses  of  dentin,  called  dentin-globules, 
which  irregularly  bound  triangular  or  stellate  cavities  of  variable  size 
(interglobular  spaces).  Sometimes  these  cavities  form  regular  zones 
near  the  peripheral  ends  of  the  tubules.  The  dentin  is  sometimes 
marked  by  concentric  lines,  indicating  a  lamellated  arrangement.  In  the 
natural  condition,  the  dentinal  tubules  are  filled  with  a  clear  liquid,  which 
penetrates  from  the  vascular  structures  contained  in  the  pulp-cavity. 

Cement.  —  Covering  the  dentin  of  the  root,  is  a  thin  layer  of  true 
bony  structure,  called  cement,  or  crusta  petrosa.  This  is  thickest  at 
the  summit  and  at  the  deeper  portions  of  the  root,  where  it  sometimes  is 
lamellated,  and  it  becomes  thinner  near  the  neck.  It  finally  becomes 
continuous  with  the  enamel  of  the  crown,  so  that  the  dentin  is  every- 
where completely  covered.  The  roots  of  the  teeth,  covered  with  the 
cement,  are  firmly  embedded  in  the  alveolar  cavities  of  the  jaws.  The 
alveoli  are  lined  with  what  is  called  dental  periosteum,  which  is  reflected 
over  the  roots  as  far  as  the  neck,  when  it  becomes  continuous  with  the 
fibrous  tissue  of  the  gums. 

Pulp-cavity.  —  In  the  interior  of  each  tooth,  extending  from  the 
apex  of  the  root  or  roots  into  the  crown,  is  the  pulp-cavity,  which  con- 
tains minute  bloodvessels  and  nervous  filaments,  held  together  by 
longitudinal  fibres  of  connective  tissue.  This  is  the  only  portion  of  the 
tooth  endowed  with  sensibility.  The  bloodvessels  and  nerves  penetrate 
by  a  foramen  at  the  extremity  of  each  root. 

The  dentin  and  enamel  of  the  teeth  must  be  regarded  as  perfected 
structures ;  for  when  the  permanent  teeth  are  lost,  they  are  not  repro- 
duced ;  and  when  these  parts  are  invaded  by  wear  or  by  decay,  they  are 
not  restored. 

The  thirty-two  permanent  teeth  are  classified  as  follows  :  — 

1.  Eight  incisors,  four  in  each  jaw,  called  the  central  and  lateral 
incisors. 

2.  Four  canines,  or  cuspidati,  two  in  each  jaw,  just  back  of  the 
incisors.  The  upper  canines  are  sometimes  called  the  eye-teeth,  and 
the  lower  canines,  the  stomach-teeth. 

3.  Eight  bicuspids  —  the  small,  or  false  molars  —  just  back  of  the 
canines;  four  in  each  jaw. 


l66  DIGESTION 

4.  Twelve  molars,  or  multicuspid,  situated  just  back  of  the  bicuspid  ; 
six  in  each  jaw. 

The  incisors  are  wedge-shaped,  flattened  antero-posteriorly,  and 
bevelled  at  the  expense  of  the  posterior  face,  giving  them  a  sharp 
cutting  edge.  Each  incisor  has  a  single  root.  The  permanent  incisors 
make  their  appearance  between  the  seventh  and  the  eighth  years. 

The  canines  are  more  conical  and  pointed  than  the  incisors,  and 
have  longer  and  larger  roots,  especially  those  in  the  upper  jaw.  Their 
roots  are  single.  The  permanent  canines  make  their  appearance 
between  the  eleventh  and  the  twelfth  years. 

The  bicuspid  teeth  are  shorter  and  thicker  than  the  canines.  Their 
opposed  surfaces  are  rather  broad  and  are  marked  by  two  eminences. 
The  upper  bicuspids  are  larger  than  the  lower.  The  roots  are  single, 
but  in  the  upper  jaw  they  are  slightly  bifurcated  at  their  extremities. 
The  permanent  bicuspids  make  their  appearance  between  the  ninth  and 
the  tenth  years. 

The  molar  teeth,  called  respectively  —  counting  from  before  back- 
ward—  the  first,  second  and  third  molars,  are  the  largest  of  all.  Their 
form  is  that  of  a  cube,  rounded  laterally  and  provided  with  four  or  five 
eminences  on  their  opposed  surfaces.  The  first  molars  are  the  largest. 
They  usually  have  three  roots  in  the  upper  jaw  and  two  in  the  lower, 
although  they  sometimes  have  four  or  even  five  roots.  The  second 
molars  are  but  little  smaller  than  the  first  and  resemble  them  in  nearly 
every  particular.  The  third  molars,  called  the  wisdom-teeth,  are  much 
smaller  than  the  others  and  are  by  no  means  so  useful  in  mastication. 
The  first  molars  are  the  first  of  the  permanent  teeth,  making  their 
appearance  between  the  sixth  and  the  seventh  years.  The  second 
molars  appear  between  the  twelfth  and  the  thirteenth  years ;  and  the 
third  molars,  between  the  seventeenth  and  the  twenty-first  years,  and 
sometimes  even  much  later.  In  some  instances  the  third  molars  are 
never  developed. 

The  upper  jaw  has  ordinarily  a  somewhat  longer  and  broader  arch 
than  the  lower ;  so  that  when  the  mouth  is  closed  the  teeth  are  not 
brought  into  exact  apposition,  but  the  upper  teeth  overlap  the  lower 
teeth  both  in  front  and  laterally.  The  lower  teeth  are  all  somewhat 
smaller  than  the  corresponding  teeth  of  the  upper  jaw  and  usually  make 
their  appearance  a  little  earlier. 

The  superior  maxillary  bones  are  immovably  articulated  with  the 
other  bones  of  the  head  and  do  not  usually  take  any  active  part  in 
mastication.  Their  inferior  borders  present  fixed  surfaces  against 
which  the  food  is  pressed  by  the  action  of  the  muscles  that  elevate 
the  lower  jaw. 


MUSCLES    OF   MASTICATION  167 

The  inferior  maxilla  is  a  single  bone.  Its  body  is  horizontal,  of  a 
horseshoe  shape,  and  in  the  alveolar  cavities  in  its  superior  border,  are 
the  lower  teeth.  Below  the  teeth,  both  externally  and  internally,  are 
surfaces  for  the  attachments  of  the  muscles  concerned  in  the  various 
movements  of  the  jaw  and  for  one  of  the  muscles  of  the  tongue. 

Temporo-maxillary  Articulation.  —  In  man  the  articulation  of  the 
lower  jaw  with  the  temporal  bone  is  such  as  to  allow  an  antero-posterior 
sliding  movement  and  a  lateral  movement,  in  addition  to  the  movements 
of  elevation  and  depression.  The  condyloid  process  is  convex,  with  an 
ovoid  surface,  the  general  direction  of  its  long  diameter  being  trans- 
verse, and  slightly  oblique  from  without  inward  and  from  before  back- 
ward. This  process  is  received  into  a  cavity  of  corresponding  shape  in 
the  temporal  bone  —  the  glenoid  fossa  —  which  is  bounded  anteriorly 
by  a  rounded  eminence  called  the  eminentia  articularis. 

Between  the  condyle  of  the  lower  jaw  and  the  glenoid  fossa,  is  an 
oblong  interarticular  disk  of  fibro-cartilage.  This  is  thicker  at  the 
edges  than  in  the  centre.  It  is  pliable  and  is  so  situated  that  when  the 
lower  jaw  is  projected  forward,  making  the  lower  teeth  project  beyond 
the  upper,  it  is  applied  to  the  convex  surface  of  the  eminentia  articularis 
and  presents  a  concave  surface  for  articulation  with  the  condyle.  One 
of  the  uses  of  this  cartilage  is  to  present  constantly  a  proper  articulating 
surface  on  the  articular  eminence  and  thus  permit  the  antero-posterior 
sliding  movement  of  the  lower  jaw.  It  is  also  important  in  the  lateral 
movements  of  the  jaw,  in  which  one  of  the  condyles  remains  in  the 
glenoid  cavity  and  the  other  is  projected,  so  that  the  bone  undergoes 
a  slight  rotation. 

Muscles  of  Masticatioft.  —  To  the  lower  jaw  are  attached  certain 
muscles  by  which  it  is  depressed,  and  others  by  which  it  is  elevated, 
projected  forward,  drawn  backward  and  moved  from  side  to  side.  The 
following  are  the  principal  muscles  concerned  in  the  production  of  these 
varied  movements :  — 

MUSCLES   OF   MASTICATION 
Muscles  that  depress  the  lower  jaw 

MUSCLE  ATTACHMENTS 

Digastric         .         .         <.         .     Mastoid  process  of  the  temporal  bone  —  lower  border  of  the 

inferior  maxilla  near  the  symphysis,  with  its  central  tendon 
held  to  the  side  of  the  body  of  the  hyoid  bone. 

Mylo-hyoid  ....  Body  of  the  hyoid  bone  —  mylo-hyoid  ridge  on  the  internal  sur- 
face of  the  inferior  maxilla. 

Genio-hyoid  ....     Body  of  the  hyoid  bone  —  inferior  genial  tubercle  on  the  inner 

surface  of  the  inferior  maxilla,  near  the  symphysis. 

Platysma  myoides  .         .         .    Clavicle,  acromion  and  fascia  —  anterior  half  of  the  body  of 

the  inferior  maxilla,  near  the  inferior  border. 


1 68  DIGESTION 

Muscles  that  elevate  the  lower  jaw  and  move  it  laterally  and  ajitero-posteriorly 

MUSCLE  ATTACHMENTS 

Temporal         ....    Temporal  fossa  —  coronoid  process  of  the  inferior  maxilla. 

Masseter  ....    Malar  process  of  the  superior  maxilla,  lower  border  and  internal 

surface  of  the  zygomatic  arch — surface  of  the  ramus  of  the 
inferior  maxilla. 

Internal  pterygoid  .  .  .    Pter}-goid  fossa  —  inner  side  of  the  ramus,  and  angle  of  the  in- 

ferior maxilla. 

External  pterygoid  .  .    Pterygoid  ridge  of  the  sphenoid,  the  surfa.-e  between  it  and  the 

pterygoid  process,  external  pterygoid  plate,  tuberosity  of  the 
palate  and  the  superior  maxillary  bone  —  inner  surface  of 
the  neck  of  the  condyle  of  the  inferior  maxilla  and  the  inter- 
articular  fibro-cartilage. 

Action  of  the  Muscles  that  depress  the  Lower  Jaw.  —  The  most 
important  of  these  muscles  have  for  their  fixed  point  of  action  the 
hyoid  bone,  which  is  fixed  by  the  muscles  e.xtending  from  it  to  the 
upper  part  of  the  thorax.  The  central  tendon  of  the  digastric,  as  it 
perforates  the  stylo-hyoid,  is  connected  with  the  hyoid  bone  by  a  loop 
of  fibrous  tissue ;  and  acting  from  this  bone  as  the  fixed  point,  the 
anterior  belly  must  of  necessity  depress  the  jaw.  The  attachments  of 
the  mylo-hyoid  and  the  genio-hyoid  render  their  action  in  depressing 
the  jaw  sufficiently  evident,  which  is  also  the  case  with  the  platysma 
myoides,  acting  from  its  attachments  to  the  upper  part  of  the  thorax. 
In  ordinary  mastication  the  upper  jaw  undergoes  a  slight  movement  of 
elevation,  and  this  becomes  somewhat  exaggerated  when  the  mouth  is 
opened  to  the  fullest  extent. 

Action  of  the  Muscles  that  elevate  the  Lower  Jaw  and  move  it  later- 
ally and  ajitero-posteriorly. — The  temporal,  masseter  and  internal 
pterygoid  muscles  are  chiefly  concerned  in  the  simple  act  of  closing  the 
jaws.  Their  anatomy  alone  gives  a  sufficiently  clear  idea  of  their  mode 
of  action ;  and  their  great  power  is  explained  by  the  number  of  their 
fibres,  by  the  attachments  of  many  of  these  fibres  to  the  strong  aponeu- 
roses by  which  they  are  covered,  and  by  the  fact  that  the  distance 
from  their  origin  to  their  insertion  is  very  short. 

The  attachments  of  the  internal  and  external  pterygoids  are  such 
that  by  their  alternate  action  on  either  side,  the  jaw  may  be  moved 
laterally,  as  their  points  of  origin  are  situated  in  front  of  and  internal  to 
the  temporo-maxillary  articulation.  The  articulation  of  the  lower  jaw  is 
such  that  in  its  lateral  movements  the  condyles  themselves  can  not  be 
sufficiently  displaced  from  side  to  side  ;  but  with  the  condyle  on  one 
side  fixed  or  moved  slightly  backward,  the  other  may  be  brought  forward 
against  the  articular  eminence,  producing  a  slight  movement  of  rotation. 

The  above  explanation  of  the  lateral  movements  of  the  jaw  presup- 
poses the    possibility  of    movements   in  an    antero-posterior   direction 


SALIVA  169 

Movements  in  a  forward  direction,  so  as  to  make  the  lower  teeth  project 
beyond  the  upper,  are  effected  by  the  pterygoids,  the  oblique  fibres  of 
the  masseter  and  the  anterior  fibres  of  the  temporal.  By  the  combined 
action  of  the  posterior  fibres  of  the  temporal,  the  digastric,  mylo-hyoid 
and  genio-hyoid,  the  jaw  is  brought  back  to  its  position.  By  the  same 
action  it  may  also  be  drawn  back  slightly  from  its  normal  position  while 
at  rest. 

Action  of  the  Tongue,  Lips  and  Cheeks,  in  Mastication.  —  The  varied 
and  complex  movements  of  the  tongue  during  mastication  are  not  easily 
described.  After  solid  food  is  taken  into  the  mouth,  the  tongue  prevents 
its  escape  from  between  the  teeth,  and  by  its  constant  movements,  rolls 
the  alimentary  bolus  over  and  over  and  passes  it  at  times  from  one  side 
to  the  other,  so  that  the  food  may  undergo  thorough  trituration.  Aside 
from  the  uses  of  the  tongue  as  an  organ  of  taste,  its  surface  is  endowed 
with  peculiar  sensibility  as  regards  the  consistence,  size  and  form  of 
different  articles  ;  and  this  is  important  in  determining  when  masti- 
cation is  completed,  although  the  thoroughness  of  mastication  is  much 
influenced  by  habit. 

Tonic  contraction  of  the  orbicularis  oris  is  necessary  to  keep  the 
liquids  within  the  mouth  during  repose  ;  and  this  muscle  is  sometimes 
brought  into  action  when  the  mouth  is  full,  to  assist  in  keeping  the  food 
between  the  teeth.  This  latter  office,  however,  is  performed  mainly  by 
the  buccinator ;  the  action  of  which  is  to  press  the  food  between  the 
teeth  and  keep  it  in  place  during  mastication,  assisting,  from  time  to 
time,  in  turning  the  alimentary  bolus  so  as  to  subject  new  portions  to 
trituration. 

Mastication  is  regulated  to  a  considerable  extent  by  the  sensibility 
of  the  teeth  to  impressions  of  hard  and  soft  substances.  It  is  necessary 
only  to  call  attention  to  the  ease  and  certainty  with  which  the  presence 
and  the  consistence  of  the  smallest  substance  between  the  teeth  are 
recognized,  to  show  the  importance  of  this  tactile  sense  in  mastication. 

Saliva 

The  liquid  which  is  mixed  with  the  food  in  mastication,  which 
moistens  the  mucous  membrane  of  the  mouth  and  which  may  be  collected 
at  any  time  in  small  quantity  by  the  simple  act  of  sputation,  is  composed 
of  the  secretions  of  a  considerable  number  and  variety  of  glands.  The 
most  important  of  these  are  the  parotid,  submaxillary  and  sublingual, 
which  usually  are  called  the  salivary  glands.  The  labial  and  buccal 
glands,  the  glands  of  the  tongue  and  general  mucous  surface  and  certain 
glandular  structures  in  the  mucous  membrane  of  the  pharynx  also  con- 


I/O 


DIGESTION 


tribute  to  the  production  of  the  saliva.  The  liquid  that  becomes  more  or 
less  thoroughly  incorporated  with  the  food  before  it  reaches  the  stomach, 
which  must  be  regarded  as  the  digestive  fluid  of  the  mouth,  is  known  as 
the  mixed  saliva  ;  but  the  study  of  the  composition  and  properties  of 
this  as  a  whole  should  be  prefaced  with  a  consideration  of  the  different 
secretions  of  which  it  is  composed.  The  salivary  glands  belong  to  the 
variety  of  glands  called  racemose ;  and  they  resemble  in  their  general 
characters  the  other  glands  belonging  to  this  class.  One  peculiarity, 
however,  in  the  histology  of  the  secreting  alveoli,  may  be  mentioned  : 
Next  the  basement-membrane,  usually  near  the  blind  extremity  of  the 
tube,  are  a  few  crescentic  cells  called  demilunes  (Giannuzzi's  crescents). 
In  the  case  of  the  submaxillary  and  sublingual  glands,  at  least,  these 
bodies  are  thought  to  produce  a  serous  secretion  (see  Plate  IV, 
Fig.  I). 

Parotid  Saliva.  —  The  parotid  is  the  largest  of  the  three  salivary 
glands.  It  is  situated  below  and  in  front  of  the  ear  and  opens  by  the 
duct  of  Steno  into  the  mouth,  at  about  the  middle  of  the  cheek,  opposite 
the  second  large  molar  tooth  of  the  upper  jaw.  The  secretion  of  this 
gland  possesses  little  or  no  viscidity. 

The  organic  matter  of  the  parotid  saliva  is  coagulable  by  heat 
(212°  Fahr.,  or  100°  C),  alcohol  or  the  strong  mineral  acids.  The  se- 
cretion is  not  so  strongly  alkahne  as  the  submaxillary  and  the  sublingual 
saliva  and  contains  a  larger  proportion  of  ptyalin.  A  sulphocyanate 
is  a  nearly  constant  constituent  of  the  parotid  saliva.  This  can  not 
be  recognized  by  the  ordinary  tests  in  the  fresh  saliva  taken  from  the 
duct  of  Steno,  but  in  the  clear  filtered  liquid  that  passes  after  the  pre- 
cipitation of  organic  matters,  there  is  a  distinct  red  color  on  the  addi- 
tion of  ferric  sulphate.  As  this  reaction  is  more  marked  in  the  mixed 
saliva,  the  methods  by  which  the  presence  of  a  sulphocyanate  is  to 
be  recognized  will  be  considered  in  connection  with  that  liquid.  In 
the  human  subject,  the  parotid  secretion  is  more  abundant  than  that  of 
any  other  of  the  salivary  glands ;  but  the  entire  quantity  in  the  twenty- 
four  hours  has  not  been  directly  estimated. 

In  the  horse,  ass  and  ox,  it  has  been  found  that  when  mastication  is 
performed  on  one  side  of  the  mouth,  the  flow  from  the  gland  on  that 
side  is  increased,  exceeding  by  several  times  the  quantity  produced  on 
the  opposite  side.  The  flow  of  saliva  from  the  parotid  takes  place  with 
increased  activity  during  mastication.  The  opening  of  the  parotid  duct 
is  so  situated  that  the  liquid  is  discharged  directly  upon  the  food  as  it 
is  undergoing  trituration  by  the  teeth  ;  and  as  the  secretion  is  more 
abundant  on  the  side  on  which  mastication  is  going  on  and  the  con- 
sistence of  the  liquid  is  such  as  to  enable  it  to  mix  readily  with  the  food, 


SALIVA  171 

the  office  of  this  gland  is  supposed  to  be  particularly  connected  with 
mastication,  although  its  flow  continues  in  small  quantity  during  the 
intervals.  Its  quantity  is  regulated  somewhat  by  the  character  of  the 
food,  being  greater  when  articles  taken  into  the  mouth  are  dry  than  when 
they  contain  considerable  moisture.  In  the  human  subject,  the  stimulus 
produced  by  sapid  substances  will  sometimes  cause  a  considerable  in- 
crease in  the  flow  of  the  parotid  saliva.  The  supposition  that  the  flow 
from  the  parotid  is  dependent  on  the  mechanical  pressure  of  the  muscles 
or  of  the  condyle  of  the  lower  jaw  during  mastication  has  no  foundation 
in  fact. 

Submaxillary  Saliva.  —  In  the  human  subject,  the  submaxillary  is  the 
second  of  the  salivary  glands  in  size.  Its  minute  structure  is  nearly  the 
same  as  that  of  the  parotid.  As  its  name  implies,  it  is  situated  beneath 
the  inferior  maxillary  bone.  It  is  in  the  anterior  part  of  what  is  known 
as  the  submaxillary  triangle  of  the  neck.  Its  excretory  duct  —  the  duct 
of  Wharton  —  is  about  two  inches  (5  centimeters)  in  length  and  passes 
from  the  gland,  beneath  the  tongue,  to  open  by  the  side  of  the  frenum. 

The  pure  submaxillary  saliva  presents  many  important  points  of 
difference  from  the  secretion  of  the  parotid.  It  may  be  obtained  by 
exposing  the  duct  and  introducing  a  tube,  when,  on  the  introduction  of 
any  sapid  substance  into  the  mouth,  the  secretion  will  flow  in  large 
pearly  drops.  This  kind  of  saliva  is  much  more  viscid  than  the  parotid 
secretion.  It  is  clear,  and  on  cooling,  it  frequently  becomes  of  a  gelati- 
nous consistence.  Its  organic  matter  is  not  coagulable  by  heat.  It 
contains  a  sulphocyanate,  but  in  small  quantity. 

The  submaxillary  gland  discharges  its  secretion  in  greatest  abun- 
dance when  sapid  substances  are  introduced  into  the  mouth ;  but  unlike 
the  parotid  saliva,  the  secretion  does  not  alternate  on  the  two  sides  with 
alternation  in  mastication.  Although  sapid  articles  excite  an  abundant 
secretion  from  the  submaxillary  glands,  they  also  increase  secretion 
from  the  parotids  and  sublinguals  ;  and,  on  the  other  hand,  movements 
of  mastication  increase  somewhat  the  flow  from  the  submaxillaries,  and 
these  glands  secrete  a  certain  quantity  of  liquid  during  the  intervals  of 
digestion. 

Sjibli7ignal  Saliva.  —  The  sublinguals,  the  smallest  of  the  salivary 
glands,  are  situated  beneath  the  tongue,  on  either  side  of  the  frenum. 
In  minute  structure  they  resemble  the  parotid  and  submaxillary  glands. 
Each  gland  has  a  number  of  excretory  ducts,  —  eight  to  twenty,  — 
which  open  into  the  mouth  by  the  side  of  the  frenum ;  and  one  of  the 
ducts,  larger  than  the  others,  joins  the  duct  of  the  submaxillary  gland 
near  its  opening  in  the  mouth. 

The  secretion  of  the  sublingual  glands  is  more  viscid,  even,  than 


172  DIGESTION 

the  submaxillary  saliva,  but  it  differs  in  the  fact  that  it  does  not  gelati- 
nize on  cooling.  It  is  so  glutinous  that  it  adheres  strongly  to  any 
vessel  and  flows  with  difficulty  from  a  tube  introduced  into  the  duct. 
Like  the  secretion  from  the  other  salivary  glands,  its  reaction  is  dis- 
tinctly alkaline.  Its  organic  matter  is  not  coagulable  by  heat,  acids  or 
the  metallic  salts. 

Secretions  from  the  Smaller  Glajids  of  the  Month,  Tongue  and 
Pharynx.  —  Beneath  the  mucous  membrane  of  the  inner  surface  of  the 
lips,  are  small,  rounded,  glandular  bodies,  opening  into  the  buccal 
cavity,  called  the  labial  glands  ;  and  in  the  submucous  tissue  of  the 
cheeks,  are  similar  bodies,  called  the  buccal  glands.  The  latter  are 
somewhat  smaller  than  the  labial  glands.  Two  or  three  of  the  buccal 
glands  are  of  considerable  size  and  have  ducts  opening  opposite  the 
last  molar  tooth.  These  are  sometimes  distinguished  as  the  molar 
glands.  There  are  also  a  few  small  glands  in  the  mucous  membrane 
of  the  posterior  half  of  the  hard  palate  ;  but  the  glands  on  the  under 
surface  of  the  soft  palate  are  larger  and  form  a  continuous  layer.  The 
glands  of  the  tongue  are  situated  beneath  the  mucous  membrane,  mainly 
on  the  posterior  third  of  the  dorsum  ;  but  a  few  are  found  at  the  edges 
and  the  tip,  and  there  is  a  gland  of  considerable  size  on  either  side  of 
the  frenum  near  the  tip.  All  these  are  small  racemose  glands,  similar 
in  structure  to  the  true  salivary  glands.  In  addition  to  these  structures, 
the  mucous  membrane  of  the  tongue  is  provided  with  simple  and  com- 
pound follicular  glands,  which  extend  over  its  entire  surface,  but  are 
most  abundant  at  the  posterior  portion,  behind  the  circumvallate 
papillae. 

In  the  pharynx  and  the  posterior  portion  of  the  buccal  cavity,  are 
the  pharyngeal  glands  and  the  tonsils.  In  the  pharynx,  particularly 
the  upper  portion,  racemose  glands,  like  those  found  in  the  mouth, 
exist  in  large  number.  The  mucous  membrane  is  provided,  also,  with 
simple  and  compound  mucous  follicles.  The  tonsils,  situated  on  either 
side  of  the  fauces  between  the  pillars  of  the  soft  palate,  consist  of  an 
aggregation  of  compound  follicular  glands.  The  number  of  glands 
entering  into  the  composition  of  each  tonsil  is  ten  to  twenty.  The 
secretion  from  these  glands  and  follicles  can  not  be  obtained,  in  the 
human  subject,  unmixed  with  the  products  of  the  true  salivary  glands. 
It  has  been  collected  in  small  quantity,  however,  from  the  inferior 
animals,  after  Hgature  of  all  the  sahvary  ducts.  This  secretion  is 
simply  a  grayish  viscid  mucus,  containing  a  number  of  leucocytes  and 
desquamated  epithelial  scales.  It  is  this  which  gives  the  turbid  and 
opaline  character  to  the  mixed  saliva,  as  the  secretions  of  the  salivary 
glands  are  all  clear.     The  products  of  these  glands  in  the  mouth  are 


PROPERTIES    AND    COMPOSITION    OF    THE    SALIVA  173 

mixed  with  the  salivary  secretions ;  and  that  from  the  posterior  part 
of  the  tongue,  the  tonsils,  and  the  pharyngeal  glands  passes  down  to 
the  stomach  with  the  alimentary  bolus. 

mixed  Saliva.  —  Although  the  study  of  the  distinct  secretions  dis- 
charged into  the  mouth  possesses  considerable  physiological  importance, 
it  is  only  the  liquid  resulting  from  their  mixture  that  can  properly  be 
considered  in  connection  with  the  general  process  of  insalivation.  On 
the  introduction  of  food,  the  quantity  of  saliva  is  increased  ;  and  the 
influence  of  the  sight,  odor  and  occasionally  even  the  thought  of 
agreeable  articles  has  already  been  mentioned. 

Quantity  of  Saliva.  —  It  is  not  easy  to  estimate  in  the  human 
subject  the  entire  quantity  of  saliva  secreted  in  the  twenty-four  hours; 
and  considerable  variations  in  this  regard  exist  in  different  persons  and 
in  the  same  individual  at  different  times.  An  approximate  estimate 
may  be  arrived  at  by  noting  as  nearly  as  possible  the  average  quantity 
secreted  during  the  intervals  of  digestion  and  adding  to  it  the  quantity 
absorbed  by  articles  of  food.  The  following  represents  the  quantities 
of  saliva  secreted  during  mastication  and  during  the  intervals  of  meals 
(Dalton):  — 

Saliva  during  mastication  .....     17.32  ounces    (491  grams). 

Saliva  secreted  in  intervals  of  mastication  .         .     27.93  ounces    (792  grams). 

Total  quantity  per  day  ....     45.25  ounces  (1283  grams). 

The  total  daily  quantity  of  saliva,  therefore,  is  a  little  more  than  two 
and  three-fourths  pounds. 

Gejieral  Properties  ajid  Conipositio7i  of  the  Saliva.  —  The  mixed 
saliva  taken  from  the  mouth  is  colorless,  somewhat  opaline,  frothy  and 
slightly  viscid.  It  has  a  faint  and  somewhat  disagreeable  odor  soon 
after  its  discharge.  If  allowed  to  stand,  it  deposits  a  whitish  sediment, 
composed  mainly  of  desquamated  epithelial  scales  with  a  few  leuco- 
cytes, leaving  the  supernatant  fluid  nearly  clear.  Its  specific  gravity 
is  variable,  ranging  between  1004  or  1006  and  1008.  Its  reaction  is 
almost  constantly  alkaline  ;  although,  under  certain  abnormal  conditions, 
it  has  been  found  neutral,  and  sometimes,  though  rarelv,  acid.  It 
becomes  slightly  opalescent  by  boiling  or  on  the  addition  of  strong 
acids ;  and  the  addition  of  absolute  alcohol  produces  an  abundant 
whitish  flocculent  precipitate.  Almost  invariably  the  mLxed  saliva 
presents  a  more  or  less  intense  blood-red  tint  on  the  addition  of  a  per- 
salt  of  iron,  which  is  due  to  the  presence  of  a  sulphocyanate  either  of 
potassium  or  of  sodium. 

A  number  of  analyses  of  the  human  mixed  saliva  have  been  made 
by  different  chemists,  presenting,  however,  few  differences,  except  in 


174 


DIGESTION 


the  relative  proportions  of  water  and  solid  ingredients,  which  probably 
are  quite  variable. 


COMPOSITIOX    OF    HUMAN    SALIVA 

Water 

Epithelium  ...... 

Ptyalin . 

Potassium  sulphocyanate    .... 
Sodium,  calcium  and  magnesium  phosphates 
Potassium  chloride ) 
Sodium  chloride      j    ' 


995.16 
1.62 

1-34 
0.06 


0.84 


The  organic  matter  of  the  mixed  saliva,  called  ptyalin,  on  the  addi- 
tion of  an  excess  of  absolute  alcohol,  is  coagulated  in  the  form  of  whit- 
ish flakes,  which  may  readily  be  separated  by  filtration.  This  is  the 
substance  described  by  Mialhe  under  the  name  of  animal  diastase.  It 
has  no  direct  influence  on  nitrogenous  alimentary  matters,  but  when 
brought  in  contact  with  hydrated  or  soluble  starch,  readily  transforms 
it,  first  into  dextrin  and  afterward  into  maltose.  The  energy  of  this 
action  is  such  that  one  part  is  sufficient  to  effect  the  transformation  of 
more  than  two  thousand  parts  of  starch. 

The  presence  of  a  certain  quantity  of  potassium  sulphocyanate  in 
the  mixed  saliva  can  be  demonstrated  by  the  addition  of  a  per-salt  of 
iron.  This  is  a  nearly  constant  and  a  normal  ingredient  of  the  human 
saliva. 

Very  little  need  be  said  concerning  the  other  inorganic  constituents 
of  saliva,  except  that  they  are  of  such  a  nature  as  almost  invariably  to 
give  a  distinctly  alkaline  reaction.  They  exist  in  small  proportion  and 
do  not  appear  to  be  connected  in  any  way  with  the  action  of  the  saliva 
as  a  digestive  secretion. 

Uses  of  the  Saliva 

In  183 1,  Leuchs  observed  that  hydrated  starch,  mixed  with  fresh 
saliva  and  warmed,  was  converted  into  sugar.  This  fact  has  since  been 
repeatedly  confirmed ;  and  it  is  now  a  matter  of  common  observation 
that  boiled  starch  taken  into  the  mouth  almost  instantly  loses  the  prop- 
erty of  striking  a  blue  color  with  iodin  and  responds  to  the  copper- 
tests  for  sugar.  Of  the  rapidity  of  this  action  one  can  easily  convince 
himself  by  the  simple  experiment  of  taking  a  little  boiled  starch  into 
the  mouth,  mixing  it  well  with  the  saliva,  and  testing  in  the  ordinary 
way.  This  can  hardly  be  done  so  rapidly  that  the  reaction  does  not 
appear,  and  the  presence  of  sugar  is  also  indicated  by  the  taste.  Al- 
though human  mixed  saliva  will  finally  exert  the  same  action  on  uncooked 
starch,  the  transformation  takes  place  much  more  slowly. 


USES    OF   THE    SALIVA  1 75 

Several  carbohydrates  are  formed  as  intermediate  products  between 
starch  and  sugar  by  the  action  of  the  salivary  enzyme.  These  are  not 
thoroughly  understood  by  physiological  chemists  for  the  reason  that  the 
size  of  the  different  molecules  has  not  been  definitely  ascertained.  The 
following,  however,  is  perhaps  the  simplest  explanation  of  these  changes. 
The  formula  for  starch  is  (CgH^QOg);/,  the  "«"  indicating  that  the  mole- 
cule is  represented  by  the  formula  multiplied  by  an  unknown  number 
not  less  than  five.  This  is  changed  into  soluble  starch,  which  forms  a 
clear  solution  in  water,  which  filters  readily  and  strikes  a  blue  color  with 
iodin.  Its  formula  is  the  same  as  for  starch,  but  the  molecule  probably 
is  larger.  Soluble  starch  is  then  converted  into  dextrin,  which  has  the 
same  formula,  but  a  smaller  molecule.  At  least  two  kinds  of  dextrin 
have  been  recognized ;  one,  erythrodextrin,  strikes  a  red  color  with 
iodin  and  is  readily  converted  into  maltose,  while  the  other,  achroodex- 
trin,  has  no  reaction  with  iodin  and  is  slowly  converted  into  maltose. 
Leaving  out  of  consideration  the  size  of  the  molecules,  2  (CgH^oOg)  + 
H2O  =  C^2^i2^iv  which  is  the  formula  for  maltose.  It  is  probable 
that  some  of  the  starch  acted  on  by  the  saliva  passes  into  the  stomach 
in  the  condition  of  achroodextrin.  A  certain  part,  also,  may  be  changed 
into  dextrose  (CgH^gOg).  A  full  discussion  of  these  changes,  however, 
belongs  to  special  treatises  on  physiological  chemistry. 

The  action  of  the  saliva  on  starch  is  due  entirely  to  the  presence  of 
ptyalin,  although  its  intensity  is  increased  in  moderately  alkaline  solu- 
tions or  by  the  addition  of  certain  salts,  especially  sodium  chloride. 
Feeble  acids  diminish  the  activity  of  this  change,  and  it  is  arrested  by 
strong  mineral  acids ;  although  direct  experiments  have  shown  that  the 
action  of  the  saliva  is  slowly  and  feebly  continued  in  the  stomach.  The 
temperature  at  which  the  action  of  the  salivary  enzyme  is  most  vigorous 
is  about  100°  Fahr.  (38°  C);  and  any  considerable  variation  from  this 
temperature  arrests  the  process. 

In  early  infancy  the  action  of  the  saliva  on  starch  is  not  so  vigorous 
as  in  the  adult;  and  it  is  said  that  immediately  after  birth  the  parotid  prod- 
uct is  the  only  one  of  the  salivary  secretions  that  contains  ptyalin.  In 
a  few  months,  however,  ptyalin  appears  in  the  submaxillary  and  sub- 
lingual secretions. 

It  is  evident  that  the  saliva,  in  addition  to  its  mechanical  action, 
transforms  a  considerable  part  of  starch  into  sugar;  but  it  is  by  no 
means  the  only  secretion  engaged  in  its  digestion,  similar  properties 
belonging  to  the  pancreatic  and  the  intestinal  juices.  The  last-named 
secretions  are  probably  more  active,  even,  than  the  saliva.  The  saliva 
acts  slowly  and  imperfectly  on  raw  starch,  which  becomes  hydrated  in 
the  stomach  and  is  digested  mainly  by  the  liquids  of  the  small  intestine. 


1/6  DIGESTION 

In  all  probability  the  saliva  does  not  digest  all  the  starch  taken  as 
food,  the  greater  part  passing  unchanged  from  the  stomach  into  the 
intestine. 

It  is  undoubtedly  the  abundant  secretion  of  the  parotid  glands  which 
becomes  most  completely  incorporated  with  the  food  during  mastication 
and  which  ser\'es  to  unite  the  dry  particles  into  a  coherent  mass.  The 
secretions  from  the  submaxillary  and  sublingual  glands  and  from  the 
small  glands  and  folUcles  of  the  mouth,  being  more  viscid  and  less  in 
quantity  than  the  parotid  secretion,  penetrate  the  alimentary  bolus  less 
easily  and  form  a  glairy  coating  on  its  exterior,  agglutinating  the 
particles  near  the  surface. 

When  the  processes  of  mastication  and  insalivation  have  been  com- 
pleted and  the  food  has  passed  into  the  pharynx,  it  meets  with  the 
products  of  the  pharyngeal  glands,  which  still  further  coat  the  surface 
with  the  viscid  secretion  that  covers  the  mucous  membrane  in  this  situ- 
ation, thus  facilitating  the  first  part  of  deglutition. 

It  has  been  observed  that  the  saliva  engages  bubbles  of  air  in  the 
alimentarv  mass.  In  mastication,  a  considerable  quantity  of  air  is  mixed 
with  the  food,  and  this  facilitates  the  penetration  of  the  gastric  juice. 
It  is  well  known  that  moist  bread  and  articles  that  can  not  become 
impregnated  in  this  way  with  air  are  not  easily  acted  on  in  the 
stomach. 

Deglutition 

Deglutition  is  the  act  by  which  solid  and  liquid  articles  are  passed 
from  the  mouth  into  the  stomach.  The  process  involves  first,  the  pas- 
sage, by  an  automatic  movement,  of  the  ahmentary  mass  through  the 
isthmus  of  the  fauces  into  the  pharynx ;  then,  rapid  contraction  of  the 
constrictors  of  the  pharynx,  by  which  it  is  forced  into  the  oesophagus ; 
and  finally,  a  peristaltic  action  of  the  muscular  walls  of  the  oesophagus, 
extending  from  its  opening  at  the  pharynx  to  the  stomach. 

Physiological  Anatomy  of  the  Parts  concerned  in  Deglutition.  —  The 
parts  concerned  in  this  process  are  the  tongue,  the  muscular  walls  of 
the  pharynx  and  the  oesophagus.  In  the  passage  of  food  and  drink 
through  the  pharynx,  it  is  necessary  to  protect  from  the  entrance  of 
foreign  matters  a  number  of  openings  that  are  exclusively  for  the  passage 
of  air.  These  are  the  posterior  nares  and  the  Eustachian  tubes  above, 
and  the  opening  of  the  larynx  below. 

The  tongue  is  the  chief  agent  in  the  passage  of  the  alimentary  bolus 
into  the  pharynx ;  but  a  study  of  all  the  muscles  brought  into  action 
would  involve  anatomical  descriptions  out  of  place  in  this  work.     The 


DEGLUTITION 


177 


movements  of  the  tongue,  however,  will  be  described  farther  on  in  con- 
nection with  the  mechanism  of  the  first  period  of  deglutition. 

The  pharynx,  in  which  the  most  complex  of  the  movements  of  deglu- 
tition take  place,  is  an  irregularly  funnel-shaped  cavity,  its  longest 
diameter  being  transverse  and  opposite  the  cornua  of  the  hyoid  bone, 
with  its  smallest  portion  at  the  opening  into  the  oesophagus.     Its  length 


Fig-  35-  —  Muscles  of  the  pharynx  (Sappey). 

1,  2,  3,  4,  4,  superior  constrictor;  5,  6,  7,  8,  middle  constrictor;  9,  10,  11,  12,  inferior  constrictor; 
13,  13,  stylo-phar}'ngeus  ;  14,  stylo-hyoid  muscle  ;  15,  stj'lo-glossus  ;  16,  hyo-g'.ossus  ;  17,  mylo-hyoid 
muscle ;   18,  buccinator  muscle  ;   19,  tensor  palati ;  20,  levator  palad. 


is  about  four  and  a  half  inches  (11.43  centimeters).  It  is  connected 
superiorly  and  posteriorly  with  the  basilar  process  of  the  occipital  bone 
and  with  the  upper  cervical  vertebras.  It  is  incompletely  separated 
from  the  cavity  of  the  mouth  by  the  velum  pendulum  palati,  a  movable 
musculo-membranous  fold  continuous  with  the  roof  of  the  mouth  and 
marked  by  a  line  in  the  centre,  which  indicates  its  original  develop- 
ment by  two  lateral  halves.     This,  which  is  called  the  soft  palate,  w^hen 


178  DIGESTION 

relaxed,  presents  a  concave  surface  looking  toward  the  mouth,  a  free 
arched  border,  and  a  conical  process  hanging  from  the  centre,  called 
the  uvula.  On  either  side  of  the  soft  palate,  are  two  curved  pillars, 
or  arches. 

The  anterior  pillars  of  the  palate  are  formed  by  the  palato-glossus 
muscle  on  either  side  and  run  obliquely  downward  and  forward,  their 
membrane  becoming  continuous  with  the  mucous  membrane  covering 
the  base  of  the  tongue.  The  posterior  pillars  are  more  closely  .  ap- 
proximated to  each  other  than  the  anterior.  They  run  obliquely  down- 
ward and  backward,  their  mucous  membrane  becoming  continuous  with 
the  membrane  covering  the  sides  of  the  pharynx.  Between  the  lower 
portion  of  the  anterior  and  posterior  pillars,  are  the  tonsils ;  and  in  the 
substance  of  and  beneath  the  mucous  membrane  of  the  palate  and 
pharynx,  are  small  glands,  which  have  already  been  described. 

The  isthmus  of  the  fauces,  or  the  strait  through  which  the  food 
passes  from  the  mouth  to  the  pharynx,  is  bounded  above  by  the  soft 
palate  and  the  uvula;  laterally,  by  the  pillars  of  the  palate  and  the 
tonsils ;  and  below,  by  the  base  of  the  tongue. 

The  openings  into  the  pharynx  above  are  the  posterior  nares  and 
the  Eustachian  tubes.  Below,  are  the  openings  of  the  oesophagus  and 
the  larynx. 

The  muscles  of  the  pharynx  are  the  superior  constrictor,  the  stylo- 
pharyngeus,  the  middle  constrictor  and  the  inferior  constrictor ;  and 
it  is  easy  to  see,  from  the  situation  of  these  muscles,  how,  by  their 
successive  action  from  above  downward,  the  food  is  passed  into  the 
oesophagus. 

The  muscles  forming  the  fleshy  portions  of  the  soft  palate  are  like- 
wise important  in  deglutition.  These  are  the  levator  palati,  the  tensor 
palati,  the  palato-glossus  and  the  palato-pharyngeus.  The  azygos  uvulae, 
which  forms  the  fleshy  portion  of  the  uvula,  has  no  important  action  in 
deglutition. 

The  mucous  membrane  of  the  pharynx,  aside  from  the  various 
glands  situated  beneath  it  and  in  its  substance,  presents  certain  peculiar- 
ities. In  the  superior  portion,  which  forms  a  cuboidal  cavity  just  behind 
the  posterior  nares,  the  membrane  is  darker  and  much  richer  in  blood- 
vessels than  in  other  parts.  Its  surface  is  smooth  and  is  provided  with 
ciliated  epithelium  like  that  which  covers  the  membrane  of  the  posterior 
nares.  Laterally,  below  the  level  of  the  opening  of  the  Eustachian 
tubes,  and  posteriorly,  at  the  point  where  it  becomes  vertical,  the  mucous 
membrane  abruptly  changes  its  character.  The  epithelial  covering  is 
here  composed  of  stratified  cells  similar  to  those  which  cover  the  mucous 
membrane  of   the  oesophagus ;    and  the   membrane  is  paler  and  less 


DEGLUTITION  1 79 

vascular.  It  is  provided  with  papillae,  some  of  which  are  simple  conical 
elevations,  while  others  present  two  to  six  conical  processes  with  a  sin- 
gle base.  These  papillae  are  rather  sparsely  distributed  over  all  that 
portion  of  the  mucous  surface  which  is  covered  with  stratified  epithe- 
lium. 

The  contractions  of  the  muscular  walls  of  the  pharynx  force  the 
alimentary  bolus  into  the  oesophagus,  a  tube  with  thick  muscular  walls, 
extending  to  the  stomach.  The  oesophagus  is  about  nine  inches  (23 
centimeters)  in  length.  It  is  cylindrical  and  slightly  constricted  at  its 
superior  and  inferior  extremities.  Its  upper  extremity  is  in  the  median 
line  behind  the  lower  border  of  the  cricoid  cartilage  and  opposite  the 
fifth  cervical  vertebra.  At  first,  as  it  descends,  it  passes  a  little  to  the 
left  of  the  cervical  vertebrae.  It  then  passes  from  left  to  right  from 
the  fourth  or  fifth  to  the  ninth  dorsal  vertebra,  to  give  place  to  the  aorta. 
It  finally  passes  a  little  to  the  left  again,  and  from  behind  forward,  to  its 
opening  into  the  stomach.  In  its  passage  through  the  diaphragm,  it  is 
surrounded  by  muscular  fibres,  so  that  when  this  muscle  is  contracted  in 
inspiration,  its  action  has  a  tendency  to  constrict  the  opening. 

The  coats  of  the  oesophagus  are  two  in  number,  unless  there  be 
included,  as  a  third  coat,  the  fibrous  tissue  which  attaches  the  mucous 
membrane  to  the  subjacent  muscular  coat. 

The  external  coat  is  composed  of  an  external  longitudinal,  and  an 
internal  circular,  or  transverse  layer  of  muscular  fibres.  In  the  superior 
portion,  the  longitudinal  fibres  are  arranged  in  three  distinct  fasciculi ; 
one  in  front,  which  passes  downward  from  the  posterior  surface  of  the 
cricoid  cartilage,  and  one  on  either  side,  extending  from  the  inferior  con^ 
strictors  of  the  pharynx.  As  the  fibres  descend,  the  fasciculi  become 
less  distinct  and  finally  form  a  uniform  layer.  The  circular  layer  is 
somewhat  thinner  than  the  external  layer.  Its  fibres  are  transverse 
near  the  superior  and  inferior  extremities  of  the  tube  and  are  somewhat 
oblique  in  the  intermediate  portion.  The  muscular  coat  is  -^q  to  -^^  o^ 
an  inch  (0.5  to  2.1  millimeters)  in  thickness. 

In  the  upper  third  of  the  oesophagus,  the  muscular  fibres  are  of  the 
red  or  striated  variety,  with  some  anastomosing  bundles  ;  but  lower  down, 
there  is  a  mixture  of  non-striated  fibres,  which  appear  first  in  the  circular 
layer.  These  latter  fibres  become  gradually  more  abundant,  until,  in  the 
lower  fourth,  they  largely  predominate.  A  few  striated  fibres,  however, 
are  found  as  low  down  as  the  diaphragm. 

The  mucous  membrane  of  the  oesophagus  is  attached  to  the  mus- 
cular tissue  by  a  dense  fibrous  layer.  It  is  quite  vascular  and  reddish 
above,  but  gradually  becomes  paler  in  the  inferior  portion.  The  mucous 
membrane  ordinarily  is  thrown  into  longitudinal  folds,  which  are  obliter 


l80  DIGESTION 

ated  when  the  tube  is  distended.  Its  epithelium  is  thick,  of  the  squa- 
mous variety,  and  is  continuous  with  and  similar  to  the  covering  of  the 
lower  portion  of  the  pharynx.  It  is  provided  with  papillae  of  the  same 
structure  as  those  found  in  the  pharynx,  the  conical  variety  predominat- 
ing. Racemose  mucous  glands  are  found  throughout  the  tube,  forming, 
by  their  aggregation  at  the  lower  extremity  just  before  it  opens  into  the 
stomach,  a  glandular  ring  (see  Plate  IV,  Fig.  2). 

Mechanism  of  Deglutitioji.  —  For  convenience  of  description,  physi- 
ologists usually  have  divided  the  process  of  deglutition  into  three 
periods.  The  first  period  is  occupied  by  the  passage  of  the  alimentary 
bolus  backward  to  the  isthmus  of  the  fauces.  This  may  appropriately 
be  considered  as  a  distinct  period,  because  the  movements  are  effected 
by  the  action  of  muscles  under  the  control  of  the  will.  The  second 
period  is  occupied  by  the  passage  of  the  food  from  the  isthmus  of  the 
fauces,  through  the  pharynx,  into  the  upper  part  of  the  oesophagus. 
The  third  period  is  occupied  by  the  passage  of  the  food  through  the 
oesophagus  into  the  stomach. 

In  the  first  period  the  tongue  is  the  important  agent.  At  the  begin- 
ning of  this  period,  the  mouth  is  closed  and  the  tongue  becomes  slightly 
increased  in  width,  and  with  the  alimentary  bolus  behind  it,  is  pressed 
from  before  backward  against  the  roof  of  the  mouth.  The  act  of  swal- 
lowing is  always  performed  with  difficulty  when  the  mouth  is  not  com- 
pletely closed ;  for  the  tongue,  from  its  attachments,  must  follow,  to  a 
certain  extent,  the  movements  of  the  lower  jaw.  The  first  part  of  the 
first  period  of  deglutition,  therefore,  is  simple ;  but  when  the  food  has 
passed  beyond  the  hard  palate,  it  comes  in  contact  with  the  hanging 
velum,  and  muscles  are  brought  into  action  which  render  this  membrane 
tense  and  oppose  it  in  a  certain  degree  to  the  backward  movement  of 
the  base  of  the  tongue.  This  is  effected  by  the  action  of  the  tensor- 
palati  and  the  palato-glossus.  The  moderate  tension  of  the  soft  palate 
admits  of  its  being  applied  to  the  smaller  morsels,  while  the  opening  is 
dilated  somewhat  forcibly  by  masses  of  greater  size. 

It  is  easy  to  see,  in  analyzing  the  first  period  of  deglutition,  that 
liquids  and  the  softer  articles  of  food  are  assisted  in  their  passage  to  the 
isthmus  of  the  fauces  by  a  slight  suction  force.  This  is  effected  by  the 
action  of  the  muscles  of  the  tongue,  elevating  the  sides  and  depressing 
the  centre  of  the  dorsum,  while  the  soft  palate  is  applied  to  the  base. 

The  movements  in  the  first  period  of  deglutition  are  under  the  con- 
trol of  the  will  but  usually  are  automatic.  When  the  food  has  been 
thoroughly  masticated,  it  requires  an  effort  to  prevent  the  act  of  swal- 
lowing. In  this  respect,  the  movements  are  like  the  acts  of  respiration, 
except  that  the  imperative  necessity  of  air  in  the  system  must,  in  a  short 


DEGLUTITION  l8l 

time,  overcome  any  voluntary  effort  by  which  respiration  has  been 
arrested. 

The  second  period  of  deglutition  involves  more  complex  and 
important  muscular  action  than  the  first.  By  a  rapid  succession  of 
movements,  the  food  is  made  to  pass  through  the  pharynx  into  the 
oesophagus.  The  movements  are  then  beyond  the  control  of  the  will 
and  belong  to  the  kind  called  reflex.  After  the  alimentary  mass  has 
passed  beyond  the  isthmus  of  the  fauces,  it  is  easy  to  observe  a  sudden 
movement  of  elevation  of  the  larynx,  by  the  action  of  muscles  which 
usually  depress  the  lower  jaw,  but  are  now  acting  from  this  bone  as 
the  fixed  point.  The  muscles  which  produce  this  movement  act  chiefly 
on  the  hyoid  bone.  They  are  the  digastric  (particularly  the  anterior 
belly),  the  mylo-hyoid,  the  genio-hyoid,  the  stylo-hyoid  and  some  of  the 
fibres  of  the  genio-glossus.  It  is  probable,  also,  that  the  thyro-hyoid 
acts  at  this  time  to  draw  the  larynx  toward  the  hyoid  bone.  With  this 
elevation  of  the  larynx,  there  is  necessarily  an  elevation  of  the  anterior 
and  inferior  parts  of  the  pharynx,  which  are,  as  it  were,  slipped  under 
the  alimentary  bolus  as  it  is  held  by  the  constrictors  of  the  isthmus  of 
the  fauces. 

Contraction  of  the  constrictor  muscles  of  the  pharynx  takes  place 
almost  simultaneously  with  the  movement  of  elevation ;  and  the  supe- 
rior constrictor  is  so  situated  as  to  grasp  the  morsel  of  food,  and  with  it 
the  soft  palate.  The  muscles,  the  constrictors  acting  from  the  median 
raphe,  draw  up  the  anterior  and  inferior  walls  of  the  pharynx  and  pass 
the  food  rapidly  into  the  upper  part  of  the  oesophagus.  These  complex 
movements  are  accomplished  with  great  rapidity,  and  the  larynx  and 
pharynx  are  afterward  returned  to  their  original  position. 

Protection  of  the  Posterior  Nares  during  tJie  Second  Period  of  Deglu- 
tition. —  When  the  act  of  deglutition  is  performed  with  regularity, 
no  part  of  the  liquids  and  solids  swallowed  finds  its  way  into  the  air- 
passages.  The  entrance  of  foreign  substances  into  the  posterior  nares 
is  prevented  in  part  by  the  action  of  the  superior  constrictors  of  the 
pharynx,  which  embrace,  during  their  contraction,  not  only  the  alimen- 
tary mass,  but  the  velum  pendulum  palati  itself,  and  in  part,  also,  by 
contraction  of  the  muscles  forming  the  posterior  pillars  of  the  soft 
palate.  During  the  first  part  of  the  second  period  of  deglutition,  the 
soft  palate  is  slightly  raised,  being  pressed  upward  by  the  morsel  of 
food. 

While  the  food  is  passing  through  the  pharynx,  the  palato-pharyn- 
geal  muscles,  which  form  the  posterior  pillars  of  the  soft  palate,  are  in 
a  condition  of  contraction  by  which  the  edges  of  the  pillars  are  nearly 
approximated,  forming,  with  the  uvula  between  them,  almost  a  complete 


l82  DIGESTION 

diaphragm  between  the  postero-superior  and  the  antero-inferior  parts  of 
the  pharynx.  This,  with  the  application  of  the  posterior  wall  of  the 
pharynx  to  the  superior  face  of  the  soft  palate,  completes  the  protection 
of  the  posterior  openings  of  the  nasal  fossae. 

Protection  of  the  Opening  of  the  Larynx  and  Uses  of  the  Epiglottis  in 
Deglutition.  —  The  entrance  of  the  smallest  quantity  of  solid  or  liquid 
foreign  matter  into  the  larynx  produces  a  violent  cough.  This  accident 
is  of  not  infrequent  occurrence,  especially  when  an  act  of  inspiration 
is  inadvertently  performed  while  solids  or  liquids  are  in  the  pharynx. 
During  inspiration,  the  glottis  is  opened,  and  at  this  time  only  can  a 
substance  of  any  considerable  size  find  its  way  into  the  respiratory  pas- 
sages. Respiration  is  interrupted,  however,  during  each  and  every  act 
of  deglutition  ;  and  there  can,  therefore,  be  hardly  any  tendency  at  this 
time  to  the  entrance  of  foreign  substances  into  the  larynx.  During  a 
regular  act  of  swallowing,  nothing  can  find  its  way  into  the  respiratory 
passages,  so  complete  is  the  protection  of  the  larynx  during  the  period 
when  the  food  passes  through  the  pharynx  into  the  oesophagus. 

It  is  evident,  from  the  anatomy  of  the  parts  and  the  necessary  results 
of  the  contractions  of  the  muscles  of  deglutition,  that  while  the  food  is 
passing  through  the  pharynx,  the  larynx,  by  its  elevation,  passes  under 
the  tongue  as  it  moves  backward,  and  the  soft  base  of  this  organ  is,  as 
it  were,  moulded  over  the  glottis.  With  the  parts  removed  from  the 
human  subject  or  from  one  of  the  inferior  animals,  the  natural  move- 
ments of  the  tongue  and  larynx  may  be  roughly  imitated,  and  it  is  seen 
that  they  must  be  sufficient  to  protect  the  larynx  from  the  entrance  of 
solid  or  semisoHd  particles  of  food.  It  is  impossible  for  the  muscles 
of  the  pharynx  to  contract  without  drawing  together  the  sides  of  the 
larynx,  to  which  they  are  attached,  and  assisting  to  close  the  glottis. 
At  the  same  time,  as  the  movements  of  respiration  are  arrested  during 
deglutition,  the  lips  of  the  glottis  are  more  nearly  approximated.  In 
addition  to  this  passive  and  incomplete  approximation  of  the  vocal 
chords,  it  has  been  observed  that  the  lips  of  the  glottis  are  accurately 
and  firmly  closed,  during  each  act  of  deglutition,  by  contraction  of  the 
adductor  muscles. 

Importance  is  justly  attached  to  the  acute  sensibility  of  the  top  of 
the  larynx  in  preventing  the  entrance  of  foreign  substances.  The 
experiments  of  dividing  all  the  nervous  filaments  distributed  to  the 
intrinsic  muscles  show  that  their  action  is  not  essential ;  but  after 
division  of  the  superior  laryngeal  —  the  nerve  which  gives  sensibility 
to  the  parts  —  it  has  been  found  that  liquids  occasionally  pass  in 
small  quantity  into  the  trachea. 

With  reference  to  the  action  of  the  epiglottis  in  contributing  to  the 


DEGLUTITION  183 

protection  of  the  larynx  during  the  second  period  of  deglutition,  obser- 
vations on  the  human  subject  only  are  to  be  relied  upon.  Such  obser- 
vations, in  cases  of  loss  of  the  epiglottis  especially,  show  that  this  part 
is  necessary  to  the  complete  protection  of  the  larynx.  While  loss  of  the 
epiglottis  may  not  interfere  always  with  the  perfect  deglutition  of  solids, 
and  even  of  liquids,  particles  of  food  and  Hquids  frequently  find  their 
way  into  the  larynx,  and  deglutition  often  is  effected  with  difficulty, 
showing  that  complete  protection  of  the  larynx  at  all  times  does  not 
exist  unless  the  epiglottis  is  intact. 

To  appreciate  the  mechanism  by  which  the  opening  of  the  larynx  is 
protected  during  the  deglutition  of  solids  and  liquids,  one  has  only  to 
carefully  follow  the  articles  as  they  pass  over  the  inclined  plane  formed 
by  the  back  of  the  tongue  and  the  anterior  and  inferior  part  of  the 
pharynx.  As  the  food  is  making  this  passage  in  obedience  to  the  con- 
traction of  the  muscles  that  carry  the  tongue  backw^ard,  draw  up  the 
larynx  and  constrict  the  pharynx,  the  soft  base  of  the  tongue  and  the 
upper  part  of  the  larynx  are  applied  to  each  other,  with  the  epiglottis, 
which  is  now  inclined  backward,  between  them.  At  the  same  time  the 
glottis  is  closed,  in  part  by  the  action  of  the  constrictor  muscles  attached 
to  the  sides  of  the  thyroid  cartilages  and  in  part  by  the  action  of  the 
intrinsic  muscles.  If  the  food  is  tolerably  consistent  and  in  the  form  of 
a  single  bolus,  it  slips  easily  from  the  back  of  the  tongue  along  the 
membrane  covering  the  anterior  and  inferior  part  of  the  pharynx ;  but 
if  it  is  liquid  or  of  soft  consistence,  a  portion  takes  this  course,  while 
another  portion  passes  over  the  epiglottis,  being  directed  by  it  into  the 
two  grooves  by  the  side  of  the  larynx.  It  is  by  these  means,  together 
with  those  by  which  the  posterior  nares  are  protected,  that  all  solids 
and  liquids  are  passed  into  the  oesophagus  and  the  second  period  of 
deglutition  is  safely  accomplished. 

The  third  period  of  deglutition  is  the  most  simple  of  all.  It  merely 
involves  contractions  of  the  muscular  walls  of  the  oesophagus,  by  which 
the  food  is  passed  into  the  stomach.  The  longitudinal  fibres  shorten 
the  tube  and  slip  the  mucous  membrane,  lubricated  with  its  glairy 
secretion,  above  the  bolus  ;  while  the  circular  fibres,  by  a  progressive 
peristaltic  contraction  from  above  downward,  propel  the  food  into  the 
stomach.  In  experiments  on  the  lower  animals,  it  has  been  observed 
that  while  the  peristaltic  contractions  of  the  upper  two-thirds  of  the 
tube  are  immediately  followed  by  a  relaxation,  which  continues  until 
the  next  act  of  deglutition,  the  lower  third  remains  contracted  for 
about  thirty  seconds  after  the  passage  of  the  food  into  the  stomach. 
During  its  contraction,  this  part  of  the  oesophagus  is  hard,  like  a  cord 
firmly  stretched.     This  is  followed  by  relaxation ;    and  alternate  con- 


l84  DIGESTION 

traction  and  relaxation  continue,  even  when  the  stomach  is  empty, 
although,  during  digestion,  the  contractions  are  frequent  in  proportion 
to  the  quantity  of  food  in  the  stomach.  The  contraction  is  always 
increased  by  pressing  the  stomach  and  attempting  to  pass  some  of  its 
contents  into  the  oesophagus.  This  provision  is  important  in  prevent- 
ing regurgitation  of  the  contents  of  the  stomach,  especially  when  the 
organ  is  exposed  to  pressure,  as  in  urination  or  defecation. 

An  approximate  estimate  of  the  duration  of  the  acts  of  deglutition  is 
given  in  the  following  quotation  from  Landois :  — 

"  According  to  Meltzer  and  Kronecker,  the  duration  of  deglutition 
in  the  mouth  is  0.3  second;  then  the  constrictors  of  the  pharynx  con- 
tract 0.9  second ;  afterward,  the  upper  part  of  the  oesophagus ;  then 
after  1.8  second,  the  middle;  and  after  another  3  seconds,  the  lower 
constrictor.  The  closure  of  the  cardia,  after  the  entrance  of  the  bolus 
into  the  stomach,  is  the  final  act  in  the  total  series  of  movements." 

A  complete  act  of  deglutition  occupies  about  six  seconds.  The  first 
act  usually  is  automatic  but  is  under  the  control  of  the  will.  The 
second  act  is  involuntary  when  once  begun,  but  it  may  be  excited  by 
the  voluntary  passage  of  solids  or  liquids  beyond  the  velum  pendulum 
palati.  It  is  impossible  to  perform  the  second  act  of  deglutition  unless 
there  be  some  article,  either  solid  or  liquid,  in  the  pharynx.  It  is  easy 
to  make  three  or  four  successful  efforts  consecutively,  in  which  there  is 
elevation  of  the  larynx,  with  the  other  characteristic  movements ;  but  a 
little  attention  will  show  that  with  each  act  a  small  quantity  of  saliva  is 
swallowed.  When  the  efforts  have  been  frequently  repeated,  the  move- 
ments become  impossible,  until  time  enough  has  elapsed  between  them 
for  the  saliva  to  collect. 

The  position  of  the  body  has  little  to  do  with  the  facility  with  which 
deglutition  is  effected.  Liquids  or  solids  may  be  swallowed  indifferently 
in  all  postures.  I  have  seen  a  juggler  pass  a  pint  of  liquid  from  the 
mouth  to  the  stomach,  while  standing  on  his  hands. 

It  is  not  very  uncommon  to  find  persons  who  have  gradually  acquired 
the  habit  of  swallowing  air  in  order  to  relieve  uncomfortable  sensations 
in  the  stomach ;  and  when  confirmed,  this  practice  occasions  persistent 
disorder  in  digestion.  A  number  of  cases  of  this  kind  were  reported 
by  Magendie,  and  in  several  it  was  carried  to  such  an  extent  as  to  pro- 
duce great  distention  of  the  abdomen.  A  curious  case  of  habitual  air- 
swallowing  was  observed  by  the  late  Dr.  Austin  Flint  and  is  reported 
in  his  work  on  the  Practice  of  Medicine. 


CHAPTER   VIII 

GASTRIC    DIGESTION 

Physiological  anatomy  of  the  stomach  —  Peritoneal  coat — Muscular  coat  —  Mucous  coat  — 
Glands  of  the  stomach  —  Closed  follicles  —  Gastric  juice  —  Secretion  of  gastric  juice  — 
Quantity  of  gastric  juice  —  Properties  and  composition  of  gastric  juice  —  Saline  constituents 
of  the  gastric  juice  —  Pawlow's  experiments  on  the  gastric  juice — Action  of  the  gas- 
tric juice  on  meats — Action  on  albumin,  fibrin,  casein  and  gelatin  —  Action  on  vegetable 
nitrogenous  substances  —  Peptones  —  Action  on  fats,  sugars  and  amylaceous  substances  — 
Duration  of  stomach  digestion  —  Conditions  that  influence  stomach  digestion  —  Move- 
ments of  the  stomach. 

Physiological  Anatomy  of  the  Stomach 

The  stomach  serves  the  double  purpose  of  a  receptacle  for  food  and 
an  organ  in  which  certain  important  digestive  processes  take  place.  It 
is  situated  in  the  upper  part  of  the  abdominal  cavity  and  is  held  in  place 
by  folds  of  the  peritoneum  and  by  the  oesophagus.  Its  form  is  not 
easily  described.  It  has  been  compared  to  a  bagpipe,  which  it  resembles 
somewhat,  when  moderately  distended.  When  empty,  it  is  flattened, 
and  in  many  parts  its  opposite  walls  are  in  contact.  When  moderately 
distended,  its  length  is  thirteen  to  fifteen  inches  (33  to  38  centimeters), 
its  greatest  diameter,  about  five  inches  (12.7  centimeters),  and  its  capac- 
ity, one  hundred  and  seventy-five  cubic  inches  (2868  cubic  centimeters), 
or  about  five  pints.  The  parts  usually  noted  in  anatomical  descriptions 
are  the  following :  a  greater  and  a  lesser  curvature ;  a  greater  and  a 
lesser  pouch  ;  a  cardiac,  or  oesophageal  opening ;  a  pyloric  opening, 
which  leads  to  the  intestinal  canal.  The  great  pouch  is  sometimes 
called  the  fundus. 

The  coats  of  the  stomach  are  three  in  number ;  the  peritoneal, 
muscular  and  mucous.  By  some  anatomists  the  fibrous  tissue  which 
unites  the  mucous  to  the  muscular  coat  is  regarded  as  a  distinct  cover- 
ing and  is  called  the  fibrous  coat. 

Peritoneal  Coat.  —  This  coat  is  a  layer  of  peritoneum,  similar  in 
structure  to  the  membrane  covering  the  other  abdominal  viscera.  It  is 
a  reflection  of  the  membrane  that  lines  the  general  abdominal  cavity, 
which,  on  the  viscera,  is  somewhat  thinner  than  it  is  on  the  walls  of  the 
cavity.  Over  the  stomach  the .  peritoneum  is  3-^  to  tt^  of  an  inch 
(83  to  125  /i)  in  thickness.     It  is  a  serous  membrane  and  consists  of 

185 


1 86 


GASTRIC    DIGESTION 


ordinary  fibrous  tissue  with  a  considerable  number  of  elastic  fibres.  It 
is  closely  adherent  to  the  subjacent  muscular  coat  and  is  not  very 
abundantly  supplied  with  bloodvessels  and  nerves.  Lymphatics  have 
been  demonstrated  onlv  in  the  subserous  structure.  The  surface  of 
the  peritoneum  is  everywhere  covered  with  regularly-polygonal  cells  of 
endothelium,  closely  adherent  to  each  other  and  presenting  a  smooth 
surface  moistened  with  a  small  quantity  of  liquid. 

Muscular  Coat.  —  Throughout  the  alimentary  canal,  from  the  cardiac 
opening  of  the  stomach  to  the  anus,  the  muscular  fibres  forming  the 
middle  coat  are  of  the  non-striated  variety.     These  fibres  are  pale,  with 


Fig.  36.  —  Lottgitudinal  fibres  of  the  stomach  (Sappey), 

I,  lesser  curvature ;  2,  2,  greater  curvature ;  3,  greater  pouch ;  4,  lesser  pouch ;  5,  6,  6,  lower  end 
of  the  oesophagus  ;  7,  7,  pylorus ;  8,  8,  longitudinal  fibres  at  the  lesser  curvature ;  9,  fibres  extending 
over  the  greater  curvature ;  10,  10,  a  very  thin  layer  of  longitudinal  fibres  over  the  anterior  surface  of 
the  stomach;  11,  circular  fibres  seen  through  the  thin  layer  of  longitudinal  fibres. 


faint  outlines,  fusiform  or  spindle-shaped,  containing  each  an  oval  longi- 
tudinal nucleus.  They  are  closely  adherent  by  their  sides  and  are  so 
arranged  as  to  dovetail  into  each  other,  forming  sheets  of  greater  or  less 
thickness  depending  upon  the  number  of  their  layers.  The  muscular 
coat  of  the  stomach  varies  in  thickness  in  different  animals.  In  the 
human  subject  it  is  thickest  in  the  region  of  the  pylorus  and  is  thinnest 
at  the  fundus.  Its  average  thickness  is  about  ^  of  an  inch  { i  milli- 
meter). In  the  pylorus  its  thickness  is  -^^  to  -jV  of  an  inch  (1.6  to  2.1 
millimeters),  and  in  the  fundus,  ^^  to  3^  of  an  inch  (0.5  to  0.7  millimeter). 
The  muscular  fibres  are  in  two  principal  layers ;  an  external  longi- 
tudinal layer  and  an  internal  circular  layer,  with  a  third  layer  of  oblique 


PHYSIOLOGICAL   ANATOMY   OF   THE   STOMACH 


187 


fibres  extending  over  the  great  pouch  only,  which  is  internal  to  the 
circular  layer.  The  longitudinal  fibres  are  continued  from  the  oesopha- 
gus and  are  most  marked  over  the  lesser  curvature.  They  are  not  con- 
tinued very  distinctly  over  the  rest  of  the  stomach.  The  circular  and 
oblique  fibres  are  best  seen  with  the  organ  everted  and  the  mucous 
membrane  removed.  The  circular  layer  is  not  very  distinct  to  the  left 
of  the  cardiac  opening,  over  the  great  pouch.  Toward  the  pylorus,  the 
layers  of  fibres  are  thicker,  and  at  the  opening  into  the  duodenum,  they 
form  a  powerful  muscular  ring,  sometimes  called  the  sphincter  of  the 
pylorus,  or  the  pyloric  muscle.     At  this  point  they  project  considerably 


Fig.  37.  —  Fibres  seen  with  the  stomach  everted  (Sappey). 

I,  I,  oesophagus;  2,  circular  fibres  at  the  oesophageal  opening;  3,  3,  circular  fibres  at  the  lesser 
curvature ;  4,  4,  circular  fibres  at  the  pylorus  ;  5,  5,  6,  7,  8,  oblique  fibres ;  9,  10,  fibres  of  this  layer 
covering  the  greater  pouch  ;  11,  portion  of  the  stomach  from  which  these  fibres  have  been  removed  to 
show  the  subjacent  circular  fibres. 


into  the  interior  of  the  organ  and  cease  abruptly  at  the  opening  into  the 
duodenum,  so  as  to  form  a  sort  of  valve,  presenting,  when  contracted,  a 
flat  surface  looking  toward  the  intestine.  The  oblique  layer  takes  the 
place,  in  great  part,  of  the  circular  fibres  over  the  great  pouch.  It 
extends  obliquely  over  the  fundus  from  left  to  right  and  ceases  at  a 
distinct  line  extending  from  the  left  margin  of  the  oesophagus  to  about 
the  junction  of  the  middle  with  the  last  third  of  the  great  curvature. 
At  about  the  line  where  the  oblique. layer  of  fibres  ceases,  the  stomach 
becomes  constricted  during  the  movements  incident  to  digestion,  divid- 
ing the  organ  into  two  tolerably  distinct  compartments.  The  pyloric 
division   has   lately  been   called   the   antrum   pylori;    and   the   rather 


1 88  GASTRIC   DIGESTION 

thickened  band  of    fibres  next   the    Hne   of  division  is  known   as  the 
sphincter  antri  pylori  (Hofmeister  and  Schiitz). 

The  bloodvessels  of  the  muscular  coat  are  quite  abundant  and  are 
arranged  in  the  peculiar  rectangular  network  which  they  always  pre- 
sent in  the  non-striated  muscular  tissue.  The  nerves  come  from  the 
pneumogastrics  and  the  sympathetic  system  and  are  demonstrated  with 
difficulty. 

Mucous  Coat. — The  mucous  membrane  of  the  stomach  is  soft  and 
velvety  in  appearance  and  of  a  reddish  gray  color.  It  is  loosely  at- 
tached to  the  submucous  muscular  tissue  and  is  thrown  into  wide  longi- 
tudinal folds,  which  become  effaced  as  the  organ  is  distended.  If  the 
mucous  membrane  is  stretched  or  if  the  stomach  is  everted  and  dis- 
tended and  the  mucus  gently  re- 
moved under  a  stream  of  water,  the 
membrane  will  be  found  marked 
fi(''J'<-;%%V''^  with  polygonal  pits,  or  depressions, 
''^'"f'^^i.  enclosed  by  ridges,  which,  in  some 
°V'*"*"\^^*  parts  of  the  organ,  are  quite  regular. 
•V'^'^S'/^*  These  are  best  seen  with  the  aid  of 
'« v^V'^t'^  a-  simple  lens,  as  many  of  them  are 
*«»8*«4i\  quite  small.  The  diameter  of  the 
1^  pits  is  variable,  but  the   average  is 

about   2  00   ^^    ^^  inch  (0.125   milli- 
meter).      This    appearance    is    not 

Fig.  -i&.  —  Pits  in  the  mucous  7>iembrane  of      -,.    ^.       ,       .  i      ^i  i  j_i 

the  stomach  and  openings  of  the  glands,   x    20     dlStmct      tOWard      the      pylorUS  \      the 

(Sappey).  membrane  here  presenting  irregular 

1, 1, 1, 2, 2. 2, 3,  pits  of  different  sizes;  4,5,  ori-   conical  projections  and  well-marked 

fices  of  the  gastric  glands.  .  ■  .  ,    .         , 

Villi  resembling  those  found  m.  the 
small  intestine.  The  surface  of  the  mucous  membrane  is  covered  with 
columnar  or  prismoidal  epithelium,  the  cells  being  regular  in  shape, 
each  with  a  clear  nucleus  and  a  distinct  nucleolus. 

The  thickness  of  the  mucous  membrane  of  the  stomach  varies  in 
different  parts.  Usually  it  is  thinnest  near  the  oesophagus  and  thickest 
near  the  pylorus.  Its  thinnest  portion  measures  y^^  to  ^-^  of  an  inch 
(0.34  to  0.5  millimeter);  its  thickest  portion,  -^^  to  -^^  of  an  inch  (1.6  to 
2.1  millimeters),  and  the  intermediate  portion,  about  ^^g  of  an  inch 
(i   millimeter). 

Glands  of  the  Stomach.  —  Extending  from  the  bottoms  of  the  pits 
in  the  mucous  membrane  of  the  stomach  to  the  submucous  connective 
tissue,  are  large  numbers  of  glands.  These  are  arranged  often  in  dis- 
tinct groups,  surrounded  with  fibrous  tissue,  each  group  belonging  to 
one  of  the  polygonal  depressions.     The  tissue  which  connects  the  tubes 


GLANDS    OF   THE    STOMACH 


189 


is  dense  but  not  abundant.  There  are  marked  differences  in  the  anat- 
omy of  the  glands  in  different  parts  of  the  stomach,  which  are  sup- 
posed to  correspond  with  differences  in  the  uses  of  various  parts  of  the 
mucous  membrane.  There  are,  indeed,  two  distinct  varieties  of  glands ; 
the  peptic  glands,  which  secrete  propepsin,  and  the  acid-glands,  which 
are  supposed  to  secrete  free  hydrochloric  acid.  The  peptic  glands  are 
most  abundant  in  the  pyloric  portion  of  the  stomach  and  around  the 


Fig.  39.  —  Glands  of  the  greater  pouch  of 
the  stomach  (Heidenhain). 


Pig.  40.  —  Pyloric  glands  (Ebstein). 


cardiac  opening.  The  so-called  acid-glands  are  found  throughout  the 
mucous  membrane,  especially  in  the  greater  pouch.  The  secretion  in 
the  pyloric  portion  of  the  stomach  is  not  acid  at  any  time,  while  the 
secretion  in  the  greater  pouch  during  digestion  is  always  strongly 
acid. 

The  pyloric  glands  are  lined  with  cells  that  may  be  called  peptic 
cells  (the  "chief  cells"  of  some  writers).  These  are  conoidal  or  cuboidal 
in  form,  and  relatively  clear,  especially  during  the  intervals  of  digestion. 
Similar   cells    are   found,   in    connection    with    the    so-called    acid-cells 


190 


GASTRIC    DIGESTION 


(parietal  cells),  in  the  secreting  portion  of  the  glands  of  the  greater 
pouch. 

The  acid-glands  are  found  throughout  the  stomach  except  near  the 
pylorus.  The  secreting  portion  of  these  glands  contains  peptic  cells, 
but  near  the  tubular  membrane  are  rounded  cells,  larger  than  the  peptic 
cells,  darker  and  more  granular,  which  are  the  acid,  or  parietal  cells. 
These  are  strongly  stained  when  treated  with  osmic  acid.  It  is  prob- 
able that  the  so-called  acid-glands  secrete  propepsin  as  well  as  an  acid, 
while  the  pyloric  glands  secrete  propepsin  but  no  acid.  In  accordance 
with  the  views  just  stated,  in  the  glands  of  the  greater  pouch,  the  acid 
is  secreted  by  the  rounded  acid-cells,  while  the  propepsin  is  secreted  by 
cells  (peptic  cells)  similar  to  those  lining  the  secreting  portion  of  the 
pyloric  glands.  During  the  intervals  of  digestion,  propepsin  is  in  pro- 
cess of  formation  by  the  peptic  cells,  and  no  acid  is  produced ;  but  acid 
begins  to  be  secreted  soon  after  food  is  received  into  the  stomach.  The 
peptic  cells,  therefore,  do  not  produce  pepsin  directly,  but  a  substance 
sometimes  called  zymogen,  but  more  properly  propepsin  or  pepsinogen, 
which  is  changed  into  pepsin,  possibly  by  the  action  of  hydrochloric  acid. 

The  glands  of  the  stomach  have  an  excretory  portion  and  a  secreting 
portion,  the  latter  presenting  two  or  more  branches.  The  excretory 
portion  is  Hned  with  cells  nearly  like  those  found  on  the  surface  of  the 
mucous  membrane.  The  secreting  portion  is  lined  with  the  peptic  and 
the  acid-cells  already    described  (see  Plate  IV,  Fig.  3). 

Closed  Follicles.  —  In  the  substance  of  the  mucous  membrane,  be- 
tween the  tubes  and  near  their  caecal  extremities,  are  occasionally  found 
closed  follicles,  like  the  solitary  glands  and  patches  of  Peyer  of  the 
intestines.  These  are  not  always  present  in  the  adult  but  frequently  are 
found  in  children.  They  usually  are  most  abundant  over  the  greater 
curvature,  though  they  may  be  found  in  other  situations.  In  their 
anatomy  they  are  identical  with  the  closed  follicles  of  the  intestines  and 
do  not  demand  special  consideration  in  this  connection. 

Gastric  Jince.  — The  observations  of  Beaumont  on  Alexis  St.  Martin, 
the  Canadian  who  had  a  large  fistulous  opening  into  the  stomach,  gave 
the  first  definite  knowledge  of  the  most  important  of  the  physiological 
properties  of  the  gastric  juice.  The  following  was  the  method  employed 
in  collecting  the  secretion  :  The  subject  was  placed  on  the  right  side  in 
the  recumbent  posture,  the  valve  of  mucous  membrane  partially  closing 
the  fistula  was  pressed  into  the  stomach,  and  a  gum-elastic  tube,  of  the 
size  of  a  large  quill,  was  passed  in  to  the  extent  of  five  to  six  inches 
(12  to  15  centimeters).  On  turning  him  upon  the  left  side  until 
the  opening  became  dependent,  the  stimulation  of  the  tube  caused  the 
secretion  to  flow,  sometimes  in  drops  and  sometimes  in  a  small  stream. 


SECRETION    OF    GASTRIC   JUICE 


191 


Since  the  publication  of  Beaumont's  experiments,  many  observations 
have  been  made  on  animals  in  which  permanent  gastric  fistulae  had 
been  established.  In  these  experiments  the  dog  is  most  frequently  used, 
as  in  this  animal  the  operation  usually  is  successful.  The  animals 
operated  upon  by  Bassow,  who  was  the  first  to  establish  a  gastric  fistula 
(1842),  were  merely  objects  of  curiosity ;  but  Blondlot  (1843)  and  others 
fixed  a  tube  in  the  stomach,  collected  the  juice  and  made  important 
observations  in  regard  to  its  action  in  digestion. 

Although  instances  of  gastric  fistula  in  the  human  subject  had  been 
reported  before  the  case  of  St.  Martin,  and  have  been  observed  since 
that  time,  the  remark- 
ably healthy  condition 
of  the  subject  and  the 
extended  experiments 
of  Beaumont  have  ren- 
dered this  case  memo- 
rable in  the  history  of 
physiology.  This  was 
the  only  instance  on 
record  in  which  normal 
gastric  juice  had  been 
obtained  from  the  hu- 
man subject ;  and  it  has 
served  as  a  standard  of 
comparison  for  subse- 
quent experiments  on 
the  inferior  animals. 

An  artificial  gastric 
juice,  prepared  by  ex- 
tracting the  active  prin- 
ciple from  the  mucous  membrane  of  the  stomach  of  different  animals 
and  adding  hydrochloric  acid,  is  useful  in  observations  in  regard  to  the 
chemistry  of  the  peculiar  enzyme,  but  liquids  prepared  in  this  way  are 
not  identical  with  the  natural  secretion.  Extracts  of  the  mucous  mem- 
brane were  made  by  Eberle  (1834),  Von  Wittich,  Briicke  and  many 
others. 

Secretion  of  Gastric  Juice.  —  It  was  observed  by  Beaumont  that  dur- 
ing the  intervals  of  digestion  the  mucous  membrane  is  comparatively 
pale,  "  and  is  constantly  covered  with  a  very  thin,  transparent,  viscid 
mucus,  lining  the  whole  interior  of  the  organ."  On  the  introduction  of 
food,  the  membrane  changes  its  appearance.  It  then  becomes  red  and 
turgid  with  blood;    small  pellucid  points  begin  to  appear  in  various 


K  £ 

Fig.  41.  —  Gastric  fistula  in  the  case  of  St.  Martin  (Beaumont). 

A,  A,  A,  B,  borders  of  the  opening  into  the  stomach ;  C,  left 
nipple ;  D,  chest ;  E,  cicatrices  from  the  wound  made  for  the  re- 
moval of  a  piece  of  cartilage ;  F,  F,  F,  cicatrices  of  the  original 
wound. 


192  GASTRIC   DIGESTION 

parts,  which  are  drops  of  gastric  juice  ;  and  these  gradually  increase  in 
size  until  the  liquid  trickles  down  the  sides  in  small  streams.  The 
membrane  is  now  invariably  of  a  strongly  acid  reaction,  while  at  other 
times  it  is  either  neutral  or  faintly  alkaline.  The  thin  watery  liquid 
thus  produced  is  the  true  gastric  juice. 

While  natural  food  is  the  proper  stimulus  for  the  stomach,  and  while, 
in  normal  digestion,  the  quantity  of  gastric  juice  is  perfectly  adapted  to 
the  work  it  has  to  perform,  it  has  been  noted  that  savory  and  highly 
seasoned  articles  ordinarily  produce  a  more  abundant  secretion  than 
those  which  are  comparatively  insipid.  An  abundant  secretion  is  like- 
wise excited  by  some  of  the  vegetable  bitters  and  even  by  the  sight  or 
odor  of  articles  of  food. 

The  recent  observations  of  Pawlow,  of  St.  Petersburg,  recall  the 
early  brilliant  experiments  of  Claude  Bernard.  Pawlow  established  an 
opening  in  the  stomach  in  the  following  way  :  He  separated  a  small 
portion  of  the  organ  from  the  main  cavity  completely,  so  that  there 
remained  only  an  external  opening  into  the  portion  thus  isolated. 
This  is  called  Pawlow's  pouch,  or  miniature  stomach.  After  feeding, 
the  gastric  juice  flowed  from  this  pouch  clear  and  unmixed  with  debris 
of  food.  He  was  thus  enabled  to  obtain  pure  gastric  juice  and  study 
its  properties,  and  to  avoid  sources  of  error  in  experiments  made  with 
gastric  juice  artificially  prepared.^ 

In  the  experiments  of  Pawlow  —  some  of  whose  conclusions  are  cer- 
tainly remarkable,  not  to  say  extravagant  —  it  appeared  that  the  juice 
flowing  from  the  miniature  stomach  after  feeding  with  different  articles 
presented  marked  differences  in  proteolytic  activity.  The  proteolytic 
action  was  most  vigorous  after  feeding  with  bread ;  and  the  juice 
collected  at  this  time  he  called  "bread-juice."  The  proteolytic  power 
was  measured  by  noting  the  quantity  of  food,  contained  in  a  graduated 
tube,  that  was  dissolved  in  a  certain  time  ;  and  bread-juice  was  found 
to  have  an  activity  of  6.64  millimeters.  The  juice  obtained  after  feed- 
ing with  meat  had  an  activity  of  3.39  millimeters.  The  activity  after 
feeding  with  milk  was  still  less,  being  only  3.26  millimeters.  Perhaps 
the  most  striking  observations  were  made  on  dogs  with  "  sham-feeding." 
In  these  experiments,  the  oesophagus  was  divided  in  the  neck,  leaving 
two  openings,  so  that  the  food  swallowed  did  not  pass  into  the  stomach. 
When  food  was  taken  in  this  way,  pure  gastric  juice  flowed  in  abun- 

1  MM.  Cade  and  Latarjet  have  recently  observed  a  case  of  "  miniature  stomach  "  of  nearly 
twenty  years'  standing  in  a  young  girl,  following  a  hernia  of  part  of  the  stomach  in  the  median 
line,  occurring  in  early  infancy.  This  little  pouch  had  become  isolated  from  the  rest  of  the 
organ.  Nearly  all  the  observations  of  Pawlow  on  dogs  were  confirmed  in  this  case.  The 
fistula  was  finally  closed  by  operation. — Journal  de  physiologie  el  de  palhologie  generale,  Paris, 
Mars,  1905,  tome  vii,  p.  221. 


PROPERTIES    AND    COMPOSITION    OF   GASTRIC   JUICE  193 

dance  from  the  stomach.  It  was  noted,  also,  that  the  sight,  odor,  or 
even  idea  of  food,  particularly  in  animals  having  a  "passionate  longing," 
excited  a  flow  of  juice.  The  secretion  thus  obtained,  Pavvlow  called 
psychic  juice.  He  found  also  that  all  the  digestive  excretions  were 
much  increased  in  quantity  when  the  appetite  was  good  and  food  was 
relished.  According  to  these  observations,  "  the  properties  of  the 
juice  correspond  with  the  requirements  of  the  food.  The  starch- 
holding  diet  receives  a  juice  rich  in  amylolytic  ferment,  the  fat-contain- 
ing, a  juice  with  much  fat-sphtting  ferment.  This  is  manifest  from  the 
strength  of  the  juice,  but  still  more  so  from  the  absolute  quantities  of 
the  ferment." 

It  has  long  been  known  that  impressions  made  on  the  gustatory 
nerves  have  a  marked  influence  in  exciting  the  action  of  the  mucous 
membrane  of  the  stomach ;  and  that  in  most  animals,  particularly  when 
they  are  very  hungry,  the  sight  and  odor  of  food  often  will  set  up  a 
secretion  of  both  saliva  and  gastric  juice.  Febrile  conditions,  the  de- 
pression resulting  from  an  excess  in  eating  and  drinking,  and  even 
purely  mental  conditions,  such  as  anger  or  fear,  vitiate,  diminish  and 
sometimes  entirely  suppress  secretion  by  the  stomach.  At  some  times, 
under  these  conditions,  the  mucous  membrane  becomes  red  and  dry, 
and  at  others  it  is  pale  and  moist. 

After  the  food  has  been  in  part  liquefied  and  absorbed  and  in  part 
reduced  to  a  pultaceous  consistence,  the  secretion  of  gastric  juice 
ceases  ;  the  movements  of  the  stomach  having  gradually  forced  that 
portion  of  the  food  which  is  but  partially  acted  on  in  this  organ  or 
is  digested  only  in  the  small  intestines  out  at  the  pylorus.  The  stomach 
is  thus  entirely  emptied,  the  mucous  membrane  becomes  pale,  and  its 
reaction  loses  its  acid  character,  becoming  neutral  or  faintly  alkahne. 

Quantity  of  Gastric  Juice.  —  Data  for  determining  the  quantity  of 
gastric  juice  secreted  in  the  twenty-four  hours  are  so  uncertain  that  it 
seems  impossible  to  fix  on  any  estimate  that  can  be  accepted  even  as 
an  approximation.  Still,  the  quantity  must  be  considerable,  in  view  of 
the  large  amount  of  alimentary  matter  acted  on  in  gastric  digestion. 
It  probably  is  not  less  than  six  pounds  (2.72  kilograms)  or  more  than 
fourteen  pounds  (6.35  kilograms).  After  this  secretion  has  performed 
its  office  in  digestion,  it  is  reabsorbed,  and  but  a  small  quantity  exists  in 
the  stomach  at  any  one  time. 

Properties  and  Composition  of  Gastric  Jnice.  —  The  juice  taken  from 
the  stomach  during  the  first  moments  of  its  secretion  and  separated 
from  mucus  and  foreign  matters  by  filtration  is  a  clear  Hquid,  of  a  faint 
yellowish  or  amber  tint  and  possessing  little  or  no  viscidity.  Its  reac- 
tion is  always  strongly  acid.     The  specific  gravity  of  the  gastric  juice 


194 


GASTRIC    DIGESTION 


in  the  case  of  St.  Martin,  according  to  the  observations  of  Beaumont 
and  SiUiman,  was  1005  ;  but  later,  F.  G.  Smith  found  it  in  one  instance, 
1008,  and  in  another,  1009.  There  is  every  reason  to  suppose  that  the 
secretion,  in  the  case  of  St.  Martin,  was  normal,  and  1005  to  1009  niay 
be  taken  as  the  range  of  specific  gravity  in  the  human  subject. 

The  gastric  juice,  if  kept  in  a  well-stoppered  bottle,  will  retain  its 
chemical  and  physiological  properties  for  an  indefinite  period.  The 
only  change  that  it  undergoes  is  the  formation  of  a  pellicle,  consisting 
of  a  vegetable  confervoid  growth,  some  of  which  breaks  up  and  falls 
to  the  bottom  of  the  vessel,  forming  a  whitish  fiocculent  sediment.  In 
addition  to  this  remarkable  property  of  resisting  putrefaction,  putre- 
factive changes  are  arrested  in  decomposing  animal  matters,  both  when 
taken  into  the  stomach  and  when  exposed  to  the  action  of  the  gastric 
juice  out  of  the  body. 

The  following  analysis  by  Bidder  and  Schmidt  gives  the  mean  of 
nine  observations  on  dogs  :  — 


COMPOSITION   OF  THE   GASTRIC   JUICE   OF  THE   DOG 


Water 

Ferment  (pepsin) 
Free  hydrochloric  acid 
Potassium  chloride 
Sodium  chloride 
Calcium  chloride 
Ammonium  chloride 
Calcium  phosphate 
Magnesium  phosphate 
Ferric  phosphate 


973.062 

17.127 

3-050 
1. 125 
2.507 
0.624 
0.468 
1.729 
0.226 
0.082 


In  another  series  of  three  observations,  in  which  the  saliva  was 
allowed  to  pass  into  the  stomach,  the  proportion  of  free  acid  was  2.337, 
and  the  proportion  of  organic  matter  was  slightly  increased. 

Organic  Constituent  of  the  Gastric  /nice.  —  Pepsin  is  a  ferment,  or 
enzyme,  peculiar  to  the  gastric  juice  and  essential  to  its  digestive  prop- 
erties. When  the  gastric  secretion  was  first  obtained,  even  by  the 
imperfect  methods  employed  anterior  to  the  observations  of  Beaumont 
and  of  Blondlot,  an  organic  matter  was  spoken  of  as  one  of  its  con- 
stituents.    The  gastric  juice  also  contains  a  milk-curdling  enzyme. 

Free  Acid  of  the  Gastric  Juice. — The  character  of  the  free  acid  was 
long  a  question  of  uncertainty  and  dispute ;  but  physiologists  now  adopt 
the  view  that  the  gastric  juice  contains  free  hydrochloric  acid,  with  pos- 
sibly a  small  quantity  of  lactic  acid.     It  is  admitted,  however,  that  the 


ACTION    OF   THE    GASTRIC   JUICE    IN    DIGESTION  195 

degree  of  acidity  is  variable,  and  that  the  normal  acid  may  be  replaced, 
without  loss  of  the  digestive  properties  of  the  secretion,  by  lactic,  oxalic, 
acetic,  formic,  succinic,  tartaric,  citric,  phosphoric,  nitric  or  sulphuric 
acid. 

Saline  Constituents  of  the  Gastric  Juice.  —  It  has  been  shown  that 
artificial  mixtures  containing  the  organic  matter  of  the  gastric  juice  and 
the  proper  proportion  of  free  acid  are  endowed  with  the  digestive  prop- 
erties of  the  normal  secretion  from  the  stomach,  and  that  these  proper- 
ties are  rather  impaired  when  an  excess  of  its  normal  saline  constituents 
is  added  or  when  the  relation  of  the  salts  to  the  water  is  disturbed  by 
concentration ;  but  physiologists  attach  little  importance  to  the  saline 
constituents,  except  sodium  chloride,  which  is  thought  to  be  concerned 
in  the  production  of  hydrochloric  acid. 

Action  of  the  Gastric  Juice  in  Digestion.  —  Certain  of  the  substances 
most  readily  attacked  by  the  gastric  juice  are  acted  on  by  weak  acid 
solutions  containing  no  organic  matter ;  but  it  is  now  well  established 
that  the  presence  of  a  peculiar  organic  matter  is  a  condition  indis- 
pensable to  actual  digestion.  It  has  also  been  shown  that  liquids  con- 
taining the  organic  constituent  of  the  gastric  juice  have  no  digestive 
properties  unless  they  also  possess  the  proper  degree  of  acidity ;  and 
it  is  as  well  settled  that  liquids  containing  acids  alone  have  no  action  on 
albumins  similar  to  that  which  takes  place  in  digestion,  and  that  when 
these  substances  are  dissolved,  it  is  simply  accidental. 

The  presence  of  any  one  particular  acid  does  not  seem  essential 
to  the  digestive  properties  of  the  gastric  juice,  so  long  as  the  proper 
degree  of  acidity  is  preserved ;  and  it  is  important  that  the  normal  acid 
can  be  replaced  by  other  acids,  for  in  case  any  salt  were  introduced 
into  the  stomach  which  would  be  decomposed  by  the  acid  of  the  gastric 
juice,  digestion  would  be  interfered  with,  unless  the  liberated  acid  could 
take  its  place. 

In  studying  the  physiological  action  of  the  gastric  juice,  it  must 
be  borne  in  mind  that  the  general  process  of  digestion  is  accomplished 
by  the  combined  as  well  as  the  successive  action  of  the  different  diges- 
tive secretions.  The  act  should  be  viewed  in  its  ensemble,  rather  than 
as  a  process  consisting  of  several  successive  and  distinct  operations,  in 
which  different  classes  of  alimentary  matters  are  dissolved  by  distinct 
liquids.  The  food  meets  with  the  gastric  juice,  after  having  absorbed 
a  large  quantity  of  saliva ;  and  it  passes  from  the  stomach  to  be  acted 
on  by  the  intestinal  secretions,  having  imbibed  both  saliva  and  gastric 
juice. 

When  the  acts  which  take  place  in  the  mouth  are  properly  per- 
formed, the  following  alimentary  substances,  comminuted  by  the  action 


196  GASTRIC    DIGESTION 

of  the  teeth  and  thoroughly  insahvated,  are  taken  into  the  stomach  : 
muscular  tissue  with  the  muscular  substance  enveloped  in  its  sarco- 
lemma,  bloodvessels,  nerves,  ordinary  fibrous  tissue  holding  the  mus- 
cular fibres  together,  interstitial  fat,  and  a  small  quantity  of  albumins 
and  corpuscles  from  the  blood,  all  combined  with  a  considerable 
quantity  of  inorganic  salts ;  albumin,  sometimes  unchanged,  but  usually 
more  or  less  thoroughly  coagulated ;  fatty  matters,  sometimes  in  the 
form  of  oil  and  sometimes  enclosed  in  vesicles,  constituting  adipose 
tissue  ;  gelatin  and  animal  matters  in  a  liquid  form  extracted  from  meats, 
as  in  soups ;  casein,  in  its  liquid  form,  united  with  butter  and  salts  in 
milk,  and  coagulated,  in  connection  with  various  other  matters,  in  cheese  ; 
vegetable  nitrogenous  matters,  of  which  gluten  may  be  taken  as  the  type  ; 
vegetable  fats  and  oils ;  sugars,  from  both  the  animal  and  vegetable 
kingdoms,  but  chiefly  from  vegetables ;  different  kinds  of  amylaceous 
substances ;  and  finally,  organic  acids  and  salts,  derived  chiefly  from 
vegetables.  These  matters,  particularly  those  from  the  vegetable  king- 
dom, are  united  with  more  or  less  innutritions  matter,  such  as  cellulose. 
They  also  are  seasoned  with  aromatic  substances,  condiments  etc., 
which  are  not  directly  used  in  nutrition. 

The  various  articles  described  as  drinks  are  taken  without  any 
considerable  admixture  with  the  saliva.  They  embrace  water  and  cer- 
tain nutritious  or  stimulant  infusions  (including  alcoholic  beverages) 
with  a  small  proportion  of  inorganic  salts  in  solution. 

Action  of  the  Gastric  Juice  on  Meats.  — The  digestion  of  meat  in  the 
stomach  is  far  from  complete.  The  parts  of  the  muscular  structure 
most  easily  attacked  are  the  fibrous  tissue  holding  the  muscular  fibres 
together,  and  the  sarcolemma,  or  sheath  of  the  fibres  themselves.  If 
the  gastric  juice  of  the  dog  is  placed  in  a  vessel  with  finely  chopped 
lean  meat  and  kept  in  contact  with  it  for  a  number  of  hours  at  about 
100°  Fahr.  (37.78°  C),  agitating  the  vessel  occasionally  so  as  to  subject, 
so  far  as  possible,  every  particle  of  the  meat  to  its  action,  the  filtered 
liquid  will  be  found  increased  in  density,  its  acidity  diminished,  and 
presenting  all  the  evidences  of  having  dissolved  a  considerable  portion 
of  the  tissue.  There  always,  however,  will  remain  a  certain  portion 
that  has  not  been  dissolved.  Its  constitution  is  nevertheless  materially 
changed  ;  for  it  no  longer  possesses  the  ordinary  character  of  muscular 
tissue  and  easily  breaks  down  between  the  fingers  into  a  pultaceous 
mass.  On  subjecting  this  residue  to  microscopical  examination,  it  is 
found  not  to  contain  any  ordinary  fibrous  tissue ;  and  the  fibres  of 
muscular  tissue,  although  presenting  the  well-marked  and  characteristic 
striae,  are  broken  into  short  pieces  and  have  very  little  tenacity.  It  is 
evidently  only  the  muscular    substance   that   remains,   the  connective 


ACTION    ON   ALBUMIN,    FIBRIN,    CASEIN    AND    GELATIN  197 

tissue  and  the  sarcolemma  having  been  dissolved.  Even  on  adding 
fresh  juice  to  the  undigested  matter,  this  is  not  dissolved  to  any  con- 
siderable extent,  the  residue  not  being  sensibly  diminished  in  quantity, 
and  the  muscular  substance  still  presenting  the  characteristic  striation. 

Whether  the  gastric  juice  be  incapable  of  acting  on  the  muscular 
substance  or  not,  the  above-mentioned  facts  clearly  show  that  muscular 
tissue  usually  is  not  completely  digested  in  the  stomach.  The  action 
of  the  gastric  juice  is  to  dissolve  the  intermuscular  fibrous  tissue  and 
the  sarcolemma,  or  sheath  of  the  muscular  fibres,  setting  the  true  mus- 
cular substance  free  and  breaking  it  up  into  small  particles.  The  mass 
of  tissue  is  thus  reduced  to  a  thin  pultaceous  condition,  and  it  passes 
into  the  small  intestine,  where  its  digestion  is  completed.  The  constitu- 
ents of  the  blood,  albumins,  corpuscles  etc.,  which  may  be  introduced 
in  small  quantity  in  connection  with  muscular  tissue,  probably  are 
completely  dissolved  in  the  stomach. 

Action  0)1  Albimiin,  Fibrm,  Casein  and  Gelatin. — The  action  of  the 
gastric  juice  on  uncooked  white  of  Q.gg  is  to  disintegrate  its  structure, 
separating  and  finally  dissolving  the  membranous  sacs  in  which  the 
albumins  are  contained.  It  also  acts  on  the  albumins,  forming  albu- 
min-peptones, which,  unlike  albumin,  are  not  coagulated  by  heat 
or  acids,  but  are  precipitated  by  alcohol,  tannin  and  many  of  the 
metallic  salts.  The  digestion  of  raw  or  imperfectly-coagulated  albu- 
mins takes  place  with  considerable  rapidity  in  the  stomach ;  and  the 
digestion  of  albumins  in  this  form  is  more  rapid  than  when  they  have 
been  coagulated  by  heat.  It  is  a  matter  of  common  as  well  as  of 
scientific  observation,  that  eggs  when  hard-boiled  are  less  easily  di- 
gested than  when  they  are  soft-boiled  or  uncooked.  The  products  of 
the  digestion  of  raw  or  of  coagulated  albumins  (albumin-peptones)  are 
essentially  the  same.  It  is  probable  that  the  entire  process  of  diges- 
tion and  absorption  of  albumins  takes  place  in  the  stomach ;  and  if  any 
albumins  pass  out  of  the  pylorus,  the  quantity  is  small. 

Fibrin,  as  distinguished  from  myosin,  is  not  a  very  important  article 
of  food.  The  action  of  the  gastric  juice  upon  it  is  more  rapid  and  com- 
plete than  on  albumins.  The  well-known  action  on  fibrin,  of  water 
slightly  acidulated  with  hydrochloric  acid,  has  led  some  physiologists 
to  assume  that  the  acid  is  the  only  constituent  in  the  gastric  juice 
necessary  to  the  digestion  of  this  substance  ;  but  observations  on  the 
comparative  action  of  acidulated  water  and  of  artificial  or  natural  gastric 
juice  show  that  the  presence  of  the  organic  matter  is  necessary  to  the 
digestion  of  this  as  well  as  of  other  nitrogenous  alimentary  substances. 
The  action  of  water  containing  a  small  proportion  of  acid  is  to  render 
fibrin  soft  and  transparent,  frequently  giving  to  the  entire  mass  a  jelly- 


igS  GASTRIC    DIGESTION 

like  consistence.  The  result  of  the  digestion  of  fibrin,  in  the  gastric 
juice  or  in  an  acidulated  fluid  to  which  pepsin  has  been  added,  is  its 
complete  solution  and  transformation  into  a  substance  that  is  not 
affected  by  heat,  acids  or  by  rennet.  The  substance  resulting  from  the 
action  of  gastric  juice  on  fibrin,  called  fibrin-peptone,  resembles  the 
albumin-peptones,  but  has  certain  distinctive  characters. 

Liquid  casein  is  immediately  coagulated  by  the  gastric  juice,  by 
the  action  of  both  the  free  acid  and  an  organic  matter  called  rennin 
(chymosin).  Once  coagulated,  casein  is  acted  on  in  the  same  way  as 
coagulated  albumen.  Casein  taken  as  an  ingredient  of  cheese  is  digested 
in  the  same  way.  The  casein  of  human  milk,  which  coagulates  only 
into  a  sort  of  jelly,  is  more  easily  digested  than  casein  from  cow's  milk. 
The  product  of  the  digestion  of  casein  is  a  soluble  substance,  not  coagu- 
lable  by  heat  or  the  acids,  called  casein-peptone. 

Gelatin  is  rapidly  dissolved  in  the  gastric  juice,  when  it  loses  the 
characters  by  which  it  is  ordinarily  recognized  and  no  longer  forms  a 
jelly  on  cooling.  This  substance  is  much  more  rapidly  disposed  of 
than  the  tissues  from  which  it  is  formed ;  and  the  products  of  its  diges- 
tion in  the  gastric  juice  resemble  the  substances  resulting  from  the 
digestion  of  the  albumins. 

Action  OH  Vegetable  Nitrogenous  Substances.  —  These  substances,  of 
which  gluten  may  be  taken  as  the  type,  are  digested  to  a  considerable 
extent  in  the  stomach.  Uncooked  gluten  is  acted  on  much  in  the  same 
way  as  fibrin,  and  cooked  gluten  behaves  like  coagulated  albumen. 
Vegetable  articles  of  food  usually  contain  gluten  in  greater  or  less 
quantity,  or  substances  resembling  it,  as  well  as  various  non-nitrogenous 
matters  and  cellulose.  The  fact  that  these  articles  are  not  easily 
attacked  in  any  portion  of  the  alimentary  canal,  unless  they  have 
been  well  comminuted  in  the  mouth,  is  shown  by  the  passage  of  grains 
of  corn,  beans  etc.,  in  the  feces.  When  properly  prepared  by  mastica- 
tion and  insalivation,  the  action  of  the  gastric  juice  is  to  disintegrate 
them,  dissolving  out  a  portion  of  the  nitrogenous  matters,  freeing  starch 
and  other  matters  so  that  they  may  be  more  easily  acted  on  in  the 
intestines,  and  leaving  the  hard  indigestible  matters,  such  as  cellulose, 
to  pass  away  in  the  feces.  The  nitrogenous  constituents  of  bread  are 
probably  acted  on  in  the  stomach  in  the  same  way  and  to  the  same 
extent  as  albumins,  fibrin  and  casein. 

Peptones.  —  The  peptones  in  solution  form  colorless  liquids,  having 
a  feeble  odor  resembling  that  of  meat.  They  are  not  coagulable  by 
heat  or  by  most  acids,  a  property  that  distinguishes  them  from  nearly 
all  the  nitrogenous  constituents  of  food.  They  are  coagulated,  hov^^ever, 
by  many  of   the  metallic  salts,  and  by  chlorin  or   tannin  in   slightly 


ACTION  ON  FATS,  SUGARS  AND  AMYLACEOUS  SUBSTANCES       199 

acidulated  solutions.  On  evaporating  peptones  to  dryness,  the  residue 
consists  of  a  yellowish  white  substance,  resembling  desiccated  white  of 
egg.  This  is  soluble  in  water,  when  it  regains  its  characteristic  proper- 
ties, but  is  insoluble  in  alcohol. 

It  is  evident  that  the  gastric  juice,  aside  from  its  action  in  preparing 
certain  articles  for  digestion  by  the  intestinal  secretions,  does  not  simply 
liquefy  certain  of  the  alimentary  matters,  but  changes  them  in  such  a 
way  as  to  render  them  osmotic  and  provides  against  the  coagulation 
which  is  so  easily  induced  in  other  proteids.  Peptones  readily  pass 
through  membranes. 

Another,  the  most  important  and  the  essential  change  exerted  by 
the  gastric  juice  on  proteids,  is  that  by  which  they  are  rendered  capa- 
ble of  assimilation  by  the  system  after  their  absorption.  Pure  albumin 
and  gelatin,  injected  into  the  blood,  are  not  assimilable  and  are  thrown 
off  by  the  kidneys ;  but  albumin  and  gelatin  that  have  been  digested 
in  gastric  juice  are  assimilated  in  the  same  way  as  though  they  had 
penetrated  by  the  natural  process  of  absorption  from  the  alimentary 
canal.  The  same  is  true  of  casein  and  fibrin.  The  action  of  pepsin  is 
essential  to  the  changes  that  occur  in  the  albuminous  alimentary  mat- 
ters, resulting  in  the  formation  of  the  various  peptones ;  and  the  change 
into  peptones  takes  place  in  all  nitrogenous  substances  that  are  dis- 
solved in  the  stomach.  This  may  occur  even  when  the  albuminous 
matters  are  somewhat  advanced  in  putrefaction  ;  and  the  gastric  juice 
possesses  antiseptic  properties,  which  accounts  for  the  frequent  innocu- 
ousness  of  animal  substances  in  various  stages  of  decomposition  when 
taken  into  the  stomach. 

The  change  of  proteids  into  peptones  in  the  stomach  is  not  direct ; 
but  the  intermediate  changes,  probably,  simply  are  hydrolytic  processes. 
The  proteids  are  changed  by  the  gastric  juice  into  a  class  of  substances 
known  as  proteoses,  which  includes  products  from  the  albumins,  globu- 
lins, gelatins  etc.,  in  their  various  stages  of  change.  The  actual  con- 
ditions between  the  proteids  of  food  and  peptones,  treating  them  as 
albumin,  probably  are  the  following :  Albumin  is  first  converted  into 
parapeptone  (acid-albumin,  syntonin)  ;  this  is  converted  into  propeptone, 
which  includes  {a)  protoalbumose,  {b)  heteroalbumose  and  (c)  deutero- 
albumose.  These  finally  are  converted  into  peptone  and  their  digestion 
is  complete. 

Action  on  Fats,  Sjigars  arid  Amylaceous  Substances.  —  Most  of  the 
fatty  constituents  of  food  are  Hquefied  at  the  temperature  of  the  body ; 
and  when  taken  in  the  form  of  adipose  tissue,  the  vesicles  in  which  the 
fatty  matters  are  contained  are  dissolved,  the  fat  is  set  free,  is  melted 
and  floats  in  the  form  of   drops  of    oil  on  the  alimentary  mass.     The 


200  GASTRIC    DIGESTION 

action  of  the  stomach,  then,  seems  to  be  to  prepare  the  fats,  chiefly  by 
dissolving  the  adipose  vesicles,  for  the  complete  digestion  that  takes 
place  in  the  small  intestine. 

The  varieties  of  sugar  of  which  glucose  is  the  type  undergo  little  if 
any  change  in  digestion  and  probably  are  to  some  extent  directly  ab- 
sorbed by  the  mucous  membrane  of  the  stomach.  This  is  not  the  case, 
however,  with  the  varieties  classed  with  cane-sugar.  It  has  been  shown 
that  cane-sugar  injected  into  the  veins  of  a  living  animal  is  not  assimi- 
lated but  is  immediately  rejected  by  the  kidneys.  When,  however,  it 
has  been  inverted  into  dextrose  and  levulose  by  the  action  of  a  dilute 
acid  or  by  digestion  in  the  gastric  juice,  it  no  longer  behaves  as  a  for- 
eign substance  and  does  not  appear  in  the  urine.  Experiments  have 
shown  that  cane-sugar,  after  digestion  for  several  hours  in  the  gastric 
juice,  is  slowly  inverted.  This  action  does  not  depend  on  any  constitu- 
ent of  the  gastric  juice  except  the  free  acid;  and  a  dilute  mixture  of 
hydrochloric  acid  had  an  equally  marked  effect.  Experiments  in  artifi- 
cial digestion  have  shown  that  cane-sugar  is  inverted  by  the  gastric 
juice  very  slowly,  the  action  of  this  secretion  in  no  way  differing  from 
that  of  very  dilute  acids.  In  the  natural  process  of  digestion,  this 
action  may  take  place  to  a  certain  extent ;  but  it  is  not  shown  to  be 
constant  or  important. 

The  action  of  gastric  juice,  unmixed  with  saliva,  on  starch  is  nega- 
tive, so  far  as  any  transformation  into  sugar  is  concerned.  When  the 
starch  is  enclosed  in  vegetable  cells,  it  is  set  free  by  the  action  of  the 
gastric  juice  on  the  nitrogenous  parts.  Raw  starch  in  the  form  of 
granules  becomes  hydrated  in  the  stomach,  on  account  of  the  elevated 
temperature  and  the  acidity  of  the  contents  of  the  organ.  This  is  not 
the  form,  however,  in  which  starch  usually  is  taken  by  the  human 
subject ;  but  when  it  is  so  taken,  the  stomach  evidently  assists  in  pre- 
paring it  for  the  more  complete  processes  of  digestion  that  are  to  take 
place  in  the  small  intestine. 

Cooked  or  hydrated  starch,  the  form  in  which  it  exists  in  bread, 
farinaceous  preparations  generally  and  ordinary  vegetables,  is  not 
affected  by  the  pure  gastric  juice  and  passes  out  at  the  pylorus  un- 
changed. It  must  be  remembered,  however,  that  the  gastric  juice  does 
not  entirely  prevent  a  continuance  of  the  action  of  the  saliva ;  and  ex- 
periments have  shown  that  gastric  juice  taken  from  the  stomach,  when 
it  contains  a  notable  quantity  of  saliva,  has,  to  a  certain  extent,  the 
power  of  transforming  starch  into  sugar. 

The  changes  which  vegetable  acids  and  salts,  the  various  inorganic 
constituents  of  foods  and  the  liquids  that  are  classed  as  drinks  undergo 
in  the  stomach  are  very  slight.     Most  of  these  substances  can  hardly  be 


DURATION    OF    STOMACH    DIGESTION  20I 

said  to  be  digested  ;  for  they  are  either  liquid  or  in  solution  in  water  and 
are  capable  of  direct  absorption  and  assimilation.  In  regard  to  most  of 
the  inorganic  salts,  they  either  exist  in  small  quantity  in  the  ordinary 
water  taken  as  drink  or  are  united  with  organic  nitrogenous  substances. 
In  the  latter  case,  they  become  intimately  combined  with  the  organic 
matters  resulting  from  gastric  digestion.  It  has  been  noted  that  the 
various  peptones  contain  the  same  inorganic  salts  that  existed  in  the 
nitrogenous  substances  from  which  they  were  formed. 

Duration  of  Stomach  Digestion.  —  Inasmuch  as  comparatively  few 
articles,  and  these  belonging  exclusively  to  the  class  of  organic  nitroge- 
nous substances,  are  completely  dissolved  in  the  stomach,  it  is  evident 
that  the  length  of  time  during  which  food  remains  in  this  organ,  or  the 
time  occupied  in  the  solution  of  food  by  gastric  juice  out  of  the  body, 
does  not  represent  the  absolute  digestibility  of  different  articles. 

There  has  certainly  never  been  presented  so  favorable  an  opportu- 
nity for  determining  the  duration  of  gastric  digestion  as  in  the  case  of 
St.  Martin.  From  a  great  number  of  observations  made  on  digestion 
in  the  stomach  itself,  Beaumont  came  to  the  conclusion  that  "the  time 
ordinarily  required  for  the  disposal  of  a  moderate  meal  of  the  fibrous 
parts  of  meat,  with  bread  etc.,  is  three  to  three  and  a  half  hours."  The 
observations  of  F.  G.  Smith,  made  upon  St.  Martin  many  years  later, 
gave  two  hours  as  the  longest  time  that  aliments  remained  in  the 
stomach.  In  a  case  of  intestinal  fistula  reported  by  Busch,  it  was 
noted  that  food  began  to  pass  out  of  the  stomach  into  the  intestines 
fifteen  minutes  after  its  ingestion  and  continued  to  pass  for  three  or  four 
hours,  until  the  stomach  was  emptied.  The  average  time  that  food  re- 
mains in  the  stomach  after  an  ordinary  meal  may  be  stated  to  be  between 
two  and  four  hours. 

Milk  is  one  of  the  articles  digested  in  the  stomach  with  greatest 
ease.  Its  highly  nutritive  properties  and  the  variety  of  its  nutritious 
constituents  render  it  most  valuable  as  an  article  of  diet,  particularly 
when  the  digestive  powers  are  impaired  and  when  it  is  important  to 
supply  the  system  with  considerable  nutriment.  Eggs  are  likewise 
highly  nutritious  and  are  easily  digested.  Raw  and  soft-boiled  eggs 
are  more  easily  digested  than  hard-boiled  eggs.  "Whipped"  eggs  are 
apparently  disposed  of  with  great  facility.  As  a  rule  the  flesh  of  fish 
is  more  easily  digested  than  that  of  the  warm-blooded  animals.  Oysters, 
especially  when  raw,  are  quite  easy  of  digestion.  The  flesh  of  mam- 
mals seems  to  be  more  easily  digested  than  the  flesh  of  birds.  Of  the 
different  kinds  of  meat,  venison,  lamb,  beef  and  mutton  are  easily 
digested,  while  veal  and  fat  pork  are  digested  with  difficulty.  Soups 
usually   are   very   easily    digested.      The  animal   substances   that   are 


202  GASTRIC   DIGESTION 

digested  most  rapidly,  however,  are  tripe,  pigs'  feet  and  brains.  Vege- 
table articles  are  digested  in  about  the  same  time  as  ordinary  animal 
food  ;  but  a  great  part  of  the  digestion  of  these  substances  takes  place 
in  the  small  intestine.  Bread  is  digested  in  about  the  time  required  for 
the  digestion  of  the  ordinary  meats. 

Conditions  that  influence  Stomach  Digestion.  —  The  various  condi- 
tions that  influence  gastric  digestion,  except  those  relating  exclusively 
to  the  character  or  the  quantity  of  food,  operate  mainly  by  modifying 
the  quantity  and  quality  of  the  gastric  juice.  It  is  seldom  that  tem- 
perature has  any  influence,  for  the  temperature  of  the  stomach  in  health 
does  not  present  variations  sufficient  to  have  any  marked  effect  on 
digestion. 

As  a  rule,  gentle  exercise,  with  repose  or  agreeable  and  tranquil 
occupation  of  the  mind,  is  more  favorable  to  digestion  than  absolute 
rest.  Violent  exercise  or  severe  mental  or  physical  exertion  is  always 
undesirable  immediately  after  the  ingestion  of  a  large  quantity  of  food, 
and  as  a  matter  of  common  experience,  has  been  found  to  retard 
digestion. 

The  effects  of  sudden  and  considerable  loss  of  blood  on  gastric 
digestion  are  very  marked.  After  a  full  meal,  the  whole  alimentary 
tract  is  deeply  congested,  and  this  condition  undoubtedly  is  necessary  to 
the  secretion,  in  proper  quantity,  of  the  various  digestive  liquids.  When 
the  entire  quantity  of  blood  in  the  economy  is  greatly  diminished  from 
any  cause,  there  is  difficulty  in  supplying  the  amount  of  gastric  juice 
necessary  for  a  full  meal,  and  disorders  of  digestion  are  likely  to  occur. 
This  is  also  true  in  inanition,  when  the  quantity  of  blood  is  greatly 
diminished.  In  this  condition,  although  the  system  craves  nourishment 
and  the  appetite  frequently  is  ravenous,  food  should  be  taken  in  small 
quantities  at  a  time. 

As  a  rule  children  and  young  persons  digest  food  that  is  adapted  to 
them  more  easily  and  in  larger  relative  quantity  than  those  in  adult  life 
or  in  old  age ;  but  ordinarily  in  old  age  digestion  is  carried  on  with 
more  vigor  and  regularity  than  the  other  vegetative  processes,  such  as 
general  assimilation,  circulation  and  respiration. 

Influence  of  the  Nervous  System  on  the  Stomach.  —  It  is  well  known 
that  mental  emotions  frequently  have  a  marked  influence  on  digestion, 
and  this,  of  course,  can  take  place  only  through  the  nervous  system. 
Of  the  two  nerves  that  are  distributed  to  the  stomach,  the  pneumogastric 
has  been  the  more  carefully  studied,  experiments  on  the  sympathetic 
being  more  difficult.  The  history  of  the  influence  of  the  pneumogas- 
trics  on  digestion,  however,  properly  belongs  to  the  physiology  of  the 
nervous  system. 


MOVEMENTS    OF    THE    STOMACH  203 

Movements  of  the  Stomach. — As  food  is  passed  into  the  stomach, 
the  organ  gradually  changes  its  form,  size  and  position.  When  the 
stomach  is  empty,  the  opposite  surfaces  of  its  lining  membrane  are  in 
contact  in  many  parts  and  are  thrown  into  longitudinal  folds.  As  the 
organ  is  distended,  these  folds  are  effaced,  the  stomach  itself  becoming 
more  rounded,  and  as  the  two  ends,  with  the  lesser  curvature,  are  com- 
paratively immovable,  the  stomach  undergoes  a  movement  of  rotation, 
by  which  the  anterior  face  becomes  superior  and  is  applied  to  the  dia- 
phragm. At  this  time  the  great  pouch  has  nearly  filled  the  left  hypo- 
chondriac region  ;  and  the  great  curvature  presents  anteriorly  and  comes 
in  contact  with  the  abdominal  walls.  Aside  from  these  changes,  which 
are  due  merely  to  distention,  the  stomach  undergoes  important  move- 
ments, which  continue  until  its  contents  have  been  dissolved  and 
absorbed  or  have  passed  out  at  the  pylorus ;  but  while  these  move- 
ments are  taking  place,  the  two  orifices  are  guarded,  so  that  the  food 
shall  remain  for  the  proper  time  exposed  to  the  action  of  the  gastric 
juice.  By  the  rhythmical  contractions  of  the  lower  extremity  of  the 
oesophagus,  regurgitation  of  food  is  prevented ;  and  the  circular  fibres, 
which  form  a  thick  ring  at  the  pylorus,  are  constantly  contracted,  so 
that  —  at  least  during  the  first  periods  of  digestion  —  only  liquids  and 
that  portion  of  food  which  has  been  reduced  to  a  pultaceous  consistence 
can  pass  into  the  small  intestine.  It  is  well  known  that  this  resistance 
at  the  pylorus  does  not  endure  indefinitely,  for  indigestible  articles  of 
considerable  size,  such  as  stones,  have  been  passed  by  the  anus  after 
having  been  introduced  into  the  stomach ;  but  observations  have  shown 
that  masses  of  digestible  matter  are  passed  by  the  movements  of  the 
stomach  to  the  pylorus,  over  and  over  again,  and  that  they  do  not  find 
their  way  into  the  intestine  until  they  have  become  softened  and  more 
or  less  disintegrated. 

The  contractions  of  the  walls  of  the  stomach  are  of  the  kind  charac- 
teristic of  non-striated  muscular  fibres.  If  the  finger  is  introduced  into 
the  stomach  of  a  living  animal  during  digestion,  it  is  gently  but  rather 
firmly  grasped  by  a  contraction,  which  is  slow  and  gradual,  enduring 
for  a  few  seconds  and  as  slowly  and  gradually  relaxing  and  extending 
to  another  part  of  the  organ.  The  movements  during  digestion  present 
certain  differences  in  different  animals ;  but  there  can  be  no  doubt  that 
the  phenomenon  is  universal.  In  dogs,  when  the  abdomen  is  opened 
soon  after  the  ingestion  of  food,  the  stomach  appears  pretty  firmly  con- 
tracted on  its  contents.  In  a  case  reported  by  Todd  and  Bowman,  in 
the  human  subject,  in  which  the  stomach  was  much  hypertrophied  and 
the  walls  of  the  abdomen  were  very  thin,  the  vermicular  movements 
could  be  distinctly  seen.     These  movements  were  active,  resembling  the 


204 


GASTRIC   DIGESTION 


peristaltic  movements  of  the  intestines,  for  which,  indeed,  they  were 
mistaken,  as  the  nature  of  the  case  was  not  recognized  during  life. 

A  peculiarity  in  the  movements  of  the  stomach  —  which  has  been 
repeatedly  observed  in  the  lower  animals,  particularly  dogs  and  cats, 
and  in  certain  cases  has  been  confirmed  in  the  human  subject  —  is  that 
at  about  the  junction  of  the  cardiac  two-thirds  with  the  pyloric  third, 
there  is  a  transverse  band  of  fibres  (the  sphincter  antri  pylori)  so  firmly 
contracted  as  to  divide  the  cavity  into  two  almost  distinct  compartments. 
It  has  also  been  noted  that  the  contractions  in  the  cardiac  division  are 
much  less  vigorous  than  near  the  pylorus ;  the  stomach  seeming  simply 
to  adapt  itself  to  the  food  by  a  gentle  pressure  as  it  remains  in  the  great 
pouch,  while  in  the  pyloric  portion,  the  movements  are  more  frequent, 
vigorous  and  expulsive. 

As  the  result  chiefly  of  the  observations  of  Beaumont,  the  following 
may  be  stated  as  a  summary  of  the  physiological  movements  of  the 
stomach  in  digestion  :  — 

The  stomach  normally  undergoes  no  movements  until  food  is  passed 
into  its  cavity.  When  food  is  received,  at  the  same  time  that  the 
mucous  membrane  becomes  congested  and  the  secretion  of  gastric  juice 
begins,  contractions  of  the  muscular  coat  occur,  which  are  at  first  slow 
and  irregular,  but  become  more  vigorous  and  regular  as  the  process  of 
digestion  advances.  After  digestion  has  become  fully  established,  the 
stomach  usually  is  divided,  by  the  firm  and  almost  constant  contraction 
of  an  oblique  band  of  fibres,  into  a  cardiac  and  a  pyloric  portion  (the 
antrum  pylori);  the  former  occupying  about  two-thirds,  and  the  latter, 
one-third  of  the  length  of  the  organ.  The  contractions  of  the  cardiac 
division  of  the  .stomach  are  uniform  and  rather  gentle ;  while  in  the 
pyloric  division  they  are  intermittent  and  more  expulsive.  The  effect 
of  the  contractions  of  the  stomach  on  the  food  contained  in  its  cavity  is 
to  subject  it  to  a  nearly  uniform  pressure  in  the  cardiac  portion,  the 
general  tendency  of  the  movement  being  toward  the  pylorus  along  the 
greater  curvature  and  back  from  the  pylorus  toward  the  great  pouch 
along  the  lesser  curvature.  At  the  constricted  part  which  separates 
the  cardiac  from  the  pyloric  portion,  there  is  an  obstruction  to  the 
passage  of  the  food  until  it  has  been  sufficiently  acted  on  by  the 
secretions  in  the  cardiac  division  to  have  become  reduced  to  a  pul- 
taceous  consistence.  The  alimentary  mass  then  passes  into  the  pyloric 
division,  and  by  a  more  powerful  contraction  than  occurs  in  other  parts 
of  the  stomach,  it  is  passed  into  the  small  intestine.  The  classical  obser- 
vations of  Beaumont  have  been  in  the  main  confirmed  by  Hofmeister 
and  Schiitz,  Cannon  and  others. 

The  revolutions  of  the  alimentary  mass,  thus    accomplished,    take 


MOVEMENTS    OF   THE    STOMACH  205 

place  slowly,  by  gentle  and  persistent  contractions  of  the  muscular  coat; 
the  food  occupying  two  or  three  minutes  in  its  passage  entirely  around 
the  stomach.  Every  time  that  a  revolution  is  accomplished,  the  contents 
of  the  stomach  are  somewhat  diminished  in  quantity ;  probably,  in  a 
slight  degree,  from  absorption  of  digested  matter  by  the  stomach  itself, 
but  chiefly  by  the  gradual  passage  of  the  softened  and  disintegrated 
mass  into  the  small  intestine.  This  process  continues  until  the  stomach 
is  emptied,  lasting  between  two  and  four  hours  ;  after  which,  the  move- 
ments of  the  stomach  cease  until  food  is  again  introduced. 

Regurgitation  of  food  by  contractions  of  the  muscular  coats  of  the 
stomach,  eructation,  or  the  expulsion  of  gas,  and  vomiting  are  not 
physiological  acts.  It  has  been  shown  that  vomiting  is  produced  by 
contractions  of  the  abdominal  muscles  and  the  diaphragm,  compressing 
the  stomach,  which  is  passive,  except  that  the  pyloric  opening  is  firmly 
closed,  the  cardiac  opening  being  relaxed.  Eructation,  although  usually 
involuntary,  is  sometimes  under  the  control  of  the  will.  When  it 
occurs,  while  it  is  difficult  or  impossible  to  prevent  the  discharge  of  the 
gas,  the  accompanying  sound  may  easily  be  suppressed.  Eructation 
frequently  becomes  a  habit,  which  in  many  persons  is  so  developed  by 
practice  that  the  act  may  be  performed  voluntarily  at  any  time.  The 
gaseous  contents  of  the  stomach  during  digestion  consist  of  oxygen, 
carbon  dioxide,  hydrogen  and  nitrogen,  in  variable  proportions. 


CHAPTER    IX 

INTESTINAL   DIGESTION 

Physiological  anatomy  of  the  small  intestine  —  Mucous  membrane  —  Intestinal  juice — Action 
of  the  intestinal  juice  in  digestion  —  Pancreatic  juice  —  Internal  secretion  by  the  pancreas 
—  Composition  and  properties  of  the  pancreatic  juice  —  Action  of  the  pancreatic  juice  on 
carbohydrates  —  Action  of  the  pancreatic  juice  on  proteids  —  Action  of  the  pancreatic  juice 
on  fats — Action  of  bile  in  digestion — Movements  of  the  small  intestine  —  Physiological 
anatomy  of  the  large  intestine  —  Ileo-csecal  valve — Peritoneal  coat  —  Muscular  coat  — 
Mucous  coat  —  Processes  of  fermentation  in  the  intestinal  canal  —  Contents  of  the  large 
intestine  —  Stercorin — Indol,  scatol,  phenol,  cresol  etc.  —  Movements  of  the  large  intes- 
tine —  Defecation  —  Gases  found  in  the  alimentary  canal. 

Physiological  Anatomy  of  the  Small  Ixtestlxe 

The  small  intestine,  extending  from  the  pyloric  opening  of  the 
stomach  to  the  ileo-csecal  valve,  is  loosely  held  to  the  spinal  column  by 
the  mesentery.  As  the  peritoneum  lining  the  cavity  of  the  abdomen 
passes  from  either  side  to  the  spinal  column,  it  comes  together  in  a 
double  fold  in  front  of  the  great  vessels  along  the  spine,  and  passing 
forward,  divides  again  into  two  layers,  which  become  continuous  with 
each  other  and  enclose  the  intestine,  forming  its  external  coat.  The 
width  of  the  mesentery  usually  is  three  to  four  inches  (7.62  to  10.16 
centimeters);  but  at  the  beginning  and  at  the  end  of  the  small  intestine, 
it  abruptly  becomes  shorter,  binding  the  duodenum  and  that  portion  of 
the  intestine  which  opens  into  the  caput  coli  closely  to  the  subjacent 
parts.  The  mesentery  thus  keeps  the  intestine  in  place,  but  it  allows  a 
certain  degree  of  motion,  so  that  the  tube  may  become  convoluted,  ac- 
commodating itself  to  the  size  and  form  of  the  abdominal  cavity.  The 
form  of  these  convolutions  is  irregular  and  is  constantly  changing.  The 
length  of  the  small  intestine,  according  to  Gray,  is  about  twenty-five 
feet  {7.6  meters) ;  but  the  canal  is  very  distensible,  and  its  dimensions 
are  subject  to  frequent  variations.  Its  average  diameter  is  about  an  inch 
and  a  quarter  (3.18  centimeters). 

The  small  intestine  is  divided  into  three  portions,  which  present 
anatomical  and  physiological  peculiarities  more  or  less  marked.  These 
are  the  duodenum,  the  jejunum  and  the  ileum. 

The  duodenum  has  received  its  name  from  the  fact  that  it  is  about 
the    length    of   the   breadth    of  twelve   fingers,  or  eight  to  ten  inches 

206 


PHYSIOLOGICAL    ANATOMY    OF   THE    SMALL   INTESTINES      20/ 


(20.32  to  25.4  centimeters).  This  part  of  the  intestine  is  wider  than  the 
constricted  pyloric  end  of  the  stomach,  with  which  it  is  continuous,  and 
is  also  much  wider  than  the  jejunum. 

The  coats  of  the  duodenum,  like  those  of  the  other  divisions  of  the 
intestinal  tube,  are  three  in  number.  The  external  is  the  serous,  or 
peritoneal  coat,  which  has 
already  been  described. 
The  middle,  or  muscular 
coat  is  composed  of  non- 
striated  muscular  fibres, 
such  as  exist  in  the 
stomach,  arranged  in  two 
layers.  The  external 
longitudinal  layer  is  not 
very  thick,  and  the  direc- 
tion of  its  fibres  can  be 
made  out  easily  only  at 
the  outer  portions  of  the 
tube,  opposite  the  attach- 
ment of  the  mesentery. 
Near  the  mesenteric  bor- 
der the  outlines  of  the 
fibres  are  faint.  This 
is  true  throughout  the 
entire  small  intestine, 
although  the  fibres  are 
most  abundant  in  the 
duodenum.  The  internal 
layer  of  fibres  is  consid- 
erably thicker  than  the 
longitudinal  layer.  These 
fibres  encircle  the  tube, 
running  usually  at  right 
angles  to  the  external 
layer,  but  some  having  an 
oblique  direction.  The 
circular  layer  is  thickest  in  the  duodenum,  diminishing  gradually  in 
thickness  to  the  middle  of  the  jejunum,  but  afterward  maintaining  a 
nearly  uniform  thickness  throughout  the  canal  to  the  ileo-c^ecal  valve. 

The  jejunum,  the  second  division  of  the  small  intestine,  is  continu- 
ous with  the  duodenum.  It  presents  no  well-marked  line  of  separation 
from  the  third  division,  but  is  considered  as  including  the  upper  two- 


Fig.  42.  —  Stomach,  liver  and  small  intestine  (Sappey). 

I,  inferior  surface  of  the  liver ;  2,  round  ligament  of  the  liver ; 
3,  gall-bladder;  4,  superior  surface  of  the  right  lobe  of  the  liver; 
5,  diaphragm  ;  6,  lower  portion  of  the  oesophagus  ;  7,  stomach  ; 
8,  gastro-hepatic  omentum. ;  9,  spleen ;  10,  gcLStro-splenic  omen- 
tian ;  11,  duodenum ;  12,  12,  small  intestine;  13,  ccEcum ;  14, 
appendix  verniiformis ;  15,  15,  transverse  colon;  16,  sigmoid 
fiexure  of  the  colon  ;  17,  urinary  bladder. 


208  INTESTINAL    DIGESTION 

fifths,  the  lower  three-fifths  being  called  the  ileum.  It  has  received  the 
name  jejunum  from  the  fact  that  it  is  almost  always  found  empty  after 
death. 

The  ileum  is  somewhat  narrower  and  thinner  than  the  jejunum, 
otherwise  possessing  no  marked  pecuUarities  except  in  its  mucous 
membrane.     This  division  of  the  intestine  opens  into  the  colon. 

Mucous  Membrane  of  the  Small  Intestine.  —  The  mucous  coat  of  the 
small  intestine  is  somewhat  thinner  than  the  lining  membrane  of  the 
stomach.  It  is  thickest  in  the  duodenum  and  gradually  becomes 
thinner  toward  the  ileum.  It  is  highly  vascular,  presenting,  like  the 
mucous  membrane  of  the  stomach,  a  great  increase  in  the  quantity  of 
blood  during  digestion.  It  has  a  peculiar  soft  and  velvety  appearance, 
and  during  digestion  is  of  a  vivid  red  color,  being  pale  pink  during  the 
intervals.  It  presents  for  anatomical  description  the  following  parts  : 
I,  folds  of  the  membrane,  called  valvulae  conniventes ;  2,  duodenal 
racemose  glands,  or  glands  of  Brunner ;  3,  intestinal  tubules,  or  folli- 
cles of  Lieberkuhn ;  4,  intestinal  villi;  5,  solitary  glands  or  follicles; 
6,  agminated  glands,  or  patches  of  Peyer. 

The  valvulae  conniventes,  simple  transverse  duplicatures  of  the 
mucous  membrane,  are  particularly  well  marked  in  man,  although  they 
are  found  in  some  of  the  inferior  animals  belonging  to  the  class  of 
mammals,  as  the  elephant  and  the  camel.  They  render  the  extent  of 
the  mucous  membrane  much  greater  than  that  of  the  other  coats  of  the 
intestine.  Beginning  at  about  the  middle  of  the  duodenum,  they  extend, 
with  no  diminution  in  number,  throughout  the  jejunum.  In  the  ileum 
they  progressively  diminish  in  number  until  they  are  lost  at  about  its 
lower  third.  There  are  about  six  hundred  of  these  folds  in  the  first 
half  of  the  small  intestine  and  two  hundred  to  two  hundred  and  fifty 
in  the  lower  half.  Where  they  are  most  abundant,  they  increase  the 
length  of  the  mucous  membrane  to  about  double  that  of  the  tube  itself ; 
but  in  the  ileum  they  do  not  increase  the  length  more  than  one-sixth. 
The  folds  are  always  transverse  and  occupy  usually  one-third  to  one- 
half  of  the  circumference  of  the  tube,  although  a  few  may  extend 
entirely  around  it.  The  greatest  width  of  each  fold  is  at  its  centre, 
where  it  measures  a  quarter  to  half  an  inch  (6.4  to  12.7  millimeters). 
From  this  point  the  width  gradually  diminishes  until  the  folds  are  lost 
in  the  membrane  as  it  is  attached  to  the  muscular  coat.  Between  the 
folds  are  found  fibres  of  connective  tissue  similar  to  those  which  -attach 
the  membrane  throughout  the  alimentary  tract.  This,  though  loose,  is 
constant,  and  it  prevents  the  folds  from  being  effaced,  even  when  the 
intestine  is  distended  to  its  utmost.  Between  the  folds  are  also  found 
bloodvessels,  nerves  and  lymphatics. 


MUCOUS    MEMBRANE    OF   THE    SMALL    INTESTINE  209 

The  position  and  arrangement  of  the  valvulae  conniventes  are  such 
that  they  move  freely  in  both  directions  and  may  be  appHed  to  the 
inner  surface  of  the  intestine  either  above  or  below  their  lines  of  attach- 
ment. It  is  evident  that  the  food,  as  it  passes  along  in  obedience  to  the 
peristaltic  movements,  must,  by  insinuating  itself  beneath  the  folds  and 
passing  over  them,  be  exposed  to  a  greater  extent  of  mucous  membrane 
than  if  these  valves  did  not  exist.  This  is  about  the  only  definite  use 
that  can  be  assigned  to  them. 

Thickly  set  beneath  the  mucous  membrane  in  the  first  half  of  the 
duodenum,  and  scattered  here  and  there  throughout  the  rest  of  its 
extent,  are  the  duodenal  racemose  glands,  or  the  glands  of  Brunner. 
These  are  not  found  in  other  parts  of  the  intestinal  canal.  In  their 
structure  they  closely  resemble  the  racemose  glands  of  the  oesophagus. 
On  dissecting  the  muscular  coat  from  the  mucous  membrane,  they  may 
be  seen  with  the  naked  eye,  in  the  areolar  tissue,  in  the  form  of  small 
rounded  bodies,  about  one-tenth  of  an  inch  (2.5  millimeters)  in  diameter. 
Examined  microscopically,  these  bodies  are  found  to  consist  of  a  large 
number  of  rounded  follicles  held  together  by  a  few  fibres  of  connective 
tissue  (see  Plate  IV,  Fig.  4).  They  have  bloodvessels  ramifying  on 
their  exterior  and  are  lined  with  glandular  epithelium.  They  communi- 
cate with  an  excretory  duct  which  penetrates  the  mucous  membrane 
and  opens  into  the  intestinal  cavity.  When  these  structures  are 
examined  in  a  fresh  preparation,  the  excretory  duct  frequently  is 
found  to  contain  a  clear  viscid  mucus  of  an  alkaline  reaction.  This 
secretion,  however,  has  not  been  obtained  in  quantity  sufficient  to  admit 
of  the  determination  of  its  chemical  or  physiological  properties. 

The  intestinal  tubules,  the  follicles  or  crypts  of  Lieberkiihn,  are 
found  throughout  the  small  and  the  large  intestine.  In  a  thin  vertical 
section  they  are  seen  closely  packed  together,  extending  through  nearly 
the  entire  thickness  of  the  mucous  membrane  (see  Plate  IV,  Fig.  4). 
Between  the  tubules  are  bloodvessels  embedded  in  a  dense  stroma  of 
fibrous  tissue,  with  non-striated  muscular  fibres.  In  vertical  sections 
the  only  situations  where  the  tubules  are  not  seen  are  in  that  portion 
of  the  duodenum  occupied  by  the  ducts  of  the  glands  of  Brunner  and 
immediately  over  the  centre  of  the  larger  soHtary  glands  and  some  of 
the  closed  follicles  which  are  collected  to  form  the  patches  of  Peyer. 
The  tubes  are  not  entirely  absent  in  the  patches  of  Peyer,  but  are  here 
collected  in  rings,  twenty  or  thirty  tubes  deep,  which  surround  each  of 
the  closed  follicles.  Microscopical  examination  of  the  surface  of  the 
mucous  membrane  by  reflected  light  shows  that  the  openings  of  the 
tubules  are  between  the  villi. 

The  tubules  in  the  human  subject  usually  are  simple,  though  some- 


2IO 


INTESTINAL   DIGESTION 


times  bifurcated,  and  are  composed  externally  of  a  structureless  base- 
ment-membrane, lined  with  a  layer  of  cylindrical  epithelium  resembling 
the  cells  that  cover  the  villi,  but  shorter.  Mixed  with  these  cells  are 
the  so-called  goblet-cells,  which  will  be  described  in  connection  with  the 
intestinal  villi.  The  goblet-cells  are  thought  to  secrete  mucus.  They 
exist  in  variable  number,  often  being  as  abundant  as  the  ordinary 
epithelial  cells.     There  is  much  difference  of  opinion  in  regard  to  the 


Fig.  43.  —  Intestinal  tubules,  X  100  (Sappey). 

A.  From  the  dog:  i,  excretory  canal;  2,  2,  primary  branches;  3,  3,  secondary  branches;  4,4, 
terminal  culs-de-sac.  D.  From  the  ox :  i,  excretory  canal ;  2,  principal  branch  dividing  into  two ;  3, 
branch  undivided  ;  4, 4,  terminal  c«/^-i/<'-jac.  C  From  the  sheep:  i,  trunk;  2,  2,  branches.  D.  Single 
tube,  from  the  pig.  E.  From  the  rabbit  and  hare:  i,  simple  gland;  2,  3,  4,  bifid  glands;  5,  com- 
pound gland  from  the  duodenum. 


office  of  the  epithelium,  which  many  histologists  regard  as  non-secretory. 
The  lumen  of  the  tubules  often  contains,  however,  a  mucus-like  secretion. 
The  length  of  the  tubules  is  about  equal  to  the  thickness  of  the  mucous 
membrane  and  is  about  y^g  of  an  inch  (0.33  millimeter).  Their  diameter 
is  about  3^"Q  of  an  inch  (0.07  millimeter).  In  man  they  are  cylindrical, 
terminating  in  a  single  rounded  blind  extremity,  which  frequently  is  a 
little  larger  than  the  rest  of  the  follicle  (see  Plate  IV,  Fig.  4).  These 
follicles  present  considerable  differences  in  the  lower  animals.  In  some 
they  are  bifid  or  branched,  but  in  man  nearly  all  are  simple.     They  are 


MUCOUS    MEMBRANE    OF   THE    SMALL    INTESTINE 


211 


, 6 


larger  in  children  than  in  the  adult  and  are  larger  in  the  colon  than  in 
the  small  intestine. 

The  intestinal  villi,  although  concerned  chiefly  in  absorption,  are 
most  conveniently  considered  in  this  connection.  These  exist  through- 
out the  small  intestine,  but  they  are  not  found  beyond  the  ileo-cascal 
valve,  although  they  cover  that  portion  of  the  valve  which  looks  toward 
the  ileum.  Their  number  is  very  large,  and  they  give  to  the  membrane 
its  peculiar  and  characteristic 
velvety  appearance.  They 
are  found  on  the  valvulae 
conniventes  as  well  as  on 
the  general  surface  of  the 
mucous  membrane.  They  are 
most  abundant  in  the  duode- 
num and  jejunum.  Sappey 
estimated,  as  an  average, 
about  6450  to  the  square 
inch  (1000  in  a  square  centi- 
meter), and  more  than  ten 
millions  (10,125,000)  through- 
out the  small  intestine.  In 
the  human  subject  the  villi 
are  in  the  form  of  flattened 
cylinders  or  cones.  In  the 
duodenum,  where  they  resem- 
ble somewhat  the  elevations 
found  in  the  pyloric  portion 
of  the  stomach,  they  are 
shorter  and  broader  than  in 
other  situations  and  are  more 
like  flattened  conical  folds. 
In  the  jejunum  and  ileum, 
they  are  in  the  form  of  long, 
flattened  cones  and  cylinders. 
As  a  rule  the  cylindrical  form  predominates  in  the  lower  portion  of  the 
intestine.  In  the  jejunum  they  attain  their  greatest  length,  measuring 
here  -^^  to  ^-^  of  an  inch  (0.83  to  1.25  millimeter)  in  length  by  if\  to  -^Iq 
of  an  inch  (0.36  to  0.21  millimeter)  in  breadth  at  their  base. 

The  structure  of  the  villi  shows  them  to  be  simple  elevations  of  the 
mucous  membrane,  provided  with  bloodvessels  and  with  lacteals,  or 
intestinal  lymphatics.  Externally  is  found  a  single  layer  of  cyHndrical 
epithelial  cells  resting  on  a  nucleated  basement-membrane  (see  Plate 


'!^~-~--d 


Fig.  44.  —  Axial  section  of  a  villus  of  a  dog 
(Kultschitzky). 

a,  layer  of  cuticularized  epithelium ;    b,  goblet-cells ; 

c,  space  between  the  attached  ends  of  the  epithelium ; 

d,  nucleated  cell  of  the  basement  membrane;  e,  non- 
striated  muscular  fibres ;  f,  reticulum  from  the  tunica 
propria;  g,  lumen  of  the  central  lymphatic.  (Most  of 
lymphoid  cells  have  been  removed  and  the  bloodvessels 
are  not  shown.) 


212  INTESTINAL    DIGESTION 

IV,  Fig.  6).  They  adhere  together  firmly  and  are  isolated  with  difficulty. 
The  borders  of  their  free  ends  are  thickened  and  finely  striated,  this 
portion  forming  a  thin  membrane  or  cuticle  covering  the  villi.  These 
cells  are  called  cuticularized  cells.  Between  the  cylindrical  cells,  in  vari- 
able number,  are  the  so-called  goblet-cells.  These  probably  are  modi- 
fied cylindrical  cells,  the  change  in  form  being  due  to  a  secretion  of 
mucin  near  their  free  extremities  which  become  swollen,  this  giving  to 
the  cells  their  peculiar  appearance.  The  mucus  finally  is  discharged, 
leaving  a  goblet-shaped  cavity,  the  nucleus  and  granular  protoplasm 
remaining  below.  Some  histologists  regard  these  as  a  distinct  kind  of 
cells  (see  Plate  IV,  Fig.  5). 

The  substance  of  the  villi  is  composed  of  amorphous  matter  in  which 
are  embedded  nuclei,  a  few  fine  fibres,  connective-tissue  cells,  lymphoid 
cells  and  non-striated  muscular  fibres.  The  bloodvessels  are  very  abun- 
dant ;  four  or  five,  and  sometimes  as  many  as  twelve  or  fifteen  arterioles 
entering  at  the  base,  ramifying  through  the  substance  of  the  villus,  but 
not  branching  or  anastomosing  or  even  diminishing  in  calibre  until,  by 
a  slightly  wavy  turn  or  loop,  they  communicate  with  the  venous  radicles, 
which  are  somewhat  larger  than  the  arterioles.  The  veins  all  converge 
to  two  or  three  branches,  finally  emptying  into  a  large  trunk  situated 
nearly  in  the  long  axis  of  the  villus  (see  Plate  V,  Fig.  i). 

The  muscular  fibres  of  the  villi  are  longitudinal,  forming  a  thin  layer 
surrounding  the  villus,  about  halfway  between  the  periphery  and  the 
centre  and  continuous  with  the  muscular  coat  of  the  intestine. 

In  the  central  portion  of  each  villus  is  a  small  lacteal,  one  of  the 
vessels  of  origin  of  the  lacteal  system,  with  an  extremely  delicate  wall 
composed  of  endothelial  cells  with  frequent  stomata  between  their  bor- 
ders. This  vessel  probably  is  in  the  form  of  a  single  tube,  either  simple 
or  presenting  a  few  short  rounded  diverticula. 

The  stomata  of  the  lacteal  vessels  are  thought  to  communicate  with 
lymph-spaces  or  canals  in  the  substance  of  the  villus.  Owing  to  the 
tenuity  of  the  walls  of  the  lacteals  in  the  villi,  it  has  been  found  impossi- 
ble to  fill  these  vessels  with  an  artificial  injection,  although  the  lymphat- 
ics subjacent  to  them  may  easily  be  distended  and  studied  in  this  way. 

No  satisfactory  account  has  been  given  of  nerves  in  the  intestinal 
villi.  If  any  exist  in  these  structures,  they  probably  are  derived  from 
the  sympathetic  system. 

The  solitary  glands,  or  follicles  (lymph-nodes),  and  the  patches  of 
Peyer,  or  agminated  glands,  have  one  and  the  same  structure,  the  only 
difference  being  that  those  called  solitary  are  scattered  singly  in  very 
variable  numbers  throughout  the  small  and  large  intestine,  while  the 
agminated  glands  consist  of  these  follicles  collected  into  patches  of  dif- 


MUCOUS    MEMBRANE    OF   THE    SMALL   INTESTINE 


213 


ferent  sizes.     These  patches  usually  are  found  in  the  ileum.     The  num 

ber  of  the  solitary  glands  is  variable  and  they  are  sometimes  absent 

The  patches  of  Peyer  are  situated  in  that  ^  ^ 

portion  of  the  intestine  opposite  the  attach- 
ment of  the  mesentery.      They  are  likewise  ^  -^ 

variable  in  number  and  are  irregular  in  size.        ^  '    .^    ^    ,  . 

They  usually  are   irregularly-oval  in  form, 

and  measure  half  an  inch  to  an  inch  and  a 

half  (12.7  to  38.1  milHmeters)  in  length  by 

three-fourths  of  an  inch  (19. i   millimeters) 

in  breadth.      Sometimes  they  are  three  to 

four  inches  {y.6  to   10.  i   centimeters)  long, 

but  the  largest  always  are  found  in  the  lower 

part  of  the  ileum.     Their  number  is  about 

twenty,  and  usually  they  are  confined  to  the 

ileum ;    but  when  they  are  very  abundant, 

—  for  they  sometimes  exist  to  the  number 

of  sixty  or  eighty,  —  they  may  be  found  in 

the  jejunum  or  even  in  the  duodenum. 
Two  varieties  of  the  patches  of  Peyer  have 

been  described ;  in  one,  the  patch  is  some- 

what  promi- 
nent, its  surface  being  slightly  raised  above 
the  general  mucous  surface ;  in  the  other, 
the  surface  is  smooth,  and  the  patch  is 
distinguished  at  first  with  some  difficulty. 
The  prominent  patches  are  covered  with 
mucous  membrane  arranged  in  folds  some- 
thing like  the  convolutions  on  the  surface 
of  the  brain.  The  valvules  conniventes 
cease  at  or  near  their  borders.  These  are 
the  only  patches  that  are  commonly  de- 
scribed as  the  glands  of  Peyer,  the  others, 
which  may  be  called  the  smooth  patches, 
frequently  being  overlooked.  The  latter 
are  covered  with  a  smooth,  thin  and  closely 
adherent  mucous  membrane.  Their  follicles 
are  small  and  abundant.  The  borders 
of  these  patches  are  much  less  strongly 
marked  than  in  those  of  the  first  variety. 

As  they  are  seen  only  on  close  examination  and  as  they  are  the  only 

patches  present  in  certain  individuals,  it  is   sometimes  said  that  the 


Fig.  45.  —  PafcA  of  Peyer  (Sappey). 

I,  I,  I,  patch  of  Peyer;  2,2,  folds 
seen  on  the  surface;  3,  3,  grooves 
between  the  folds  ;  4,  4,  fossettes  be- 
tween some  of  the  folds  ;  5,  5,  5,  5,  5, 

5.  5i  5,  valvulse  conniventes;  6,  6,  6, 

6,  solitary  glands  ;  7,  7,  7,  7,  smaller 
solitary  glands  ;  8,  8,  solitary  glands 
on  the  valvulce  conniventes. 


Fig.  46.  —  Pafch  of  Peyer  seen  from 
its  attached  surface  (Sappey). 

I,  I,  serous  coat  of  the  intestine; 
2,  2,  2,  2,  serous  coat  removed  to  show 
the  patch  ;  3,  3,  fibrous  coat  of  the  in- 
testine; 4,  4,  patch;  5,  5,  5,  5,  5,  5,  5, 
5,  valvulas  conniventes. 


214 


INTESTINAL    DIGESTION 


patches  of  Peyer  are  wanting.  They  usually  are  in  less  number  than 
the  first  variety. 

The  villi  are  large  and  prominent  on  the  mucous  membrane  cover- 
ing the  first  variety  of  Peyer's  patches,  especially  at  the  summit  of  the 
folds.  In  the  second  variety  the  villi  are  the  same  as  over  other  parts 
of  the  mucous  membrane,  except  that  they  are  placed  more  irregularly 
and  are  not  so  abundant. 

The  follicles  of  the  patches  of  Peyer  are  closed  and  are  somewhat 
pear-shaped,  with  their  pointed  projections  directed  toward  the  lumen 
of  the  intestine.  Just  above  the  follicle,  there  usually  is  a  small  open- 
ing in  the  mucous  membrane,  surrounded  with  a  ring  of  intestinal 
tubules,  and  leading  to  a  cavity,  the  base  of  which  is  convex  and  is 
formed  by  the  conical  projection  of  the  follicle.  The  diameter  of  the 
follicles  is  y^g  to  2V  o^  tV  ^^  ^^  ^^^^  (o-34  to  i  or  2  millimeters).  The 
small  follicles  usually  are  covered  by  mucous  membrane  and  have  no 
opening  leading  to  them.  Each  follicle  consists  of  a  rather  strong 
capsule  composed  of  an  almost  homogeneous  or  slightly  fibrous  mem- 
brane, enclosing  a  semifluid,  grayish  substance,  cells,  bloodvessels  and 
possibly  lymphatics.  The  semifluid  matter  is  of  an  albuminous  charac- 
ter. The  cells  are  small,  rounded  and  interspersed  with  small  free 
nuclei.  The  bloodvessels  have  rather  a  peculiar  arrangement.  In  the 
first  place  they  are  distributed  between  the  follicles,  so  as  to  form  a 
rich  network  surrounding  each  one.  Capillary  branches  are  sent  from 
these  vessels  into  the  interior  of  the  foUicle,  returning  in  the  form  of 
loops.  Lymphatic  vessels  have  not  been  distinctly  shown  within  the 
investing  membrane.  They  have  been  demonstrated  surrounding  the 
follicles,  but  it  is  still  doubtful  whether  they  exist  in  their  interior.  All 
that  is  known  is  that,  during  digestion,  the  number  of  lacteals  coming 
from  the  Peyerian  patches  is  greater  than  in  other  parts  of  the  mucous 
membrane;  but  vessels  containing  a  milky  liquid  are  not  seen  within  the 
follicles. 

The  description  of  the  follicles  of  the  patches  of  Peyer  answers,  in 
general  terms,  for  the  solitary  glands,  except  that  the  latter  exist  in  both 
the  small  and  large  intestines.  They  are  sometimes  called  lymph-nodes 
—  a  name  given  to  the  lymphatic  glands  ^ — from  their  close  resemblance 
to  these  bodies  in  their  general  structure  (see  Plate  V,  Fig.  5). 

Intestinal  Juice 

Nearly  all  observers  agree  that  the  intestinal  juice  which  they  have 
been  able  to  collect  is  yellow,  thin  and  strongly  alkaline;  but  some 
have  found  it  thin  and  opalescent,  while  others  state  that  it  is  viscid 


INTESTINAL  JUICE  215 

and  clear.  In  a  case  of  fistula  into  the  upper  third  of  the  intestine  in 
the  human  subject,  produced  by  a  penetrating  wound  of  the  abdomen, 
Busch  found  a  secretion  that  was  white  or  of  a  pale  rose-color,  rather 
viscid  and  strongly  alkaline.  The  maximum  proportion  of  solid  matter 
which  it  contained  was  7.4  and  the  minimum,  3.87  per  cent.  The  secre- 
tion apparently  could  not  be  obtained  in  sufficient  quantity  for  ultimate 
analysis.  The  nature  of  this  case  made  it  impossible  that  there  should 
be  any  admixture  of  food,  pancreatic  juice,  bile  or  the  secretion  of  the 
duodenal  glands ;  and  during  the  process  of  digestion,  the  lower  part  of 
the  intestine  undoubtedly  produced  a  normal  fluid. 

From  what  has  been  ascertained  by  experiments  on  the  lower  animals 
and  observations  on  the  human  subject,  the  intestinal  juice  has  been 
shown  to  possess  the  following  characters :  Its  quantity  in  any  portion 
of  the  mucous  membrane  that  can  be  examined  is  small ;  but  when  the 
extent  of  the  canal  is  considered,  it  is  evident  that  the  entire  quantity 
of  intestinal  juice  must  be  considerable.  Vella  estimated  the  quantity 
secreted  by  a  dog  in  one  hour  at  about  11.6  ounces  (360  grams).  The 
secretion  is  viscid  and  adheres  to  the  mucous  membrane.  It  usually  is 
either  colorless  or  of  a  pale  rose-tint.  Its  reaction  is  alkaline.  In  regard 
to  its  composition,  little  of  a  definite  character  has  been  learned.  All 
that  can  be  said  is  that  its  solid  constituents  are  in  a  proportion  of  about 
five  and  a  half  parts  per  hundred  (Busch)  or  about  two  and  a  half  parts 
per  hundred  (Thiry).  There  is  reason  to  beheve  that  in  most  observa- 
tions on  secretions  from  the  small  intestine,  the  normal  intestinal  juice 
was  not  obtained ;  and  beyond  the  fact  that  the  mucous  membrane  pro- 
duces a  secretion  or  secretions,  nothing  is  known  of  the  mode  of  action  of 
its  glandular  structures.  Among  the  enzymes  that  have  been  described, 
is  erepsin  (Otto  Cohnheim).  This  is  supposed  to  act  on  proteoses  and 
peptones,  splitting  them  into  simpler  substances ;  but  the  statements 
of  observers  in  regard  to  this  special  action  are  far  from  satisfactory. 
As  regards  the  relative  importance  of  secretions  by  the  glands  of 
Brunner  and  the  foUicles  of  Lieberkiihn,  nothing  definite  can  be  said. 

Action  of  tJie  Intestijial  Juice  in  Digestion.  — The  physiological  action 
of  the  intestinal  juice  has  lately  been  studied  in  dogs  by  Pawlow,  with 
important  results.  He  discovered,  especially  in  the  duodenal  secretion, 
a  new  ferment  to  which  he  gave  the  name  enterokinase.  This  is  a  true 
proteid  ferment,  its  activity  being  destroyed  by  boiling.  Mixed  with  the 
pancreatic  juice,  the  intestinal  secretion  increases  the  activity  of  both 
the  amylolytic  and  fat-splitting  ferments.  The  duodenal  secretion  in- 
creases especially  the  activity  of  the  proteolytic  ferment. 

In  1858  Busch  reported  a  case  of  fistula  in  the  human  subject,  in 
which  the  opening  was  supposed  to  be  in  the  upper  third  of  the  small 


2l6  INTESTINAL    DIGESTION 

intestine.  Later,  following  the  observations  of  Thiry  (1864),  the  intes- 
tinal juice  was  obtained  by  what  is  known  as  the  Thiry-Vella  method. 
The  experiment  of  Thiry,  modified  by  Vella,  is  the  following :  The  ab- 
domen of  a  dog  is  opened  and  a  portion  of  the  small  intestine,  twelve 
to  twenty  inches  (30  to  50  centimeters)  in  length,  is  cut  away  from  the 
rest  of  the  tract.  The  two  cut  ends  of  the  intestine  are  then  connected, 
leaving  a  portion  isolated  but  attached  to  the  mesentery,  each  end  of 
which  is  connected  with  an  opening  in  the  abdominal  walls  so  as  to 
leave  two  fistulous  openings.  The  parts  are  then  allowed  to  heal,  and 
what  is  supposed  to  be  pure  intestinal  juice  may  be  collected  from  the 
isolated  portion.  While  it  must  be  admitted  that  this  is  an  imperfect 
way  of  obtaining  a  normal  secretion,  the  observations  are  of  consider- 
able value.  The  result  of  these  experiments  has  been  to  show  that  the 
intestinal  secretion  inverts  cane-sugar  into  dextrose  and  levulose  (invert- 
sugar)  and  may  have  a  like  action  on  milk-sugar  and  maltose.  The 
majority  of  observations  have  failed  to  show  any  action  on  starch  or 
fats.  The  ferment  acting  on  the  sugars  has  been  called  invertin 
(Paschutin). 

Pancreatic  Juice 

The  pancreas  is  situated  transversely  in  the  upper  part  of  the  ab- 
dominal cavity  and  is  closely  applied  to  its  posterior  wail.  Its  form  is 
elongated,  presenting  an  enlarged  thick  portion,  called  the  head,  which 
is  attached  to  the  duodenum,  a  body  and  a  pointed  extremity,  which 
latter  is  in  close  relation  to  the  hilum  of  the  spleen.  Its  average  weight 
is  four  to  five  ounces  (114.4  to  141. 7  grams);  its  length  is  about 
seven  inches  (17.78  centimeters);  its  greatest  breadth,  about  an  inch 
and  a  half  (3.81  centimeters);  and  its  thickness,  three-quarters  of  an 
inch  (1.91  centimeters).  It  lies  behind  the  peritoneum,  which  covers 
only  its  anterior  surface. 

There  are  nearly  always,  in  the  human  subject,  two  pancreatic  ducts 
opening  into  the  duodenum  ;  one  which  opens  in  common  with  the 
ductus  communis  choledochus,  and  one  which  opens  about  an  inch 
(25.4  millimeters)  above  the  main  duct.  The  main  duct  is  about  an 
eighth  of  an  inch  (3.2  millimeters)  in  diameter  and  extends  along  the 
body  of  the  gland,  becoming  larger  as  it  approaches  the  opening. 
The  second  duct  is  smaller  and  becomes  diminished  in  calibre  as  it 
passes  to  the  duodenum.  In  general  appearance  and  in  minute  struc- 
ture, the  pancreas  nearly  resembles  the  parotid.  It  differs,  however, 
from  the  salivary  glands  in  some  important  particulars.  It  is  rather 
softer  and  looser  in  texture  and  has  no  distinct  fibrous  covering.  Its 
alveoli  contain   secreting  cells,  but  here  and  there  are  found  groups 


PANCREATIC   JUICE 


217 


of  smaller,  spindle-shaped  bodies  called  centro-acinar  cells,  the  groups 
constituting  the  islands  of  Langerhans  (see  Plate  V,  Fig.  4).  It  is 
thought  that  these  cells  are  not  concerned  in  the  production  of  pan- 
creatic juice,  but  produce,  by  what  is  known  as  internal  secretion,  a  sub- 
stance taken  up  by  the  blood  or  lymph,  which  is  instrumental  in  the 
normal  consumption  of  sugar.  Removal  of  the  entire  pancreas  is 
followed  by  glycosuria,  which  may  be  relieved  by  transplantation 
of  parts  of  the  pancreas  in  any  of  the  tissues  or  even  under  the  skin. 


20   12    19 


Fig.  47.  —  The  pancreas  ;  its  direction,  relations  and  two  excretory  ducts  (Sappey). 

I,  first  portion  of  the  duodenum  ;  2,  second  portion  ;  3,  third  portion ;  4,  4,  head  of  the  pancreas  ; 
5,  middle  portion;  6,  terminal  extremity;  7,  7,  principal  duct;  8,  accessory  duct;  g,  left  lobe  of  the 
liver;  10,  right  lobe;  11,  anterior  portal  eminence;  12,  lobus  Spigelii ;  13,  antero-posterior  groove; 
14,  gall-bladder;  15,  hepatic  duct;  16,  cystic  duct;  17,  ductus  communis  choledochus ;  18,  trunk  of 
the  portal  vein;  19,  coeliac  axis;  20,  hepatic  artery;  21,  coronary  gastric  artery;  22,  cardiac  portion 
of  the  stomach  ;  23,  splenic  artery;  24,  spleen  ;  25,  left  kidney ;  26,  right  kidney ;  27,  superior  mesenteric 
artery  and  vein ;  28,  inferior  vena  cava. 

The  glycolytic  enzyme,  however,  has  not  been  isolated.  '  A  few  cases 
of  what  is  now  known  as  pancreatic  diabetes  have  been  observed  in  the 
human  subject.  The  pancreas  is  abundantly  supplied  with  blood. 
The  larger  arterial  branches  ramify  in  the  loose  connective  tissue  be- 
tween the  lobes,  into  which  they  send  twigs  that  break  up  into  capillary 
plexuses  surrounding  the  individual  acini,  lying  in  close  relation  with 
the  epithelium  (see  Plate  V,  Fig.  3). 

Composition  and  Properties  of  the  Pancreatic  Juice.  —  One  of  the 
most  ingenious  of  the  many  experiments  on  digestion  made  by  Pawlow 
is  the  establishment  of  a  permanent  pancreatic  fistula.     It  is  not  neces- 


2l8  INTESTINAL    DIGESTION 

sary  to  go  into  the  technical  details  of  this  operation,  and  it  is  sufficient 
to  say  that  he  succeeded  in  maintaining  an  open  communication  with 
the  duodenum  at  the  site  of  the  opening  of  the  principal  pan- 
creatic duct  and  secured  normal  pancreatic  juice  in  considerable  quan- 
tity. The  Hquid  thus  obtained  is  viscid,  slightly  opalescent  and  has 
a  strongly  alkahne  reaction.  Bernard  found  the  specific  gravity  of  the 
pancreatic  juice  of  the  dog  to  be  1040.  The  normal  secretion  from 
a  temporary  fistula  in  a  dog  has  been  observed  with  a  specific  gravity 
of  1019  (Flint).  The  quantity  of  organic  matters  in  the  normal  juice  is 
very  great,  so  that  the  liquid  is  solidified  by  heat.  This  coagulability 
is  one  of  the  properties  by  which  the  normal  secretion  may  be  distin- 
guished from  that  which  has  undergone  alteration. 

COMPOSITION   OF  THE   PANCREATIC  JUICE   OF  THE   DOG  (BERNARD) 

Water .       900-920 

Organic  matters,  precipitable  by  alcohol  and  containing  always 

a  little  lime  (amylopsin,  trypsin,  steapsin)        ....         90-  73.60 
Sodium  carbonate 


Sodium  chloride 
Potassium  chloride 
Calcium  phosphate 


10-     6.40 


I 000     I 000 


An  enzyme,  almost  if  not  quite  identical  with  ptyalin,  may  be  extracted 
from  the  normal  juice  by  nearly  the  same  processes  as  those  employed 
in  the  isolation  of  the  active  principle  of  the  saliva.  On  account  of 
its  vigorous  action  on  starch  this  substance  has  been  called  amylopsin. 

Trypsin  is  an  enzyme  capable  of  acting  on  the  proteids,  changing 
them  into  peptones.  The  secreting  cells  of  the  gland  produce  a  sub- 
stance called  trypsinogen,  which  is  changed  into  trypsin.  The  action 
of  trypsin  on  the  proteids  is  increased  by  the  addition  of  small  quanti- 
ties of  sodium  chloride,  sodium  glycocholate  or  sodium  carbonate  and 
is  diminished  by  acids. 

A  substance  called  steapsin,  capable  of  decomposing  fats  into  fatty 
acids  and  glycerin,  has  been  described  as  one  of  the  organic  constitu- 
ents of  the  pancreatic  juice.  This  action  upon  fats,  which  was  noted 
by  Bernard,  though  slight,  probably  assists  in  their  emulsification. 

The  inorganic  constituents  of  the  pancreatic  juice,  beyond  giving  the 
secretion  an  alkaline  reaction,  do  not  possess  any  special  physiological 
interest,  inasmuch  as  they  do  not  seem  to  be  essential  to  its  peculiar 
digestive  properties. 

The  entire  quantity  of  pancreatic  juice  secreted  in  the  twenty-four 
hours   has  been  variously  estimated  by  different  observers.     Bernard 


PANCREATIC   JUICE  219 

was  able  to  collect  from  a  dog  of  medium  size  eighty  to  one  hundred 
grains  (5.2  to  6.5  grams)  in  an  hour.  There  is  no  accurate  basis 
for  an  estimate  of  the  quantity  secreted  in  the  twenty-four  hours  in 
the  human  subject  or  of  the  quantity  necessary  for  the  digestion  of  a 
given  quantity  of  food. 

Unlike  the  gastric  juice,  the  pancreatic  juice,  under  ordinary  con- 
ditions of  heat  and  moisture,  rapidly  undergoes  decomposition,  and 
in  warm  and  stormy  weather  the  alteration  is  marked  in  a  few  hours ; 
but  at  a  temperature  of  50°  to  70°  Fahr.  (10"  to  21°  C),  it  occupies 
two  or  three  days.  As  it  decomposes,  the  liquid  acquires  an  offensive 
putrefactive  odor,  and  its  coagulability  diminishes  until  finally  it  is  not 
affected  by  heat.  The  alkalinity,  however,  increases  in  intensity,  and 
when  neutralized  with  an  acid,  there  is  a  considerable  evolution  of 
carbon  dioxide. 

Pawlow  found  that  an  abundant  pancreatic  secretion  was  excited 
by  acids ;  and  it  is  probable  that  the  acid  contents  of  the  stomach, 
passing  into  the  duodenum,  act  as  a  powerful  stimulus  to  the  gland. 
He  also  showed  that  dogs  with  a  permanent  fistula  suffered  from 
erosion  of  the  parts  with  which  the  secretion  came  in  contact.  This 
trouble,  however,  was  obviated  by  having  the  animals  rest  on  a  bed  of 
sand  or  sawdust,  which  absorbed  the  liquid  as  it  was  discharged. 

The  secretion  from  the  pancreas  was  collected  by  Pawlow  by  attach- 
ing over  the  opening  in  the  abdomen  the  large  end  of  a  funnel.  The 
liquid  thus  obtained  had  a  powerful  action  on  proteids,  starch,  cane- 
sugar  and  fats.  Like  the  gastric  juice,  the  pancreatic  secretion  pre- 
sented marked  differences  in  activity  after  feeding  with  different  articles. 
Its  proteolytic  action  was  strongest  after  feeding  with  milk  and  less 
with  meat  and  bread;  its  amylolytic  action  was  strongest  with  bread- 
feeding  and  less  with  meat  and  milk;  and  its  fat-splitting  action  was 
strongest  after  milk-feeding,  less  with  bread,  and  intermediate  with  meat. 

In  addition  to  the  great  increase  in  the  activity  of  the  pancreatic 
secretion  produced  by  the  presence  of  the  intestinal  juice,  it  is  supposed 
that  the  spleen  secretes  a  kinase  which  is  carried  to  the  pancreas, 
unites  with  trypsinogen  and  forms  tripsin.  It  can  not  be  thought, 
however,  that  this  union  is  essential  to  the  production  of  an  active 
trypsin ;  for  this  enzyme  is  formed  in  animals  from  which  the  spleen 
has  been  removed,  perhaps  by  the  action  of  intestinal  secretions  con- 
taining enterokinase.  The  activity  of  the  pancreatic  secretion,  par- 
ticularly in  the  acidification  of  fats,  is  much  increased  by  the  addition 
of  bile.  This  well-known  fact  was  confirmed  by  Pawlow.  Added  to 
its  other  action,  the  pancreatic  juice  curdles  milk,  by  virtue  of  a  milk- 
clotting  ferment. 


220  INTESTINAL    DIGESTION 

Action  of  the  Pancreatic  Juice  on  Carbohydrates.  —  The  action  of  the 
pancreatic  juice  in  transforming  starch  into  sugar  was  first  observed 
in  1844,  by  Valentin,  who  experimented  with  an  artificial  liquid  made 
by  infusing  pieces  of  the  pancreas  in  water.  Bouchardat  and  Sandras 
first  noted  this  property  in  the  normal  pancreatic  secretion.  In  man, 
some  of  the  amylaceous  matters  are  acted  on  by  the  saliva,  but  most 
of  the  starch  taken  as  food  is  rapidly  digested  in  the  small  intestine. 
It  is  possible  that  the  bile  assists  in  this  process  to  a  slight  extent. 
In  the  transformation  of  starch  into  sugar  in  the  small  intestine,  the 
same  intermediate  processes  are  observed  as  occur  in  the  action  of  the 
saliva ;  but  the  change  in  the  intestine  into  glucose  is  more  rapid. 
It  is  stated  that  amylopsin  is  not  present  in  the  pancreas  of  the  new- 
born infant  (Korowin),  and  that  in  early  infancy  —  before  the  second  or 
third  month  —  the  pancreatic  extract  will  not  digest  starch. 

As  cane-sugar  passes  from  the  stomach  into  the  duodenum,  it  is 
almost  instantly  inverted ;  but  this  is  due  entirely  to  the  action  of  the 
intestinal  juice.     The  pancreatic  juice  does  not  act  on  the  sugars. 

Action  of  the  Pancreatic  Juice  on  Proteids.  —  Reference  has  already 
been  made  to  the  relative  importance  of  intestinal  digestion  ;  and  it  has 
been  apparent  that  the  process  of  disintegration  of  food  in  the  stomach 
is  not  final,  even  as  regards  many  of  the  nitrogenous  substances,  but 
is  rather  preparatory  to  the  complete  liquefaction  of  these  matters, 
which  takes  place  in  the  small  intestine.  In  experiments  in  which  the 
pancreas  has  been  partially  destroyed  in  dogs,  there  was  rapid  emacia- 
tion, with  great  voracity,  and  the  passage,  not  only  of  unchanged  fats 
and  starch,  but  of  undigested  nitrogenous  matters  in  the  dejections. 
The  voracious  appetite,  progressive  emaciation  and  the  passage  of  all 
classes  of  alimentary  substances  in  the  feces,  after  this  operation,  in- 
dicate the  great  importance  of  the  pancreatic  juice  in  digestion ;  but 
the  precise  mode  of  action  on  the  proteids  is  even  now  a  question  of 
some  obscurity.  If  the  bile  is  shut  off  from  the  intestine  and  dis- 
charged externally  by  a  fistulous  opening,  the  same  voracity  and  ema- 
ciation are  observed  ;  and  yet  there  is  no  single  alimentary  substance 
on  which  the  bile,  of  itself,  has  been  shown  to  exert  a  decided  digestive 
action.  Furthermore,  the  pancreatic  juice  evidently  is  adapted  to  act 
on  alimentary  matters  after  they  have  been  subjected  to  the  action  of 
the  stomach,  a  preparation  that  is  essential  to  proper  intestinal  diges- 
tion ;  and  once  passed  into  the  intestine,  the  food  comes  in  contact  with 
a  mixture  of  pancreatic  juice,  intestinal  juice  and  bile.  Nitrogenous 
alimentary  substances,  when  exposed  to  the  action  of  the  pancreatic 
juice  out  of  the  body,  rapidly  become  softened  and  dissolved  in  some 
of  their  parts,  but  soon  undergo  putrefaction.     Analogous  changes  take 


ACTION    OF    THE    BILE    IN    DIGESTION  221 

place  in  starchy  and  fatty  matters  when  they  are  exposed  to  the  action 
of  the  pancreatic  juice  out  of  the  body,  and  they  pass  through  the 
various  stages  of  transformation  respectively  into  lactic  acid  and  the 
fatty  acids.  Putrefactive  action,  however,  does  not  readily  take  place 
in  proteids  that  have  been  precipitated  after  having  been  cooked,  or  in 
raw  gluten  or  casein.  The  presence  of  fat  also  interferes  with  putre- 
faction. 

Trypsin,  in  an  alkaline  medium,  changes  proteids  into  their  respec- 
tive peptones,  in  much  the  same  way  and  involving  nearly  the  same 
intermediate  processes  as  in  the  digestion  of  these  substances  by  the 
gastric  juice,  except  that  the  first  change  is  into  alkali-albumin  instead  of 
acid-albumin.  In  the  upper  part  of  the  intestine  the  vigor  of  this  pro- 
teolytic action  is  much  increased  by  admixture  with  the  intestinal  secre- 
tions ;  and  in  the  lower  part,  where  the  contents  are  more  strongly 
alkaline,  the  activity  of  the  process  is  increased  by  sodium  carbonate. 
If  the  action  of  the  pancreatic  juice  on  proteids  is  prolonged  in  vitro, 
the  changes  continue  and  substances  are  formed  which  yield  leucin, 
tyrosin  and  other  analogous  products.  The  final  putrefactive  changes 
resulting  in  indol,  skatol,  phenol,  etc.,  some  of  which  have  a  distinctly 
fecal  odor,  probably  are  due  to  the  action  of  micro-organisms. 

Action  of  the  Pancreatic  Jjtice  on  Fats.  — The  pancreatic  juice  is  the 
only  digestive  secretion  that  is  capable  of  forming  a  complete  and 
permanent  emulsion  with  fats,  and  this  persists  when  the  emulsion  is 
diluted  with  water.  Steapsin,  extracted  from  the  fresh  pancreas,  has 
the  property  of  decomposing  the  fats  into  their  fatty  acids  and  glycerin  ; 
but  the  fatty  acids  do  not  appear  in  the  chyle.  The  emulsification  of  the 
fats  by  the  pancreatic  juice  is  to  a  great  extent  a  mechanical  process, 
dependent  on  the  general  physical  characters  of  the  liquid ;  but 
although  the  fat  contained  in  the  lacteal  vessels  is  always  neutral,  it 
is  thought  that  steapsin  assists  in  rendering  the  emulsion  fine  and 
permanent. 

Action  of  the  Bile  in  Digestion 

The  physiological  anatomy  of  the  liver  and  the  general  properties 
and  composition  of  the  bile  will  be  considered  again  in  connection  with 
the  physiology  of  secretion  and  excretion  ;  and  here  it  will  be  necessary 
only  to  study  the  action  of  the  bile  in  digestion. 

The  question  whether  the  bile  is  simply  excrementitious  or  is  con- 
cerned in  digestion  was  formerly  the  subject  of  much  discussion  ;  but  it 
is  now  admitted  by  all  physiologists  that  the  action  of  the  bile  in  diges- 
tion and  absorption,  whatever  its  office  may  be  as  an  excretion,  is  essen- 
tial to  life.     The  experiments  of  Swann,  Nasse,  Bidder  and  Schmidt, 


222  INTESTINAL   DIGESTION 

Bernard  and  others,  who  have  discharged  all  the  bile  by  a  fistula  into 
the  gall-bladder,  communication  between  the  bile-duct  and  the  duodenum 
having  been  cut  off,  show  that  dogs  operated  on  in  this  way  have  a 
voracious  appetite,  but  die  of  inanition  after  having  lost  four-tenths  of 
the  body-weight.  The  following  is  an  example  of  experiments  of  this 
kind  (Flint,  1861):  A  fistula  was  made  into  the  gall-bladder  of  a  dog, 
after  excising  a  great  part  of  the  common  bile-duct.  The  animal 
suffered  no  immediate  effects  from  the  operation,  but  died  at  the  end  of 
thirty-eight  days,  having  lost  37^  per  cent  in  weight.  He  had  a  vora- 
cious appetite,  was  fed  as  much  as  he  would  eat,  was  protected  from 
cold  and  was  carefully  prevented  from  hcking  the  bile.  During  the 
progress  of  the  experiment,  various  observations  were  made  on  the  flow 
of  bile.  During  the  last  five  or  six  days,  the  animal  was  ravenous  but 
was  not  allowed  to  eat  all  that  he  would  at  one  time.  At  that  time  he 
was  fed  twice  a  day,  but  he  would  not  eat  fat,  even  when  very  hungry. 
During  the  last  day,  when  too  weak  to  stand,  he  attempted  to  eat  while 
lying  down. 

Human  bile  is  moderately  viscid,  of  a  dark  golden-brown  color,  an 
alkaline  reaction  and  a  specific  gravity  of  about  1028.  Among  other 
constituents  —  which  will  be  described  in  connection  with  the  physiology 
of  secretion  —  it  contains  sodium  united  with  two  acids  peculiar  to 
the  bile,  called  glycocholic  and  taurocholic  acids.  Sodium  taurocho- 
late  is  much  more  abundant  than  the  glycocholate.  The  viscidity  of 
the  bile  is  due  to  mucus  derived  in  part  from  the  hning  membrane  of 
the  gall-bladder  and  in  part,  probably,  from  little  racemose  glands 
attached  to  the  larger  bile-ducts  in  the  substance  of  the  liver.  The 
so-called  biliary  salts,  sodium  taurocholate  and  sodium  glycocholate,  are 
probably  the  constituents  of  the  bile  that  are  concerned  in  digestion. 

Although  the  bile  is  constantly  discharged  in  certain  quantity  into 
the  duodenum,  its  flow  presents  marked  variations  corresponding  with 
certain  stages  of  the  digestive  process.  In  fasting  animals,  the  gall- 
bladder is  distended  with  bile  ;  but  in  animals  opened  soon  after  feedings 
it  is  nearly  always  found  empty.  The  actual  secretion  of  bile  by  the 
liver  also  is  influenced  by  digestion. 

Disregarding  slight  variations,  it  may  be  stated,  in  general  terms^ 
that  the  bile  begins  to  increase  in  quantity  immediately  after  eating ; 
that  its  flow  is  at  its  maximum  from  the  second  to  the  eighth  hour,  dur- 
ing which  time  the  quantity  does  not  vary  to  any  great  extent ;  after  the 
eighth  hour  it  begins  to  diminish,  and  from  the  twelfth  hour  to  the  time 
of  feeding  it  is  at  its  minimum. 

One  of  the  uses  which  has  been  ascribed  to  the  bile  is  that  of  stimu- 
lating peristaltic  movements  of  the  small  intestine  and  of  preventing 


ACTION    OF   THE    BILE    IN    DIGESTION  223 

putrefactive  changes  in  the  intestinal  contents  and  the  abnormal  devel- 
opment of  gas ;  but  observations  on  this  point  have  been  somewhat 
conflicting.  During  the  first  few  days  of  the  experiment  just  described, 
the  dejections  were  very  rare;  but  they  afterward  became  regular,  and 
at  one  time  there  was  even  a  tendency  to  diarrhoea.  There  can  be  little 
doubt,  however,  that  the  bile  restrains  putrefaction  of  the  contents  of 
the  intestinal  canal,  particularly  when  animal  food  has  been  taken.  The 
feces  in  the  dog  with  biliary  fistula  were  always  extremely  offensive. 
Bidder  and  Schmidt  found  this  to  be  the  case  in  dogs  fed  entirely  on 
meat ;  but  the  feces  were  nearly  odorless  when  the  animals  were  fed  on 
bread  alone. 

It  has  been  shown  that  the  bile  of  itself  has  little  action  on  the 
different  classes  of  alimentary  substances.  In  the  feces  of  animals 
with  biliary  fistula,  the  only  peculiarity  observed  —  aside  from  the 
putrefactive  odor  and  the  absence  of  the  coloring  matter  of  the  bile  — 
has  been  the  presence  of  an  abnormal  proportion  of  fat.  This  was 
noted  in  the  feces  of  a  patient  suffering  from  jaundice  apparently  due 
to  temporary  obstruction  of  the  bile-duct  (Flint). 

It  is  difificult  to  associate  the  bile  directly  with  the  digestion  of 
proteids  or  of  carbohydrates,  although  imperfectly  digested  meats  as 
well  as  fats  are  found  in  the  feces  when  bile  has  been  shut  off  from 
the  small  intestine.  It  was  noted,  however,  by  Bidder  and  Schmidt,  in 
an  animal  with  a  biliary  fistula  and  the  bile-duct  obliterated,  that  the 
proportion  of  fat  was  1.90  parts  per  1000  of  chyle  ;  while  in  an  animal 
with  the  biliary  passages  intact,  the  proportion  was  32.79  parts  per 
1000.  In  animals  operated  on  in  this  way,  there  frequently  is  a  distaste 
for  fatty  articles  of  food.  In  the  observation  made  in  1861  (Flint)  the 
dog  refused  fat  meat  even  when  very  hungry  and  when  lean  meat  was 
taken  with  avidity.  Later  observations  have  shown  that  the  bile  assists 
the  pancreatic  secretion  in  the  splitting  and  emulsification  of  fats,  and 
it  is  probable  that  it  also  facilitates  their  absorption,  although  in  what 
way  is  not  apparent.  While  it  is  the  digestion  and  absorption  of  fats 
that  seem  to  be  most  seriously  disturbed  in  cases  of  biliary  fistula,  the 
rapid  loss  of  weight  and  strength  shows  great  interference  with  the 
digestion  and  absorption  of  other  constituents  of  food.  It  is  impor- 
tant to  note,  also,  that  the  secretion  of  bile,  though  constant,  is  greatly 
increased  when  food  passes  into  the  intestinal  canal. 

Although  it  has  been  shown  that  the  presence  of  bile  in  the  small 
intestine  is  necessary  to  proper  digestion  and  even  essential  to  life,  and 
although  the  variations  in  the  flow  of  bile  with  digestion  are  now  well 
established,  physiologists  have  but  little  definite  information  concerning 
the  exact  mode  of  action  of  the  bile  in  intestinal  digestion  and  absorp- 


224  INTESTINAL   DIGESTION 

tion.     Nearly  all  that  can  be  said  on  this  subject  is  that  the  action  of 
the  bile  seems  to  be  auxiliary  to  that  of  the  other  digestive  secretions. 


Movements  of  the  Small  Intestine 

By  the  contractions  of  the  muscular  coat  of  the  small  intestine,  the 
alimentary  mass  is  made  to  pass  along  the  canal,  sometimes  in  one 
direction  and  sometimes  in  another,  the  general  tendency,  however, 
being  toward  the  caecum ;  and  the  partially  digested  matters  that 
pass  out  at  the  pylorus  are  prevented  from  returning  to  the  stomach 
by  the  peculiar  arrangement  of  the  fibres  which  constitute  the  pyloric 
muscle.  Once  in  the  intestine,  the  food  is  propelled  along  the  canal 
by  peculiar  movements  that  have  been  called  peristaltic,  when  the 
direction  is  toward  the  large  intestine,  and  antiperistaltic,  when  the 
direction  is  reversed.  These  movements  are  of  the  character  peculiar 
to  the  non-striated  muscular  fibres ;  they  are  slow  and  gradual,  the 
contraction  enduring  for  a  certain  time  and  being  followed  by  a  corre- 
spondingly slow  and  gradual  relaxation.  Both  the  circular  and  the 
longitudinal  muscular  layers  participate  in  these  movements. 

So  far  as  has  been  ascertained  by  observations  on  the  human  sub- 
ject and  warm-blooded  animals,  the  regular  intestinal  movements  are 
excited  by  the  passage  of  alimentary  matters  from  the  stomach  through 
the  tube  during  the  natural  process  of  digestion.  By  a  slow  and 
gradual  action  of  the  muscular  coat  of  the  intestine,  its  contents  are 
passed  along,  occasionally  the  action  being  reversed  for  a  time,  until 
the  indigestible  residue,  mixed  with  a  certain  quantity  of  intestinal 
secretion,  more  or  less  modified,  is  discharged  into  the  caput  coli. 
These  movements  apparently  are  not  continuous,  and  they  depend  in 
some  degree  on  the  quantity  of  matter  contained  in  different  parts 
of  the  intestinal  tract.  Judging  from  the  movements  in  the  inferior 
animals  after  the  abdomen  has  been  opened,  the  intestines  are  always 
changing  their  position,  mainly  by  the  action  of  their  longitudinal  mus- 
cular fibres,  so  that  the  force  of  gravity  does  not  oppose  the  onward 
passage  of  their  contents  so  much  as  if  the  relative  position  of  the 
parts  were  constant. 

The  gases  found  in  the  intestine  have  an  important  mechanical 
ofifice.  They  are  useful,  in  the  first  place,  in  keeping  the  canal  con- 
stantly distended  to  the  proper  degree,  thus  avoiding  the  liability  to 
disturbances  in  the  circulation  and  facilitating  the  passage  of  the  ali- 
mentary mass  in  obedience  to  the  peristaltic  contractions.  They  also 
support  the  walls  of  the  intestine  and  protect  these  parts  against  con- 
cussions, in  walking,  leaping  etc.     The  gases  are  useful,  likewise,  in 


PHYSIOLOGICAL    ANATOMY    OF   THE    LARGE    INTESTINE        225 

offering  an  elastic  but  resisting  mass  upon  which  the  compressing 
action  of  the  abdominal  muscles  may  be  exerted  in  straining  and  in 
expiration. 

There  can  be  hardly  any  question  that  the  normal  movements 
of  the  intestine  are  due  principally  to  the  impression  made  on  the 
mucous  membrane  by  the  alimentary  matters,  to  which  may  be  added, 
perhaps,  the  stimulating  action  of  the  bile.  The  vigorous  peristaltic 
movements  that  occur  soon  after  death  have  been  explained  in  various 
ways.  It  has  been  shown  that  these  movements  are  not  due  to  a 
lowering  of  the  temperature  or  to  exposure  of  the  intestines  to  the  air. 

The  nerves  distributed  to  the  small  intestine  are  derived  from  the 
sympathetic  and  from  branches  of  the  pneumogastric,  which  latter 
come  from  the  nerve  of  the  right  side  and  are  distributed  to  the  entire 
intestinal  tract,  from  the  pylorus  to  the  ileo-caecal  valve.  The  intestine 
receives  no  filaments  from  the  left  pneumogastric.  Throughout  the 
intestinal  tract,  is  a  plexus  of  non-medullated  nerve-fibres  with  groups 
of  nerve-cells,  lying  between  the  longitudinal  and  circular  layers  of  the 
muscular  coat.  This  is  known  as  Auerbach's  plexus.  From  this 
plexus,  fine  non-medullated  filaments  are  given  off,  which  form  a  wider 
plexus,  also  with  ganglion-cells,  situated  just  beneath  the  mucous  mem- 
brane. This  is  called  the  plexus  of  Meissner.  In  experiments  on  the 
lower  animals  it  has  been  shown  that  stimulation  of  the  pneumogastrics 
excites  peristaltic  movements  of  the  intestines  ;  but  in  some  animals 
these  nerves  seem  to  contain  inhibitory  as  well  as  motor  fibres,  although 
it  is  probable  that  the  principal  inhibitory  nerves  belong  to  the  sym- 
pathetic system.  Observations  on  these  points,  however,  are  somewhat 
conflicting. 

It  is  difficult  to  estimate  the  time  occupied  in  intestinal  digestion 
and  absorption  in  man.  In  the  dog  the  small  intestine  is  nearly  empty 
in  six  to  nine  hours  after  full  feeding,  but  .in  the  carnivora  the  intestine 
is  relatively  short  and  the  indigestible  residue  of  food  is  small  (Halli- 
burton). In  the  human  subject,  the  passage  of  an  ordinary  meal 
through  the  small  intestine  occupies  probably  about  twelve  hours 
(Kirkes). 

Physiological  Anatomy  of  the  Large  Intestine 

The  length  of  the  large  intestine  is  about  five  feet  (1.5  meter).  Its 
■diameter  is  greatest  at  the  caecum,  where  it  measures,  when  moderately 
distended,  two  and  a  half  to  three  and  a  half  inches  (6.35  to  8.89  centi- 
meters). The  average  diameter  of  the  tube  beyond  the  caecum  is  one  and 
two-thirds  to  two  and  two-thirds  inches  (4.23  to  6.^^  centimeters).  Pass- 
ing from  the  caecum,  the  canal  diminishes  in  calibre,  gradually  and  very 

Q 


226 


INTESTINAL   DIGESTION 


slightly,  to  where  the  sigmoid  flexure  opens  into  the  rectum.  This  is 
the  narrowest  portion  of  the  canal.  Beyond  this,  the  rectum  gradually 
increases  in  diameter,  forming  a  kind  of  pouch,  which  abruptly  dimin- 
ishes in  size  near  the  external  opening,  to  form  the  anus. 

The  general  direction 
of  the  large  intestine  is 
from  the  caecum,  in  the 
right  iliac  fossa,  to  the 
left  iliac  fossa,  thus  en- 
circling the  convoluted 
small  intestine,  in  the 
form  of  a  horseshoe. 
From  the  caecum  to  the 
rectum,  the  canal  is 
known  as  the  colon. 
The  first  division  of  the 
colon,  called  the  ascend- 
ing colon,  passes  almost 
directly  upward  to  the 
under  surface  of  the 
liver;  the  canal  here 
turns  at  nearly  a  right 
angle,  passes  across  the 
upper  part  of  the  abdo- 
men and  is  called  the 
transverse  colon  ;  it  then 
passes  downward  at 
nearly  a  right  angle, 
forming  the  descending 
colon.  The  last  division 
of  the  colon,  called  the 


Fig.  48.  —  Stomack,  pancreas  and  large  intestine  (Sappey). 

I,  anterior  surface  of  the  liver;  2,  gall-bladder;  3,  3,  section 
of  the  diaphragm  ;  4,  posterior  surface  of  the  stomach  ;  5,  lobus      sigmoid     flcXUrC     is    sitU 
Spigelii  of  the  liver;  6,  cceliac  axis;  7,  coronary  artery  of  the  ° 

stomach;  8,  splenic  artery;  9,  spleen;  10,  pancreas;  11,  supe- 
rior mesenteric  vessels;  12,  duodenum;  13,  upper  extremity  of 
the  small  intestine;  14,  lower  end  of  the  ileum  ;  15,  15,  mesentery  ; 
16,  ccBcum  ;  i-j,  appendix  vermiformis  ;  \%,  ascending  coloti  ;  19, 
19,  transverse  colon  ;  20,  descending  colon  ;  21,  sigmoid  flexure  of 
the  colon  ;  22,  rectum  ;  23,  urinary  bladder. 


ated  in  the  left  iliac  fossa 
and  is  in  the  form  of  the 
italic  letter  5.  This  ter- 
minates  in    the   rectum, 


which  is  not  straight, 
as  its  name  would  imply,  but  presents  at  least  three  distinct  curvatures, 
as  follows  :  it  passes  first  in  an  oblique  direction  from  the  left  sacro-iUac 
symphysis  to  the  median  line  opposite  the  third  piece  of  the  sacrum  ; 
it  then  passes  downward  in  the  median  line,  following  the  concavity 
of  the  sacrum  and  coccyx ;  and  the  lower  portion,  which  is  about  an 


PHYSIOLOGICAL   ANATOMY    OF    THE   LARGE    INTESTINE        22/ 

inch  (2.54  centimeters)  in  length,  turns  backward  to  terminate  in  the 
anus. 

The  caecum,  or  caput  coli,  presents  a  rounded  dilated  cavity  continu- 
ous with  the  colon  above  and  communicating  by  a  transverse  slit  with 
the  ileum.  At  its  lower  portion  is  a  small  cylindrical  tube,  opening 
below  and  a  little  posterior  to  the  opening  of  the  ileum,  called  the 
vermiform  appendix.  This  is  covered  with  peritoneum  and  has  a  mus- 
cular and  a  mucous  coat.  It  is  sometimes  free  and  sometimes  provided 
with  a  short  fold  of  mesentery  for  a  part  of  its  length.  The  coats  of  the 
appendix  are  very  thick.  The  muscular  coat  consists  of  longitudinal 
fibres  only.  The  mucous  membrane  is  provided  with  tubules  and  closed 
follicles,  the  latter  frequently  being  very  abundant.  This  little  tube 
usually  contains  a  quantity  of  clear  viscid  mucus.  The  uses  of  the 
vermiform  appendix  are  unknown. 

Ileo-ccscal  Valve.  — The  opening  by  which  the  small  intestine  commu- 
nicates with  the  caecum  is  provided  with  a  valve,  known  as  the  ileo-cascal 
valve,  situated  at  the  inner  and  posterior  portion  of  the  caecum.  The 
small  intestine,  at  its  termination,  presents  a  shallow  concavity,  which  is 
provided  with  a  horizontal  buttonhole  slit,  opening  into  the  caecum. 
The  surface  of  the  valve  which  looks  toward  the  small  intestine  is 
covered  with  a  mucous  membrane  provided  with  villi  and  in  all  respects 
resembling  the  general  mucous  lining  of  the  small  intestine.  Viewed 
from  the  caecum,  a  convexity  is  observed  corresponding  to  the  concavity 
upon  the  other  side.  The  caecal  surface  of  the  valve  is  covered  with  a 
mucous  membrane  identical  with  the  general  mucous  lining  of  the  large 
intestine.  It  is  evident,  from  an  examination  of  these  parts,  that  press- 
ure from  the  ileum  opens  the  slit  and  allows  the  easy  passage  of  the 
semifluid  contents  of  the  intestine ;  but  pressure  from  the  caecal  side 
approximates  the  lips  of  the  valve,  and  the  greater  the  pressure  the  more 
firmly  is  the  opening  closed.  The  valve  itself  is  composed  of  folds 
formed  of  the  fibrous  tissue  of  the  intestine,  and  circular  muscular  fibres 
from  both  the  small  and  the  large  intestine,  the  whole  being  covered 
with  mucous  membrane.  The  Hps  of  the  valve  unite  at  either  extremity 
of  the  slit  and  are  prolonged  on  the  inner  surface  of  the  caecum,  form- 
ing two  raised  bands,  or  bridles  ;  and  these  become  gradually  effaced 
and  are  thus  continuous  with  the  general  lining  of  the  canal.  The  pos- 
terior bridle  is  a  little  longer  and  more  prominent  than  the  anterior. 
These  assist  somewhat  in  enabling  the  valve  to  resist  pressure  from  the 
caecal  side.  The  longitudinal  layer  of  muscular  fibres  and  the  peritoneum 
pass  directly  over  the  attached  edge  of  the  valve  and  are  not  involved 
in  its  folds.  These  give  strength  to  the  part,  and  if  they  are  divided 
over  the  valve,  gentle  traction  suffices  to  draw  out  and  obliterate  the 


228  INTESTINAL    DIGESTION 

folds,  leaving  a  simple  and  unprotected  communication  between  the 
large  and  the  small  intestine.  Some  modern  observers  attribute  closing 
of  the  ileo-caecal  opening  to  contraction  of  circular  muscular  fibres,  which 
constitute  a  sphincter  (ileo-colic  sphincter).  These,  indeed,  have  been 
demonstrated  in  the  cat,  dog  and  rabbit.  It  is  possible  that  such  an 
arrangement  and  action  may  exist  in  man. 

Peritoneal  Coat.  —  Like  most  of  the  other  abdominal  viscera,  the 
large  intestine  is  covered  by  peritoneum.  The  caecum  is  covered  by 
this  membrane  only  anteriorly  and  laterally.  It  usually  is  bound  down 
closely  to  the  subjacent  parts,  and  its  posterior  surface  is  without  a  serous 
investment  ;  although  sometimes  it  is  completely  covered  and  there  may 
be  even  a  short  mesocaecum.  The  ascending  colon  is  likewise  covered 
with  peritoneum  only  in  front  and  is  closely  attached  to  the  subjacent 
parts.  The  same  arrangement  is  found  in  the  descending  colon.  The 
transverse  colon  is  almost  completely  invested  with  peritoneum  ;  and 
the  two  folds  forming  the  transverse  mesocolon  separate  to  pass  over 
the  tube  above  and  below,  uniting  again  in  front,  to  form  the  great 
omentum.  The  transverse  colon  consequently  is  quite  movable.  In 
the  course  of  the  colon  and  the  upper  part  of  the  rectum,  particularly  on 
the  transverse  colon,  are  found  a  number  of  little  sacculated  pouches 
filled  with  fat,  called  the  appendices  epiploicae.  The  sigmoid  flexure  of 
the  colon  is  covered  by  peritoneum,  except  at  the  attachment  of  the  iliac 
mesocolon.  This  division  of  the  intestine  is  quite  movable.  The  upper 
portion  of  the  rectum  is  almost  completely  covered  by  peritoneum  and 
is  loosely  held  in  place.  The  middle  portion  is  closely  bound  down,  and 
is  covered  by  peritoneum  only  anteriorly  and  laterally.  The  lowest 
portion  of  the  rectum  has  no  peritoneal  covering. 

Muscular  Coat.  —  The  muscular  fibres  of  the  large  intestine  have  an 
arrangement  quite  different  from  that  which  exists  in  the  small  intestine. 
The  external  longitudinal  layer,  instead  of  extending  over  the  whole 
tube,  is  arranged  in  three  distinct  bands,  which  begin  in  the  caecum  at 
the  vermiform  appendix.  Passing  along  the  ascending  colon,  one  of  the 
bands  is  situated  anteriorly,  and  the  others,  latero-posteriorly.  In  the 
transverse  colon  the  anterior  band  becomes  inferior  and  the  two  latero- 
posterior  bands  become  respectively  postero-superior  and  postero-inferior. 
In  the  descending  colon  and  the  sigmoid  flexure,  the  muscular  bands 
resume  the  relative  position  which  they  had  in  the  ascending  colon.  As 
these  longitudinal  fibres  pass  to  the  rectum,  the  anterior  and  the  external 
bands  unite  to  pass  down  on  the  anterior  surface  of  the  canal,  while  the 
posterior  band  passes  down  on  its  posterior  surface.  Thus  the  three 
bands  here  become  two.  These  two  bands  as  they  pass  downward, 
though  remaining  distinct,  become  much  wider ;  and  longitudinal  mus- 


PHYSIOLOGICAL   AxNATOMY    OF    THE    LARGE    INTESTINE       229 

cular  fibres  beginning  at  the  rectum  are  situated  between  them,  so  that 
this  part  of  the  canal,  especially  in  its  lower  portion,  is  covered  with 
longitudinal  fibres  in  a  nearly  uniform  layer. 

MiLcoiis  Coat.  —  The  mucous  lining  of  the  large  intestine  presents 
several  points  of  difference  from  the  corresponding  membrane  in  the 
small  intestine.  It  is  paler,  somewhat  thicker  and  firmer,  and  is  more 
closely  adherent  to  the  subjacent  parts.  In  no  part  of  this  mem- 
brane are  there  any  folds,  like  those  which  form  the  valvulae  con- 
niventes  of  the  small  intestine ;  and  the  surface  is  smooth  and  free 
from  villi. 

Throughout  the  entire  mucous  membrane,  from  the  ileo-cascal  valve 
to  the  anus,  are  orifices  that  lead  to  simple  follicular  glands.  These 
structures  resemble  in  all  respects  the  follicles  of  the  small  intestine, 
except  that  they  are  a  little  longer,  owing  to  the  greater  thickness  of  the 
membrane,  are  wider  and  rather  more  abundant.  Among  these  small 
follicular  openings  are  found,  scattered  irregularly  throughout  the 
membrane,  larger  openings  which  lead  to  utricular  glands,  resembling 
the  closed  follicles  in  general  structure,  except  that  they  have  an 
opening  into  the  cavity  of  the  intestine,  that  is  sometimes  so  large 
as  to  be  visible  to  the  naked  eye  (see  Plate  V,  Fig.  5).  The  num- 
ber of  these  glands  is  variable,  and  they  exist  throughout  the  intestine, 
together  with  the  closed  follicles,  except  in  the  rectum.  In  the  caecum 
and  colon,  isolated  closed  follicles  usually  are  found,  which  are  identical 
in  structure  with  the  solitary  glands  of  the  small  intestine.  These  are 
variable  both  in  number  and  size. 

The  mucous  membrane  of  the  rectum,  in  the  upper  three-fourths  of 
its  extent,  does  not  differ  materially  from  that  of  the  colon.  In  the 
lower  fourth,  the  fibrous  tissue  by  which  the  lining  membrane  is  united 
to  the  subjacent  muscular  coat  is  loose,  and  the  membrane,  when  the 
canal  is  empty,  is  thrown  into  a  great  number  of  irregular  folds.  At 
the  site  of  the  internal  sphincter,  five  or  six  little  semilunar  valves  have 
been  observed,  with  their  concavities  directed  toward  the  colon.  These 
form  an  irregular  festooned  line  which  surrounds  the  canal ;  their  folds, 
however,  are  small  and  have  no  tendency  to  obstruct  the  passage  of 
fecal  matters.  The  simple  follicles  are  particularly  abundant  in  the 
rectum,  and  the  membrane  is  constantly  covered  with  a  thin  coating  of 
mucus.  Another  peculiarity  to  be  noted  in  the  mucous  membrane  of 
the  lower  portion  of  the  rectum  is  its  great  vascularity,  the  veins,  espe- 
cially, being  very  abundant. 

The  rectum  terminates  in  the  anus,  a  buttonhole  orifice,  situated 
a  little  in  front  of  the  coccyx,  which  is  kept  closed  and  somewhat 
retracted,  except  during   the    passage  of    the    feces,  by  the    powerful 


230  INTESTINAL    DIGESTION 

external  sphincter.  This  muscle  is  composed  of  striated  fibres,  arranged 
in  the  form  of  an  ellipse,  its  long  diameter  being  antero-posterior. 

It  is  now  almost  universally  admitted  that  the  digestion  of  all  classes 
of  alimentary  substances  is  completed  either  in  the  stomach  or  in  the 
small  intestine,  and  that  the  mucous  membrane  of  the  large  intestine 
does  not  produce  a  secretion  endowed  with  well-marked  digestive  prop- 
erties. The  simple  follicles,  the  closed  follicles  and  the  utricular  glands 
produce  a  glairy  mucus,  which,  so  far  as  is  known,  serves  merely  to  lubri- 
cate the  canal.  This  has  never  been  obtained  in  sufficient  quantity  to 
admit  of  any  accurate  investigation  into  its  properties. 

In  the  human  subject  those  portions  of  the  food  which  resist  the 
successive  and  combined  action  of  the  different  digestive  secretions  are 
derived  chiefly  from  the  vegetable  kingdom.  Hard  vegetable  seeds, 
the  cortex  of  the  cereals,  spiral  vessels,  and,  indeed,  all  parts  composed 
largelv  of  cellulose  pass  through  the  intestinal  canal  without  much 
change.  These  substances  form,  in  the  feces,  the  greatest  part  of 
what  can  be  recognized  as  the  residue  of  matters  taken  as  food.  It 
is  well  known  that  an  exclusively  animal  diet,  particularly  if  the  nutri- 
tious matters  are  taken  in  a  concentrated  and  readily  assimilable  form, 
leaves  very  little  undigested  matter  to  pass  into  the  large  intestine,  and 
gives  to  the  feces  a  character  quite  different  from  that  which  is  observed 
in  herbivorous  animals  or  in  man  when  subjected  to  an  exclusively  vege- 
table diet.  The  characters  of  the  residue  of  the  digestion  of  albuminous 
substances  are  not  very  distinct.  As  a  rule  the  proteids  can  not  be 
recognized  in  the  healthy  feces  by  the  ordinary  tests. 

Absorption  of  various  articles  of  food  in  a  liquid  form  may  take  place 
with  great  activity  in  the  large  intestine,  although  it  has  not  been  shown 
that  the  secretions  in  this  part  of  the  alimentary  canal  have  any  distinct 
digestive  properties  ;  still,  as  is  seen  in  rectal  alimentation,  eggs,  milk 
and  meat-extracts  may  be  taken  up  by  the  mucous  membrane,  and  they 
enter  the  circulation  in  such  a  form  that  they  contribute  to  nutrition. 

Processes  of  Fermetitation  in  the  Intestinal  Canal.  —  The  processes 
of  fermentation  in  the  intestines  are  not  properly  digestive  and  are  to  a 
great  extent  due  to  the  action  of  micro-organisms,  which  exist  here  in 
great  numbers  and  variety.  Some  of  the  substances  resulting  from 
intestinal  fermentations  have  already  been  described.  Indol  (CgH-N), 
skatol  (C9H9N),  phenol  (CgH-OH)  and  cresol  (CeH^.OH.CHg)  probably 
result  from  the  action  of  micro-organisms ;  but  their  production  may  be 
arrested  or  retarded  by  the  action  of  certain  drugs,  such  as  calomel, 
salicylic  acid  and  other  so-called  antiseptics.  The  fermentative  changes 
in  the  intestines  involve  the  formation  of  certain  gases,  which  will  be 
described  at  the  close  of  this  chapter. 


CONTENTS    OF    THE    LARGE    INTESTINE  23 1 

Contents  of  the  Large  Intestine 

When  the  contents  of  the  small  intestine  have  passed  the  ileo-caecal 
valve,  they  become  changed  in  their  general  character,  partly  from 
admixture  with  the  secretions  of  this  portion  of  the  canal,  and  are  then 
known  as  the  feces.  The  most  notable  changes  relate  to  consistence, 
color  and  odor.  The  odor,  especially,  of  normal  fecal  matter  is  decidedly 
characteristic. 

Fecal  matter  has  a  much  firmer  consistence  than  the  contents  of  the 
ileum,  which  is  due  to  partial  absorption  of  the  liquid  portions.  As  a 
rule  the  consistence  is  great  in  proportion  to  the  length  of  time  that 
the  feces  remain  in  the  large  intestine  ;  and  this  is  variable  in  different 
persons  and  in  the  same  person,  in  health,  depending  somewhat  on 
the  character  of  food.  The  color  changes  from  the  yellow,  more  or 
less  bright,  which  is  observed  in  the  ileum,  to  the  dark  yellowish-brown, 
characteristic  of  feces.  Although  the  bile-pigment  can  not  usually  be 
recognized  by  the  ordinary  tests,  it  is  a  product  of  bilirubin  that  gives 
to  the  contents  of  the  large  intestine  their  peculiar  color,  which  is  lost 
when  the  bile  is  not  discharged  into  the  duodenum.  In  the  large 
intestine,  bilirubin  (C32H3QN40g)  is  changed  into  hydrobilirubin,  or 
stercobilin  (C32H^N^O-).  In  a  specimen  of  normal  human  feces, 
which  had  been  dried,  extracted  with  alcohol,  the  alcoholic  extract 
precipitated  with  ether  and  the  precipitate  dissolved  in  distilled  water, 
it  was  impossible  to  detect  the  biliary  salts  by  Pettenkofer's  test.  The 
color  of  the  feces  varies  considerably  under  different  forms  of  diet. 
With  a  mixed  diet  the  color  is  yellowish  brown  ;  with  an  exclusively 
flesh-diet  it  is  much  darker ;    and  with  a  milk-diet  it  is  more    yellow. 

The  odor  of  the  feces,  which  is  characteristic  and  quite  different 
from  that  of  the  contents  of  the  ileum,  is  variable  and  is  due  in  part  to 
the  peculiar  decomposition  of  the  residue  of  the  food,  in  part  to  putre- 
factive products  and  in  part  to  matters  secreted  by  the  mucous  mem- 
brane of  the  colon  and  of  the  glands  near  the  anus.  Indol  has  what  may 
be  called  a  fecal  odor.  The  odor  of  skatol  is  intensely  fetid.  Skatol, 
however,  may  be  prepared  artificially  from  indigo,  when  it  is  odorless. 

The  quantity  of  feces  in  the  twenty-four  hours,  according  to  Wehsarg, 
is  about  4.6  ounces  (128  grams).  This  was  the  mean  of  seventeen  obser- 
vations ;  the  largest  quantity  being  10.8  ounces  (306  grams),  and  the 
smallest,  2.4  ounces  (68  grams). 

The  reaction  of  the  feces  is  variable,  depending  chiefly  on  the 
character  of  the  food.  Marcet  found  the  human  excrements  always 
alkahne.  Wehsarg,  on  the  other  hand,  usually  found  the  reaction  acid, 
but  frequently  it  was  alkaline  or  neutral. 


232  INTESTINAL    DIGESTION 

The  proportions  of  water  and  solid  matter  in  the  feces  are  variable. 
Berzelius  found  in  the  healthy  human  feces,  y^.T,  parts  of  water  and 
26.7  parts  of  solid  residue.  The  average  of  seventeen  observations  by 
Wehsarg  was  the  same.  In  the  observations  of  Wehsarg,  the  mean 
quantity  of  solid  matter  discharged  in  the  feces  in  the  twenty-four 
hours  was  463  grains  (30  grams),. the  extremes  being  882.8  grains  (57.2 
grams),  and  251.6  grains  (16.28  grams).  The  proportion  of  undigested 
matters  in  the  solid  residue  was  very  small,  averaging  but  little  more 
than  ten  per  cent,  the  mean  quantity  in  the  twenty-four  hours  in  ten 
observations  being  but  52.5  grains  (3.4  grams).  This  was  found,  how- 
ever, to  be  very  variable;  the  largest  quantity  being  126.5  grains  (8.2 
grams),  and  the  smallest,  12.5  grains  (0.81  gram). 

Microscopical  examination  of  the  feces  reveals  various  vegetable  and 
animal  structures  that  have  escaped  the  action  of  the  digestive  fluids. 
Wehsarg  also  found  a  "finely  divided  fecal  matter"  of  indefinite  struc- 
ture, but  containing  partly  disintegrated  intestinal  epithelium.  Crystals 
of  cholesterin  were  never  observed.  Whenever  the  matter  is  neutral  or 
alkaline,  crystals  of  ammonio-magnesian  phosphate  are  found.  Mucus 
is  also  found  in  variable  quantity,  with  desquamated  epithelium  and  a 
few  leucocytes.  In  addition,  recent  microscopical  researches  have 
shown  the  presence  of  spores  of  yeast  and  a  great  variety  of  bacteria, 
which  latter  exist  in  the  feces  in  great  abundance.  These  organisms 
probably  excite  many  of  the  so-called  putrefactive  changes  in  the  intes- 
tinal contents,  which  result  in  the  formation  of  indol,  phenol,  skatol, 
cresol  etc.  According  to  Senator,  these  putrefactive  products  do  not 
exist  in  the  meconium.  The  quantity  of  inorganic  salts  in  the  feces  is 
not  great.  In  addition  to  ammonio-magnesian  phosphate,  magnesium 
phosphate,  calcium  phosphate  and  a  small  quantity  of  iron  have  been 
found.  The  chlorides  are  either  absent  or  are  present  only  in  small 
quantity. 

Marcet  has  pretty  generally  found  in  the  human  feces  a  substance 
possessing  the  characters  of  margaric  acid,  and  volatile  fatty  acids ;  the 
latter  free,  however,  from  butyric  acid.  He  also  found  a  coloring 
matter,  which  probably  is  a  modification  of  bile-pigment.  Cystin  is 
mentioned  as  an  occasional  constituent. 

In  addition  to  the  matters  just  enumerated,  the  following  substances 
have  been  extracted  from  the  normal  feces  :  — 

Excrctm  and  Excretolcic  Acid.  —  Excretin  (CgoHggO)  was  obtained 
from  the  normal  feces,  by  Marcet,  in  1854.  This  substance  crystallizes 
from  an  ethereal  solution  in  two  or  three  days,  in  the  form  of  long  silky 
crystals.  Examined  with  the  microscope,  these  are  found  to  consist  of 
acicular,  four-sided    prisms  of    variable    size.      Excretin  is  insoluble  in 


STERCORIN  233 

water,  slightly  soluble  in  cold  alcohol,  but  very  soluble  in  ether  and  in 
hot  alcohol.  Its  alcoholic  solutions  are  faintly  though  distinctly  alka- 
line. Its  fusing-point  is  between  203"^  and  205'  Fahr.  (g-,"  and  96°  C.;. 
It  may  be  boiled  with  potassium  hydrate  for  hours  without  undergoing 
change.  The  quantity  of  excretin  contained  in  the  feces  is  not  large. 
Only  12.6  grains  (0.816  gram)  were  obtained  by  ]\Iarcet  from  nine 
evacuations.  In  1857  Marcet  assigned  to  excretin  the  formula 
CygHygOg;  but  the  formula  C2oHggO  is  now  given  in  works  on  physio- 
logical chemistry. 

There  exists  little  definite  information  regarding  the  production  of 
excretin.  Marcet  examined  on  one  occasion  the  contents  of  the  small 
intestine  of  a  man  who  had  died  of  disease  of  the  heart,  without  findina: 
any  excretin.  It  is  probable  that  this  substance  is  formed  in  the  large 
intestine,  although  further  observations  are  needed  on  this  point. 

The  substance  called  excretoleic  acid  is  indefinite  in  its  composition 
and  properties.  It  is  described  as  an  olive-colored  fatty  acid,  insoluble 
in  water,  non-saponifiable  and  very  soluble  in  ether  and  in  hot  alcohol. 
It  fuses  between  JJ^  and  79'  Fahr.  (25^  and  26.11^  C),  but  its  existence 
is  doubtful. 

Stercorin. — This  substance  was  discovered  in  the  feces  in  1862 
(Flint;.  As  it  is  one  of  the  most  abundant  and  characteristic  constitu- 
ents of  stercoraceous  matters,  it  may  properly  be  called  stercorin.  Ster- 
corin may  be  extracted  in  the  following  way :  The  feces  are  first 
evaporated  to  dryness,  pulverized  and  treated  with  ether.  The  ether- 
extract  is  then  passed  through  animal  charcoal,  fresh  ether  being  added 
until  the  original  quantity  of  the  ether-extract  has  passed  through.  It 
is  impossible  to  entirely  decolorize  the  solution  by  this  process ;  but  it 
should  pass  through  perfectly  clear  and  of  a  pale-amber  color.  The 
ether  is  then  evaporated  and  the  residue  is  extracted  with  boiling 
alcohol.  The  alcoholic  solution  is  evaporated,  and  the  residue  is  treated 
with  a  solution  of  potassium  hydrate  for  one  or  two  hours  at  a  tempera- 
ture a  little  below  the  boiling-point,  by  which  the  fats  are  dissolved. 
The  mixture  is  then  largely  diluted  with  water,  thrown  upon  a  filter 
and  washed  until  the  liquid  which  passes  through  is  neutral  and  per- 
fectly clear.  The  filter  is  then  dried  and  the  residue  is  washed  out  with 
ether.  The  ether-solution  is  then  evaporated,  extracted  with  boiling 
alcohol  and  the  alcoholic  solution  is  evaporated.  The  residue  of  this 
last  evaporation  is  stercorin,  which  may  be  purified  by  recrystallization. 

When  first  obtained,  stercorin  is  a  clear,  slightly  amber,  oily  sub- 
stance, of  about  the  consistence  of  Canada  balsam  used  in  microscopical 
preparations.  In  four  or  five  days  it  begins  to  show  characteristic 
crystals.     These  are  few  in  number  at  first,  but  soon  the  entire  mass 


234 


INTESTINAL    DIGESTION 


assumes  a  crystalline  form.  In  one  analysis,  from  seven  and  a  half 
ounces  (202.5  grams)  of  normal  human  feces  (the  entire  quantity  for  the 
twenty-four  hours),  10.417  grains  (0.675  gram)  of  stercorin  were  ob- 
tained, the  extract  consisting  entirely  of  crystals.  This  was  all  the 
stercorin  to  be  extracted  from  the  regular  daily  evacuation  of  a  healthy 
male  twenty-six  years  of  age,  weighing  about  one  hundred  and  sixty 
pounds  (72.58  kilograms).  In  the  absence  of  other  investigations,  the 
daily  quantity  of  this  substance  excreted  may  be  assumed  to  be  not  far 
from  ten  grains  (0.648  gram). 

In  many  regards  stercorin  bears  a  close  resemblance  to  cholesterin, 
which  is  a  monatomic  alcohol.      It  is  neutral,  inodorous  and  insoluble 

in  water  and  in  a  solution  of 
potassium  hydrate.  It  is  soluble 
in  ether  and  in  hot  alcohol,  but 
is  almost  insoluble  in  cold  alco- 
hol. A  red  color  is  produced 
when  it  is  treated  with  strong 
sulphuric  acid.  It  may  easily  be 
distinguished  from  cholesterin, 
however,  by  the  form  of  its 
crystals. 

Stercorin    crystallizes    in    the 
form    of    thin    delicate    needles, 
frequently      mixed      with      clear 
rounded  globules,  which  probably 
are  composed   of  the   same  sub- 
stance in  a  non-crystalline  form. 
The  crystals  often  are  arranged 
in  bundles.     They  are  not  to  be  confounded  with  excretin,  which  crys- 
tallizes in  the  form  of  regular  four-sided  prisms,  or  with  the  thin  rhom- 
boidal  or  rectangular  tablets  of  cholesterin. 

There  can  be  no  doubt  in  regard  to  the  origin  of  the  stercorin  found 
in  feces.  When  the  bile  is  not  discharged  into  the  duodenum,  as  proba- 
bly is  the  case  for  a  time  in  icterus  accompanied  with  clay-colored 
evacuations,  stercorin  is  not  to  be  discovered  in  the  dejections.  In  one 
case  of  this  kind,  in  which  the  feces  were  subjected  to  examination,  the 
matters  extracted  with  hot  alcohol  were  entirely  dissolved  by  boiling  for 
fifteen  minutes  with  a  solution  of  potassium  hydrate,  showing  the 
absence  of  cholesterin  and  stercorin.  In  another  examination  of  the 
feces  from  this  patient,  made  nineteen  days  after,  when  the  icterus  had 
almost  entirely  disappeared  and  the  evacuations  had  become  normal, 
stercorin  was  discovered.     These  facts  show  that  the  cholesterin  of  the 


Fig.  49.  — Crystals  of  stercorin,  X  20  (Flint,  1862; 
recrystallized,  1897). 


MOA'E.MEXTS    OF    THE    LARGE    INTESTINE  235 

bile,  in  its  passage  through  the  intestine,  is  changed  into  stercorin. 
Both  these  substances  are  crystalHzable,  non-saponifiable,  are  extracted 
by  the  same  chemical  manipulations  and  behave  in  the  same  way  when 
treated  with  sulphuric  acid.  Stercorin  must  be  regarded  as  a  modifi- 
cation of  cholesterin,  which  is  the  excrementitious  constituent  of  the 
bile. 

The  change  of  cholesterin  into  stercorin  is  directly  connected  with 
the  process  of  intestinal  digestion.  If  an  animal  is  kept  for  some  days 
without  food,  cholesterin  will  be  found  in  the  feces,  although,  for  a  few 
days,  stercorin  is  also  present.  It  is  a  fact  commonly  recognized  by 
those  who  have  analyzed  the  feces,  that  cholesterin  does  not  exist  in  the 
normal  evacuations  ;  but  whenever  digestion  is  arrested,  the  bile  being 
constantly  discharged  into  the  duodenum,  cholesterin  is  found  in  large 
quantity.  For  example,  in  hibernating  animals,  cholesterin  is  always 
present  in  the  feces.  The  same  is  true  of  the  contents  of  the  intestines 
during  foetal  life;  the  meconium  always  containing  a  large  quantity  of 
cholesterin,  which  disappears  from  the  evacuations  when  the  digestive 
function  becomes  established.  The  formula  for  stercorin  is  C.^yH^^O. 
Its  physiological  relations  will  be  considered  in  connection  with  the 
excretory  office  of  the  liver. 

Indol,  Skatol,  Phejiol,  Cresol  etc.  —  The  so-called  putrefactive  pro- 
cesses, which  begin  in  the  small  intestine,  are  more  marked  in  the  large 
intestine  and  give  rise  to  certain  products  which  have  the  characteristic 
fecal  odor.  Certain  of  these  substances  may  be  produced  by  the  pro- 
longed action,  out  of  the  body,  of  the  pancreatic  juice  on  proteids. 
The  pancreatic  juice,  in  an  alkaline  medium,  changes  the  trypsin-pep- 
tones  into  leucin,  tyrosin,  hypoxanthin  and  asparaginic  acid.  By  still 
further  prolonging  this  action,  indol,  skatol,  phenol  and  cresol,  with 
some  other  analogous  substances  and  volatile  fatty  acids,  are  formed, 
and  there  is  an  evolution  of  certain  gases.  It  is  probable  that  these 
products  are  formed  in  abnormal  quantities  in  the  small  intestine  in 
certain  cases  of  intestinal  dyspepsia.  Methyl  mercaptan  (CHgSH)  is 
sometimes  found  in  small  quantity  in  the  intestines.  This  substance 
has  a  peculiarly  penetrating  and  disagreeable  odor.  It  probably  is  pro- 
duced by  bacterial  decomposition  of  proteids. 

Move^nents  of  the  Large  Intesthie.  —  Movements  of  the  general 
character  noted  in  the  small  intestine  occur  in  the  large  intestine,  al- 
though the  peculiarities  in  the  arrangement  of  the  muscular  fibres  and 
the  more  solid  consistence  of  the  contents  render  these  movements  in 
the  large  intestine  somewhat  distinctive.  In  all  instances  where  the 
movements  have  been  observed  in  the  human  subject  or  in  the  lower 
animals,  they  have  been  found  to  be  less  vigorous  and  rapid  than  the 


236  INTESTINAL    DIGESTION 

contractions  of  the  small  intestine.  Indeed,  when  the  abdominal  organs 
are  exposed,  either  in  a  living  animal  or  immediately  after  death,  move- 
ments of  the  large  intestine  ordinarily  are  not  observed,  except  on  the 
application  of  mechanical  or  electric  stimulation  ;  and  they  are  then 
more  circumscribed  and  much  less  marked  than  in  any  other  part  of  the 
alimentary  canal.  That  the  feces  remain  for  a  considerable  time  in 
some  of  the  sacculated  pouches  of  the  colon,  is  evident  from  the  ap- 
pearance which  they  sometimes  present  of  having  been  moulded  to  the 
shape  of  the  canal.  This  appearance  is  frequently  observed  in  the 
dejections,  which  are  then  said  to  be  "  figured." 

In  the  caecum,  the  pressure  of  matters  received  from  the  ileum  forces 
the  mass  onward  into  the  ascending  colon,  and  the  contractions  of  its 
muscular  fibres  probably  are  slight  and  inefficient.  Once  in  the  colon, 
it  is  easy  to  see  how  the  contractions  of  the  muscular  structure  —  the 
longitudinal  bands  shortening  the  canal,  and  the  transverse  fibres  con- 
tracting below  and  relaxing  above  —  are  capable  of  passing  the  fecal 
mass  slowly  onward.  Although  the  transverse  fibres  are  thin  and 
apparently  of  little  power,  their  contraction  is  sufficient  to  empty  the 
sacculi,  when  assisted  by  the  movements  of  the  longitudinal  fibres,  espe- 
cially as  the  canal  is  never  completely  filled  and  the  feces  are  frequently 
in  the  form  of  small  moulded  lumps.  By  these  slow  and  gradual  move- 
ments, the  contents  of  the  large  intestine  are  passed  toward  the  sigmoid 
flexure  of  the  colon,  where  they  are  arrested  until  the  period  arrives  for 
their  final  discharge.  The  time  occupied  in  the  passage  of  the  feces 
through  the  ascending,  transverse  and  descending  colon  undoubtedly  is 
variable  in  different  persons,  as  great  variations  are  observed  in  the  in- 
tervals between  the  acts  of  defecation.  During  their  passage  along  the 
colon,  the  contents  of  the  canal  assume  more  and  more  of  the  normal 
fecal  consistence  and  odor  and  become  slightly  coated  with  the  mucous 
secretion  of  the  parts. 

The  accumulation  of  feces  usually  takes  place  in  the  sigmoid  flex- 
ure of  the  colon ;  and  under  normal  conditions,  the  rectum  is  found 
empty  and  contracted.  This  part  of  the  colon  is  much  more  movable 
than  other  portions  of  the  large  intestine.  At  certain  intervals,  the 
fecal  matter  is  passed  into  the  rectum  and  is  then  almost  immediately 
discharged  from  the  body. 

Defecation.  —  In  health,  expulsion  of  fecal  matters  takes  place  with 
regularity  usually  once  in  the  twenty-four  hours.  This  rule,  however, 
is  by  no  means  invariable,  and  dejections  may  occur  habitually  twice  in 
the  day  or  every  second  or  third  day  within  the  limits  of  health.  At  the 
time  when  defecation  ordinarily  takes  place,  a  peculiar  sensation  is  ex- 
perienced calling  for  an  evacuation  of  the  bowels ;  and  if  this  is  disre- 


GASES    FOUND    IN    THE    ALIMENTARY   CANAL 


237 


garded,  the  desire  may  pass  away,  after  a  little  time  the  act  becoming 
impossible.  It  is  probable  that  the  feces  are  then  passed  out  of  the 
rectum  by  antiperistaltic  action.  The  sensation  that  leads  to  an  effort 
to  discharge  the  feces  is  due  to  the  accumulation  of  matters  in  the 
sigmoid  flexure,  which  finally  present  at  the  contracted  upper  portion 
of  the  rectum. 

The  above  is  the  mechanism  of  the  descent  of  fecal  matter  into  the 
rectum  in  defecation,  as  the  act  is  usually  performed  ;  but  under  certain 
conditions,  feces  must  accumulate  in  the  dilated  portion  of  the  rectum. 
Ordinarily,  the  discharge  of  feces  takes  place  only  after  the  efforts  have 
been  continued  for  a  certain  time,  and  when  the  evacuation  is  "  figured," 
the  whole  length  discharged  frequently  exceeds  so  much  the  length 
of  the  rectum,  that  it  is  evident  that  a  portion  of  it  must  have  come 
from  the  colon ;  but  in  cases  in  which  the  feces  are  very  liquid,'  or  when 
the  usual  call  for  an  alvine  evacuation  has  not  been  regarded  and  has 
become  imperative,  the  discharge  of  matters  at  the  moment  when  the 
sphincter  is  relaxed  shows  that  the  rectum  has  been  more  or  less  dis- 
tended. 

The  diaphragm  and  the  abdominal  muscles  compress  the  abdominal 
organs,  and  consequently  those  contained  in  the  pelvis,  and  assist  in  the 
expulsion  of  the  contents  of  the  rectum.  The  diaphragm  is  the  most 
important  of  the  voluntary  muscles  concerned  in  this  process ;  and  dur- 
ing the  act  of  straining,  the  lungs  are  moderately  filled  and  respiration 
is  for  the  time  interrupted.  The  vigor  of  these  efforts  depends  to  a 
considerable  extent  on  the  consistence  of  the  fecal  mass,  violent  con- 
tractions frequently  being  required  for  the  expulsion  of  hardened  feces 
that  have  accumulated  during  long  constipation.  Although  more  or  less 
straining  usually  takes  place,  the  contractions  of  the  muscular  coats  of 
the  rectum  frequently  are  competent  of  themselves  to  expel  the  feces, 
especially  when  they  are  soft. 

Gases  found  in  the  Alimentary  Canal 

The  gases  in  the  stomach  appear  to  have  no  definite  ofifice.  They 
usually  exist  in  small  quantity  and  are  sometimes  absent.  The  oxygen 
and  nitrogen  are  derived  from  bubbles  of  air  incorporated  with  the  ali- 
mentary bolus  during  mastication  and  insalivation.  The  other  gases 
probably  are  evolved  from  the  food  during  digestion  ;  at  least,  there 
is  no  satisfactory  evidence  that  they  are  produced  in  any  other  way. 
Magendie  and  Chevreul  collected  and  analyzed  a  small  quantity  of  gas 
from  the  stomach  of  an  executed  criminal  a  short  time  after  death  and 
ascertained  that  it  had  the  following  composition  :  — 


238 


INTESTINAL   DIGESTION 


GASES   CONTAINED    IN  THE   .STOMACH 

Oxygen 1 1 .00 

Carbon  dioxide 14.00 

Pure  hydrogen 3.55 

Nitrogen 7145 

100.00 

Magendie  and  Chevreul  found  three  gases  in  the  small  intestine. 
Their  examinations  were  made  on  three  criminals  soon  after  execution. 
The  first  was  twenty-four  years  of  age,  and  two  hours  before  execution, 
he  had  eaten  bread  and  Gruyere  cheese  and  had  drunk  red  wine  and 
water.  The  second,  who  was  executed  at  the  same  time,  was  twenty- 
three  years  of  age,  and  the  conditions  as  regards  digestion  were  the 
same.  The  third  was  twenty-eight  years  of  age,  and  four  hours  before 
death,  he  ate  bread,  beef  and  lentils,  and  drank  red  wine  and  water. 
The  following  was  the  result  of  the  analyses  :  — 

GASES   CONTAINED    IN   THE   SMALL   INTE.STINE 


First  Criminal 

Second  Criminal 

Third  Criminal 

Carbon  dioxide 

Pure  hydrogen 

Nitrogen 

24-39 
55-53 
20.08 

40.00 

51.15 

8.85 

25.00 

8.40 

66.60 

100.00 

100.00 

100.00 

No  oxygen  was  found  in  either  of  the  examinations,  and  the  quan- 
tities of  the  other  gases  were  so  variable  as  to  lead  to  the  supposition 
that  their  proportion  is  not  at  all  definite.  Reference  has  already  been 
made  to  the  mechanical  office  of  these  gases  in  intestinal  digestion. 
The  presence  of  any  considerable  quantity  of  gas,  however,  in  the 
stomach  does  not  seem  necessary  to  normal  gastric  digestion,  except 
as  bubbles  of  air  render  the  alimentary  mass  spongy  and  thus  facilitate 
the  penetration  of  the  gastric  juice.  The  importance  of  this  has  already 
been  considered  in  connection  with  mastication  and  insalivation. 

In  the  large  intestine,  the  constitution  of  the  gases  presented  the 
same  variability  as  in  the  small  intestine.  Carburetted  hydrogen  was 
found  in  all  the  analyses.  In  the  large  intestine  of  the  first  criminal 
and  in  the  rectum  of  the  third,  were  found  traces  of  hydrogen  mono- 
sulphide.  The  following  is  the  result  of  the  analyses  in  the  cases  just 
cited.  In  the  third,  the  gaseous  contents  of  the  caecum  and  the  rectum 
were  analyzed  separately  :  — 


ORIGIN    OF    THE    INTESTINAL   GASES 


239 


GASES    CONTAINED   IN   THE   LARGE   INTESTINE 


First  Criminal 

Second  Criminal 

Third  Criminal 

Carbon  dioxide 

Carburetted  hydrogen  and  traces 

of  hydrogen  monosulphide  . 
Pure  hydrogen  and  carburetted 

hydrogen    

Pure  hydrogen 

Carburetted  hydrogen  .... 
Nitrogen 

43-5° 
5-47 

51-03 

70.00 

11.60 
18.40 

Caecum 
12.50 

7.50 
12.50 
67.50 

Rectum 
42.86 

II. 18 
45.96 

100.00 

100.00 

100.00 

100.00 

07'igin  of  the  Intestinal  Gases. — The  most  reasonable  view  to  take 
of  the  origin  of  the  gases  normally  found  in  the  intestines  is  that  they 
are  given  off  from  the  articles  of  food  in  their  various  stages  of  diges- 
tion and  decomposition.  That  this  is  the  principal  source  of  the  intes- 
tinal gases,  there  can  be  no  doubt ;  and  it  is  well  known  that  certain 
articles  of  food,  particularly  vegetables,  generate  much  more  gas  than 
others.  The  principal  gases  found  in  the  intestinal  canal  may  all  be 
obtained  from  the  food.  Some  of  them,  as  hydrogen  and  carburetted 
hydrogen,  do  not  exist  in  the  blood  ;  and  it  is  difficult  to  conceive  how 
they  can  be  generated  in  the  intestine  except  by  decomposition  of  cer- 
tain of  the  articles  of  food.  Gases  are  not  found  in  the  aUmentary  canal 
of  the  foetus. 


CHAPTER   X 

ABSORPTION  — LYMPH   AND  CHYLE 

Absorption  by  bloodvessels — Absorption  by  lymphatic  and  lacteal  vessels — Physiological 
anatomy  of  the  lymphatic  and  lacteal  vessels — Structure  of  the  lymphatic  and  lacteal 
vessels — Lymphatic  glands  —  Absorption  of  proteids  by  the  lacteals  —  Absorption  of 
sugar  and  salts  by  the  lacteals  —  Absorption  of  water  by  the  lacteals  —  Absorption  by  the 
skin — Absorption  by  the  respiratory  surface  —  Absorption  from  closed  cavities,  reservoirs 
of  glands,  etc.  —  Absorption  of  fats  and  insoluble  substances  —  Influence  of  the  condition 
of  the  blood  and  of  the  vessels  on  absorption  —  Influence  of  the  nervous  system  on  absorp- 
tion—  Osmosis  —  Mechanism  of  the  passage  of  liquids  through  membranes  —  Osmotic 
pressure  —  Lymph  and  chyle  —  Properties  and  composition  of  lymph  —  Corpuscular  ele- 
ments of  the  lymph  —  Origin  and  uses  of  the  lymph  —  Properties  and  composition  of  chyle 
—  Composition  of  chyle —  Microscopical  characters  of  the  chyle  —  Movements  of  the  lymph 
and  chyle. 

Absorption  by  Bloodvessels 

That  solutions  pass  through  the  walls  of  the  capillaries  and  of  the 
small  veins  and  that  absorption  actually  takes  place  in  great  part  by 
bloodvessels  are  facts  which  hardly  demand  discussion  at  the  present 
day.  Soluble  substances  that  have  disappeared  from  the  alimentary 
canal  have  been  found  repeatedly  in  the  blood  coming  from  this  part, 
even  when  the  lymphatics  had  been  divided  and  communication  existed 
only  through  the  bloodvessels  ;  and  it  has  been  shown  that  during  ab- 
sorption, the  blood  of  the  portal  vein  is  rich  in  proteids,  sugar  and  other 
matters  resulting  from  digestion. 

In  the  mouth  and  oesophagus,  the  sojourn  of  alimentary  matters  is 
so  brief  and  the  changes  which  they  undergo  are  so  slight,  that  no  con- 
siderable absorption  takes  place.  It  is  evident,  however,  that  the 
mucous  membrane  of  the  mouth  is  capable  of  absorbing  certain  soluble 
matters,  from  the  effects  that  are  constantly  observed  when  the  smoke 
or  the  juice  of  tobacco  is  retained  in  the  mouth  even  for  a  short  time. 
A  certain  proportion  of  the  constituents  of  food  that  are  dissolved  by  the 
gastric  juice  and  converted  into  peptones  is  taken  up  directly  by  the 
bloodvessels  of  the  stomach.  It  may,  indeed,  be  assumed,  as  a  general 
law,  that  alimentary  matters  are  in  great  part  absorbed  so  soon  as  their 
digestive  transformations  in  the  alimentary  canal  have  been  accomplished. 

In  the  passage  of  the  food  along  the  intestinal  canal,  as  the  diges- 
tion of  the  proteids  is  completed,  these  matters  are  absorbed.  The 
greatest  part  of  the  food  is  absorbed  by  the  intestinal  mucous  mem- 

240 


ABSORPTION    BY   LYMPHATIC    AND    LACTEAL   VESSELS 


241 


brane,  and,  with  the  ahmentary  substances  proper,  a  large  quantity  of 
secreted  fluid  is  reabsorbed.  This  is  particularly  marked  as  regards 
the  bile.  The  biliary  salts  disappear  as  the  alimentary  mass  passes 
down  the  intestine  and  undoubtedly  are  absorbed,  although  they  are  so 
changed  that  they  can  not  be  detected  in  the  blood  by  the  ordinary 
tests.  In  this  portion  of  the  alimentary  canal,  it  will  be  remembered,  a 
large  absorbing  surface  is  provided  by  the  arrangement  of  the  mucous 
membrane  in  folds,  forming  the  valvulae  conniventes,  and  by  the  pres- 
ence of  villi,  which  are  found  throughout  the  small  intestine.  A  cer- 
tain portion  of  the  gaseous  contents  of  the  intestines  is  also  taken  up, 
although  it  is  not  easily  ascertained  what  particular  gases  are  thus 
absorbed. 


Absorption  by  Lymphatic  and  Lacteal  Vessels 

Physiological  Anatomy  of  the  Lymphatic  and  Lacteal  Vessels.  —  The 
lacteals  are  the  intestinal  lymphatics ;  and  during  the  intervals  of  intes- 


Fig.  50.  —  Origin  of  lymphatics  (Landois). 

I.  From  the  central  tendon  of  the  diaphragm  of  the  rabbit  (semidiagrammatic)  ;  s,  lymph-canals 
communicating  by  x  with  the  lymphatic  vessel  L  ;  a,  origin  of  the  lymphatic  by  a  union  of  lymph- 
canals ;  f,  ^,  endothelium.     II.    Perivascular  canal. 

tinal  absorption  they  carry  a  liquid  that  is  identical  with  the  contents  of 
other  lymphatic  vessels.  In  their  structure,  also,  the  lacteals  are  identi- 
cal with  the  general  lymphatics. 

In  the  connective  tissues  —  which  are  so  widely  distributed  in  the 
body — ^  there  are  always  found  irregularly-shaped  stellate  spaces,  which 
communicate  with  each  other  by  branching  canals,  called  lymph-spaces. 


242  ABSORPTION  — LYMPH    AND    CHYLE 

These  spaces  contain  a  liquid  and  large  numbers  of  leucocytes.  The 
leucocytes  in  these  spaces  may  be  called  lymph-corpuscles,  as  they 
eventually  find  their  way  into  the  true  lymphatic  vessels ;  but  they 
are  thought  to  be  corpuscles  that  have  passed  through  the  stomata 
of  the  capillary  bloodvessels.  The  connective-tissue  lymph-spaces,  by 
certain  of  their  branches,  finally  communicate  with  the  lymph-capillaries, 
through  what  have  been  regarded  as  the  stomata  of  these  vessels.  These 
anatomical  data  have  led  to  the  following  view  in  regard  to  the  relations 
between  the  blood,  the  lymph  and  the  tissues. 

Nutrient  matters  are  supplied  to  the  parts  by  transudation  through 
the  walls  of  the  capillary  bloodvessels ;  and  effete  matters  pass  from 
the  lymph-spaces  into  the  true  lymphatic  vessels  to  be  carried  to  the 
venous  system.  In  certain  tissues  and  organs,  however,  such  as  the 
cornea  and  fibrous  membranes,  the  lymph-spaces  or  canals  supply 
the  nutrient  liquid  ;  and  in  the  glands,  possibly  they  supply  part  of  the 
material  used  in  the  formation  of  the  secretions. 

In  the  serous  membranes  and  in  analogous  structures,  there  are 
large  numbers  of  openings  into  the  cavities ;  and  the  peritoneum,  pleura, 
pericardium,  tunica  vaginalis  testis,  chambers  of  the  eye,  labyrinth  of 
the  internal  ear  and  subarachnoid  space  are  to  be  regarded  as  lymph- 
sacs,  the  contained  liquids  being  lymph,  without,  however,  presenting 
the  so-called  lymph-corpuscles. 

The  relations  between  the  bloodvessels  and  the  smallest  lymphatics 
are  very  close  in  certain  parts.  In  the  cerebro-spinal  centres,  the 
smallest  vessels  of  bone,  the  retina  and  the  liver,  is  a  system  of  canals 
which  completely  surround  the  small  bloodvessels  and  are  connected 
with  the  lymphatic  trunks,  or  reservoirs,  described  by  Fohmann,  and 
found  beneath  the  pia  mater.  These  are  called  perivascular  canals  ; 
and  the  contained  liquid  is  true  lymph,  containing  leucocytes.  They 
exceed  the  bloodvessels  in  diameter  by  Y2V0"  ^^  ?^o  °^  ^^  ^'^^^  (^°  ^^ 
62  fi). 

The  capillary  lymphatics  have  been  studied  in  various  parts  by 
means  of  mercurial  injections ;  but  the  presence  of  valves  in  the  small 
trunks  renders  it  necessary  to  make  these  injections  from  the  periphery. 
The  vessels  have  been  injected  in  certain  situations  with  mercury,  by 
simply  puncturing  with  a  fine-pointed  canula  the  parts  in  which  the 
plexus  is  supposed  to  exist,  and  allowing  the  liquid  to  diffuse  itself 
gently.  Following  the  course  of  the  vessels,  the  injection  passes  into 
the  larger  trunks  and  thence  to  the  lymphatic  glands.  The  regularity 
of  the  plexus  through  which  the  liquid  is  first  diffused  and  the  passage 
of  the  injection  through  the  larger  vessels  to  the  glands  are  proof  that 
the  lymphatics  have  been  penetrated  and  that  the  appearances  observed 


ANATOMY    OF    LYMPHATIC   AND    LACTEAL   VESSELS 


243 


are  not  the  result  of  infiltration  in  the  tissue.  It  does  not  appear  that 
the  vessels  composing  this  plexus  vary  much  in  size.  They  are  quite 
elastic,  and  after  distention  by  injection,  they  return  to  a  very  small 
diameter  when  the  fluid  is  allowed  to  escape. 

The  lacteal  system  presents  essentially  the  same  anatomical  charac- 
ters as  the  general  lymphatics,  and  the  vessels  are  filled  with  colorless 
lymph  during  the  intervals  of  digestion.  In  many  situations  the  lym- 
phatics present  in  their  course  little  solid  structures,  called  lymphatic 
glands,  although,  as  regards  structure  and  office,  they  are  not  true 
glandular  organs.  The  smallest  capillary  lymphatics  have  a  diameter 
of  about  -g-^-Q  of  an  inch  (83  (x).  This  may  be  taken  as  their  average 
diameter  in  primitive  plexuses.  The  plexus,  when  the  vessels  are 
abundant,  as  they  are  in  certain  parts  of  the  cutaneous  surface,  resem- 
bles  an    ordinary   plexus 


of  capillary  bloodvessels, 
except  that  the  walls  of 
the  lymphatics  are  thin- 
ner and  their  diameter  is 
greater.  The  vessels  are 
lined  by  endothelial  cells, 
the  borders  of  which  are 
brought  into  view  by  the 
action  of  silver  nitrate. 

The  smallest  lym- 
phatic vessels  are  by  far 
the  most  abundant.  They 
are  arranged  in  the  form 
of  a  fine  plexus,  superficially  situated  in  the  skin.  A  second  plexus 
exists  just  beneath  the  skin,  composed  of  vessels  of  much  greater 
diameter.  The  skin  is  thus  enclosed  between  two  plexuses  of  capillary 
lymphatics.  A  plexus  analogous  to  the  superficial  plexus  of  the  skin 
is  found  just  beneath  the  surface  of  the  mucous  membranes.  These 
may,  indeed,  be  classed  with  the  superficial  lymphatics.  The  deep 
lymphatics  are  much  larger  and  less  abundant,  and  their  origin  is  less 
easily  made  out.  These  accompany  the  deeper  veins  in  their  course. 
They  receive  the  lymph  from  the  superficial  vessels. 

No  valvular  arrangement  is  found  in  the  smallest  lymphatics ;  but 
the  vessels  coming  from  the  primitive  plexuses,  as  well  as  the  large 
vessels,  contain  valves  in  great  numbers.  These  valves,  being  closely 
set  in  the  vessels,  give  to  them,  when  filled  with  injection,  a  peculiar 
and  characteristic  beaded  appearance. 

The  course  of  the  lymphatics  usually  is  direct.    As  they  pass  toward 


Fig.  51.  —  Lymphatic  plexus,  showing  the  endothelium 
(Belaieff). 


244 


ABSORPTION  —  LYMPH    AND    CHYLE 


the  great  trunks  by  which  they  communicate  with  the  venous  system, 
they  present  a  pecuHar  anastomosis  with  the  adjacent  vessels,  called 
anastomosis  by  bifurcation  ;  that  is,  as  a  vessel  passes  along  with  other 
vessels  nearly  parallel  with  it,  it  bifurcates,  and  the  two  branches  pass 
into  the  nearest  vessels  on  either  side.  These  anastomoses  are  quite 
frequent,   and  they  usually  occur  between  vessels  of    equal  size.      In 


Fig.  52.  —  Superficial 
lymphatics  of  the  skin  0/  the 
palmar  surface  of  the  finger 
(Sappey). 


—  Deep  lymphatics  of  the  skin  of 
the  finger  (Sappey). 
I,  I,  deep  network  of  cutaneous  lym- 
phatics ;  2,  2,  2,  2,  lymphatic  trunks  con- 
nected with  this  network. 


Fig.  54.  —  The  same  fin- 
ger, lateral  view,  showing 
lymphatic  trunks  cottnected 
with  the  supetficial  net- 
work (Sappey). 


their  course  the  vessels  pass  through  the  so-called  lymphatic  glands,  or 
nodes. 

A  notable  peculiarity  in  the  lymphatic  vessels  is  that  they  vary  very 
little  in  size,  being  nearly  as  large  at  the  extremities  as  they  are  near 
the  trunk.  In  their  course  they  are  always  much  smaller  than  the 
veins  and  do  not  progressively  enlarge  as  they  pass  on  to  the  great 
lymphatic  trunks.  The  largest  vessels  that  pass  from  the  skin  are 
2^5  to  -^^  of  an  inch  (i  to  2  miUimeters)  in  diameter,  and  the  larger 
vessels,  in  their  course,  have  a  diameter  of  ^^2  ^o  \  <^f  ^■'^  vcvzh.  (2  to 
3  millimeters).     As  in  the  case  of  the  smallest  lymphatics  of  the  primi- 


ANATOMY    OF   LYMPHATIC   AND    LACTEAL   VESSELS 


245 


f 


'N 


'^' 


i 


tive  plexuses,  the  elasticity  of  the  walls  of  the  vessels  renders  their 
diameter  greatly  dependent  on  the  pressure  of  liquid  in  their  interior. 
Many  anatomists  have  noticed  that  vessels  which  are  hardly  perceptible 
while  empty  are  capable  of  being  dilated  to  the  diameter  of  half  a  line 
(about  I  millimeter)  or  more,  returning  to  their  original  size  so  soon  as 
the  distending  liquid  is 
removed. 

In  the  lymphatics  of 
the  skin,  the  only  impor- 
tant peculiarity  not  yet 
mentioned  is  that  the 
vessels  appear  to  be  un- 
equally distributed  in  dif- 
ferent parts  of  the  surface. 
They  are  particularly 
abundant  in  the  scalp  over 
the  biparietal  suture,  the 
soles  of  the  feet  and  the 
palms  of  the  hand,  the  fin- 
gers at  the  lateral  portion 
of  the  last  phalanges,  and 
the  scrotum.  In  the  me- 
dian portion  of  the  scro- 
tum they  attain  their 
highest  degree  of  devel- 
opment. They  are  also 
found,  though  in  less 
number,  originating  from 
around  the  median  line  on 
the  anterior  and  posterior 
surface  of  the  trunk,  the 
posterior  median  portion 
of  the  extremities,  the 
skin  over  the  mammae 
and  around  the  orifices  of  the  mucous  passages.  Lymphatic  vessels 
have  been  demonstrated  in  the  anterior  portion  of  the  forearm,  the 
thigh  and  the  leg,  and  in  the  middle  portion  of  the  face,  although  they 
are  demonstrated  with  difficulty  in  these  situations.  If  thev  exist  at  all 
in  other  portions  of  the  cutaneous  surface,  they  are  not  abundant. 

In  the  mucous  membranes  the  lymphatics  are  very  abundant. 
Here  are  found,  as  in  the  skin,  two  distinct  layers  which  enclose 
between  them  the  entire  thickness  of   the  mucous    membrane.      The 


■f 


/ 


^^g-     55-  —  Superficial     lym- 
phatics of  the  arm  (Sappey). 


Fig.     56.  —  Superficial    lym- 
phatics of  the  leg  (Sappey). 


246  ABSORPTION  — LYMPH    AND    CHYLE 

more  superficial  of  these  layers  is  composed  of  a  rich  plexus  of  small 
vessels,  and  beneath  the  mucous  membrane  is  a  plexus  consisting  of 
vessels  of  larger  size.  The  superficial  plexus  is  very  rich  in  the  mixed 
structure  which  forms  the  lips  and  the  glans  penis,  and  around  the 
orifices  of  the  mouth,  the  nares,  the  vagina  and  the  anus.  There  are 
certain  mucous  membranes  in  which  the  lymphatics  have  never  been 
injected.  In  the  serous  membranes  lymphatics  have  been  demon- 
strated in  great  abundance.  Lymphatics  have  also  been  observed 
taking  their  origin  in  the  voluntary  muscles,  the  diaphragm,  the  heart 
and  the  non-striated  muscular  coats  of  the  hollow  viscera,  although 
their  investigation  in  these  situations  is  difficult. 

Lymphatics  are  found  coming  from  the  lungs  in  great  numbers. 
These  arise  in  the  walls  of  the  air-cells  and  surround  each  pulmonary 
lobule  with  a  close  plexus.  The  deep  vessels  follow  the  course  of  the 
bronchial  tubes,  passing  through  the  bronchial  glands  and  the  glands  at 
the  bifurcation  of  the  trachea,  to  empty  into  the  thoracic  duct  and  the 
great  lymphatic  duct  of  the  right  side. 

In  the  glandular  system,  including  the  ductless  glands,  and  in  the 
ovaries,  the  lymphatic  vessels  are,  as  a  rule,  more  abundant  than  in  any 
other  parts  of  the  body.  They  are  especially  abundant  in  the  testicles, 
the  ovaries,  the  liver  and  the  kidneys. 

The  lymphatic  vessels  from  the  superficial  and  deep  portions  of  the 
head  and  face  on  the  right  side,  and  those  from  the  superficial  and  deep 
portions  of  the  right  arm,  the  right  half  of  the  chest,  and  the  mammary 
gland,  with  a  few  vessels  from  the  lungs,  pass  into  the  great  lymphatic 
duct  (ductus  lymphaticus  dexter),  which  empties  into  the  venous  system 
at  the  junction  of  the  right  subclavian  with  the  internal  jugular.  This 
vessel  is  about  an  inch  (25.4  millimeters)  in  length  and  -^2  ^o  i  of  an 
inch  (2  to  3  millimeters)  in  diameter.  It  is  provided  with  a  pair  of  semi- 
lunar valves  at  its  opening  into  the  veins,  which  effectually  prevents  the 
ingress  of  blood.  The  vessels  from  the  inferior  extremities  and  those 
from  the  lower  portions  of  the  trunk,  the  pelvic  viscera,  the  abdominal 
organs  generally  and  the  left  half  of  the  body  above  the  abdomen  empty 
into  the  thoracic  duct. 

In  their  course,  the  lymphatics  pass  through  the  small,  flattened,  oval 
bodies,  called" the  lymphatic  glands,  or  nodes,  which  are  abundant  in  the 
groin,  the  axilla,  the  pelvis  and  some  other  parts.  Two  to  six  vessels, 
called  vasa  afferentia,  penetrate  each  node,  having  first  broken  up  into 
a  number  of  smaller  vessels  just  before  they  enter.  They  pass  out 
by  a  number  of  small  vessels  which  unite  to  form  one,  two  or  three 
trunks,  usually  of  larger  size  than  the  vasa  efferentia.  The  vessels 
which  thus  emerge  from  the  glands  are  called  vasa  efferentia. 


ANATOMY   OF   LYMPHATIC   AND    LACTEAL   VESSELS 


247 


The  lymphatics  of  the  small  intestine,  called  lacteals,  pass  from  the 
intestine  between  the  folds  of  the  mesentery  to  empty,  sometimes  bv 
one  and  sometimes  by  four  or  five  trunks,  into  the  receptaculum  chyH. 
In  their  course,  the  lacteals  pass  through  several  sets  of  lymphatic 
glands,  which  are  here  called  mesenteric  glands. 


Fig.  57-  —  Stomach,  intestine  and  mesentery,  with  the  'mesenteric  bloodvessels  and  lacteals  (copied 
and  reduced  about  one-halt  from  a  figure  in  the  original  work  of  Asellius,  published  in  1628). 

A,  A,  A,  A,  A,  mesenteric  arteries  and  veins ;  B,  B,  B,  B,  B,  B,  B,  B,  B,  B,  lacteals ;  C,  C,  C,  C, 
mesentery ;  D,  D,  stomach  ;  E,  pyloric  portion  of  the  stomach  ;  F,  duodenum  ;  G,  G,  G,  jejunum  ; 
H,  H,  H,  H,  H,  ileum ;  /,  arteiy  and  vein  on  the  fundus  of  the  stomach ;  K,  portion  of  the  omentum. 


The  thoracic  duct,  into  which  most  of  the  lymphatic  vessels  empty, 
is  a  vessel  with  delicate  walls  and  about  the  size  of  a  goose-quill.  It 
begins  by  a  dilatation,  more  or  less  marked,  called  the  receptaculum  chyli. 
This  is  situated  on  the  second  lumbar  vertebra.  The  canal  passes 
upward  in  the  median  line  for  the  inferior  half  of  its  length.  It  then 
inclines  to  the  left  side,  forms  a  semicircular  curve  something  like  the 


248 


ABSORPTION  — LYMPH    AND    CHYLE 


arch  of  the  aorta,  and  empties  at  the  junction  of  the  left  subclavian  with 
the  internal  jugular  vein.  It  diminishes  in  size  from  the  receptaculum 
to  its  middle  portion  and  becomes  larger  again  near  its  termination.  It 
occasionally  bifurcates  near  the  middle  of  the  thorax,  but  the  branches 
become  reunited  a  short  distance  above.  At  its  opening  into  the  venous 
system,  there  usually  is  a  valvular  fold,  but  this  is  not  constant.  There 
is  always,  however,  a  pair  of  semilunar  valves  in  the  duct,  three-quarters 

of  an  inch  to  an  inch  (19  to 
25  millimeters)  from  its  ter- 
mination, which  prevents  the 
entrance  of  blood  from  the 
venous  system. 

The  foregoing  sketch  of  the 
descriptive  anatomy  of  what 
has  been  called  the  absorbent 
system  of  vessels  shows  that 
they  may  collect  liquids,  not 
only  from  the  intestinal  canal 
during  digestion,  but  from 
nearly  every  tissue  and  organ 
in  the  body,  and  that  these 
are  finally  received  into  the 
venous  circulation. 

Structure  of  the  Lymphatic 
and  Lacteal  Vessels.  —  The 
lymphatic  vessels,  even  those 
of  largest  size,  are  remarka- 
ble for  the  delicacy  and  trans- 
parency of  their  walls.  This 
is  illustrated  in  the  case  of 
the  lacteals,  which  are  hardly 
visible  in  the  transparent 
mesentery,  unless  filled  with 
chyle.  On  account  of  the  difficulty  in  studying  the  lymphatics  at  their 
origin,  except  by  means  of  injections  or  by  reagents  which  stain  the 
vessels,  investigations  into  the  structure  of  the  smallest  vessels  have 
not  been  very  satisfactory.  It  is  supposed,  however,  that  the  vessels 
here  cotisist  of  a  single  coat,  resembling,  in  this  regard,  the  capillary 
bloodvessels.  Belaieff  has  described  in  the  capillary  lymphatics  of  the 
penis  a  lining  of  endothelial  cells  arranged  in  a  single  layer.  These 
cells  are  oval,  polygonal,  fusiform,  or  dentated,  with  their  long  diameter 
in  the  direction  of  the  axis  of  the  vessels. 


Fig.  58.  —  riioracu  duct  (Mascagni). 

I,  thoracic  duct ;  2,  great  lymphatic  duct ;  3,  receptacu- 
lum chyli ;  4,  curve  of  the  thoracic  duct  just  before  it  empties 
into  the  venous  system. 


STRUCTURE    OF    LYMPHATIC    AND    LACTEAL   VESSELS 


249 


In  all  but  the  capillary  lymphatics,  although  the  walls  are  very  thin, 
three  distinct  coats  can  be  distinguished.  The  internal  coat  consists 
of  an  elastic  membrane  lined  with  oblong  endothelial  cells.  This  coat 
readily  gives  way  when  the  vessels  are  forcibly  distended.  The  middle 
coat  is  composed  of  longitudinal  fibres  of  connective  tissue,  with  delicate 
elastic  fibres,  and  non-sti'iated  muscular  fibres  arranged  transversely. 
The  external  coat  is  composed  of  the  same  structures  as  the  middle  coat, 
but  most  of  the  fibres  are  arranged  longitudinally.  In  this  coat  the 
muscular  fibres  do  not  form  a  continuous  sheet,  but  are  collected  into 
separate  fasciculi,  which  have  a  direction  either  longi- 
tudinal or  oblique.  The  fibres  of  connective  tissue  are 
abundant  and  unite  the  vessels  to  the  surrounding  parts. 
The  internal  and  the  middle  coats  are  closely  adherent 
to  each  other;  but  the  external  coat  may  readily  be 
separated  from  the  others.  Bloodvessels  have  been 
found  in  the  walls  of  the  lymphatics,  and  the  existence 
of  vasomotor  nerves  is  probable. 

The  walls  of  the  lymphatic  vessels  are  closely  ad- 
herent to  the  surrounding  tissues  ;  so  closely,  indeed,  that 
even  a  small  portion  of  a  vessel  is  detached  with  diffi- 
culty, and  the  vessels,  even  those  of  large  size,  can  not  be 
followed  out  and  isolated  for  any  considerable  distance. 

In  all  the  lymphatic  vessels,  beginning  a  short  dis- 
tance from  their  plexuses  of  origin,  are  semilunar  valves, 
usually  arranged  in  pairs  with  their  concavities  looking 
toward  the  larger  trunks.  These  folds  are  formed  of 
the  middle  and  inner  coats ;  but  the  fold  formed  from 
the  lining  membrane  is  by  far  the -wider,  so  that  the  free 
edges  of  the  valves  are  thinner  than  the  portion  attached 
to  the  vessel.  The  valves  are  most  abundant  in  the 
superficial  vessels.  The  distance  between  the  valves  is  -^^  ^o  i  of  an 
inch  (2  to  3  millimeters)  near  the  origin  of  the  vessels,  and  \  to  |-  of  an 
inch  (6  to  8  millimeters)  in  their  course.  In  the  lymphatics  between 
the  muscles  the  valves  are  less  abundant.  They  are  relatively  few  in  the 
vessels  of  the  head  and  neck  and  in  all  that  have  a  direction  from  above 
downward.  Although  there  are  valves  in  the  thoracic  duct,  they  are 
not  so  abundant  as  in  the  smaller  vessels. 

In  their  anatomy  and  general  properties,  the  lymphatics  bear  a  close 
resemblance  to  the  veins.  Although  much  thinner  and  more  trans- 
parent, their  coats  have  nearly  the  same  arrangement.  The  arrange- 
ment of  valves  is  the  same  ;  and  in  both  systems,  the  folds  prevent 
reflux  of  liquids  when  the  vessels  are  subjected  to  pressure. 


Fig.  59. —  Valves 
of  the  lymphatics 
(Sappey) . 


250  ABSORPTION  —  LYMPH   AND    CHYLE 

The  lymphatics  are  very  elastic ;  and  it  has  been  shown  that  the 
larger  vessels  and  those  of  medium  size  are  contractile,  although  the 
action  of  their  muscular  fibres,  like  that  of  all  fibres  of  the  non-striated 
variety,  is  slow  and  gradual. 

An  important  point  in  connection  with  the  anatomy  of  the  lymphatic 
vessels  is  the  question  of  the  existence  of  openings  in  their  walls,  which 
might  allow  the  passage  of  solid  particles  or  of  emulsions.  Anatomical 
observations  have  indicated  the  existence  of  stomata,  of  variable  size 
and  irregular  shape,  in  the  smallest  vessels ;  and  an  argument  in  favor 
of  the  existence  of  these  openings  is  the  fact  of  the  actual  passage, 
through  the  walls  of  the  vessels,  of  fatty  particles,  the  entrance  of 
which  can  not  be  explained  by  the  well-known  laws  of  endosmosis. 
The  anatomical  evidence  of  the  existence  of  openings  is  derived  mainly 
from  preparations  stained  with  silver  nitrate.  It  is  assumed  that  silver 
nitrate  stains  the  solid  parts  of  tissues  and  the  borders  of  the  endothelial 
cells,  and  that  non-nucleated  areas  which  do  not  present  any  staining 
are  necessarily  open.  In  preparations  of  the  lymphatics,  the  solution 
of  silver  is  seen  staining  the  tissues  and  especially  the  borders  of  the 
endothelial  cells  lining  the  vessels ;  but  there  are  areas  between  these 
cells  where  no  staining  is  observed  and  in  which  no  nuclei  are  brought 
out  by  staining  with  carmin. 

LympJiatic  Glands.  —  In  the  course  of  the  lymphatic  vessels,  are 
small  lenticular  bodies,  called  lymphatic  glands,  or  nodes.  The  number 
of  these  is  very  great,  although  it  is  estimated  with  difficulty,  from  the 
fact  that  many  of  them  are  very  small  and  may  escape  observa- 
tion. It  may  be  stated  as  an  approximation  that  there  are  six  or  seven 
hundred  lymphatic  glands  in  the  body.  Their  size  and  form  are  also 
variable  within  the  limits  of  health.  They  usually  are  flattened  and 
lenticular,  some  as  large  as  a  bean  and  others  as  small  as  a  small  pea 
or  even  a  pin's-head.  They  are  arranged  in  two  sets ;  one  superficial, 
corresponding  with  the  superficial  lymphatic  vessels,  and  a  deep  set, 
corresponding  with  the  deep  vessels.  The  superficial  glands  are  most 
abundant  in  the  folds  at  the  flexures  of  the  great  joints  and  about  the 
great  vessels  of  the  head  and  neck.  The  deep-seated  glands  are  most 
abundant  around  the  vessels  coming  from  the  glandular  viscera.  A  dis- 
tinct set  of  large  glands  is  found  connected  with  the  lymphatic  vessels 
between  the  folds  of  the  mesentery.  These  are  known  as  the  mesen- 
teric glands.  All  the  lymphatic  vessels  pass  through  glands  before 
they  empty  into  the  great  lymphatic  trunks,  and  most  of  them  pass 
through  several  glands  in  their  course. 

The  normal  glands  are  of  a  grayish  white  or  reddish  color,  of  about 
the  consistence  of  the  liver,  presenting  a  hilum  where  the  larger  blood- 


LYMPHATIC    GLANDS 


251 


vessels  enter  and  the  efferent  vessels  emerge,  and  are  covered,  except 
at  the  hilum,  with  a  delicate  membrane  composed  of  inelastic  fibres, 
a  few  elastic  fibres  and  non-striated  muscular  fibres.  Their  exterior  is 
somewhat  tuberculated,  from  the  projections  of  the  follicles  just  beneath 
the  investing  membrane.  The  interior  of  the  glands  is  soft  and  pulpy. 
It  presents  a  coarsely-granular  cortical  substance,  of  a  reddish  white 
or  gray  color,  which  is  |-  to  ^  of  an  inch  (4  to  6  millimeters)  in  thick- 
ness in  the  largest  glands. 
The  medullary  portion,  which 
comes  to  the  surface  at  the 
hilum,  is  lighter  colored  and 
is  coarser  than  the  cortical 
substance.  Throughout  the 
gland  are  found  delicate 
fasciculi  of  fibrous  tissue  con- 
nected with  the  investing 
membrane,  which  serve  as  a 
fibrous  skeleton  for  the  gland 
and  divide  its  substance  into 
alveoli.  The  structure  is  far 
more  delicate  in  the  cortical 
than  in  the  medullary  portion. 
Within  the  alveoli  are  irreg- 
ularly-oval closed  follicles 
(lymph-nodules),  about  o^^  of 
an  inch  (100  /x)  in  diameter, 
filled  with  liquid  and  with 
cells  like  those  contained  in 
the  solitary  glands  of  the  in- 
testines   and    the    patches    of      ^^Z-  ^'^-  —  Lymphatics  and  lymphatic  glands  [)s\2AC.'3.%r{\). 

Pever  The     cells  ■  some-  ^'  ^PP^""  extremity  of  the  thoracic  duct,  passing  behind 

^       '  '  the  internal  jugular  vein ;  2,  opening  of  the  thoracic  duct 

times      called     Ivmph-Cells into  the  internal  jugular  and   left  subclavian  veins.     The 

,      1      ,    ',  .     ,  Ivmphatic  glands  are  seen  in  the  course  of  the  vessels. 

are  situated  at  the  periphery     ' 

of  the  nodules  ;  and  in  the  centre  is  a  relatively  clear  zone  called  the 
germ-centre.  The  nodules  do  not  occupy  the  medullary  portion  of  the 
glands,  which  is  composed  chiefly  of  a  network  of  lymphatic  capillaries 
mixed  with  rather  coarse  bands  of  fibrous  tissue.  The  follicular  struc- 
tures in  the  lymphatic  glands  resemble  the  closed  follicles  in  the  mucous 
membrane  of  the  intestinal  canal  and  the  Malpighian  bodies  of  the 
spleen  (see  Plate  VIII). 

In  the  substance  of  the  lymphatic  glands  are  great  numbers  of  lymph- 
spaces  or  canals,  which  probably  are  lined  with  endothelium  ;  and  these 


252  ABSORPTION  — LYMPH    AND    CHYLE 

spaces  communicate  with  the  efferent  vessels  by  stomata.  The  afferent 
vessels,  two  to  six  in  number,  penetrate  the  gland  and  probably  empty 
their  contents  into  the  lymph-spaces.  The  lymph  is  then  collected  from 
the  lymph-spaces  by  the  vasa  efferentia,  one  to  three  in  number,  which 
are  always  larger  than  the  afferent  vessels. 

The  lymphatic  glands  are  supplied  with  blood,  sometimes  by  one 
but  usually  by  several  small  arteries,  which  penetrate  at  the  hilum. 
These  vessels  pass  directly  to  the  medullary  portion  and  there  break  up 
into  several  coarse  branches  to  be  distributed  to  the  cortical  substance, 
where  they  ramify  in  a  delicate  capillary  network,  with  rather  wide 
meshes,  in  the  closed  follicles  of  this  portion  of  the  gland.  This  capil- 
lary plexus  also  receives  branches  from  small  arterial  twigs  which  pene- 
trate the  capsule  at  different  points.  Returning  on  themselves  in  loops, 
the  vessels  unite  to  form  one  or  more  large  veins,  which  emerge  usually 
at  the  hilum. 

Very  little  is  known  regarding  the  distribution  of  nerves  in  the 
lymphatic  glands.  A  few  filaments  from  the  sympathetic  system  enter 
with  the  arteries,  but  they  have  not  been  traced  to  their  final  distribution. 
The  entrance  of  filaments  from  the  cerebro-spinal  system  has  not  been 
demonstrated. 

The  uses  of  the  lymphatic  glands  are  somewhat  obscure.  They  are 
supposed,  however,  to  have  an  important  office  in  the  elaboration  of  the 
corpuscular  elements  of  the  lymph  and  chyle ;  and  it  has  been  observed 
that  the  lymph  contained  in  vessels  that  have  not  passed  through  glands 
is  relatively  poor  in  corpuscles,  while  the  large  trunks  and  the  efferent 
vessels  contain  them  in  large  numbers. 

Absorption  of  Protcids  by  tJie  Lactcals.  —  Comparative  analyses  of  the 
lymph  and  chyle  show  in  the  latter  an  excess  of  proteid  constituents  ; 
and  it  is  natural  to  infer  that  the  excess  of  these  matters  in  the 
chyle  is  due  to  absorption  of  proteids  from  the  intestinal  canal.  Lane 
collected  the  chyle  from  the  lacteals  of  a  donkey,  seven  and  a  half  hours 
after  a  full  meal  of  oats  and  beans,  and  compared  its  composition  with 
that  of  the  lymph.  The  analyses  were  made  by  Rees,  who  found  that 
the  chyle  contained  about  three  times  as  much  albumin  and  fibrin  as  the 
lymph.  While  by  far  the  greatest  part  of  the  products  of  digestion  of 
proteids  is  absorbed  by  bloodvessels,  there  can  be  no  doubt  that  a  small 
portion  is  also  taken  up  by  the  lacteals. 

Absorption  of  Sugar  and  Salts  by  the  Lacteals.  —  Small  quantities  of 
sugar  and  sometimes  lactic  acid  have  been  detected  in  chyle  from  the 
thoracic  duct  in  the  herbivora ;  and  the  presence  of  sugar  in  both  lymph 
and  chyle  has  also  been  observed.  While  the  products  of  the  digestion 
of  saccharine  and  amylaceous  matters  are  taken  up  mainly  by  blood- 


ABSORPTION    BY    THE    RESPIRATORY    SURFACE  253 

vessels,  a  small  quantity  is  also  absorbed  by  the  lacteals.  In  the  com- 
parative analyses  of  the  chyle  and  lymph  by  Rees,  the  proportion  of 
inorganic  salts  was  found  to  be  considerably  greater  in  the  chyle.  The 
great  excess  in  the  quantitv  of  blood  coming  from  the  intestine,  and  the 
rapidity  of  its  circulation,  as  compared  with  the  chyle,  explain  the  more 
rapid  penetration  by  osmosis  of  the  soluble  products  of  digestion. 

Absorption  of  Water  by  the  Lacteals.  —  There  can  be  no  doubt  that  a 
small  portion  of  the  liquids  taken  as  drink  finds  its  way  into  the  circula- 
tion by  the  lacteals,  although  the  greatest  part  passes  directly  into  the 
bloodvessels.  When  an  animal  has  taken  solid  food  only  and  is  killed 
during  digestion,  the  thoracic  duct  contains  but  a  small  quantity  of  chyle ; 
but  when  the  animal  has  taken  liquids  with  the  food,  the  thoracic  duct 
and  the  lacteals  are  distended. 

Aside  from  the  entrance  of  gases  into  the  blood  from  the  pulmonary 
surface,  physiological  absorption  is  confined  almost  entirely  to  the  mu- 
cous membrane  of  the  alimentary  canal.  It  is  true  that  liquids  may  find 
their  way  into  the  circulation  through  the  skin,  the  lining  membrane  of 
air-passages,  the  reservoirs,  ducts  and  parenchyma  of  glands,  the  serous 
and  other  closed  cavities,  areolar  tissue,  the  conjunctiva,  muscular  tis- 
sue, and,  in  fact,  all  parts  that  are  supplied  with  bloodvessels  ;  but 
here  the  absorption  of  foreign  matters  is  occasional  or  accidental  and 
is  not  connected  with  general  nutrition. 

Absorption  by  the  Skin.  —  It  is  now  admitted  that  absorption  may  take 
place  from  the  general  surface,  although  at  one  time  this  was  a  question 
much  discussed  by  physiologists.  The  proofs,  however,  of  the  entrance 
of  certain  medicinal  preparations  from  the  surface  of  the  body  are  con- 
clusive. The  question  of  most  importance  in  this  connection  relates  to 
the  normal  action  of  the  skin  as  an  absorbing  surface.  Looking  at  this 
subject  from  a  purely  physiological  point  of  view,  absorption  from  the 
skin,  under  ordinary  conditions,  must  be  very  slight,  if,  indeed,  it  takes 
place  at  all.  There  are,  nevertheless,  facts  that  render  it  certain  that 
water  may  be  absorbed  by  the  skin  and  relieve  in  some  degree  the  sen- 
sation of  thirst. 

Absorption  by  the  Respiratory  Surface.  —  Animal  and  vegetable 
emanations  may  be  taken  into  the  blood  by  the  lungs  and  produce 
well-marked  pathological  conditions.  Many  contagious  diseases  are 
propagated  in  this  way,  as  well  as  some  fevers  and  other  general 
diseases  that  are  not  contagious.  In  regard  to  certain  poisonous  gases 
and  volatile  matters,  the  effects  of  their  absorption  by  the  lungs  are 
even  more  striking.  Carbon  monoxide  and  arsine  produce  death 
almost  instantly,  even  when  inhaled  in  very  small  quantity.  The 
vapor  of  pure  hydrocyanic  acid  acts  frequently  with  great  promptness 


254  ABSORPTION  — LYMPH   AiND   CHYLE 

through  the  lungs.  Turpentine,  iodin  and  many  medicinal  substances 
may  be  introduced  with  great  rapidity  by  inhalation  of  their  vapors  ; 
and  the  serious  effects  produced  by  the  emanations  from  lead  or  mer- 
cury, in  persons  who  work  in  these  articles,  are  well  known.  Water 
and  substances  in  solution,  when  injected  into  the  respiratory  passages, 
are  rapidly  absorbed ;  and  poisons  administered  in  this  way  manifest 
their  peculiar  effects  with  great  promptness.  Experimenters  on  this 
subject  have  shown  the  facility  with  which  liquids  may  be  absorbed 
from  the  lungs  and  the  air-passages,  but  it  must  be  remembered  that 
the  natural  conditions  are  seldom  such  as  to  admit  of  this  action. 

Absorption  from  Closed  Cavities,  Reservoirs  of  Glands,  etc.  —  Facts 
in  pathology,  showing  absorption  from  closed  cavities,  areolar  tissue, 
the  muscular  and  nervous  tissues,  the  conjunctiva,  and  other  parts,  are 
sufficiently  well  known.  In  cases  of  effusion  of  serum  into  the  pleural, 
peritoneal,  pericardial  or  synovial  cavities,  in  which  recovery  takes 
place,  the  liquid  becomes  absorbed.  It  has  been  shown  by  experiment 
that  warm  water  injected  into  these  cavities  is  disposed  of  in  the  same 
way.  Effusions  into  the  areolar  tissue  usually  are  removed  by  absorp- 
tion. In  cases  of  penetration  of  air  into  the  pleura  or  the  general 
areolar  tissue,  absorption  likewise  takes  place,  showing  that  gases  may 
be  taken  up  in  this  way  as  well  as  liquids.  Effusions  of  blood  beneath 
the  skin  or  the  conjunctiva  or  in  the  muscular  or  nervous  tissue  may 
become  entirely  or  in  part  absorbed.  As  regards  absorption  from  the 
areolar  tissue,  the  administration  of  remedies  by  the  hypodermatic 
method  is  a  familiar  evidence  of  the  facility  with  which  soluble  sub- 
stances are  taken  into  the  blood  when  introduced  beneath  the  skin. 

Under  some  conditions,  absorption  takes  place  from  the  reservoirs 
of  glands,  the  watery  portions  of  the  secretions  usually  being  taken  up, 
leaving  the  solid  and  the  organic  matters.  It  is  supposed  that  the  bile 
becomes  inspissated  when  it  has  remained  for  a  time  in  the  gall-bladder, 
even  when  the  natural  flow  of  the  secretion  is  not  interrupted.  Cer- 
tainly, when  the  duct  is  obstructed,  absorption  of  a  portion  of  the  bile 
takes  place,  as  is  shown  by  coloration  of  the  conjunctiva  and  even  of 
the  general  surface.  The  serum  of  the  blood,  under  these  conditions, 
is  strongly  colored  with  bile.  It  is  probable,  also,  that  some  of  the 
watery  portions  of  the  urine  are  reabsorbed  by  the  mucous  membrane 
of  the  urinary  bladder  when  the  urine  has  been  long  confined  in  its  cavity, 
although  this  reabsorption  is  ordinarily  very  slight.  Absorption  may  take 
place  from  the  ducts  and  the  parenchyma  of  glands,  although  this  occurs 
chiefly  when  foreign  substances  have  been  injected  into  these  parts. 

Absorption  of  Fats  and  Insoluble  Substances.  —  In  studying  the 
mechanism  of  the  penetration  of  fatty  particles  into  the  intestinal  villi, 


INFLUENCE  OF    THE    NERVOUS    SYSTEM    ON  ABSORPTION      255 

it  has  been  ascertained  that  the  epithelium  plays  an  important  part  in 
this  process.  During  the  digestion  of  fat,  these  cells  become  filled 
with  fatty  granules.  It  has  not  been  demonstrated  precisely  how  fatty 
particles  penetrate  the  epithelium,  but  the  fact  can  not  be  doubted. 
From  the  epithelium,  the  particles  of  emulsion  pass  into  the  substance 
of  the  villi  —  probably  into  the  lymph-spaces  and  canals  —  and  from 
these  they  readily  find  their  way  into  the  lymphatic  capillaries.  It  has 
been  shown  that  fatty  emulsion  will  pass  more  easily  through  porous 
septa  that  have  been  moistened  with  bile ;  and  it  is  probably  in  this 
way  mainly  that  the  bile  aids  in  the  passage  of  the  fine  particles  of  fat 
into  the  lacteals. 

As  a  rule,  insoluble  substances,  with  the  exception  of  the  fats,  are 
never  regularly  absorbed,  no  matter  how  finely  they  may  be  divided. 
The  apparent  exceptions  to  this  are  mercury  in  a  state  of  minute  sub- 
division like  an  emulsion,  and  carbonaceous  particles.  As  regards  mer- 
cury, it  is  well  known  that  minute  particles  in  the  form  of  unguents 
may  be  introduced  into  the  system  by  prolonged  frictions  ;  but  this  can 
not  be  taken  as  an  instance  of  physiological  absorption.  The  passage 
of  small  carbonaceous  particles  through  the  pulmonary  membrane 
seems  to  be  purely  mechanical.  The  same  thing  possibly  may  occur 
when  fine  sharp  particles  of  carbon  are  introduced  into  the  alimentary 
canal. 

Influence  of  the  Condition  of  the  Blood  and  of  the  Vessels  on  Absorp- 
tion.—  After  loss  of  blood  or  its  deterioration  and  concentration  from 
prolonged  abstinence,  absorption  takes  place  with  great  activity.  This 
is  well  known,  both  as  regards  the  entrance  of  water  and  alimentary 
substances  and  the  absorption  of  drugs.  It  was  at  one  time  quite  a 
common  practice  to  bleed  before  administering  certain  remedies,  in  order 
to  produce  a  more  speedy  action. 

The  rapidity  of  the  circulation  has  an  important  influence  in  facilitat- 
ing absorption ;  and  this  process  usually  is  active  in  proportion  to  the 
vascularity  of  different  parts.  During  intestinal  absorption,  the  increase 
in  the  activity  of  the  circulation  in  the  mucous  membrane  is  very  marked 
and  undoubtedly  has  an  influence  on  the  rapidity  with  which  the  prod- 
ucts of  digestion  are  taken  up. 

Influence  of  the  Nervous  System  on  Absorption.  —  It  is  certain  that 
absorption,  especially  in  the  stomach,  is  subject  to  certain  variations 
which  can  hardly  be  dependent  on  anything  but  nervous  action.  Liquids 
that  usually  are  readily  absorbed  from  the  stomach  are  sometimes  retained 
for  a  time  and  are  afterward  rejected  in  nearly  the  condition  in  which 
they  were  taken.  It  is  probable,  however,  that  the  most  important  influ- 
ences thus  exerted  by  the  nervous  system  are  effected  through  the  circu- 


256  ABSORPTION  — LYMPH    AND    CHYLE 

lation.  When  it  is  remembered  that  the  small  arteries  may  become  so 
contracted  under  the  influence  of  the  vasomotor  nerves  that  their  calibre 
is  nearly  obliterated,  of  course  retarding  in  a  corresponding  degree  the 
capillary  and  venous  circulation  in  the  parts,  and  again,  that  the  same 
vessels  may  be  so  dilated  as  to  admit  to  a  particular  part  many  times 
more  blood  than  it  ordinarily  receives,  it  becomes  apparent  that  absorp- 
tion may  be  profoundly  affected  through  this  system  of  nerves.  It  has 
been  ascertained  that  while  a  section  of  some  of  the  nerves  distributed 
to  the  alimentary  canal  will  slightly  retard  the  absorption  of  the  poison- 
ous substances  the  process  is  never  entirely  arrested. 

Osmosis 

If  liquids  pass  through  the  substance  of  an  animal  membrane,  it  is 
evident  that  the  membrane  itself  must  be  capable  of  taking  up  a  certain 
portion  by  imbibition ;  and  this  must  be  considered  as  the  starting-point 
in  absorption.  Imbibition  is,  indeed,  a  property  common  to  animal 
tissues ;  but  it  is  a  well-known  fact  that  the  tissues  do  not  imbibe  all 
solutions  with  the  same  degree  of  activity.  Distilled  water  is  the  liquid 
taken  up  in  greatest  quantity,  and  saline  solutions  enter  the  substance 
of  the  tissues  usually  in  an  inverse  ratio  to  their  density.  In  regard 
to  mixtures  of  alcohol  and  water,  imbibition  is  in  an  inverse  pro- 
portion to  the  quantity  of  alcohol  present.  Among  the  other  con- 
ditions that  have  a  marked  influence  on  imbibition,  is  temperature ; 
and  it  is  a  familiar  fact  that  dried  animal  membranes  may  be  more 
rapidly  softened  in  warm  than  in  cold  water.  While  nearly  all  the 
structures  of  the  body,  after  desiccation,  will  imbibe  liquids,  the  mem- 
branes through  which  the  processes  of  absorption  are  most  active  are, 
as  a  rule,  most  easily  permeated ;  and  the  character  of  the  Hquid,  the 
temperature,  etc.,  have  a  great  influence  on  the  activity  of  this  process. 

Mechanism  of  the  Passage  of  Liquids  through  Membranes. — ^The 
passage  of  liquids  through  membranes  is  called  osmosis,  and  this  is  in 
obedience  to  what  is  known  as  osmostic  pressure.  In  the  case  of  two 
Hquids  passing  in  opposite  directions,  the  stronger  current  is  called 
endosmotic,  and  the  weaker,  exosmotic.  In  the  passage  of  hquids  into 
the  vessels,  in  physiological  absorption,  the  process  usually  is  called 
endosmosis. 

It  is  now  definitely  ascertained  that  the  following  conditions  are 
necessary  for  the  operation  'of  endosmosis  and  exosmosis  :  — 

I.  That  both  liquids  be  capable  of  "wetting"  the  interposed  mem- 
brane, or  in  other  words,  that  the  membrane  be  capable  of  imbibing 
both  liquids.  If  but  one  of  the  liquids  can  wet  the  membrane,  the 
current  takes  place  in  only  one  direction. 


OSMOSIS 


257 


2.  That  the  Hquids  be  miscible  with  each  other  and  be  differently 
constituted.  Although  it  is  found  that  the  currents  are  most  active 
when  liquids  are  of  different  densities,  this  condition  is  not  indispen- 
sable ;  for  currents  will  take  place  between  solutions  of  different  sub- 
stances, such  as  salt,  sugar  or  albumin,  even  when  they  have  the  same 
density. 

Diffusion  of  liquids  takes  place  in  accordance  with  the  law  of 
diffusion  of  gases,  formulated  by  Boyle.  The  molecules  of  gases  are 
in  constant  movement  and  would  pass  into  space  unless  restrained  or 
confined  by  the  walls  of  a  containing  vessel  or  by  the  force  of  gravity. 
The  pressure  of  a  gas  is  equal  to  the  pressure  required  to  keep  it  at 
a  certain  degree  of  concentration.  At  the  surface  of  the  earth,  this  is 
measured  by  the  barometer  and  is  equal  to  about  30  inches  (i 
meter)  of  mercury.  One  atmosphere  is  equal  to  a  pressure  of  14.7 
pounds  to  the  square  inch  (about  i  kilogram  to  the  square  centimeter). 
The  pressure  of  a  gas  increases  with  elevation  in  temperature,  by  9^3 
of  the  pressure  at  32°  Fahr.  (0°  C.)  for  each  rise  of  1°  C.  From  this 
the  hypothetical,  or  absolute,  zero  has  been  calculated  to  be  —  273°  C. 
Van't  Hoff  and  others  have  shown  that  osmotic  pressure  obeys  this 
law  within  certain  limits. 

Osmotic  pressure  is  the  force  exerted  by  various  solutions  —  such  as 
a  salt  or  a  cane-sugar  solution  —  which  draws  pure  water  through  a 
permeable  layer,  such  as  an  animal  membrane  or  unglazed  porcelain. 
If  both  liquids  are  capable  of  penetrating  the  membrane,  currents  pass 
in  both  directions  until  diffusion  is  complete  and  both  solutions  are  of 
equal  density. 

In  order  to  measure  osmotic  pressure,  it  is  necessary  to  use  a  mem- 
brane that  will  allow  a  current  in  one  direction  only.  This  is  called  a 
semipermeable  membrane.  If  unglazed  porcelain  is  impregnated  with 
copper  ferrocyanide,  it  is  rendered  impermeable  to  certain  solutions, 
such  as  common  salt  and  cane-sugar,  while  it  admits  the  passage  of 
water.  A  good  example  of  a  semipermeable  membrane  is  the  mem- 
brane of  a  hen's  egg.  This  is  impermeable  to  albumin  but  not  to 
water.  Exposing  this  membrane  by  removing  part  of  the  shell,  an 
egg-endosmometer  may  be  constructed  that  will  measure  the  osmotic 
pressure  of  albumin. 

It  has  been  ascertained  that  a  one  per  cent  solution  of  sodium 
chloride  has  an  osmotic  pressure  of  five  meters  (about  two  hundred 
inches)  of  mercury,  which  is  equal  to  six  and  a  half  atmospheres.  A 
two  per  cent  solution  has  double  this  pressure.  While  the  pressure  is 
in  direct  ratio  to  the  concentration  of  the  solution,  it  has  not  been 
possible,  thus  far,  to  measure  the  pressure  of  solutions  higher  than  six 


2S8  ABSORPTION  — LYMPH    AND    CHYLE 

per  cent  of  cane-sugar  in  water,  which  is  only  about  one-fifth  of  a 
normal  solution.  Physicists  are  still  unacquainted  with  the  cause  of 
osmosis ;  and  while  the  bearing  of  the  prevailing  theories  of  osmotic 
pressure,  electrolysis  and  dissociation  into  anions  and  cations  on  absorp- 
tion, nutrition  and  secretion  are  undoubtedly  of  the  highest  physiological 
importance,  this  is  not  yet  entirely  clear. 

In  no  experiments  performed  out  of  the  body,  can  the  conditions 
favorable  to  the  passage  of  liquids  through  membranes  in  accordance 
with  purely  physical  laws  be  realized  as  they  exist  in  the  living  organism. 
The  great  extent  of  the  absorbing  surfaces ;  the  delicacy  and  permea- 
bility of  the  membranes  ;  the  rapidity  with  which  substances  are  carried 
on  by  the  torrent  of  the  circulation,  so  soon  as  they  pass  through  these 
membranes ;  the  uniformity  of  the  pressure,  notwithstanding  the  pene- 
tration of  liquids,  —  all  these  favor  the  physical  phenomena  of  absorption 
in  a  way  that  can  not  be  imitated  in  artificially-constructed  apparatus. 
Within  the  bloodvessels  albuminous  matters  exist  in  a  form  that  does 
not  permit  them  to  pass  through  membranes,  while  the  peptones  are 
highly  osmotic.  The  sugars,  also,  pass  through  the  walls  of  the  ves- 
sels with  faciUty,  as  well  as  various  salts  and  medicinal  substances  in 
solution.  The  fats,  as  has  been  stated,  pass  mainly  into  the  lacteals, 
by  a  process  already  described,  which  can  not  be  fully  explained  by  the 
laws  of  osmosis. 

Lymph  and  Chyle 

It  is  estimated  that  the  total  quantity  of  lymph  and  chyle  produced 
in  the  twenty-four  hours  in  a  man  weighing  one  hundred  and  forty-three 
pounds  (65  kilograms)  is  about  6.6  pounds  (3000  grams).  Reasoning 
from  experiments  made  on  dogs  thirteen  hours  after  feeding,  when  the 
liquid  which  passes  up  the  thoracic  duct  may  be  assumed  to  be  pure 
unmixed  lymph,  the  total  quantity  of  lymph  alone,  produced  in  the 
twenty-four  hours  by  a  man  of  ordinary  weight,  would  be  about  4.4 
pounds  (2000  grams).  These  estimates  can  be  accepted  only  as 
approximate,  and  they  do  not  indicate  the  entire  quantity  of  lymph 
actually  contained  in  the  organism. 

There  are  no  very  satisfactory  recent  researches  in  regard  to  the 
physiological  variations  in  the  quantity  of  lymph.  In  comparing  the 
quantity  of  liquid  in  the  lymphatics  of  the  neck  in  dogs,  during  digestion 
and  absorption,  with  the  quantity  which  they  contained  soon  after  diges- 
tion was  completed,  it  has  been  found  that  while  digestion  and  absorption 
were  going  on  actively,  the  vessels  of  the  neck  contained  scarcely  any 
liquid ;  but  the  quantity  gradually  increased  after  these  processes  were 
completed  (Collard  de  Martigny). 


PROPERTIES    AND    COMPOSITION    OF    LYMPH 


259 


Properties  and  Composition  of  Lymph.  —  Lymph  taken  from  the 
vessels  in  various  parts  of  the  system,  or  the  liquid  discharged  from  the 
thoracic  duct  during  the  interv^als  of  digestion,  is  either  transparent  and 
colorless  or  of  a  slightly  yellowish  or  greenish  tint.  When  allowed  to 
stand  for  a  short  time,  it  becomes  faintly  tinged  with  red,  and  frequently 
it  has  a  pale  rose-color  when  first  discharged.  Microscopical  examina- 
tion shows  that  this  reddish  color  is  dependent  on  the  presence  of  a  few 
red  blood-corpuscles,  which  are  entangled  in  the  clot  as  the  lymph  coagu- 
lates, thus  accounting  for  the  deepening  of  the  color  when  the  liquid 
has  been  allowed  to  stand. 

Lymph  has  no  decided  or  characteristic  odor.  It  is  slightly  saline 
in  taste,  almost  insipid.  Its  specific  gravity  is  much  lower  than  that  of 
the  blood.  In  the  dog  it  is  about  1022.  A  few  minutes  after  discharge 
from  the  vessels,  both  lymph  and  chyle  .undergo  coagulation.  This 
process,  as  regards  the  chemical  changes  involved,  is  identical  with  the 
coagulation  of  the  blood,  in  which  the  leucocytes  play  an  important 
part.  Lymph  collected  from  the  thoracic  duct  in  the  large  ruminants 
coagulates  at  the  end  of  five,  ten  or  twelve  minutes,  and  sets  into  a  mass 
having  exactly  the  form  of  the  vessel  in  which  it  is  contained.  The  clot 
is  tolerably  consistent,  but  there  is  never  any  spontaneous  separation  of 
serum. 

Although  many  analyses  have  been  made  of  lymph  from  the  human 
subject,  the  conditions  under  which  it  has  been  obtained  render  it  prob- 
able that  in  the  majority  of  instances  it  w^as  not  entirely  normal.  It  will 
be  necessary,  therefore,  to  compare  these  analyses  with  observations 
on  the  inferior  animals ;  as  in  the  latter,  it  has  been  collected  under 
conditions  which  leave  no  doubt  as  to  its  normal  character.  The  fol- 
lowing is  an  analysis  by  Lassaigne  of  specimens  of  lymph  collected  by 
Colin  from  the  thoracic  duct  of  a  cow,  under  the  most  favorable 
conditions  :  — 

COMPOSITION   OF   LYMPH    FROM   A   COW 

Water 964.0 

Fibrin      .............  0.9 

Albumin 28.0 

Fatty  matters 0.4 

Sodium  chloride 5.0 

Sodium  carbonate,  sodium  phosphate  and  sodium  sulphate    .         .         .  1.2 

Calcium  phosphate 0.5 

1 000.0 

The  proportions  given  in  the  table  are  by  no  means  invariable,  the 
differences  in  coagulability  indicating  differences  in  the  proportion  of 
fibrin-factors,  and  the  degree  of  lactescence  showing  variations  in  the 


26o  ABSORPTION  — LYMPH    AND    CHYLE 

quantity  of  fatty  matters.  The  table  may  be  taken,  however,  as  an 
approximation  of  the  average  composition  of  the  lymph  of  these  animals 
during  the  intervals  of  digestion. 

Analyses  of  human  lymph  show  a  larger  proportion  of  solid  con- 
stituents than  was  found  by  Lassaigne  in  the  lymph  of  the  cow.  This 
excess  is  pretty  uniformly  distributed  throughout  all  the  constituents, 
with  the  exception  of  the  fatty  matters  and  fibrin ;  the  former  existing 
largely  in  excess  in  the  human  lymph,  while  the  latter  is  smaller  in 
quantity  than  in  the  lymph  of  the  cow. 

The  distinctive  characters  of  the  different  constituents  of  the  lymph 
do  not  demand  extended  consideration,  inasmuch  as  most  of  them  have 
already  been  treated  of  in  connection  with  the  blood.  In  comparing, 
however,  the  composition  of  the  lymph  with  that  of  the  blood,  the  great 
excess  of  solid  constituents  in  the  latter  is  at  once  apparent. 

In  nearly  all  analyses  the  proteids  have  been  found  to  be  very  much 
less  in  quantity  in  lymph  than  in  the  blood.  This  usually  is  most 
marked  in  regard  to  the  fibrin-factors ;  but  as  before  stated,  the  propor- 
tion of  all  these  substances  is  variable.  On  account  of  this  deficiency, 
lymph  is  much  inferior  to  the  blood  in  coagulability ;  and  the  coagulum, 
when  formed,  is  soft  and  friable.  There  does  not  appear,  however, 
to  be  any  actual  difference  between  the  coagulating  constituents  of  the 
lymph  and  of  the  blood.  Fatty  matters  usually  have  been  found  to  be 
more  abundant  in  the  lymph  than  in  the  blood ;  but  their  proportion 
is  even  more  variable  than  that  of  the  proteid  constituents.  Very  little 
is  to  be  said  concerning  the  ordinary  inorganic  constituents  of  the 
lymph.  It  has  been  shown  that  nearly  if  not  quite  all  the  inorganic 
matters  found  in  the  blood  are  contained  in  lymph  in  varying  propor- 
tions. Some  analyses  have  given  a  small  quantity  of  iron.  These  facts 
indicate  a  remarkable  correspondence  in  composition  between  lymph 
and  blood.  All  the  constituents  of  the  blood,  except  the  red  corpuscles, 
exist  in  lymph,  the  only  difference  being  in  their  relative  proportions. 
In  addition  to  the  constituents  of  the  lymph  ordinarily  given,  the 
presence  of  glucose,  and  more  lately,  the  existence  of  a  considerable 
proportion  of  urea,  have  been  demonstrated.  It  has  not  been  ascer- 
tained how  the  sugar  contained  in  the  lymph  takes  its  origin. 

The  lymph  of  the  dog  contains  about  forty  parts  per  hundred  in 
volume  of  carbon  dioxide,  of  which  seventeen  parts  may  be  extracted 
by  the  gas-pump  and  twenty-three  parts,  by  acids.  In  addition,  the 
lymph  contains  a  trace  of  oxygen  and  one  or  two  parts  of  nitrogen. 

Corpuscular  Elements  of  the  Lymph.  —  In  every  part  of  the  lym- 
phatic system,  in  addition  to  a  few  minute  fatty  granules,  there  are 
found  certain  corpuscular  elements  known  as  lymph-corpuscles  (leuco- 


ORIGIN    AND    USES    OF    THE    LYMPH  261 

cytes).  These  exist,  not  only  in  the  clear  lymph,  but  in  the  opaque 
liquid  contained  in  the  lacteals  during  absorption.  Eighty-two  hundred 
leucocytes  have  been  counted  in  0.061  cubic  inch  (i  cubic  centimeter) 
of  lymph  from  a  dog. 

The  leucocytes  found  in  lymph  and  chyle  are  rather  less  uniform  in 
size  and  general  appearance  than  the  leucocytes  of  the  blood.  Their 
average  diameter  is  about  25V0  ^^  ^^  ^^*^^  (10  A^)!  but  some  are  larger, 
and  others  are  as  small  as  -^-q-q-q  of  an  inch  (5  fx).  Some  of  these  cor- 
puscles are  quite  clear  and  transparent,  presenting  but  few  granules 
and  an  indistinct  nuclear  appearance  in  their  centre  ;  but  others  are 
granular  and  quite  opaque.  They  present  the  same  adhesive  character 
in  the  lymph  as  in  the  blood,  and  frequently  they  are  found  collected 
in  masses  in  different  parts  of  the  lymphatic  system.  In  other  regards, 
these  bodies  present  the  same  characters  as  the  leucocytes  of  the  blood, 
and  they  need  not,  therefore,  be  further  described,  but  the  variety 
known  as  lymphocytes  predominates.  In  addition  to  leucocytes 
and  a  certain  number  of  fatty  granules,  a  few  small  clear  globules  or 
granules,  about  ygVo  ^f  an  inch  (3.3  /x)  in  diameter  are  almost  con- 
stantly present  in  the  lymph.  They  are  insoluble  in  ether  and  acetic 
acid  but  are  dissolved  by  ammonia. 

Origin  and  Uses  of  the  Lymph.  —  There  can  hardly  be  any  doubt 
concerning  the  source  of  most  of  the  liquid  portions  of  the  lymph,  for 
they  can  be  derived  only  from  the  blood.  Although  the  exact  relations 
between  the  smallest  lymphatics  and  the  bloodvessels  have  not  been 
made  out  in  all  parts  of  the  system,  there  is  manifestly  no  anatomical 
reason  why  water,  mixed  with  albuminous  matters  and  holding  salts  in 
solution,  should  not  pass  from  the  blood  into  the  lymphatics ;  and  this 
is  rendered  nearly  certain  by  the  fact  that  the  lymphatics  surround  many 
of  the  bloodvessels.  In  comparing  the  composition  of  the  lymph  with 
that  of  blood-plasma,  it  is  seen  that  their  constituents  are  nearly  identi- 
cal, the  only  variations  being  in  their  relative  proportions. 

One  of  the  most  important  physiological  facts  in  the  chemical  history 
of  the  lymph  is  the  constant  existence  of  a  considerable  proportion  of 
urea.  This  can  not  be  derived  from  the  blood,  for  its  proportion  is 
greater  in  the  lymph,  notwithstanding  the  fact  that  this  liquid  is  being 
constantly  discharged  into  the  bloodvessels.  The  urea  existing  in  the 
lymph  probably  is  derived  in  some  way  from  the  liver ;  it  is  discharged 
then  into  the  blood,  and  is  constantly  being  eliminated  by  the  kidneys. 

The  positive  facts  on  which  to  base  any  precise  ideas  in  regard  to 
the  general  office  of  the  lymph  are  not  many.  From  the  composition 
of  this  liquid,  its  mode  of  circulation  and  the  fact  that  it  is  being  con- 
stantly discharged  into  the  blood,  it  would  not  seem  of  itself  to  have 


262  ABSORPTION  — LYMPH    AND    CHYLE 

important  uses  in  the  active  processes  of  nutrition.  The  quantity  and 
the  proportion  of  solid  constituents  are  rather  increased  than  diminished 
in  animals  deprived  of  food  and  drink  for  several  days ;  while  starvation 
always  impoverishes  the  blood  from  the  first.  On  the  other  hand,  urea, 
one  of  the  most  important  of  the  products  of  katabolism,  undoubtedly 
is  taken  up  by  the  lymph  and  conveyed  to  the  blood. 

Pivpertics  and  Composition  of  Chyle.  —  During  the  intervals  of  diges- 
tion, the  intestinal  lymphatics  and  the  thoracic  duct  carry  lymph  ;  but 
so  soon  as  absorption  of  the  products  of  digestion  begins,  certain  nutri- 
tive matters  are  taken  up  in  quantity  by  these  vessels,  and  their  contents 
are  known  under  the  name  of  chyle. 

In  the  human  subject  and  in  carnivorous  animals,  the  chyle,  taken 
from  the  lacteals  near  the  intestine,  where  it  is  nearly  pure,  or  from  the 
thoracic  duct,  when  it  is  mixed  with  lymph,  is  a  white,  opaque,  milky 
liquid,  of  a  slightly  saline  taste  and  an  odor  said  to  resemble  that  of  the 
semen.  The  odor  is  also  said  to  be  characteristic  of  the  animal  from 
which  chyle  is  taken ;  although  this  is  not  very  marked,  except  on  the 
.addition  of  a  concentrated  acid.  The  reaction  of  the  chyle  is  either 
alkaline  or  neutral.  Its  specific  gravity  is  less  than  that  of  the  blood ; 
but  it  is  variable  and  depends  on  the  quality  of  food  and  particularly 
the  quantity  of  liquids  ingested. 

The  differences  in  the  appearance  of  the  chyle  in  different  animals 
depend  chiefly  on  the  food.  The  chyle  is  milky  in  the  carnivora,  espe- 
cially after  fats  have  been  taken  in  quantity ;  but  in  dogs  nourished  with 
articles  containing  but  little  fat,  its  appearance  is  hardly  lactescent.  The 
chyle  is  almost  transparent  in  herbivora  fed  with  hay  or  straw. 

It  is  impossible  to  give  an  accurate  estimate  of  the  entire  quantity 
of  chyle  taken  up  by  the  lacteal  vessels.  When  it  finds  its  way  into  the 
thoracic  duct,  it  is  immediately  mixed  with  all  the  lymph  from  the  lower 
extremities ;  and  the  large  quantities  that  have  been  collected  from 
this  vessel  give  no  idea  of  the  quantity  of  chyle  absorbed  from  the  intes- 
tinal canal.  No  attempt  will  be  made,  therefore,  to  give  even  an  approxi- 
mate estimate  of  the  absolute  quantity  of  chyle ;  but  it  is  evident  that 
this  is  variable,  depending  on  the  nature  of  the  food  and  the  quantity  of 
liquids  ingested. 

Like  the  lymph,  the  chyle,  when  removed  from  the  vessels,  under- 
goes coagulation.  Different  specimens  vary  considerably  as  regards 
rapidity  of  coagulation.  Chyle  from  the  thoracic  duct  usually  coagu- 
lates in  a  few  minutes.  The  first  portion  of  the  liquid  collected  from 
the  human  subject  by  Rees  —  the  chyle  was  collected  in  this  case  in  two 
portions  —  coagulated  in  an  hour.  Received  into  an  ordinary  glass  ves- 
sel, the  chyle  separates  more  or  less  completely,  after  coagulation,  into 


COMPOSITION    OF    CHYLE  263 

clot  and  serum.  The  serum  is  quite  variable  in  quantity  and  is  never 
clear.  Its  milkiness  does  not  depend  entirely  on  the  presence  of  parti- 
cles of  emulsified  fat,  and  it  is  not  rendered  transparent  by  ether.  It 
contains,  also,  leucocytes  and  granular  matter. 

Observations  have  been  made  with  reference  to  the  influence  of  dif- 
ferent kinds  of  food  on  the  chyle ;  but  these  have  not  been  followed  by 
any  definite  results  that  can  be  applied  to  the  human  subject.  It  is 
usual  to  find  the  chyle  liquid  in  the  lacteals  and  in  the  thoracic  duct  for 
many  hours  after  death  ;  but  it  soon  coagulates  after  exposure  to  the  air. 
Although  the  entire  lacteal  system  is  sometimes  found,  in  the  human 
subject  and  in  the  inferior  animals,  filled  with  opaque  coagulated  chyle, 
the  liquid  does  not  often  coagulate  in  the  vessels. 

Composition  of  Chyle.  —  Analyses  of  the  milky  liquid  taken  from  the 
thoracic  duct  during  full  digestion  by  no  means  represent  the  composi- 
tion of  pure  chyle  ;  and  it  is  only  by  collecting  the  liquid  from  the  mesen- 
teric lacteals,  that  it  can  be  obtained  without  a  large  admixture  of  lymph. 
In  the  human  subject,  it  is  rare  even  to  have  an  opportunity  to  take  the 
contents  of  the  thoracic  duct  in  cases  of  sudden  death  during  digestion ; 
and  in  most  of  the  inferior  animals,  it  is  difficult  to  obtain  liquid  from 
the  small  lacteals  in  quantity  sufficient  for  accurate  analysis. 

In  the  analysis  by  Rees,  the  liquid  was  taken  from  the  thoracic  duct 
of  a  vigorous  man,  a  little  more  than  an  hour  after  his  execution  by  hang- 
ing. The  subject  was  apparently  in  perfect  health  up  to  the  moment  of 
death.  The  evening  before,  he  ate  two  ounces  (56.7  grams)  of  bread 
and  four  ounces  (113.4  grams)  of  meat.  At  seven  a.m.,  one  hour  before 
execution,  he  took  two  cups  of  tea  and  a  piece  of  toast ;  and  he  drank  a 
glass  of  wine  just  before  mounting  the  scaffold.  When  the  dissection 
was  made,  the  body  was  yet  warm,  although  the  weather  was  quite  cold. 
The  thoracic  duct  was  rapidly  exposed  and  divided,  and  about  six  flui- 
drachms  (22.2  cubic  centimeters)  of  milky  chyle  were  collected.  The 
hquid  was  neutral  and  had  a  specific  gravity  of  1 024.  The  following 
was  its  approximate  composition  :  — 

COMPOSITION   OF   HUMAN   CHYLE   FROM   THE  THORACIC   DUCT 

Water 904.8 

Albumin,  with  traces  of  fibrinous  matter       ......  70.8 

Aqueous  extractive       ..........  5.6 

Alcholic  extractive        ..........  5.2 

Alkaline  chlorides,  carbonates  and  sulphates,  with  traces  of  alkaline 

phosphates,  and  oxides  of  iron           .......  4.4 

Fatty  matters 9.2 

I 000.0 


264  ABSORPTION  — LYMPH    AND   CHYLE 

The  difference  in  chemical  composition  between  the  unmixed  lymph 
and  the  chyle  is  illustrated  in  a  comparative  examination  of  these  two 
liquids  taken  from  a  donkey.  They  were  collected  by  Lane,  the  chyle 
being  taken  from  the  lacteals  before  reaching  the  thoracic  duct.  The 
animal  was  killed  seven  hours  after  a  full  meal  of  oats  and  beans. 
The  following  analyses  were  made  by   Rees :  — 

COMPOSITION  OF  CHYLE  AND  LYMPH   BEFORE   REACHING  THE 
THORACIC   DUCT 


Water 

Albuminous  matter 

Fibrinous  matter  ........ 

Animal  extractive  matters  soluble  in  water  and  alcohol 
Animal  extractive  matters  soluble  in  water  only  . 
Fatty  matters        ........ 

C  Alkaline  chlorides,  sulphates  and  carbonates,  with  1 
^'  1       traces  of  alkaline  phosphates,  and  oxide  of  iron.  \ 


Chyle 

Lymph 

902.37 

965.36 

35-i6 

12.00 

370 

1.20 

3-32 

2.40 

12.33 

I3I9 

36.01 

a  trace 

7.11 

5.85 

1000.00 

1000.00 

The  above  analyses  show  a  marked  difference  in  the  proportion  of 
solid  constituents.  The  chyle  contained  about  three  times  as  much 
albumin  and  fibrin  as  the  lymph,  with  a  larger  proportion  of  salts. 
The  proportion  of  fatty  matters  in  the  chyle  was  very  great,  while  in 
the  lymph  there  existed  only  a  trace.  The  individual  constituents  of 
the  chyle  given  in  the  above  tables  do  not  demand  further  considera- 
tion than  they  have  already  received  under  the  head  of  lymph.  The 
albuminous  matters  are  in  part  derived  from  the  food,  and  in  part  from 
the  blood  through  admixture  with  lymph.  The  fatty  matters  are  derived 
in  greatest  part  from  the  food.  So  far  as  has  been  ascertained  by 
analyses  of  the  chyle  for  inorganic  salts,  it  has  been  found  to  contain 
essentially  the  same  inorganic  constituents  as  the  blood-plasma. 

Microscopical  CJiaracters  of  the  CJiylc. — The  milky  appearance  of  the 
chyle  as  contrasted  with  the  lymph  is  due  to  the  presence  of  a  large 
number  of  minute  fatty  granules.  The  liquid  becomes  much  less  opaque 
when  treated  with  ether,  which  dissolves  many  of  the  fatty  particles. 
In  fact,  the  chyle  of  the  thoracic  duct  is  nothing  more  than  lymph  to 
which  an  emulsion  of  fat  in  a  liquid  containing  albuminous  matters  and 
salts  is  temporarily  added  during  the  process  of  intestinal  absorption. 
The  quantity  of  fatty  granules  in  the  chyle  varies  considerably  with  the 
diet,  and  it  usually  diminishes  progressively  from  the  smaller  to  the 
larger  vessels,  on  account  of  the  constant  admixture  of  lymph.  The  size 
of  the  granules  is  pretty  uniformly  250F0  ^^  T2ioo  ^^  ^^^  m(i\i  (i  to  2  /a). 
They  are  much  smaller  and  more  uniform  in  size  in  the  lacteals  than 


MOVEMENTS  OF  THE  LYMPH  AND  THE  CHYLE       265 

in  the  intestine.  Their  constitution  is  not  constant ;  and  they  are  com- 
posed of  the  different  varieties  of  fat  taken  as  food,  mixed  in  various 
proportions.  The  ordinary  corpuscular  elements  of  the  lymph  are  also 
found  in  variable  quantity  in  the  chyle. 

Movements  of  the  Lymph  and  the  Chyle 

Compared  with  the  current  of  blood,  the  movements  of  the  lymph 
and  chyle  are  feeble  and  irregular ;  and  the  character  of  these  move- 
ments is  such  that  they  are  evidently  due  to  a  variety  of  causes.  As 
regards  constituents  derived  directly  from  the  blood,  the  lymph  may  be 
said  to  undergo  a  true  circulation ;  inasmuch  as  there  is  a  constant 
transudation  at  the  peripheral  portion  of  the  vascular  system,  of  liquids 
that  are  returned  to  the  circulating  blood  by  the  communications  of  the 
lymphatic  system  with  the  great  veins.  The  constituents  of  the  lymph, 
however,  are  not  derived  entirely  from  the  blood,  a  considerable  portion 
resulting  from  interstitial  absorption  in  the  general  lymphatic  system  ; 
and  the  chyle  contains  certain  nutritive  matters  absorbed  by  the  lacteal 
vessels.  These  are,  physiologically,  the  most  important  constituents  of 
the  lymph  and  chyle ;  and  they  are  taken  up  simply  to  be  carried  to  the 
blood  and  do  not  pass  again  from  the  general  vascular  system  into  the 
lymphatics. 

So  far  as  the  mode  of  origin  of  the  lymph  and  chyle  has  any  bearing 
on  the  movements  of  these  liquids  in  the  lymphatic  vessels,  there  is  no 
difference  between  the  imbibition  of  new  matters  from  the  tissues  or 
from  the  intestinal  canal  and  the  transudation  of  the  liquid  portions  of 
the  blood ;  for  the  mechanism  of  the  passage  of  liquids  from  the  blood- 
vessels is  such  that  the  motive  power  of  the  blood  can  not  be  felt.  An 
illustration  of  this  is  in  the  mechanism  of  the  production  of  the  liquid 
portions  of  the  secretions.  So  far  as  the  flow  in  the  vessels  of  medium 
size  is  concerned,  the  movement  probably  is  continuous,  subject  only 
to  certain  momentary  obstructions  or  accelerations  from  various  causes  ; 
but  in  the  large  vessels  situated  near  the  thorax  and  in  those  within  the 
chest,  the  movements  are  in  a  marked  degree  remittent,  or  they  may 
even  be  intermittent.  All  experimenters  who  have  observed  the  flow  of 
lymph  or  chyle  from  a  fistula  in  the  thoracic  duct  have  noted  a  constant 
acceleration  with  each  act  of  expiration ;  and  an  impulse  synchronous 
with  the  pulsations  of  the  heart  has  frequently  been  observed. 

The  fact  that  the  lymphatic  system  is  never  distended,  and  the  ex- 
istence of  valves,  by  which  different  portions  may  become  isolated, 
render  it  impossible  to  estimate  the  general  pressure  in  these  vessels. 
This  undoubtedly  is  subject  to  great  variations  in  the  same  vessels  at 
different  times  as  well  as  in  different  parts  of  the  lymphatic  system. 


266  ABSORPTION  —  LYMPH    AND    CHYLE 

The  general  rapidity  of  the  current  in  the  lymphatic  vessels  has  never 
been  accurately  estimated.  As  a  natural  consequence  of  the  variations 
in  the  distention  of  these  vessels,  the  rapidity  of  the  circulation  must 
be  subject  to  frequent  modifications.  It  has  been  calculated  that  the 
rapidity  of  the  flow  in  the  thoracic  duct  is  about  one  inch  (25.4  milli- 
meters) per  second.  This  estimate,  however,  can  be  only  approximate  ; 
and  it  is  evident  that  the  flow  must  be  much  less  rapid  in  vessels  near 
the  periphery  than  in  the  large  trunks,  as  the  liquid  moves  in  a  space 
that  rapidly  becomes  contracted  as  it  approaches  the  openings  into  the 
venous  system. 

Various  influences  combine  to  produce  the  movements  of  liquids  in 
the  lymphatic  system,  some  being  constant  in  their  operation,  and  others, 
intermittent  or  occasional.  These  will  be  considered,  as  nearly  as  pos- 
sible, in  the  order  of  their  relative  importance. 

The  forces  of  osmosis  and  transudation  are  undoubtedly  the  main 
causes  of  the  lymphatic  circulation,  more  or  less  modified,  however,  by 
influences  that  may  accelerate  or  retard  the  current ;  but  this  action  is 
capable  in  itself  of  producing  the  regular  movement  of  the  lymph  and 
chyle.  It  is  a  force  that  is  in  constant  operation,  as  is  seen  in  cases  of 
Hgation  of  the  thoracic  duct,  a  procedure  which  must  finally  aboHsh  all 
other  forces  that  aid  in  producing  the  lymphatic  circulation.  When 
the  receptaculum  chyli  is  ruptured  as  a  consequence  of  obstruction  of 
the  thoracic  duct,  the  vessel  gives  way  as  the  result  of  the  constant 
osmotic  action,  in  the  same  way  that  the  exposed  membranes  of  an 
Qgg  may  be  ruptured  when  immersed  in  water. 

The  situations  in  which  the  osmotic  force  originates  are  at  the 
periphery,  where  the  single  wall  of  the  vessels  is  thin,  and  where  the 
extent  of  absorbing  surface  is  large.  If  liquids  can  penetrate  with  such 
rapidity  and  force  through  the  walls  of  the  bloodvessels,  where  their 
entrance  is  opposed  by  the  pressure  of  liquid  already  in  their  interior, 
they  certainly  must  pass  without  difficulty  through  the  walls  of  the 
lymphatics,  where  there  is  no  lateral  pressure  to  oppose  their  entrance, 
except  that  produced  by  the  weight  of  the  column  of  liquid.  This 
pressure  is  readily  overcome ;  and  the  valves  in  the  lymphatic  system 
effectually  prevent  any  backward  current. 

In  describing  the  anatomy  of  the  lymphatic  system,  it  has  already 
been  stated  that  the  large  vessels  and  those  of  medium  size  are  provided 
with  non-striated  muscular  fibres  and  are  contractile.  This  has  been 
demonstrated  by  physiological  as  well  as  anatomical  investigations  ;  and 
it  is  not  uncommon  to  see  the  lacteals  become  reduced  in  size  to  mere 
threads,  even  while  under  observation.  Although  experiments  usually 
have  failed  to  demonstrate  any  rhythmical  contractions  in  the  lymphatic 


J 


MOVEMENTS    OF   THE    LYMPH   AND    THE    CHYLE  267 

system,  it  is  probable  that  the  vessels  contract  on  their  contents,  when 
they  are  unusually  distended,  and  thus  assist  the  circulation,  the  action 
of  the  valves  opposing  a  regurgitating  flow.  This  action,  however,  can 
not  have  any  considerable  and  regular  influence  on  the  general  current. 
Contractions  of  voluntary  muscles,  especially  compression  of  the 
abdominal  organs  by  contraction  of  the  abdominal  muscles,  peristaltic 
movements  of  the  intestines  and  pulsations  of  large  arteries  situated 
against  the  lymphatic  trunks,  particularly  the  thoracic  aorta,  are  all 
capable  of  increasing  the  rapidity  of  the  circulation  of  the  lymph  and 
chyle.  The  contractions  of  voluntary  muscles  assist  the  lymphatic 
circulation  in  precisely  the  way  in  which  they  influence  the  flow  of 
blood  in  the  venous  system  ;  and  there  is  nothing  to  be  added  to  what 
has  been  said  on  this  subject  in  connection  with  the  venous  circulation. 
While  a  vis  a  tergo  must  be  regarded  as  by  far  the  most  important 
agent  in  the  production  of  the  lymphatic  circulation,  movement  of  the 
contents  of  the  thoracic  duct  receives  constant  and  important  aid  from 
the  respiratory  acts. 


CHAPTER   XI 

SECRETION 

Classification  of  the  secretions  —  Mechanism  of  the  production  of  the  true  secretions  —  Mechan- 
ism of  the  production  of  the  excretions  —  Influence  of  the  composition  and  pressure  of  the 
blood  on  secretion  —  Influence  of  the  nervous  system  on  secretion  —  Paralytic  secretion  by 
glands —  Anatomical  classification  of  glandular  organs  —  Secreting  membranes —  Follicular 
glands  —  Tubular  glands —  Racemose  glands,  simple  and  compound  —  Ductless,  or  blood- 
glands  —  Secretions  and  excretions  —  Synovial  membranes  and  synovia  —  Mucous  mem- 
branes and  mucus — Mechanism  of  the  secretion  of  mucus  —  Composition  and  varieties  of 
mucus  —  General  uses  of  mucus  —  Physiological  anatomy  of  the  sebaceous,  ceruminous 
and  Meibomian  glands — Ordinary  sebaceous  matter  —  Smegma  of  the  prepuce  and  labia 
minora  —  Vernix  caseosa  —  Cerumen  —  Mammary  secretion — Mechanism  of  the  secre- 
tion of  milk  —  General  conditions  which  modify  the  lacteal  secretion  —  Properties  and 
composition  of  milk  —  Microscopical  characters  of  milk  —  Composition  of  the  milk  — 
Colostrum  —  Lacteal  secretion  in  the  newly  born. 

In  the  sense  in  which  the  term  secretion  usually  is  received,  it  em- 
braces most  of  the  processes  in  which  there  is  a  separation  of  matters 
from  the  blood  or  lymph  by  glandular  organs  or  a  formation,  by  such 
organs,  of  new  liquids,  out  of  materials  furnished  by  the  blood  or  lymph. 
It  is  probable,  however,  that  most  of  the  secretions  are  derived  directly 
from  the  blood  and  not  from  the  lymph  contained  in  the  glandular  sub- 
stance. While  secretion  may  be  treated  of  as  a  distinct  process,  it  is 
intimately  connected  with  general  metabolism.  As  a  rule,  secretions 
are  homogeneous  liquids  without  formed  anatomical  elements,  except 
as  accidental  constituents,  such  as  desquamated  epithelium  in  mucus  or 
in  sebaceous  matter.  The  secretions  are  either  discharged  from  the 
body,  when  they  are  called  excretions,  or,  after  having  performed  their 
proper  office  as  secretions,  are  absorbed  in  a  more  or  less  modified  form. 
Secretions,  therefore,  are  liquids  holding  certain  substances  in  solution 
and  sometimes  containing  peculiar  ferments — but  not  necessarily  pos- 
sessing formed  anatomical  elements  —  separated  from  the  blood  or 
formed  by  special  organs  out  of  materials  furnished  by  the  blood. 
Secreting  parts  may  be  membranes,  follicles,  collections  of  follicles, 
or  tubes.  In  the  latter  instances  they  are  called  glands.  This  defini- 
tion includes  the  excretions.  It  is  not  strictly  correct  to  speak  of 
formed  anatomical  elements  as  products  of  secretion,  except  in  the 
instance  of  fatty  particles  in  milk.  The  leucocytes  found  in  pus,  the 
spermatozoids  of  the  seminal  fluid,  and  the  ovum,  which  are  sometimes 

268 


CLASSIFICATION    OF    THE    SECRETIONS  269 

spoken  of  as  products  of  secretion,  are  anatomical  elements  developed 
in  the  way  in  v/hich  such  structures  are  ordinarily  formed. 

Classification  of  the  Secretions.  —  Certain  secretions  are  formed  by 
special  organs  and  have  important  uses  that  do  not  involve  their  dis- 
charge from  the  body.  These  may  be  classed  as  the  true  secretions ; 
and  the  most  striking  examples  are  the  digestive  liquids.  Each  one  of 
these  is  formed  by  a  special  gland  or  set  of  glands,  which  usually  has 
no  other  office ;  and  they  are  never  produced  by  any  other  part.  It  is 
the  gland  that  produces  the  characteristic  constituent  or  constituents  of 
the  true  secretions ;  and  the  matters  thus  formed  do  not  preexist  either 
in  the  blood  or  in  the  lymph.  The  office  which  the  true  secretions  have 
to  perform  usually  is  not  continuous ;  and  when  this  is  the  case,  the 
flow  of  the  secretion  is  intermittent,  taking  place  only  when  its  action  is 
required.  When  the  parts  that  produce  one  of  the  true  secretions  are 
destroyed,  the  characteristic  constituents  of  this  secretion  do  not  accu- 
mulate in  the  blood  nor  are  they  formed  vicariously  by  other  organs  ;  the 
effect  is  absence  of  the  secretion,  with  the  disturbances  consequent  to 
the  loss  of  its  physiological  action. 

Certain  other  of  the  liquids  of  the  body  are  composed  of  water, 
holding  one  or  more  characteristic  constituents  in  solution  that  result 
from  the  physiological  wear  of  the  tissues.  These  matters  have  no  office 
to  perform  in  the  economy  and  are  separated  from  the  blood  to  be  dis- 
charged from  the  body.  Such  products  may  be  classed  as  excretions, 
the  urine  being  the  type  of  liquids  of  this  kind.  The  characteristic 
constituents  of  the  excretions  have  their  origin  in  the  tissues  and  are 
products  of  the  changes  going  on  in  all  organized  living  structures. 
They  preexist  in  the  blood  or  lymph  and  may  be  eliminated,  either  con- 
stantly or  occasionally,  by  a  number  of  organs.  As  they  are  produced 
continually  in  the  substance  of  the  tissues  or  organs  and  are  taken  up 
by  the  blood,  they  are  constantly  separated  from  the  blood  by  the 
proper  eliminating  organs.  When  the  glands  which  thus  eliminate  these 
substances  are  destroyed  or  when  their  efficiency  is  seriously  impaired, 
the  excrementitious  matters  may  accumulate  in  the  blood  and  give  rise, 
directly  or  indirectly,  to  toxic  phenomena.  These  effects,  however,  are 
often  retarded  by  the  vicarious  action  of  other  organs. 

There  are  some  liquids,  such  as  the  bile,  that  have  important  uses  as 
secretions  and  nevertheless  contain  excrementitious  matters.  In  these 
instances,  it  is  only  the  excrementitious  matters  that  are  discharged 
from  the  organism.  In  the  sheaths  of  some  tendons  and  of  muscles,  in 
the  substance  of  muscles  and  in  some  other  situations,  liquids  are  found 
which  simply  lubricate  the  parts  and  which  contain  very  little  organic 
matter,  with  but  a  small  proportion  of  inorganic  salts. 


270  SECRETION 

It  is  difficult  to  draw  a  line  rigorously  between  transudation  and 
some  of  the  phenomena  of  secretion ;  particularly  as  experiments  on 
dialysis  have  shown  that  simple  osmotic  membranes  are  capable  of  sepa- 
rating complex  solutions,  allowing  certain  constituents  only  to  pass. 
This  fact  explains  why  the  transuded  liquids  do  not  contain  all  the  solu- 
ble constituents  of  the  blood  in  the  proportions  in  which  they  exist 
in  the  plasma.  All  secreted  liquids,  both  the  true  secretions  and  the 
excretions,  contain  many  of  the  inorganic  salts  of  the  blood-plasma. 

The  secretions  proper  usually  are  classified  as  serous  (albuminous) 
and  mucous  ;  the  former  being  entirely  liquid  and  the  latter  presenting 
more  or  less  viscidity.  It  is  thought,  also,  that  cells  producing  these 
two  kinds  of  secretions  differ  somewhat  from  each  other  in  their  histo- 
logical characters. 

Mechanism  of  the  Production  of  tJie  True  Secretions.  —  Although  the 
characteristic  constituents  of  the  true  secretions  are  not  to  be  found 
in  the  blood  or  in  any  other  of  the  animal  liquids,  they  often  can  be 
extracted  from  the  glands,  particularly  during  their  intervals  of  so-called 
repose.  This  has  been  repeatedly  demonstrated  in  regard  to  many  of 
the  digestive  secretions,  as  the  saliva,  the  gastric  juice  and  the  pan- 
creatic juice;  and  artificial  liquids,  possessing  certain  of  the  physiologi- 
cal properties  of  the  natural  secretions,  have  been  prepared  by  simply 
extracting  the  glandular  tissue  with  an  appropriate  menstruum.  There 
can  be  no  doubt,  therefore,  that  during  the  periods  when  the  secretions 
are  not  discharged,  the  glands  are  taking  from  the  blood  matters  which 
are  to  be  transformed  into  the  characteristic  constituents  of  the  individ- 
ual secretions,  and  that  this  is  constant,  bearing  a  close  resemblance 
to  the  general  process  of  nutrition.  Certain  anatomical  elements  in 
the  glands  have  the  power  of  selecting  proper  materials  from  the  blood 
and  causing  them  to  undergo  peculiar  transformations ;  in  the  same 
way  that  the  muscular  tissue  takes  from  the  blood  albuminous  matters 
and  transforms  them  into  its  own  substance.  The  exact  nature  of  this 
process  is  not  understood. 

In  all  secreting  organs,  epithelium  is  found  which  produces  the  pe- 
culiar constituents  of  the  different  secretions.  The  epithelial  cells  lining 
the  tubes  or  folHcles  of  the  glands  constitute  the  only  peculiar  structures 
of  these  parts,  the  rest  being  made  up  of  basement-membrane,  connec- 
tive tissue,  bloodvessels,  nerves,  and  other  structures  that  are  distributed 
generally  in  the  economy ;  and  these  cells  alone  contain  the  constituents 
of  the  secretions.  It  has  been  found,  for  example,  that  the  liver-cells 
contain  the  glycogen  formed  by  the  liver  ;  and  it  has  been  further  shown 
that  when  the  cellular  structures  of  the  pancreas  have  been  destroyed, 
the  secretion  is  no  longer  produced.     There  can  be  hardly  any  doubt  in 


MECHANISM    OF    PRODUCTION    OF    TRUE    SECRETIONS         2/1 

regard  to  the  application  of  tliis  principle  to  the  glands  generally,  both 
secretory  and  excretory.  Indeed,  it  is  well  known  to  pathologists,  that 
when  the  secreting  tubes  of  the  kidney  have  become  denuded. of  their 
epithelium,  they  are  no  longer  capable  of  separating  from  the  blood  the 
peculiar  constituents  of  the  urine. 

As  regards  the  origin  of  the  characteristic  constituents  to  the  true 
secretions,  it  is  impossible  to  entertain  any  other  view  than  that  they 
are  produced  in  the  epithelial  structures  of  the  glands.  While  the 
secretions  contain  inorganic  salts  in  solution  derived  from  the  blood,  the 
organic  constituents,  such  as  ptyalin,  pepsin  and  trypsin,  are  readily 
distinguished  from  all  other  albuminous  substances  by  their  peculiar 
physiological  properties. 

It  may  be  stated,  then,  as  a  general  proposition,  that  the  character- 
istic constituents  of  the  true  secretions,  as  contradistinguished  from  the 
excretions,  are  formed  by  the  epithelial  structures  of  the  glands,  out  of 
materials  furnished  mainly  by  the  blood.  Their  formation  is  not  con- 
fined to  what  is  usually  termed  the  period  of  activity  of  the  glands,  or 
the  time  when  the  secretions  are  poured  out,  but  it  takes  place  more  or 
less  constantly  when  no  liquid  is  discharged.  It  is  more  than  probable, 
indeed,  that  the  formation  of  the  peculiar  and  characteristic  constituents 
of  the  secretions  takes  place  with  as  much,  or  even  more  activity  in  the 
intervals  of  secretion  as  during  the  discharge  of  liquid  ;  and  most  of 
the  glands  connected  with  the  digestive  system  seem  to  require  certain 
intervals  of  repose  and  are  capable  of  discharging  their  secretions  for  a 
limited  time  only.     This  condition  of  a  gland  is  called  resting. 

When  a  secreting  organ  is  called  into  activity  —  like  the  gastric 
mucous  membrane  or  the  pancreas,  following  the  introduction  of  food 
into  the  alimentary  canal  —  a  marked  change  in  its  condition  occurs. 
The  circulation  in  the  part  is  then  much  increased  in  activity,  thus  fur- 
nishing water  and  the  inorganic  constituents  of  the  secretion.  This 
difference  in  the  quantity  of  blood  in  the  glands  during  their  activity 
may  be  observ^ed  when  the  organs  are  exposed  in  a  li^•ing  animal  and  is 
one  of  the  important  conditions  bearing  on  the  mechanism  of  secretion. 
In  all  the  secretions  proper,  then,  there  are  intervals,  either  of  complete 
repose,  as  is  the  case  with  the  gastric  juice  or  the  pancreatic  juice,  or 
periods  when  the  activity  of  the  secretion  is  greatly  diminished,  as  in 
the  case  of  the  saliva.  The  resting  periods  are  necessary  to  the  proper 
action  of  the  secreting  glands ;  forming  a  marked  contrast  with  the  con- 
stant action  of  organs  of  excretion.  It  is  well  known,  for  example,  that 
digestion  is  seriously  disturbed  when  the  act  is  too  prolonged  on  account 
of  the  habitual  ingestion  of  an  excessive  quantity  of  food. 

While  the  mechanism  of  secretion  is  not  understood  in  all  its  details 


2/2  SECRETION 

as  regards  all  the  secretions,  in  certain  glands  the  processes  have  been 
studied  with  fairly  definite  results.  In  some  of  the  salivary  glands,  in 
the  peptic  cells  and  in  the  cells  of  the  pancreas,  it  has  been  shown  that 
the  so-called  ferments,  or  enzymes,  are  not  formed  directly.  The  secret- 
ing cells  are  divided  into  two  portions,  or  zones ;  an  outer  zone,  next  the 
tubular  membrane,  and  an  inner  zone,  next  the  lumen  of  the  tube  or 
follicle.  In  the  inner  zone,  during  the  intervals  of  actual  secretion, 
there  appears  a  substance  which  is  afterward  changed  into  the  true 
ferment ;  so  that  there  probably  is  a  zymogenic,  or  ferment-forming 
substance,  first  produced  by  the  cells.  It  is  thought  that  the  substance 
produced  by  the  secreting  cells  of  the  salivary  glands  is  not  ptyahn  but 
a  zymogen  that  is  readily  converted  into  ptyalin,  called  ptyalinogen ; 
but  this  substance  has  not  been  isolated.  The  parotid  is  classed  as  a 
serous  gland.  In  the  viscid  forms  of  saliva,  there  appears  to  be  first 
formed  a  substance  called  mucinogen,  afterward  changed  into  mucin, 
on  which  the  viscidity  of  the  secretion  depends. 

A  good  example  of  the  changes  which  secreting  cells  undergo  when 
a  resting  gland  becomes  active  may  be  observed  in  the  pancreas.  If  the 
pancreas  is  removed  from  a  fasting  animal  and  its  structure  is  fixed  and 
stained,  the  cells  lining  the  secreting  alveoli  are  seen  rather  sharply 
divided  into  the  two  zones  already  mentioned.  The  outer  zone,  next 
the  alveolar  membrane,  is  narrow  and  stains  deeply.  The  inner  zone  is 
wide  and  granular  and  is  but  slightly  stained.  When  the  gland,  how- 
ever, is  taken  from  an  animal  in  full  digestion,  the  outer  zone  occupies 
the  greater  part  of  the  cell,  being  deeply  stained ;  and  the  inner  zone 
has  become  very  narrow.  It  seems,  indeed,  that  the  granular  matter  of 
the  inner  zone  is  used  in  the  production  of  the  active  principles  of  the 
secretion.  A  short  time  after  secretion  has  ceased,  the  gland  will  be 
found  to  have  returned  to  its  resting  condition  and  the  granules  of  the 
inner  zone  are  restored.  These  processes  take  place  in  all  glands  and 
mark  their  resting  and.  active  conditions. 

In  the  salivary  glands  that  produce  viscid  secretions — ^the  submaxil- 
lary and  sublingual  —  the  parenchyma  presents  two  kinds  of  acini,  serous 
and  mucous.  The  so-called  serous  acini  are  the  more  abundant  and  are 
thought  to  produce  true  saliva,  while  the  mucous  acini  secrete  only  the 
viscid  matters  that  are  mixed  with  the  saliva. 

In  the  production  of  pepsin,  the  peptic  cells  first  form  pepsinogen, 
which  is  afterward  changed  into  pepsin.  In  the  pancreas,  trypsinogen 
is  formed  in  the  cells,  and  this  is  changed  into  trypsin.  The  general 
name  zymogen  has  been  given  to  the  substances  that  are  changed  into 
the  digestive  ferments  ;  although,  as  is  evident,  this  is  not  identical  in 
the  different  glands. 


INFLUENCE    OF    THE   BLOOD    ON    SECRETION  273 

The  theory  that  the  discharge  of  the  secretions  is  due  simply  to 
mechanical  causes  and  is  attributable  solely  to  the  increase  in  the  press- 
ure of  blood  can  not  be  sustained.  Blood-pressure  undoubtedly  has 
considerable  influence  on  the  activity  of  secretion ;  but  the  flow  will  not 
always  take  place  in  obedience  to  simple  pressure,  and  secretion  may  be 
excited  for  a  limited  time  without  any  increase  in  the  quantity  of  blood 
circulating  in  the  gland. 

The  glands  possess  a  peculiar  excitability,  manifested  by  their  action 
in  response  to  proper  stimulation.  During  secretion  they  usually  receive 
an  increased  quantity  of  blood ;  but  this  is  not  indispensable,  and  secre- 
tion may  be  excited  without  any  modification  of  the  circulation.  This 
excitabihty  disappears  after  the  artery  supplying  the  part  with  blood 
has  been  tied  for  a  number  of  hours ;  and  secretion  can  not  then  be 
excited  even  when  the  blood  is  again  allowed  to  circulate.  If  the  gland 
is  not  deprived  of  blood  for  too  long  a  period,  however,  the  excitability 
is  soon  restored. 

Mechajiism  of  the  Production  of  the  Excretions.  —  Certain  glands 
separate  from  the  blood  excrementitious  matters  that  are  of  no  use  in 
the  economy  and  are  discharged  from  the  body.  These  matters  are 
different  in  their  mode  of  production  from  the  characteristic  constituents 
of  the  secretions.  Their  formation  takes  place  in  the  tissues  and  is  con- 
nected with  the  general  process  of  nutrition  ;  and  in  the  excreting  glands 
there  is  simply  a  separation  of  products  already  formed,  probably  by 
cellular  action  similar  to  that  observed  in  secreting  organs.  The  action 
of  the  excreting  organs  is  constant,  and  there  is  not  that  regular  periodic 
increase  in  the  activity  of  the  circulation  observed  in  secreting  organs ; 
but  it  has  been  noted  that  the  blood  coming  from  the  kidneys  is  nearly 
as  red  as  arterial  blood,  showing  that  the  quantity  of  blood  which  these 
organs  receive  is  greater  than  the  amount  required  for  mere  nutrition, 
the  excess,  as  in  the  secreting  organs,  furnishing  the  water  and  inorganic 
salts  that  are  found  in  the  urine.  It  has  also  been  shown  that  when  the 
secretion  of  urine  is  interrupted,  the  blood  of  the  renal  veins  becomes 
dark  like  the  blood  in  the  general  venous  system. 

Excretion  is  not,  under  all  conditions,  confined  to  the  ordinary  excre- 
tory organs.  When  their  action  is  disturbed,  certain  of  the  secreting 
glands,  as  the  follicles  of  the  stomach  and  intestine,  may  for  a  time 
eliminate  excrementitious  matters ;  but  this  is  abnormal  and  is  analo- 
gous to  the  elimination  of  foreign  matters  from  the  blood  by  the  glands. 

Influence  of  the  Composition  and  Pressure  of  the  Blood  oji  Secretion. — 
Under  normal  conditions,  the  composition  of  the.  blood  has  little  to  do 
with  the  action  of  secreting  organs,  as  it  simply  furnishes  the  materials 
out  of  which  the  characteristic  constituents  of  the  secretions  are  formed  ; 


274  SECRETION 

but  when  certain  foreign  matters  are  taken  into  the  system  or  are  injected 
into  the  bloodvessels,  they  are  eliminated  by  the  different  glandular 
organs,  both  secretory  and  excretory.  These  organs  seem  to  possess  a 
power  of  selection  in  the  elimination  of  different  substances.  Thus, 
sugar  and  potassium  ferrocyanide  are  eliminated  in  greatest  quantity  by 
the  kidneys ;  the  salts  of  iron,  by  the  kidneys  and  the  gastric  tubules ; 
and  iodin,  by  the  salivary  glands. 

The  discharge  of  secretions  is  almost  always  accompanied  with  an 
increase  in  the  pressure  of  blood  in  the  vessels  supplying  the  glands ; 
and  it  has  been  shown,  also,  that  an  increase  in  the  pressure,  when  the 
nerves  of  the  glands  do  not  exert  an  opposing  influence,  increases  the 
activity  of  secretion  ;  but  this  does  not  demonstrate  that  secretion  is 
due  simply  to  an  increase  in  the  pressure  of  blood  in  the  glands,  although 
this  undoubtedly  exerts  an  important  influence.  It  is  necessary  that 
other  conditions  should  be  favorable  to  the  act  of  secretion  for  this 
influence  to  be  effective.  Experiments  have  shown  that  pain  may  com- 
pletely arrest  the  secretion  of  urine,  operating  undoubtedly  through  the 
nervous  system.  When  the  flow  of  urine  is  arrested  by  pain,  an  increase 
in  the  pressure  of  blood  in  the  part  fails  to  excite  secretion. 

Influence  of  the  Nervous  System  on  Secretioji.  —  The  fact  that  the 
secretions  usually  are  intermittent  in  their  flow,  being  discharged  in 
obedience  to  impressions  which  are  made  only  when  there  is  a  demand 
for  their  physiological  action,  would  naturally  lead  to  the  supposition 
that  they  are  regulated,  to  a  great  extent,  through  the  nervous  system ; 
particularly  as  it  is  now  well  established  that  the  nerves  are  capable  of 
modifying  and  regulating  local  circulations.  This  applies  to  a  certain 
extent  to  the  excretions,  which  are  also  subject  to  considerable  modi- 
fications. 

In  regard  to  many  of  the  glands,  it  has  been  shown  that  the  influ- 
ence of  the  vasomotor  nerves  is  antagonized  by  certain  other  nerves, 
which  latter  are  called  the  motor  nerves  of  the  glands.  The  motor 
nerve  of  the  submaxillary  is  the  chorda  tympani ;  and  as  both  this  nerve 
and  the  sympathetic,  which  latter  contains  the  vasomotor  filaments, 
together  with  the  excretory  duct  of  the  gland,  can  easily  be  exposed 
and  operated  on  in  a  living  animal,  many  experiments  have  been  per- 
formed on  this  gland.  When  the  parts  are  exposed  and  a  tube  is 
introduced  into  the  salivary  duct,  division  of  the  sympathetic  induces 
secretion,  with  an  increase  in  the  circulation  in  the  gland,  the  blood 
in  the  vein  becoming  red.  On  the  other  hand,  division  of  the  chorda 
tympani,  the  sympathetic  being  intact,  arrests  secretion,  and  the 
venous  blood  coming  from  the  gland  becomes  dark.  If  the  nerves 
are  now  stimulated  alternately,  it  will  be  found  that  stimulation  of  the 


ANATOMICAL   CLASSIFICATIOxM    OF    GLANDULAR    ORGANS      275 

sympathetic  produces  contraction  of  the  vessels  of  the  gland  and  arrests 
secretion,  while  a  stimulus  applied  to  the  chorda  tympani  increases  the 
circulation  and  excites  secretion.  Enough  is  known  of  the  nervous 
influences  that  modify  secretion,  to  admit  of  the  inference  that  other 
glands  are  supplied  with  nerves  through  which  certain  reflex  phenomena 
affecting  their  secretions  take  place.  As  reflex  phenomena  involve  the 
action  of  nerve-centres,  it  becomes  a  question  to  determine  whether  any 
particular  parts  of  the  central  nervous  system  preside  over  the  various 
secretions.  Experiments  showing  the  existence  of  such  centres  are  not 
wanting,  but  it  will  be  more  convenient  to  treat  of  these  in  connection 
with  the  physiology  of  the  nervous  system. 

Mental  emotions,  pain  and  various  conditions,  the  influence  of  which 
on  secretion  has  long  been  observed,  operate  through  the  nervous  sys- 
tem. Many  familiar  instances  of  this  kind  may  be  mentioned :  such  as 
the  secretion  of  tears ;  arrest  or  production  of  the  salivary  secretions  ; 
sudden  arrest  of  the  secretion  of  the  mammary  glands  from  violent 
emotion;  increase  in  the  secretion  of  the  kidneys  or  of  the  intestinal 
tract  from  fear  or  anxiety ;  with  other  examples  which  it  is  unnecessary 
to  enumerate. 

Paralytic  Secretion  by  Glands.  —  The  effects  of  destruction  of  the 
nerves  distributed  to  the  parenchyma  of  some  of  the  glandular  organs 
are  remarkable.  If  the  nerves  distributed  to  the  kidney  are  destroyed, 
not  only  is  secretion  arrested  in  the  great  majority  of  instances,  but  the 
renal  tissue  becomes  softened  and  broken  down.  After  division  of  the 
nerves  of  the  salivary  glands,  these  organs  become  atrophied,  but  they 
do  not  undergo  the  peculiar  putrefactive  changes  observed  in  the  kid- 
neys. The  same  effect  is  produced  when  the  nerves  are  paralyzed 
by  introducing  a  few  drops  of  a  solution  of  curare  at  the  origin  of  the 
artery  distributed  to  the  submaxillary  gland.  Other  glands  have  so- 
called  motor  nerves,  stimulation  of  which  excites  secretion,  but  such 
nerves  have  been  most  satisfactorily  isolated  and  studied  in  connection 
with  the  salivary  secretions.  When  the  motor  nerves  of  the  salivary 
glands  are  divided,  in  the  course  of  a  day  or  two  the  secretion  becomes 
abundant  and  watery  and  loses  its  normal  characters.  After  about  eight 
days,  the  secretion  begins  to  diminish  and  the  glands  undergo  atrophy. 
The  increased  secretion  first  observed  is  called  "paralytic." 

Anatomical  Classification  of  Glandular  Organs.  —  The  organs  which 
produce  the  different  secretions  are  susceptible  of  a  classification  accord- 
ing to  their  anatomical  peculiarities,  which  greatly  facilitates  their  study. 
They  may  be  divided  as  follows  :  — 

I.  Secreting  Membranes.  —  Examples  of  these  are  the  synovial 
membranes. 


2/6  SECRETION 

2.  Follicular  Glands.  —  Examples  of  these  are  the  simple  mucous 
follicles  and  the  simple  follicles  of  Lieberkuhn. 

3.  Tiibiilar  Glands.  —  Examples  of  these  are  the  ceruminous  glands, 
the  sudoriparous  glands  and  the  kidneys. 

4.  Racemose  Glands,  Simple  and  Compound. —  Examples  of  the  simple 
racemose  glands  are  the  sebaceous  and  Meibomian  glands,  the  tracheal 
glands  and  the  glands  of  Brunner.  Examples  of  the  compound  race- 
mose glands  are  the  salivary  glands,  the  pancreas,  the  lachrymal  glands 
and  the  mammary  glands. 

5.  Ductless,  or  Blood-Glands.  —  Examples  of  these  are  the  thymus, 
the  thyroid,  the  suprarenal  capsules  and  the  spleen. 

The  liver  is  a  glandular  organ  that  can  not  be  placed  in  any  one  of 
the  above  divisions.  The  lymphatic  glands  and  other  parts  connected 
with  the  lymphatic  and  the  lacteal  system  are  not  true  glandular  organs. 
These  are  sometimes  called  conglobate  glands. 

The  general  structure  of  secreting  membranes  and  of  the  follicular 
glands  is  quite  simple.  The  secreting  parts  consist  of  a  membrane, 
usually  homogeneous,  covered  on  the  secreting  surface  with  epithelial 
cells.  Beneath  this  membrane  ramify  the  bloodvessels  which  furnish 
materials  for  the  secretions.  The  follicular  glands  are  simply  digital 
inversions  of  this  structure,  with  rounded  blind  extremities,  the  epithe- 
lium lining  the  follicles. 

The  tubular  glands  have  essentially  the  same  structure  as  the  fol- 
licles, except  that  the  tubes  are  long  and  more  or  less  convoluted.  The 
more  complex  of  these  organs  contain  connective  tissue,  bloodvessels, 
nerves  and  lymphatics. 

The  compound  racemose  glands  are  composed  of  branching  ducts, 
around  the  extremities  of  which  are  arranged  collections  of  rounded  fol- 
licles, like  bunches  of  grapes.  In  addition  to  the  epithelium,  basement 
membrane  and  bloodvessels,  these  organs  contain  connective  tissue, 
lymphatics,  non-striated  muscular  fibres  and  nerves.  In  the  simple 
racemose  glands  the  excretory  duct  does  not  branch. 

The  ductless  glands  contain  bloodvessels,  lymphatics,  nerves,  some- 
times non-striated  muscular  fibres,  and  a  peculiar  structure  called  pulp, 
which  is  composed  of  liquid  with  cells  and  occasionally  with  closed 
vesicles.  These  are  sometimes  called  blood-glands,  because  they  are 
supposed  to  modify  the  blood  as  it  passes  through  their  substance. 

The  testicles  and  the  ovaries  are  not  simple  glandular  organs;  for 
in  addition  to  the  production  of  mucous  or  watery  secretions,  their  prin- 
cipal office  is  to  develop  certain  anatomical  elements,  the  spermatozoids 
and  the  ova.  The  physiology  of  these  organs  will  be  considered  in 
connection  with  embryology. 


SYNOVIAL   MEMBRANES   AND    SYNOVIA  277 

Secretions  and  Excretions.  —  The  products  of  the  various  glands 
may  be  divided,  according  to  their  uses,  into  secretions  proper  and  excre- 
tions. Some  of  the  true  secretions  have  certain  mechanical  uses ;  some, 
like  mucus,  are  thrown  off  in  small  quantity  without  being  actually 
excrementitious  ;  while  others,  like  the  digestive  secretions,  are  produced 
at  certain  intervals  and  are  taken  up  again  by  the  blood. 

The  serous  cavities  are  now  regarded  as  sacs  connected  with  the 
lymphatic  system  ;  and  the  liquids  of  these  cavities  are  not  classed  with 
the  secretions. 

Synovial  Membt'anes  and  Synovia.  —  The  true  synovial  membranes 
are  found  in  the  diarthrodial,  or  movable  articulations ;  but  in  various 
parts  of  the  body  are  found  closed  sacs,  sheaths  etc.,  which  resemble 
synovial  membranes  both  in  structure  and  in  their  office.  Every  mov- 
able joint  is  enveloped  in  a  capsule,  which  is  closely  adherent  to  the 
edges  of  the  articular  cartilage  and  even  is  reflected  over  its  surface  for 
a  short  distance ;  but  it  is  now  the  common  opinion  that  the  cartilage 
which  incrusts  the  articulating  extremities  of  the  bones,  though  bathed 
in  synovia,  is  not  itself  covered  with  a  distinct  membrane. 

The  fibrous  portion  of  the  synovial  membranes  is  dense  and  resist- 
ing. It  is  composed  of  ordinary  fibrous  tissue,  with  a  few  elastic  fibres 
and  bloodvessels.  The  internal  surface  is  lined  with  small  cells  of  flat- 
tened endothelium  with  rather  large  rounded  nuclei.  These  cells  exist 
in  one,  two,  three  or  sometimes  four  layers. 

In  most  of  the  joints,  especially  those  of  large  size,  as  the  knee  and 
the  hip,  the  synovial  membrane  is  thrown  into  folds  which  contain 
adipose  tissue.  In  nearly  all  the  joints,  the  membrane  presents  fringed 
vascular  processes  called  synovial  fringes.  These  are  composed  of 
looped  vessels  of  considerable  size  ;  and  when  injected  they  bear  a 
certain  resemblance  to  the  choroid  plexus.  The  edges  of  these  fringes 
present  a  number  of  leaf-like  membranous  appendages,  in  a  great 
variety  of  curious  forms.  They  usually  are  situated  near  the  attach- 
ment of  the  membrane  to  the  cartilage. 

The  arrangement  of  the  synovial  bursae  is  very  simple.  Wherever 
a  tendon  plays  over  a  bony  surface,  there  is  a  delicate  membrane  in  the 
form  of  an  irregularly-shaped  closed  sac,  one  layer  of  which  is  attached 
to  the  tendon,  and  the  other,  to  the  bone.  These  sacs  are  lined  with  an 
endothelium  like  that  found  in  the  synovial  cavities,  and  they  secrete  a 
true  synovial  fluid.  Bursas  are  also  found  beneath  the  skin,  especially 
in  parts  where  the  integument  moves  over  bony  prominences,  as  the 
olecranon,  the  patella  and  the  tuberosities  of  the  ischium.  These  sacs, 
sometimes  called  bursas  mucosae,  are  much  more  common  in  man  than 
in   the  inferior  animals,  and  they  have  essentially  the  same  uses  as 


278  SECRETION 

the  deep-seated  bursas.  The  form  of  both  the  superficial  and  deep- 
seated  bursae  is  irregular,  and  their  interior  frequently  is  traversed  by 
small  bands  of  fibrous  tissue.  The  synovial  sheaths,  or  vaginal  pro- 
cesses, line  the  canals  in  which  the  long  tendons  play,  particularly  the 
tendons  of  the  flexors  and  extensors  of  the  fingers  and  toes.  They 
have  essentially  the  same  structure  as  the  bursae,  and  present  two 
layers,  one  of  which  lines  the  canal,  while  the  other  is  reflected  over 
the  tendon.  The  vascular  folds,  described  in  connection  with  the 
articular  synovial  membranes,  are  found  in  many  of  the  bursae  and  the 
synovial  sheaths. 

The  quantity  of  synovia  in  the  joints  is  sufficient  to  lubricate  freely 
the  articulating  surfaces.  When  perfectly  normal  it  is  either  colorless 
or  of  a  pale  yellowish  tinge.  It  is  so  viscid  that  it  is  with  difficulty 
poured  from  one  vessel  into  another.  This  peculiar  character  is  due 
to  the  presence  of  an  organic  substance  called  synovin,  a  kind  of 
mucin.  When  this  organic  matter  has  been  extracted  and  mixed  with 
water,  it  gives  to  the  liquid  the  peculiar  viscidity  of  the  synovial  secre- 
tion. The  reaction  of  the  synovia  is  faintly  alkaline,  on  account  of  the 
presence  of  a  small  quantity  of  sodium  carbonate.  The  secretion,  espe- 
cially when  the  joints  have  been  much  used,  usually  contains  in  suspension 
pale  endothelial  cells  and  a  few  leucocytes.  The  synovia  of  the  human 
subject  contains  about  sixty-four  parts  per  thousand  of  organic  mat- 
ter, with  sodium  chloride,  sodium  carbonate,  calcium  phosphate  and 
ammonio-magnesian  phosphate. 

The  synovial  secretion  is  produced  by  the  general  surface  of  the 
membrane  and  not  by  any  special  glands.  The  folds  and  fringes  were 
at  one  time  supposed  to  be  most  active  in  secreting  the  organic  matter, 
but  there  is  no  evidence  that  they  have  any  such  special  office. 

Mucous  Membranes  and  Mucus.  —  A  distinct  anatomical  division  of 
the  mucous  membranes  may  be  made  into  two  classes ;  first,  those 
provided  with  squamous  epithelium,  and  second,  those  provided  with 
columnar  or  conoidal  epithelium.  All  the  mucous  membranes  line 
cavities  or  tubes  communicating  with  the  exterior. 

The  following  are  the  principal  situations  in  which  the  first  variety 
of  mucous  membranes,  covered  with  squamous  epithelium,  is  found  :  the 
mouth,  the  lower  part  of  the  pharynx,  the  oesophagus,  the  conjunctiva, 
the  female  urethra  and  the  vagina.  In  these  situations  the  membrane 
is  composed  of  a  chorion  made  up  of  inelastic  and  elastic  fibrous  tissue 
with  capillaries,  lymphatics  and  nerves.  The  elastic  fibres  are  small 
and  quite  abundant.  The  membrane  itself  is  loosely  united  to  the 
subjacent  parts.  The  chorion  is  provided  with  vascular  papillae,  more 
or  less  marked ;  but  in  all  situations  except  the  pharynx,  the  epithelial 


MUCOUS    MEMBRANES    AND    MUCUS  279 

covering  fills  the  spaces  between  the  papillae,  so  that  the  membrane 
presents  a  smooth  surface.  Between  the  chorion  and  the  epithelium, 
is  an  amorphous  basement-membrane.  The  mucous  glands  open  on 
the  surface  of  the  membrane  by  their  ducts;  but  the  glandular  struc- 
ture is  situated  in  the  submucous  tissue.  Certain  of  these  glands  have 
been  described  in  connection  with  the  anatomy  of  the  mucous  membrane 
of  the  mouth,  pharynx  and  oesophagus.  They  usually  are  simple 
racemose  glands,  presenting  a  collection  of  follicles  arranged  around 
the  end  of  a  single  excretory  duct  and  lined  or  filled  with  rounded 
nucleated  epithelium.  The  squamous  epithelium  covering  these  mem- 
branes usually  exists  in  several  layers  and  presents  great  variety, 
both  in  form  and  size.  This  is  called  stratified  epithelium.  The  most 
superficial  layers  are  of  large  size,  flattened  and  irregularly  polygonal. 
The  deeper  layers  are  smaller  and  more  rounded.     The  size  of  the  cells 

i^  25''^o  ^^  ¥o"o  ^^  ^^  ^"^^  (^°  ^°  ^3  '"')•  They  are  pale  and  slightly 
granular,  each  with  a  small  ovoid  nucleus  and  one  or  two  nucleoli. 

The  second  variety  of  mucous  membranes,  covered  with  columnar 
epithelium,  is  found  lining  the  alimentary  canal  below  the  cardiac 
opening  of  the  stomach,  the  biliary  passages,  the  excretory  ducts  of  all 
the  glands,  the  nasal  passages,  the  upper  part  of  the  pharynx,  the 
uterus  and  Fallopian  tubes,  the  bronchia,  the  Eustachian  tubes  and  the 
male  urethra.  In  certain  situations  this  variety  of  epithelium  is  pro- 
vided on  its  free  surface  with  little  hair-like  processes  called  cilia.  Dur- 
ing life  the  cilia  are  in  constant  motion,  producing  a  current  usually 
in  the  direction  of  the  mucous  orifices.  Ciliated  epithelium  is  found 
throughout  the  nasal  passages,  beginning  about  three-quarters  of  an 
inch  (19  millimeters) within  the  nose;  in  the  upper  part  of  the  pharynx; 
the  posterior  surface  of  the  soft  palate ;  the  Eustachian  tube ;  the 
tympanic  cavity ;  the  larynx,  trachea  and  bronchial  tubes,  until  they 
become  less  than  -^^  of  an  inch  (0.5  millimeter)  in  diameter;  the  neck 
and  body  of  the  uterus ;  the  Fallopian  tubes ;  the  internal  surface  of 
the  eyelids ;  and  the  ventricles  of  the  brain.  Mucous  membranes  of 
this  variety  are  formed  of  a  chorion,  a  basement-membrane  and  epithe- 
lium. The  chorion  is  composed  of  inelastic  and  elastic  fibres,  a  few 
non-striated  muscular  fibres,  amorphous  matter,  bloodvessels,  nerves 
and  lymphatics.  It  is  less  dense  and  less  elastic  than  the  chorion  of 
the  first  variety  and  is  more  closely  united  to  the  subjacent  parts.  The 
surface  of  these  membranes  is  smooth,  the  only  exception  being  the 
mucous  membrane  of  the  pyloric  portion  of  the  stomach  and  of  the 
small  intestines.  These  membranes  are  provided  with  follicular  glands, 
extending  through  their  entire  thickness  and  terminating  in  rounded 
extremities,   sometimes   single    and   sometimes    double,   which    rest  on 


28o  SECRETION 

the  submucous  structure.  Many  of  them  are  provided,  also,  with 
simple  racemose  glands,  the  ducts  passing  through  the  membrane,  and 
the  glandular  structure  being  situated  in  the  submucous  areolar  tissue. 
The  columnar  epithelium  covering  these  membranes  rests  on  an  amor- 
phous structure  called  basement-membrane.  The  epithelium  usually 
presents  but  few  layers,  and  sometimes,  as  in  the  intestinal  canal,  there 
is  only  a  single  layer.  The  cells  are  prismoidal,  with  a  large  free 
extremity  and  a  pointed  attached  end.  The  cells  of  the  lower  strata 
are  shorter  and  more  rounded  than  those  in  the  superficial  layer.  The 
cells  are  pale  and  closely  adherent  to  each  other  by  their  sides,  each 
with  a  moderate-sized  oval  nucleus  and  one  or  two  nucleoli.  The  length 
of  the  cells  is  g^^^  to  q^q  of  an  inch  (30  to  40  fi),  and  their  diameter, 
3F0  0  ^°  2  5Vo^  °^  ^^  ^"^'^  (8  to  10  /x).  When  villosities  exist  on  the  sur- 
face of  the  membranes,  the  cells  follow  the  elevations  and  do  not  fill 
up  the  spaces  between  them,  as  in  most  of  the  membranes  covered  with 
stratified  epithelium. 

The  mucous  membrane  of  the  urinary  bladder,  of  the  ureters  and 
of  the  pelvis  of  the  kidneys  can  not  be  classed  in  either  of  the  above 
divisions.  In  these  situations  the  membrane  is  covered  with  mixed 
epithelium,  presenting  all  varieties  of  form  between  the  squamous  and 
the  columnar,  some  of  the  cells  being  caudate  and  quite  irregular  in 
shape. 

MecJianism  of  the  Secretion  of  M?ic2ts.  —  Nearly  every  one  of  the 
many  secretions  known  under  the  general  name  of  mucus  is  made  up  of 
the  products  of  several  different  glandular  structures.  Certain  mem- 
branes which  do  not  possess  glands,  as  the  mucous  lining  of  the  ureters 
and  of  a  great  portion  of  the  urinary  bladder,  are  capable  of  secreting 
mucus.  The  mucous  membrane  of  the  stomach  produces  an  alkaline 
viscid  secretion  during  the  intervals  of  digestion,  when  the  gastric 
glands  do  not  act ;  and  the  gastric  glands,  during  digestion,  secrete  a 
liquid  of  an  entirely  different  character.  The  secretion  produced  by 
the  follicles  of  the  small  intestine  likewise  has  peculiar  digestive  prop- 
erties. These  considerations  and  the  fact  that  the  entire  extent  of  the 
mucous  membranes  is  covered  with  more  or  less  secretion  show  that 
the  general  epithelial  covering  of  these  membranes  is  capable  of  secret- 
ing a  liquid  which  forms  one  of  the  constituents  of  what  is  ordinarily 
recognized  as  mucus.  It  is  impossible,  however,  to  separate  the  secre- 
tion" of  the  superficial  layer  of  cells  from  the  other  secretions  found  on 
the  mucous  membranes  ;  and  it  will  be  more  convenient  to  regard  as 
mucus  the  secretion  found  upon  mucous  membranes,  except  when,  as 
in  the  case  of  the  gastric  or  the  intestinal  juice,  a  special  secretion  can 
be  recognized  by  certain  distinctive  physiological  properties. 


COMPOSITION    AND   VARIETIES    OF    MUCUS  28 1 

In  the  membranes  covered  with  columnar  epithelium,  which  usually 
are  provided  with  simple  follicles,  the  secretion  is  produced  mainly  by 
these  follicles  but  in  p^rt  by  the  epitheUum  covering  the  general  sur- 
face. In  certain  parts,  particularly  the  intestinal  mucous  membrane, 
mixed  with  the  ordinary  columnar  epithelium,  are  the  so-called  goblet- 
cells  that  are  supposed  to  produce  and  discharge  a  viscid  secretion 
containing  mucin  or  mucinogen.  These  cells  have  already  been 
described.  (See  page  212.)  The  membranes  covered  with  squamous 
epithehum  usually  contain  but  few  follicles  and  are  provided  with  simple 
racemose  glands  situated  in  the  submucous  structure,  which  are  to  be 
regarded  as  appendages  to  the  membrane.  The  secretion  is  here  pro- 
duced by  the  epithelium  on  the  free  surface  and  is  mixed  with  secre- 
tions of  the  mucous  glands. 

There  is  nothing  to  be  said  in  regard  to  the  mechanism  of  the  secre- 
tion of  mucus  in  addition  to  what  has  already  been  stated  in  connection 
with  the  general  mechanism  of  secretion.  Mucous  membranes  are 
quite  vascular ;  and  the  cells  covering  the  membrane  and  lining  the 
follicles  and  glands  attached  to  it  have  the  property  of  taking  from  the 
blood  the  materials  necessary  for  the  formation  of  the  secretion.  These 
matters  pass  out  of  the  cells  upon  the  surface  of  the  membrane  in  con- 
nection with  water  and  inorganic  salts  in  varying  proportions.  Many 
of  the  cells  themselves  are  thrown  off  and  are  found  in  the  secretion, 
together  with  a  few  leucocytes,  which  latter  are  produced  on  mucous 
surfaces  with  great  facility. 

Composition  and  Varieties  of  Miicns.  —  All  the  varieties  of  mucus 
are  more  or  less  viscid ;  but  this  character  is  variable  in  secretions  from 
different  membranes,  in  some  of  them  the  secretion  being  quite  liquid, 
and  in  others,  almost  semisolid.  The  different  kinds  of  mucus  vary 
considerably  in  general  appearance.  Some  are  clear  and  colorless ;  but 
the  secretion  usually  is  grayish  and  semitransparent.  Examined  with 
the  microscope,  in  addition  to  the  mixture  of  epithelium  and  occasional 
leucocytes,  which  give  to  the  liquid  its  semiopaque  character,  the  mass 
of  the  secretion  presents  a  finely-striated  appearance,  as  if  it  were  com- 
posed of  thin  layers  of  nearly  transparent  substance  with  many  folds. 
These  delicate  strias  usually  do  not  interlace  with  each  other,  and  they 
are  rendered  more  distinct  by  the  action  of  acetic  acid.  This  appear- 
ance, with  the  peculiar  effect  of  the  acid,  is  characteristic  of  mucus. 
Some  varieties  of  mucus  present  very  fine  pale  granules  and  a  few 
small  globules  of  oil. 

On  the  addition  of  water,  mucus  is  somewhat  swollen  but  is  not 
dissolved.  An  exception  to  this  is  the  secretion  of  the  conjunctival 
mucous  membrane,  which  is  coagulated  by  water.     As  a  rule  the  re- 


282  SECRETION 

action  of  mucus  is  alkaline  ;  the  only  exception  to  this  being  the  vaginal 
mucus,  which  is  very  liquid  and  is  distinctly  acid. 

It  is  difficult  to  get  an  exact  idea  of  the  composition  of  normal 
mucus,  from  the  fact  that  the  quantity  secreted  by  the  membranes  in 
their  natural  condition  is  small,  being  just  sufficient  to  lubricate  their 
surface.  All  varieties,  however,  contain  an  organic  matter  called 
mucin,  which  gives  to  the  liquid  its  viscidity.  They  likewise  present 
a  considerable  variety  of  inorganic  salts,  as  sodium  chloride,  potassium 
chloride,  alkaline  lactates,  sodium  carbonate,  calcium  phosphate,  a  small 
proportion  of  the  sulphates,  and  in  some  varieties,  traces  of  iron  and 
silica.  Of  all  these  constituents,  mucin  is  the  most  important,  as  it 
gives  to  the  secretion  its  characteristic  properties.  Like  other  nitroge- 
nous substances,  mucin  is  coagulable  by  various  reagents.  It  is  im- 
perfectly coagulated  by  heat ;  and  after  desiccation  it  can  be  made  to 
assume  its  peculiar  consistence  by  the  addition  of  a  small  quantity  of 
water.  It  is  coagulated  by  acetic  acid  and  by  a  small  quantity  of  the 
strong  mineral  acids,  being  redissolved  in  an  excess  of  the  latter.  It 
also  is  coagulated  by  strong  alcohol,  forming  a  fibrinous  clot  soluble  in 
hot  and  cold  water.  Mucin  may  be  readily  isolated  by  adding  water 
to  a  specimen  of  normal  mucus,  filtering,  and  precipitating  with  an 
excess  of  alcohol.  If  this  precipitate,  after  having  been  dried,  is  ex- 
posed to  water,  it  assumes  the  viscid  consistence  peculiar  to  mucin. 
This  property  serves  to  distinguish  it  from  albumin  and  other  nitroge- 
nous matters. 

Goicral  Uses  of  Mucus.  — The  smooth,  viscid  and  adhesive  character 
of  mucus,  forming,  as  it  does,  a  coating  for  the  mucous  membranes, 
serves  to  protect  these  parts,  enables  their  surfaces  to  move  freely 
one  upon  the  other,  and  modifies  to  a  certain  extent  the  process  of 
absorption.  Aside  from  these  mechanical  uses,  it  has  been  shown  that 
mucus,  in  connection  with  the  epithelial  covering  of  the  mucous  mem- 
branes, is  capable  of  prev'enting  the  absorption  of  certain  substances. 
It  is  well  known,  for  example,  that  venoms  may  be  applied  with  im- 
punity to  certain  mucous  surfaces,  while  they  produce  poisonous  effects 
if  introduced  into  the  circulation.  These  agents  are  not  neutralized  by 
the  secretions  of  the  parts,  for  they  will  produce  their  characteristic 
effects  when  removed  from  the  mucous  surfaces  and  introduced  into 
the  circulation ;  and  it  is  reasonable  to  suppose  that  the  mucous  mem- 
branes are  capable  of  resisting  their  absorption. 

Physiological  Aiiatomy  of  tJic  Sebaceous,  Cerinnijious  and  Meibomian 
Glands.  —  The  true  sebaceous  glands  are  found  in  all  parts  of  the 
skin  that  are  provided  with  hair ;  and  as  nearly  every  part  of  the 
general  surface  presents  either  the  long,  the  short  or  the  downy  hairs, 


SEBACEOUS,    CERUMINOUS    AND    MEIBOMIAN    GLANDS         283 


these  glands  are  very  widely  distributed.  They  exist,  indeed,  in  greater 
or  less  numbers  in  all  parts  of  the  skin  except  the  palms  of  the  hands 
and  the  soles  of  the  feet.  In  the  labia  minora  in  the  female,  and  in 
portions  of  the  prepuce  and  glans  penis  of  the  male,  parts  not  provided 
with  hair,  small  racemose  sebaceous  glands  are  found,  which  produce 
secretions  differing  somewhat  from  that  formed  by  the  ordinary  glands. 


\    i   I1/-6    F 


Fig.  61.  —  Sebaceous  glands  (Sappey). 

A,  a  gland  in  its  most  rudimentary  form:  i,  rudimentary  hair-follicle;  2,  downy  hair;  3,  simple 
sebaceous  follicle.  B,  a  gland  more  developed:  i,  hair-follicle;  2,  simple  sebaceous  follicle.  C,  a 
gland  with  two  follicles:  i,  hair-follicle;  2,  simple  follicle;  3,  follicle  imperfectly  divided.  D,  a  com- 
pound gland:  i,  hair-follicle;  2,  lobule  with  three  follicles;  3,  lobule  with  four  follicles.  E,  a  gland 
with  four  lobules  :  i,  hair-follicle  ;  2,  2,  first  lobule  ;  3,  second  lobule  ;  4,  4,  third  lobule  ;  5,  fourth 
lobule;  6,  excretory  duct  with  a  hair  passing  through  it.  i%  a  gland  with  four  lobules  :  i,  hair- follicle; 
2,  2,  first  lobule;   3,  second  lobule ;  4,  third  lobule;  5,  fourth  lobule ;  6,  excretory  duct. 

The  glands  in  the  areola  of  the  nipple  in  the  female  are  large  and  are 
connected  with  small  downy  hairs. 

Nearly  all  the  sebaceous  glands  are  either  simple  racemose  glands, 
that  is,  presenting  a  number  of  follicles  connected  with  a  single  ex- 
cretory duct,  or  compound  racemose  glands,  presenting  several  ducts, 
with  their  follicles,  opening  by  a  common  tube.  Although  there  are 
these  variations  in    the   size  and    arrangement   of   the  glands   of   the 


284  SECRETION 

general  surface,  they  produce  essentially  the  same  secretion,  and  their 
anatomical  differences  consist  simply  in  a  multiplication  of  follicles  (see 
Plate  VII,  Fig.  7). 

The  differences  in  the  size  of  the  sebaceous  glands  bear  a  certain 
relation  to  the  size  of  the  hairs  with  which  they  are  connected  ;  and  as 
a  rule,  the  largest  glands  are  connected  with  the  small  downy  hairs. 
These  distinctions  in  size  are  so  marked,  that  the  glands  may  be  divided 
into  two  classes ;  those  connected  with  the  long  hairs  of  the  head,  face, 
chest,  axilla,  genital  organs  and  with  the  coarse  short  hairs,  and  those 
connected  with  the  fine  downy  hairs. 

The  glands  connected  with  the  larger  hair-follicles  are  of  the  simple 
racemose  variety  and  are  j^q  to  -^q  of  an  inch  (0.21  to  0.64  millimeter) 
in  diameter.  Two  to  five  of  these  glands  usually  are  found  arranged 
around  each  hair-follicle.  They  discharge  their  secretion  at  about  the 
junction  of  the  upper  third  with  the  lower  two-thirds  of  the  hair-follicle. 
The  follicles  of  the  long  hairs  of  the  scalp  usually  are  provided  each  with 
a  pair  of  sebaceous  glands,  measuring  -^^-^  to  j\  of  an  inch  (0.21  to  0.34 
millimeter)  in  diameter.  Encircling  the  hairs  of  the  beard,  the  chest, 
axilla  and  genital  organs,  are  large  glands,  some  of  them  ^q  of  an  inch 
(0.64  millimeter)  in  diameter,  arranged  in  groups  of  four  to  eight. 

The  glands  connected  with  the  follicles  of  the  small  downy  hairs  are 
so  large  as  compared  with  the  hair-follicles  that  the  latter  seem  rather 
as  appendages  to  the  glandular  structures.  These  glands  are  of  the 
compound  racemose  variety  and  present  sometimes  as  many  as  fifteen 
culs-de-sac.  The  largest  are  found  on  the  nose,  the  ear,  the  caruncula 
lachrymalis,  the  penis  and  the  areola  of  the  nipple,  where  they  measure 
g^Q  to  j^2  of  3-^  inch  (0.51  to  2.1  millimeters).  The  glands  connected 
with  the  downy  hairs  of  other  parts  usually  are  smaller.  The  glands 
of  Tyson,  situated  on  the  corona  and  cervix  of  the  glans  penis,  are 
sebaceous  glands  of  the  compound  racemose  variety. 

The  follicles  composing  the  simple  glands  and  the  follicular  termina- 
tions of  the  simple  and  compound  racemose  glands  are  formed  of  a 
delicate  structureless  or  slightly  granular  membrane,  with  an  external 
layer  of  inelastic  and  small  elastic  fibres  and  are  lined  with  cells.  Next 
the  membrane,  the  cells  are  polyhedric,  pale  and  granular,  most  of  them 
presenting  a  nucleus  and  a  nucleolus ;  but  the  follicle  itself  contains 
fatty  granules  and  the  other  constituents  of  the  sebaceous  matter,  with 
cells  filled  with  fatty  particles.  These  cells  abound  in  the  sebaceous 
matter  as  it  is  discharged  from  the  duct.  The  great  quantity  of  fatty 
granules  and  globules  found  in  the  ducts  and  follicles  of  the  sebaceous 
glands  renders  them  dark  and  opaque  when  examined  with  the  micro- 
scope by  transmitted  light,  except  when  studied  in  very  thin  sections, 


SEBACEOUS,    CERUMLNOUS   AND    MEIBOMIAN    GLANDS 


285 


and  their  appearance  is  quite  distinctive.     The  larger  glands  are  sur- 
rounded with  capillary  bloodvessels. 

The  ceruminous  glands  produce  a  secretion  resembling  the  sebaceous 
matter  in  many  regards ;  but  in  their  anatomy  they  are  almost  identical 
with  the  sudoriparous  glands.  They  belong  to  the  variety  of  glands  called 
tubular,  and  they  consist  of  a  nearly  straight  tube  which  penetrates  the 
skin,  and  a  rounded  or  ovoid  coil  situated  in  the  subcutaneous  structure.' 
These  glands  are  found  only  in  the 
cartilaginous  portion  of  the  external 
auditory  meatus,  where  they  exist  in 
great  number. 

The  ducts  of  the  ceruminous 
glands  are  short  and  nearly  straight, 
simply  penetrating  the  different  layers 
of  the  skin,  and  are  y^  to  5^  of  an 
inch  (36  to  50  fi)  in  diameter.  Their 
openings  are  rounded  and  about  2y-o 
of  an  inch  (93  /x)  in  diameter.  They 
sometimes  terminate  in  the  upper  part 
of  one  of  the  hair-follicles.  They 
present  an  external  coat  of  fibrous 
tissue  and  are  lined  with  several 
layers  of  small,  pale,  nucleated  epi- 
thelial cells. 

The  glandular  coil  is  an  ovoid  or 
rounded,  brownish    mass. 


1 
120 


to  -h 


Meibomian  glands  of  the  upper  lid, 
X  7  (Sappey). 


or  ^^g-  of  an  inch  (0.21  to  0.51  or  1.6  Fig.  62. 
millimeter)  in  diameter.     It  is  simply 

I.J.I  ,  •  -.u  tU  I,  I,  free  border  of  the  lid;  2,  2,  anterior  lip 

a  convoluted  tube  contmuous  with  the  ^  „  '  '.  ,  k  ,  tv  <>  „  „ioc).»c .  \  \  ^^=t»ri^.-  v.^ 

penetrated  by  the  eyelashes  ;  3,  3,  posterior  lip, 

excretory    duct    and    terminating    in    a    with  the  openings  of  the  Meibomian  glands;  4,  a 

,  ,.,  ,  IT  .  gland  passing  obliquely  at  the  summit;  5,  an- 

somewhat   dilated   rounded   extremity,     other  gland  bent  upon  itself;  6,  6,  two  glands  in 

It    occasionally  presents    small   lateral    the  form  of  racemose  glands  at  their  origin  ;  7.  a 

^  very  small  gland ;  8,  a  medium-sized  gland. 

protrusions.       The    diameter   of   the 

tube  is  g-^Q  to  2^-0  of  an  inch  (83  to  100  /x).  It  has  a  fibrous  coat,  with 
a  longitudinal  layer  of  non-striated  muscular  fibres,  and  externally  a  few 
elastic  fibres.  It  is  lined  by  a  single  layer  of  irregularly-polygonal  cells, 
which  are  2 wo  ^o  T2V0  o^  ^^  'vi\Q\\  (12  to  20  ft)  in  diameter.  These  cells 
contain  a  number  of  brownish  or  yellowish  pigmentary  granules.  The 
glandular  portion  of  the  tube  contains  a  clear  liquid  mixed  with  a  granu- 
lar substance  containing  cells.  In  addition  to  the  ceruminous  glands, 
sebaceous  follicles  are  found  connected  with  the  hair-follicles. 

The  Meibomian  glands  have  essentially  the  same  structure  as  the 


286  SECRETION 

ordinary  sebaceous  glands.  Their  ducts,  however,  are  longer,  and  the 
terminal  follicles  are  arranged  in  a  peculiar  manner  by  the  sides  of 
the  tubes  along  their  entire  length.  These  glands  are  situated  partly 
in  the  substance  of  the  tarsal  cartilages,  between  their  posterior  surfaces 
and  the  conjunctival  mucous  membrane.  They  are  placed  at  right 
angles  to  the  free  border  of  the  eyelids,  opening  on  the  inner  edge  and 
occupying  the  entire  width  of  the  cartilages.  Twenty-five  to  thirty 
glands  are  found  in  the  upper  lid,  and  twenty  to  twenty-five,  in  the 
lower  lid. 

Each  Meibomian  gland  consists  of  a  nearly  straight  excretory  duct, 
■30^7  to  2^0  o^  ^^  ^^^^  (^3  ^*^  ^'-"^  ^)  ^^  diameter,  communicating  laterally 
with  compound  racemose  acini,  or  collections  of  follicles,  measuring  3^^ 
to  y|-5  of  an  inch  (83  to  200  /x).  Fifteen  or  twenty  of  these  collections 
of  follicles  are  found  on  either  side  of  the  duct  in  glands  of  medium 
length.  Most  of  the  excretory  ducts  are  nearly  straight,  but  some  are 
turned  upon  themselves  near  their  upper  extremities. 

In  general  structure  there  is  little  if  any  difference  between  the 
terminal  follicles  of  the  Meibomian  glands  and  the  folUcles  of  the  ordi- 
nary sebaceous  glands.  They  are  lined  with  cells  2^5Vo^  to  joVo  *^f  ^^ 
inch  (10  to  20  /x)  in  diameter.  The  cells  contain  fatty  globules,  but 
these  do  not  coalesce  into  large  drops,  such  as  are  often  seen  in  the 
ordinary  sebaceous  cells.  The  follicles  and  ducts  are  filled  with  the 
whitish  oleaginous  matter  which  constitutes  the  Meibomian  secretion, 
or  the  sebum  palpebrale. 

In  addition  to  the  Meibomian  secretion,  the  edges  of  the  palpebral 
orifice  receive  a  small  quantity  of  secretion  from  ordinary  sebaceous 
glands  of  the  compound  racemose  variety  (ciliary  glands),  which  are 
appended  in  pairs  to  each  of  the  follicles  of  the  eyelashes,  and  from 
sebaceous  glands  attached  to  the  small  hairs  of  the  caruncula  lachry- 
malis. 

Ordinary  Sebaceous  Matter.  —  Although  it  may  be  inferred,  from 
the  great  number  of  sebaceous  glands  opening  on  the  cutaneous  surface, 
that  the  amount  of  sebaceous  matter  must  be  considerable,  it  has  been 
impossible  to  collect  the  normal  secretion  in  quantity  sufficient  for  ulti- 
mate analysis.  In  some  parts,  as  the  skin  of  the  nose,  where  the  glands 
are  particularly  abundant,  a  certain  quantity  of  oily  secretion  is  some- 
times observed,  giving  to  the  surface  a  greasy  appearance.  This  may 
be  collected  in  small  quantity  on  a  glass  slide  and  examined  micro- 
scopically. It  then  presents  a  number  of  strongly  refracting  fatty 
globules  with  a  few  epithelial  cells.  The  cells,  however,  are  not  abun- 
dant in  the  secretion  as  it  is  discharged  upon  the  general  surface ;  but 
if  the  contents  of  the  ducts   and  follicles  are  examined,  cells  will  be 


VERNIX    CASEOSA  287 

found  in  great  number.  Most  of  the  cells,  indeed,  remain  in  the  glands, 
and  the  oily  matter  only  is  discharged.  The  object  of  this  secretion  is 
to  lubricate  the  general  cutaneous  surface  and  give  to  the  hairs  the 
softness  characteristic  of  them  in  a  healthy  condition. 

The  chemical  constituents  of  the  sebaceous  matter  are  largely  fatty. 
The  solid  matters  consisted  of  olein,  270  parts,  palmitin,  135  parts, 
caseous  matter,  129  parts,  gelatin,  d,"/  parts,  a  little  albumin,  butyric 
acid  and  sodium  butyrate,  with  sodium  phosphate,  sodium  chloride, 
sodium  sulphate  and  traces  of  calcium  phosphate.  Cholesterin,  which 
is  present  so  frequently  in  the  contents  of  sebaceous  cysts,  does  not 
exist  in  the  normal  secretion. 

During  the  later  months  of  pregnancy  and  during  lactation,  the 
sebaceous  glands  of  the  areola  of  the  nipple  become  distended  with  a 
grayish  white  opaque  secretion  containing  oily  globules  and  granules. 
Frequently  the  secretion  also  contains  a  large  number  of  epithelial  cells. 
During  the  periods  above  indicated,  the  secretion  here  is  always  much 
more  abundant  than  in  the  ordinary  sebaceous  glands. 

Smegma  of  the  Prepuce  and  of  tJie  Labia  Minora.  —  In  the  folds  of 
the  prepuce  of  the  male  and  on  the  inner  surface  and  folds  of  the  labia 
minora  in  the  female,  a  small  quantity  of  a  whitish  grumous  matter,  of 
a  cheesy  consistence,  is  sometimes  found,  particularly  when  proper  at- 
tention is  not  paid  to  cleanliness.  The  matter  which  thus  collects  in 
the  folds  of  the  prepuce  has  really  little  analogy  with  the  ordinary 
sebaceous  secretion.  Examination  with  the  miscroscope  shows  that  it 
is  composed  almost  entirely  of  irregular  scales  of  epithelium,  which  do 
not  present  the  fatty  granules  and  globules  usually  observed  in  the  cells 
derived  from  the  sebaceous  glands.  The  production  of  this  substance 
probably  is  independent  of  the  secretion  of  sebaceous  matter,  as  it  is 
formed  chiefly  in  parts  of  the  prepuce  in  which  the  sebaceous  glands  are 
wanting. 

The  smegma  of  the  labia  minora  is  of  the  same  character  as  the 
smegma  preputiale  ;  but  it  contains  drops  of  oil  and  the  other  products 
of  sebaceous  glands  found  in  these  parts. 

Verfiix  Caseosa.  —  The  surface  of  the  foetus  at  birth  and  near  the  end 
of  utero-gestation  usually  is  covered  with  a  whitish  coating,  or  smegma, 
called  the  vernix  caseosa.  This  is  most  abundant  in  the  folds  of  the  skin ; 
but  it  nearly  always  covers  the  entire  surface  with  a  coating  of  greater 
or  less  thickness  and  of  about  the  consistence  of  lard.  There  are  great 
differences  in  foetuses  at  term  as  regards  the  quantity  of  vernix  caseosa. 
In  some  the  coating  is  so  slight  that  it  is  observed  only  on  close  inspec- 
tion. There  are  few  analyses  that  give  accurately  the  chemical  com- 
position of  this  substance ;    and  the   best  idea  of  its  constitution  and 


288  SECRETION 

mode  of  formation  can  be  formed  from  microscopical  examinations.  If 
a  small  quantity  is  scraped  from  the  surface  and  is  spread  out  upon  a 
glass  slide  with  a  little  glycerin  and  water,  it  will  be  found,  on  micro- 
scopical examination,  to  consist  of  a  large  number  of  epithelial  cells  with 
a  few  small  fatty  granules.  These  cells,  after  desiccation,  constitute 
about  ten  per  cent  of  the  entire  mass.  The  fatty  granules  are  few  and 
do  not  seem  to  be  necessary  constituents  of  the  vernix,  as  they  are 
of  the  sebaceous  matter.  In  fact,  the  vernix  caseosa  must  be  regarded 
as  the  residue  of  the  secretion  of  the  sebaceous  glands  rather  than  an 
accumulation  of  true  sebaceous  matter. 

The  office  of  the  vernix  caseosa  is  protective.  In  making  a  micro- 
scopical preparation  of  the  cells  with  water,  it  becomes  evident  that  the 
coating  is  penetrated  by  the  liquid  with  difficulty,  even  when  mixed  with 
it  as  thoroughly  as  possible.  The  protecting  coat  of  vernix  caseosa 
allows  the  skin  to  perform  its  office  in  utero ;  and  at  birth,  when  this 
coating  is  removed,  the  surface  is  found  in  a  condition  perfectly  adapted 
to  extra-uterine  existence. 

Cerumen.  —  A  peculiar  substance  of  a  waxy  consistence  is  secreted 
by  the  glands  that  have  been  described  in  the  external  auditory  meatus, 
under  the  name  of  ceruminous  glands,  mixed  with  the  secretion  of 
sebaceous  glands  connected  with  the  short  hairs  in  this  situation.  It  is 
difficult  to  ascertain  what  share  these  two  sets  of  glands  have  in  the  for- 
mation of  the  cerumen.  The  waxy  portion  of  the  secretion  probably 
is  produced  by  the  sebaceous  glands,  and  the  convoluted  glands,  com- 
monly known  as  the  ceruminous  glands,  produce  a  secretion  resembling 
sweat.  This  view  is  to  a  certain  extent  reasonable ;  for  the  sebaceous 
matter  is  not  removed  from  the  meatus  by  friction,  as  in  other  situations, 
and  would  have  a  natural  tendency  to  accumulate  ;  but  the  contents  of 
the  ducts  of  the  ceruminous  glands  differ  materially  from  the  liquid 
found  in  the  ducts  of  the  ordinary  sudoriparous  glands,  containing 
granules  and  fatty  globules  such  as  exist  in  the  cerumen.  Although  the 
glands  of  the  ear  are  analogous  in  structure,  and  to  a  certain  extent  in 
the  character  of  their  secretion,  to  the  sudoriparous  glands,  their  secre- 
tion is  peculiar.  The  perspiratory  glands  of  the  axilla  and  of  some  other 
parts  also  produce  secretions  differing  somewhat  from  ordinary  perspira- 
tion. So  far  as  can  be  ascertained,  the  cerumen  is  produced  by  both 
sets  of  glands.  The  sebaceous  glands  attached  to  the  hair-follicles 
probably  secrete  most  of  the  oleaginous  and  waxy  matter,  while  the  so- 
called  ceruminous  glands  produce  a  secretion  of  much  greater  fluidity, 
but  containing  granular  and  fatty  matters. 

The  consistence  and  general  appearance  of  cerumen  are  variable 
within  the   limits  of  health.     When  first  secreted,  it  is  of  a  yellowish 


MAMMARY    SECRETION  289 

color  and  about  the  consistence  of  honey,  becoming  darker  and  more 
viscid  on  exposure  to  the  air.  It  has  a  decidedly  bitter  taste.  It  readily 
forms  a  sort  of  emulsive  mixture  with  water. 

Examined  microscopically,  the  cerumen  is  found  to  contain  semisoHd 
dark  granules  of  an  irregularly  polyhedric  shape,  with  epithelium  from 
the  sebaceous  glands,  and  epidermic  scales,  both  isolated  and  in  layers. 
Sometimes,  also,  a  few  crystals  of  cholesterin  are  found. 

Chemical  examination  shows  that  cerumen  is  composed  of  oily 
matters  fusible  at  a  low  temperature,  a  peculiar  organic  matter  resem- 
bling mucin,  with  sodium  salts  and  a  certain  quantity  of  calcium  phos- 
phate. The  yellow  coloring  matter  is  soluble  in  alcohol ;  and  the  residue 
after  evaporation  of  the  alcohol  is  soluble  in  water  and  may  be  precipi- 
tated from  a  watery  solution  by  neutral  lead  acetate  or  tin  chloride. 
This  extract  has  a  bitter  taste. 

The  cerumen  lubricates  the  external  meatus,  accumulating  about  the 
hairs  in  the  canal.  Its  bitter  taste  is  supposed  to  be  useful  in  preventing 
the  entrance  of  insects. 

Meibomian  Secretion.  —  Little  is  known  concerning  any  special  prop- 
erties of  the  Meibomian  secretion  except  that  it  mixes  in  the  form  of  an 
emulsion  with  water  more  readily  than  the  other  sebaceous  matters.  It 
is  produced  in  small  quantity,  mixed  with  mucus  and  the  secretion  from 
the  sebaceous  glands  attached  to  the  eyelashes  and  the  glands  of  the 
caruncula  lachrymalis,  and  smears  the  edges  of  the  palpebral  opening. 
This  oily  coating  on  the  edges  of  the  lids,  unless  the  tears  are  produced 
in  excessive  quantity,  prevents  their  overflow  upon  the  cheeks,  and  the 
excess  is  carried  away  by  the  nasal  duct. 

Mammary  Secretion 

The  mammary  glands  are  among  the  most  remarkable  organs  in  the 
economy ;  not  only  on  account  of  the  peculiar  character  of  their  secre- 
tion, which  is  unlike  the  product  of  any  other  of  the  glands,  but  from 
the  changes  which  they  undergo  at  different  periods,  both  in  size  and 
structure.  Rudimentary  in  early  life  and  in  the  male  at  all  periods  of 
life,  these  organs  are  fully  developed  in  the  adult  female  only  in  the 
later  months  of  pregnancy  and  during  lactation.  In  the  female,  after 
puberty,  the  mammary  glands  undergo  a  rapid  increase  in  size ;  but 
even  then  they  are  not  fully  developed. 

PJiysiological  Anatomy  of  the  Mammary  Glands. — The  form,  size 
and  situation  of  the  mammae  in  the  adult  female  are  too  well  known  to 
demand  more  than  a  passing  mention.  These  organs  are  almost  invari- 
ably double  and  are  situated  on  the  anterior  portion  of  the  thorax,  over 


290 


SECRETION 


the  great  pectoral  muscles.  In  women  who  have  never  borne  children, 
they  usually  are  firm  and  nearly  hemispherical,  with  the  nipple  at  the 
most  prominent  point.  In  women  who  have  borne  children,  the  glands 
during  the  intervals  of  lactation  are  larger,  are  held  more  loosely  to  the 
subjacent  parts  and  often  are  flabby  and  pendulous.  The  areola  of  the 
nipple,  also,  is  darker. 

In  both  sexes  the  mammary  glands  are  nearly  as  much  developed  at 
birth  as  at  any  time  before  puberty.  They  make  their  appearance  at 
about  the  fourth  month,  in  the  form  of  little  elevations  of  cutaneous 
structure,  which  soon  begin  to  send  off  processes  beneath  the  skin  that 
are  destined  to  be  developed  into  the  lobes  of  the  glands.  In  the  foetus 
at  term,  the  glands  measure  hardly  more  than  one-third  of  an  inch  (8.5 
millimeters)  in  diameter.  At  this  time  there  are  twelve  to  fifteen  lobes 
in  each  gland,  and  each  lobe  is  penetrated  by  a  duct,  with  but  few 
branches,  composed  of  fibrous  tissue  and  lined  with  cylindrical  epithe- 
lium. The  ends  of  these  ducts  frequently  are  somewhat  dilated  ;  but 
what  have  been  called  the  gland-vesicles  do  not  make  their  appearance 
before  puberty.  In  the  adult  male,  the  glands  are  half  an  inch  to  two 
inches  (12.7  to  50.8  millimeters)  broad,  and  yV  to  ^  of  an  inch  (2.1  to 
6.4  millimeters)  in  thickness.  In  their  structure,  however,  they  pre- 
sent little  if  any  difference  from  the  rudimentary  glands  of  the  infant. 

As  the  time  of  puberty  approaches  in  the  female,  the  rudimentary 
ducts  of  the  different  lobes  become  more  and  more  ramified.  Instead  of 
each  duct  having  but  two  or  three  branches,  the  lobes,  as  the  gland  en- 
larges, are  penetrated  by  innumerable  ramifications  which  have  gradually 
been  developed  as  processes  from  the  rhain  duct.  It  is  important  to  re- 
member, however,  that  these  branches  are  never  so  abundant  or  so  long 
during  the  intervals  of  lactation  as  they  are  when  the  gland  is  in  full 
activity. 

Between  the  fourth  and  fifth  months  of  utero-gestation,  the  mam- 
mary glands  of  the  mother  begin  to  increase  in  size;  and  at  term  they 
are  much  larger  than  during  the  unimpregnated  state.  At  this  time  the 
breasts  become  quite  hard,  and  the  surface  near  the  areola  is  somewhat 
uneven,  from  the  great  development  of  the  ducts.  The  nipple  also  is 
increased  in  size,  the  papillae  on  its  surface  and  on  the  areola  are  more 
largely  developed  and  the  areola  becomes  larger,  darker  and  thicker. 
The  glandular  structure  of  the  breasts  during  the  latter  half  of  preg- 
nancy becomes  so  far  developed,  that  if  the  child  is  born  at  the  seventh 
month,  the  lacteal  secretion  may  be  established  at  the  usual  time  after 
parturition.  Even  when  parturition  takes  place  at  term,  a  few  days 
elapse  before  secretion  is  fully  established,  and  the  first  product  of  the 
glands,  called  colostrum,  is  somewhat  different  from  fully-formed  milk. 


PHYSIOLOGICAL   ANATOMY   OF   THE   MAMMARY   GLANDS       291 

The  only  parts  of  the  covering  of  the  breasts  that  present  any 
peculiarities  are  the  areola  and  the  nipple.  The  surface  of  the  nipple 
is  covered  with  papillae,  which  are  largely  developed  near  the  summit. 
It  is  covered  with  epithelium  in  several  layers,  the  lower  strata  being 
filled  with  pigmentary  granules.  The  true  skin  covering  the  nipples  is 
composed  of  inelastic  and  elastic  fibres,  containing  a  large  number  of 
sebaceous  glands,  but  no  hair-follicles  or  sudoriparous  glands.  These 
glands  are  of  the  racemose  variety  and  not  in  the  form  of  simple  follicles. 
The  nipple  contains  the  lactiferous  ducts,  fibres  of  inelastic  and  elastic 
tissue,  with  a  large  number  of  non-striated  muscular  fibres.  The  mus- 
cular fibres  have  no  definite  direction,  but  are  so  abundant  that  when 
contracted  the  nipple  becomes  firm  and  hard. 

The  areola  does  not  lie,  like  the  general  integument  covering  the 
gland,  on  a  bed  of  adipose  tissue,  but  it  is  closely  adherent  to  the  sub- 
jacent glandular  structure.  The  skin  here  is  much  thinner  and  more 
delicate  than  in  other  parts,  and  the  pigmentary  granules  are  very 
abundant  in  some  of  the  lower  strata  of  epidermic  cells,  particularly 
during  pregnancy.  The  true  skin  of  the  areola  is  composed  of  inelastic 
and  elastic  fibres  and  lies  on  a  distinct  layer  of  non-striated  muscular 
fibres.  The  arrangement  of  the  muscular  fibres  —  sometimes  called  the 
subareolar  muscle  —  is  quite  regular,  forming  concentric  rings  around 
the  nipple.  These  fibres  are  supposed  to  be  useful  in  compressing  the 
ducts  during  the  discharge  of  milk.  The  areola  presents  the  following 
structures  :  papillae,  considerable  smaller  than  those  on  the  nipple  ;  hair- 
follicles,  containing  small  rudimentary  hairs ;  sudoriparous  glands ;  and 
sebaceous  glands  connected  with  the  hair-follicles.  The  sebaceous 
glands  are  large,  and  their  situation  is  indicated  by  little  prominences 
on  the  surface  of  the  areola,  which  are  especially  marked  during 
pregnancy. 

The  mammary  gland  itself  is  of  the  compound  racemose  variety.  It 
is  covered  in  front  with  a  subcutaneous  layer  of  fat,  and  posteriorly  it  is 
enveloped  in  a  fibrous  membrane  loosely  attached  to  the  pectoralis  major 
muscle.  A  considerable  quantity  of  adipose  tissue  also  is  found  in  the 
substance  of  the  gland  between  the  lobes. 

Separated  from  the  adipose  and  fibrous  tissue,  the  mammary  gland 
is  found  divided  into  lobes,  fifteen  to  twenty-four  in  number.  These 
are  subdivided  into  lobules  made  up  of  a  greater  or  less  number  of  acini. 
The  secreting  structure  is  of  a  reddish  yellow  color  and  is  distinctly 
granular,  presenting  a  decided  contrast  to  the  pale  and  uniformly 
fibrous  appearance  of  the  gland  during  the  intervals  of  lactation.  If 
the  ducts  are  injected  from  the  nipple  and  followed  into  the  substance 
of  the  gland,  each  one  will  be  found  distributing  its  branches  to  a  dis- 


292  SECRETION 

tinct  lobe ;  so  that  the  organ  is  really  made  up  of  a  number  of  glands 
identical  in  structure. 

The  canals  that  discharge  the  milk  at  the  nipple  are  called  lactifer- 
ous or  galactophorous  ducts.  They  are  ten  to  fourteen  in  number.  The 
openings  of  the  ducts  at  the  nipple  are  small,  measuring  only  -^^  to  ^^q 
of  an  inch  (0.42  to  0.64  millimeter).  As  each  duct  passes  downward, 
it  enlarges  in  the  nipple  to  ^h  or  tV  of  an  inch  (i  or  2  millimeters)  in 
diameter,  and  beneath  the  areola  it  presents  an  elongated  dilatation, 
1^  to  ^  of  an  inch  (4.2  to  8.5  miUimeters)  in  diameter,  called  the  sinus  of 
the  duct.  During  lactation  a  considerable  quantity  of  milk  collects  in 
these  sinuses,  which  serve  as  reservoirs.  Beyond  the  sinuses,  the  calibre 
of  the  ducts  measures  ^^2  to  ^  of  an  inch  (2.1  to  4.2  millimeters).  The 
ducts  penetrate  the  lobes,  branching  and  subdividing,  to  terminate  in 
the  collections  of  alveoli  which  form  the  acini.  There  is  no  anasto- 
mosis between  the  different  lactiferous  ducts,  and  each  one  is  distributed 
independently  to  one  or  more  lobes. 

The  lactiferous  ducts  have  three  distinct  coats.  The  external  coat 
is  composed  of  anastomosing  fibres  of  elastic  tissue  with  some  inelastic 
fibres.  The  middle  coat  is  composed  of  non-striated  muscular  fibres, 
arranged  longitudinally  and  existing  throughout  the  duct  from  its  open- 
ing at  the  nipple  to  the  secreting  alveoli.  The  internal  coat  is  a  thin 
amorphous  membrane,  lined  with  flat  polygonal  cells  during  the  inter- 
vals of  lactation  and  even  during  pregnancy,  the  cells  being  cylindrical 
in  form  and  frequently  presenting  multiple  nuclei,  when  milk  is  secreted. 

The  acini  of  the  gland,  which  are  very  abundant,  are  visible  to  the 
naked  eye,  in  the  form  of  small  rounded  granules  of  a  reddish  yellow 
color.  Between  the  acini,  there  exists  a  certain  quantity  of  ordinary 
white  fibrous  tissue  with  a  number  of  adipose  vesicles.  The  presence 
of  adipose  tissue  in  considerable  quantity  in  the  substance  of  the  glandu- 
lar structure  is  peculiar  to  the  mammary  glands.  Each  acinus  is  made 
up  of  twenty  to  forty  secreting  vesicles,  or  alveoli.  These  vesicles  are 
irregular  in  form,  often  varicose,  and  sometimes  they  are  enlarged 
and  imperfectly  bifurcated  at  their  extremities.  During  lactation  their 
diameter  is  ^^^  to  g^g  of  an  inch  (60  to  80  /jl). 

During  the  intervals  of  lactation,  as  the  lactiferous  ducts  become  re- 
tracted, the  glandular  alveoli  disappear ;  and  in  pregnancy,  as  the  gland 
takes  on  its  full  development,  the  ducts  branch  and  extend  themselves, 
and  the  vesicles  are  gradually  developed  around  their  extremities. 

MecJianisni  of  tJic  Secretion  of  Milk. — With  the  exception  of  water 
and  inorganic  matters,  all  the  important  and  characteristic  constituents 
of  the  milk  are  formed  in  the  substance  of  the  mammary  glands.  The 
secreting  structures  separate  from  the  blood  a  great  variety  of  inorganic 


CONDITIONS   WHICH    MODIFY    THE    LACTEAL    SECRETION      293 

salts ;  and  milk  furnishes  all  the  inorganic  matter  necessary  for  the  nutri- 
tion of  the  infant,  even  containing  a  small  quantity  of  iron. 

The  lactose,  or  sugar  of  milk,  the  casein  and  the  fatty  particles  are 
all  produced  in  the  gland.  The  peculiar  kind  of  sugar  here  found  does 
not  exist  anywhere  else  in  the  organism.  Even  when  the  secretion  of 
milk  is  most  active,  different  varieties  of  sugar,  such  as  glucose  or  cane- 
sugar,  injected  into  the  bloodvessels  of  a  living  animal,  are  not  eliminated 
by  the  mammary  glands  as  they  are  by  the  kidneys ;  and  their  presence 
in  the  blood  does  not  influence  the  quantity  of  lactose  found  in  the  milk. 

Casein  is  produced  in  the  mammary  glands,  probably  by  a  peculiar 
transformation  of  the  proteid  constituents  of  the  blood.  The  fatty 
globules  are  likewise  produced  in  the  substance  of  the  gland,  and  the 
peculiar  kind  of  fat  that  exists  in  this  secretion  is  not  found  in  the  blood. 
The  mechanism  of  the  production  of  fat  in  the  mammary  glands  is  some- 
what obscure.  During  full  activity  of  the  lacteal  secretion,  however, 
small  fatty  globules  appear  in  the  cells  lining  the  alveoli,  particularly 
that  portion  of  the  cells  next  the  lumen,  and  these  finally  are  discharged 
into  the  ducts. 

As  regards  the  mechanism  of  the  formation  of  the  peculiar  and 
characteristic  constituents  of  milk,  the  mammary  glands  are  to  be 
classed  among  the  organs  of  secretion  and  not  with  those  of  elimina- 
tion, or  excretion ;  for  none  of  these  matters  preexist  in  the  blood  and 
they  all  appear  first  in  the  substance  of  the  glands. 

During  the  period  of  secretion,  the  glands  receive  a  larger  supply  of 
blood  than  at  other  times.  Pregnancy  favors  the  development  of  the 
secreting  portions  of  the  glands  but  does  not  induce  secretion.  On  the 
contrary,  when  pregnancy  occurs  during  lactation,  it  diminishes  and 
modifies,  and  it  may  arrest  the  secretion  of  milk.  The  secreting  action 
of  the  mammary  glands  is  nearly  continuous.  When  the  secretion  of 
milk  has  become  fully  established,  while  there  may  be  certain  times 
when  it  is  formed  in  greater  quantity  than  at  others,  there  is  no  actual 
intermission  in  its  production. 

General  Conditions  whicJi  modify  the  Lacteal  Secretion.  —  Very  little 
is  known  concerning  the  physiological  conditions  which  modify  the 
secretion  of  milk.  When  lactation  is  fully  established,  the  quantity  and 
quality  of  the  milk  secreted  become  adapted  to  the  requirements  of  the 
child  at  different  periods  of  its  existence.  In  studying  the  composition' 
of  the  milk,  therefore,  it  will  be  found  to  vary  considerably  in  different 
stages  of  lactation.  It  is  evident  that  as  the  development  of  the  child 
advances,  a  constant  increase  of  nourishment  is  demanded ;  and  as  a 
rule  the  mother  is  capable  of  supplying  all  the  nutritive  requirements  of 
the  infant  for  eight  to  twenty  months. 


294 


SECRETION 


During  the  time  when  such  an  amount  of  nutritive  matter  is  fur- 
nished to  the  child,  the  quantity  of  food  taken  by  the  mother  is  sensibly 
increased ;  but  observations  have  shown  that  the  secretion  of  milk  is 
not  much  influenced  by  the  character  of  the  food.  It  is  necessary  that 
the  mother  should  be  supplied  with  good  nutritious  articles ;  but  so  far 
as  solid  food  is  concerned,  there  seems  to  be  no  great  difference  between 
a  coarse  and  a  delicate  alimentation  ;  and  the  milk  of  females  in  the 
lower  walks  of  life,  when  the  general  condition  is  normal,  is  fully  as 
good  as  in  women  who  are  able  to  live  luxuriously.  It  is,  indeed,  a  fact 
commonly  recognized  by  physiologists,  that  the  secretion  of  milk  is  little 
influenced  by  any  special  diet,  provided  the  alimentation  be  sufficient 
and  of  the  quality  ordinarily  required  by  the  system  and  that  it  contain 
none  of  the  few  articles  of  food  known  to  have  a  special  influence  on 
lactation.  It  is  common,  however,  for  women  to  become  quite  fat 
during  lactation  ;  which  shows  that  the  fatty  constituents  of  the  food  do 
not  pass  exclusively  into  the  milk,  but  that  there  is  a  tendency,  at  the 
same  time,  to  a  deposition  of  adipose  tissue  in  the  situations  in  which  it 
ordinarily  is  found.  It  is  a  matter  of  common  experience,  that  certain 
articles,  such  as  acids  and  fermentable  substances,  often  disturb  the 
digestive  organs  of  the  child  without  producing  any  change  in  the  milk 
that  can  be  recognized  by  chemical  analysis.  The  individual  differences 
in  women,  in  this  regard,  are  very  great. 

The  statements  in  regard  to  solid  food  do  not  apply  to  liquids.  Dur- 
ing lactation  there  is  always  an  increased  demand  for  water  and  for  liq- 
uids generally ;  and  if  these  are  not  supplied  in  sufficient  quantity,  the 
secretion  of  milk  is  diminished  and  its  quality  is  almost  always  impaired. 
It  is  a  curious  fact,  which  has  been  fully  established  by  observations  on 
the  human  subject  and  the  inferior  animals,  that  while  the  quantity  of 
milk  is  increased  by  taking  a  large  amount  of  simple  water,  the  solid 
constituents  also  are  increased  and  the  milk  retains  all  its  nutritive 
qualities. 

Alcohol,  especially  when  largely  diluted,  as  in  malt-liquors  and  other 
mild  beverages,  is  well  known  to  influence  the  secretion  of  milk. 
Drinks  of  this  kind  almost  always  temporarily  increase  the  activity  of 
the  secretion,  and  sometimes  they  produce  an  effect  on  the  child ;  but 
direct  and  accurate  observations  on  the  actual  passage  of  alcohol  into 
the  milk  are  wanting.  During  lactation  the  moderate  use  of  drinks  con- 
taining a  small  proportion  of  alcohol  frequently  is  beneficial,  particularly 
in  assisting  the  mother  to  sustain  the  unusual  drain  on  the  system. 
There  are,  however,  few  instances  of  normal  lactation  in  which  their 
use  is  absolutely  necessary. 

It  is  well  known  that  the  secretion  of  milk  may  be  profoundly  af- 


QUANTITY    OF   MILK  295 

fected  by  violent  mental  emotions.  This  is  the  case  in  respect  to  many 
other  secretions,  as  the  saliva  and  the  gastric  juice.  It  is  hardly  neces- 
sary, however,  to  cite  many  of  the  instances  of  modification  or  arrest  of 
the  secretion  from  this  cause  that  are  quoted  by  authors.  Vernois  and 
Becquerel  reported  a  case  in  which  a  hospital  wetnurse,  who  lost  her 
only  child  from  pneumonic  fever,  became  violently  affected  with  grief 
and  presented  as  a  consequence  an  immediate  diminution  in  the  quantity 
of  her  milk,  with  a  great  reduction  in  the  proportion  of  salts,  sugar  and 
butter.  In  this  case  the  proportion  of  casein  was  increased.  Astley 
Cooper  reported  two  cases  in  which  the  secretion  of  milk  was  instanta- 
neously and  permanently  arrested  by  terror.  These  cases  are  types  of 
many  others,  cited  by  writers,  of  the  influence  of  mental  emotions  on 
secretion. 

Direct  observations  on  the  influence  of  spinal  nerves  on  the  mam- 
mary glands  are  few  and  unsatisfactory.  The  operation  of  dividing  the 
nerves  distributed  to  these  glands,  which  has  occasionally  been  practised 
on  animals  in  lactation,  has  not  been  observed  to  produce  any  sensible 
diminution  in  the  quantity  of  the  secretion.  It  is  difficult,  however,  to 
operate  on  all  the  nerves  distributed  to  these  organs.  There  are  no 
observations  indicating  the  situation  of  a  nerve-centre  presiding  over 
the  secretion  of  milk,  although  such  a  centre  may  exist. 

Quantity  of  Milk.  —  It  is  difficult  to  form  a  reliable  estimate  of  the 
average  quantity  of  milk  secreted  by  the  human  female  in  the  twenty- 
four  hours.  The  quantity  undoubtedly  varies  very  much  in  different 
persons ;  some  women  being  able  to  nourish  two  children,  while  others, 
though  apparently  in  perfect  health,  furnish  hardly  enough  food  for 
one.  The  quantity  that  can  be  drawn  from  a  full  breast  usually  is 
about  two  fluidounces  (60  grams).  This  may  be  assumed  to  be  about 
the  quantity  contained  in  the  lactiferous  ducts  when  they  are  moderately 
distended.  Taking  into  consideration  the  variations  in  the  quantity  of 
milk  secreted  by  different  women,  it  may  be  assumed  that  the  daily  pro- 
duction is  between  two  and  three  pints  (950  and  1420  grams). 

Certain  conditions  of  the  female  are  capable  of  materially  influenc- 
ing the  quantity  of  milk  secreted.  It  is  evident  that  the  secretion 
usually  is  somewhat  increased  within  the  first  few  months  of  lactation, 
when  the  progressive  development  of  the  child  demands  an  increase  in 
the  quantity  of  nourishment.  If  the  menstrual  function  becomes  re- 
established during  lactation,  the  milk  usually  is  diminished  in  quantity 
during  the  periods,  but  sometimes  it  is  not  affected,  either  in  its  quantity 
or  composition.  Should  the  female  become  pregnant,  there  commonly 
is  a  great  diminution  in  the  quantity  of  milk,  and  that  which  is  secreted 
is  regarded   ordinarily  as  possessing  little  nutritive  value.      In  obedi- 


296  SECRETION 

ence  to  a  popular  prejudice  —  apparently  well  founded  —  the  child  usu- 
ally is  taken  from  the  breast  so  soon  as  pregnancy  is  recognized.  No 
marked  and  constant  variations  have  been  observed  in  the  quantity  of 
milk  in  females  of  different  ages. 

Properties  and  Composition  of  Milk.  —  The  general  appearance  and 
characters  of  ordinary  cow's  milk  are  sufficiently  familiar.  Human 
milk  is  neither  so  white  nor  so  opaque  as  cow's  milk,  having  ordinarily 
a  slightly  bluish  tinge.  After  secretion  has  become  fully  established, 
milk  possesses  no  viscidity  and  is  nearly  opaque.  It  is  almost  inodor- 
ous, of  a  peculiar  soft  and  sweetish  taste,  and  when  perfectly  fresh  it 
has  a  decidedly  alkaline  reaction.  The  taste  of  human  milk  is  sweeter 
than  that  of  cow's  milk.  A  short  time  after  its  discharge  from  the 
gland,  the  reaction  of  milk  becomes  first  amphoteric  and  afterward 
faintly  acid  ;  but  this  change  takes  place  more  slowly  in  human  milk 
than  in  the  milk  of  most  of  the  inferior  animals. 

The  average  specific  gravity  of  human  milk  is  1032  ;  although  this 
is  subject  to  considerable  variation,  the  minimum  of  eighty-nine  obser- 
vations being  1025,  and  the  maximum,  1046  (Vernois  and  Becquerel). 
The  observations  of  most  physiological  chemists  have  shown  that  this 
average  is  nearly  correct. 

Milk  is  not  coagulated  by  heat,  even  after  prolonged  boiling ;  but  a 
thin  pellicle  then  forms  on  the  surface.  Although  a  small  quantity  of 
albumin  exists  in  the  milk,  this  does  not  coagulate  on  the  surface  by  the 
action  of  the  heat,  for  the  scum  does  not  form  when  the  liquid  is  heated 
in  a  vacuum  or  in  an  atmosphere  of  carbon  dioxide  or  of  hydrogen. 

When  milk  is  coagulated  by  any  substance  acting  on  the  casein  or 
when  it  coagulates  spontaneously,  it  separates  into  a  curd,  composed  of 
casein  with  most  of  the  fatty  particles,  and  a  nearly  clear,  greenish  yel- 
low serum,  called  whey.  This  separation  occurs  spontaneously  at  a 
variable  time  after  the  discharge  of  the  milk,  taking  place  much  sooner 
in  warm  than  in  cold  weather.  It  is  a  curious  fact  that  fresh  milk  fre- 
quently is  coagulated  during  a  thunder  storm,  which  probably  is  due  to 
electric  action  on  the  ions  that  enter  into  the  constitution  of  the  casein 
molecules. 

On  being  allowed  to  stand  for  a  short  time,  milk  separates,  without 
coagulating,  into  two  tolerably  distinct  portions.  A  large  proportion  of 
the  globules  rises  to  the  top,  forming  a  yellowish  white  and  very  opaque 
liquid,  called  cream,  leaving  the  lower  portion  poorer  in  globules  and 
of  a  decidedly  bluish  tint.  In  healthy  milk  the  stratum  of  cream  forms 
one-fifth  to  one-third  of  the  entire  mass  of  the  milk.  In  the  human 
subject  the  skim-milk  is  not  white  and  opaque,  but  it  is  nearly  as  trans- 
parent as  whey.     The  specific  gravity  of  the  cream  from  milk  of  the 


MICROSCOPICAL   CHARACTERS   OF    THE    MILK  297 

average  specific  gravity  of  1032  is  about  1024.  The  specific  gravity  of 
skim-milk  is  about  1034. 

Microscopical  Characters  of  the  Milk.  —  Milk  contains  a  great  number 
of  minute  spherical  globules,  of  highly  refractive  power,  held  in  sus- 
pension in  a  clear  liquid.  These  are  known  as  milk-globules  and  are 
composed  of  palmitin,  olein,  fatty  matters  peculiar  to  milk,  with  a  little 
lecithin  and  sometimes  a  very  small  quantity  of  cholesterin.  The 
globules  also  contain  a  small  quantity  of  a  yellow  lipochrome,  or  fat- 
pigment.     The  specific  gravity  of  pure  milk- fat  is  949  to  996. 

Human  milk-globules  are  g^s'oTo  ^^  T2T0  ^^  ^^  vi\c\y  (i  to  20  /u.)  in 
diameter.  They  usually  are  distinct  from  each  other,  but  they  may 
occasionally  become  collected  into 
groups  without  indicating  anything 
abnormal.  In  a  perfectly  normal 
condition  of  the  glands,  when  the 
lacteal  secretion  has  become  fully 
established,  the  milk  contains  noth- 
ing but  a  clear  liquid  with  these 
globules  in  suspension.  The  pro- 
portion of  fatty  matters  in  milk  is 
twenty-five  to  thirty-eight  parts  per 
thousand ;  and  this  gives  an  idea  of 
the  proportion  of  globules  that  are 
seen  on  microscopical  examination.  t?-     >=        u  -u.   ,  1.  ,     ^ 

^  ■Tig-  0'^.  — Human    milk-globules  from   a 

In    some     regards     milk     does    not    healthy  lylng-in  woman  etgkt  days  after  delivery, 

present   the   characters  of   a  simple   ^  '*°° 

emulsion.  When  shaken  with  ether,  the  mixture  remains  opaque ;  but 
the  fatty  matters  are  dissolved  on  the  addition  of  potassium  hydrate. 
Dilute  acetic  acid  added  to  milk  causes  the  globules  to  run  together. 
These  reactions  have  led  to  the  view  that  the  milk-globules  have  a 
membrane  that  is  dissolved  by  potassium  hydrate  and  by  acetic  acid. 
It  is  probable  that  the  butter  in  normal  milk  does  not  exist  precisely  in 
the  form  of  a  simple  emulsion,  but  that  the  globules  have  a  very  thin 
caseous  coating. 

In  view  of  the  action  of  various  reagents  on  the  milk-globules,  the 
only  alternative,  if  the  existence  of  a  caseous  coating  is  denied,  is  the 
opinion  that  the  addition  of  potassium  hydrate  or  of  acetic  acid  renders 
the  casein  incapable  of  holding  the  fat  in  the  condition  of  an  emulsion. 
There  is  actually,  however,  little  more  than  a  verbal  difference  between 
these  two  opinions. 

Composition  of  the  Milk.  —  The  following  table,  compiled  from 
analyses  by  various  chemists,  gives  the  constituents  of  human  milk :  — 


298 


SECRETION 


COMPOSITION   OF   HUMAN   MILK 


Water         .... 

Casein  (desiccated)     . 

Lactoprotein 

Lactalbumin  and  lactoglobulin 

r  Palmitin  . 
Butter,  25  to  38  \  Olein 

I  Butyrin,  caprin 
Sugar  of  millc  (lactose) 
Sodium  lactate  ( ?) 
Sodium  chloride 
Potassium  chloride 
Sodium  carbonate 
Calcium  carbonate 
Calcium  phosphate 
Magnesium  phosphate 
Sodium  phosphate 
Ferric  phosphate  ( ?) 
Sodium  sulphate 
Potassium  sulphate 


,  caproin,  capryl 


(Oxygen  i 

Nitrogen  12 

Carbon  dioxide  16 


n  etc 


902.717 
29.000 
1. 000 
traces 
17.000 
7.500 
0.500 
37.060 
0.420 
0.240 
1.440 
0.053 
0.069 
2.310 
0.420 
0.225 
0.032 
0.074 


to 
to 
to 
to 
to 
to 
to 
to 
to 
to 
to 
to 
to 
to 
to 
to 
to 
to 
traces 


863.149 

39.000 

2.770 

0.880 

25.840 

1 1 .400 

0.760 

49.000 

0.450 

o  340 

1.830 

o  056 
0.070 

3-440 

0.640 

0.230 

0.070 

0.075 


30  parts  per  1000  in  volume. 


The  proportion  of  water  in  milk  is  subject  to  certain  changes,  but 
these  are  not  so  considerable  as  might  be  expected  from  the  great 
variations  in  the  entire  quantity  of  the  secretion.  As  regards  the 
quantity  of  milk  in  the  twenty-four  hours,  the  influence  of  drinks,  even 
when  nothing  but  pure  water  is  taken,  is  very  marked ;  and  although 
the  activity  of  the  secretion  is  much  increased  by  fluid  ingesta,  the 
quality  of  the  milk  usually  is  not  affected,  and  the  proportion  of  water 
to  the  solid  matters  remains  about  the  same. 

Nitivgeiions  ConstitiLcnts  of  Milk.  —  Little  remains  to  be  said  con- 
cerning the  nitrogenous  constituents  of  human  milk  after  what  has  been 
stated  in  connection  with  alimentation.  The  different  constituents  of 
this  class  undoubtedly  have  the  same  nutritive  office  and  they  appear 
to  be  identical  in  all  varieties  of  milk,  the  only  difference  being  in  their 
relative  proportions.  It  is  a  matter  of  common  experience,  indeed,  that 
the  milk  of  many  of  the  lower  animals  will  take  the  place  of  human 
milk,  when  prepared  so  as  to  make  the  proportions  of  its  different 
constituents  approximate  the  composition  of  the  natural  food  of  the 
child.  A  comparison  of  the  composition  of  human  milk  and  of  cow's 
milk  shows  that  the  former  is  poorer  in  nitrogenous  matters  and  richer 
in  butter  and  sugar ;  and  consequently,  the  upper  strata  of  cow's  milk, 


NON-NITROGENOUS   CONSTITUENTS   OF   MILK  299 

properly  sweetened  and  diluted  with  water,  very  nearly  represent  the 
ordinary  breast-milk. 

Casein  is  by  far  the  most  important  of  the  nitrogenous  constitu- 
ents of  milk,  and  it  supplies  nearly  all  of  this  kind  of  nutritive  matter 
demanded  by  the  child.  Lactoprotein  is  not  so  well  defined,  and  lact- 
albumin,  a  proteid  resembling  serum-albumin,  with  lactoglobulin,  exists 
in  milk  in  small  quantities.  These  proteids,  however,  are  of  little 
physiological  interest. 

The  coagulation  of  milk  depends  on  the  reduction  of  casein  from 
a  liquid  to  a  semisolid  condition.  When  milk  is  allowed  to  coagulate 
spontaneously,  the  change  is  effected  by  the  action  of  the  lactic  acid 
which  results  from  a  change  in  a  part  of  the  sugar  of  milk.  Casein,  in 
fact,  is  coagulated  by  nearly  all  acids,  even  the  feeble  acids  of  organic 
origin.  It  differs  from  albumin  in  this  regard  and  in  the  fact  that  it  is 
not  coagulated  by  heat.  If  fresh  milk  is  slightly  raised  in  temperature 
and  treated  with  an  infusion  of  the  gastric  mucous  membrane  of  the 
calf,  coagulation  will  take  place  in  five  or  ten  minutes,  the  clear  Hquid 
still  retaining  its  alkaline  reaction.  The  action  on  casein  of  the  rennin 
of  the  gastric  juice  has  already  been  described  in  connection  with 
gastric  digestion. 

No7i-Nitrogenous  ConsHtnents  of  Milk.  —  Non-nitrogenous  matters 
exist  in  abundance  in  the  milk.  The  liquid  casein  and  the  water  hold 
the  fats  in  the  condition  of  a  fine  and  permanent  emulsion.  This  fat 
may  easily  be  separated  from  milk  and  is  known  under  the  name  of 
butter.  In  human  milk  the  butter  is  much  softer  than  in  the  milk  of 
many  of  the  inferior  animals,  particularly  the  cow ;  but  it  is  composed 
of  essentially  the  same  constituents,  although  in  different  proportions. 
In  different  animals,  there  are  developed,  even  after  the  discharge  of 
the  milk,  certain  odorous  matters  that  are  more  or  less  characteristic  of 
the  animal  from  which  the  butter  is  taken. 

The  greatest  part  of  the  butter  consists  of  palmitin.  It  contains  in 
addition,  olein,  and  a  small  proportion  of  peculiar  fats  —  which  have  not 
been  very  well  determined  —  called  butyrin,  caprin,  caproi'n,  caprylin, 
with  some  other  analogous  substances.  Palmitin  and  olein  are  found  in 
the  fat  throughout  the  body  ;  but  the  last-named  substances  are  peculiar 
to  the  milk.  These  are  especially  liable  to  acidification,  and  the  acids 
resulting  from  their  decomposition  give  the  peculiar  odor  and  flavor  to 
rancid  butter. 

Sugar  of  milk,  or  lactose,  is  the  most  abundant  of  the  solid  con- 
stituents of  the  mammary  secretion.  It  is  this  that  gives  to  the  milk 
its  peculiar  sweetish  taste,  although  this  variety  of  sugar  is  much  less 
sweet  than  cane-sugar.     The  chief  peculiarities  of  milk-sugar  are  that 


300  SECRETION 

it  readily  undergoes  change  into  lactic  acid  in  the  presence  of  nitroge- 
nous ferments,  and  that  it  takes  on  alcoholic  fermentation  slowly  and 
with  difficulty.  In  the  fermentation  of  milk,  the  lactose  is  changed  into 
galactose  and  dextrose  and  then  into  alcohol  and  carbon  dioxide.  In 
some  parts  of  the  world  alcoholic  beverages  made  from  milk  are  in 
common  use. 

biorganic  Constituents  of  Milk.  — It  is  probable  that  many  inorganic 
salts  exist  in  the  milk,  that  are  not  given  in  the  table  ;  and  the  separa- 
tion of  these  from  their  combinations  with  organic  matters  is  one  of  the 
most  difficult  problems  in  physiological  chemistry.  This  must  be  the 
case,  for  during  the  first  months  of  extra-uterine  existence,  the  child 
derives  all  the  inorganic  as  well  as  the  organic  matters  necessary  to 
nutrition  and  development,  from  the  breast  of  the  mother.  The  re- 
action of  milk  depends  on  the  presence  of  alkaline  carbonates,  and 
these  are  important  in  preserving  the  fluidity  of  casein.  It  is  not 
determined  precisely  in  what  form  iron  exists  in  the  milk,  but  its 
presence  here  is  undoubted.  A  comparison  of  the  composition  of  the 
milk  with  that  of  the  blood  shows  that  most  of  the  important  inorganic 
matters  found  in  the  latter  exist  also  in  the  milk. 

Carbon  dioxide,  nitrogen  and  oxygen  exist  in  solution  in  milk.  Of 
these  gases,  carbon  dioxide  is  the  most  abundant.  It  is  well  known 
that  the  presence  of  gases  in  solution  in  liquids  renders  them  more 
agreeable  to  the  taste,  and  carbon  dioxide  increases  materially  their 
solvent  properties.  Aside  from  these  considerations,  the  uses  of  the 
gaseous  constituents  of  the  milk  are  not  apparent. 

In  addition  to  the  constituents  given  in  the  table  of  composition, 
the  milk  contains  small  quantities  of  nuclein,  dextrin,  urea,  cholesterin, 
lecithin,  hypoxanthin,  fluorin  and  silica. 

A  study  of  the  composition  of  the  milk  fully  confirms  the  fact  that 
this  is  a  typical  aliment  and  presents  in  itself  the  proper  proportion 
and  variety  of  material  for  the  nourishment  of  the  body  during  the 
period  when  development  is  going  on  with  its  maximum  of  activity. 
The  form  in  which  its  different  nutritive  constituents  exist  is  such  that 
they  are  easily  digested  and  are  assimilated  with  great  rapidity. 
Human  breast-milk  is  the  natural  food  of  the  infant.  It  is  immune  or 
partially  immune  and  may  confer  some  immunity  on  the  nursing 
child.  It  is  bacteriologically  pure  (Welsh).  Passing  directly  from 
breast  to  mouth,  it  is  secure  from  contamination.  It  can  not  be  ade- 
quately replaced  by  any  artificial  substitute. 

Variations  in  the  Composition  of  Milk.  —  If  the  composition  of  the 
milk  is  compared  at  different  periods  of  lactation,  it  will  be  found  to 
undergo  important  changes  during  the  first  few  days.     In  fact,  the  first 


COLOSTRUM  301 

liquid  secreted,  after  parturition,  is  so  different  from  ordinary  milk  that 
it  has  been  called  by  another  name.  It  is  then  known  as  colostrum,  the 
peculiar  properties  of  which  will  be  considered  under  a  distinct  head. 
As  the  secretion  of  milk  becomes  established,  the  Hquid,  from  the  first 
to  the  fifteenth  day,  gradually  becomes  diminished  in  density  and  in  its 
proportion  of  water  and  of  sugar,  while  there  is  a  progressive  increase 
in  the  proportion  of  most  of  the  other  constituents — butter,  casein 
and  the  inorganic  salts.  The  milk,  therefore,  so  far  as  one  can  judge 
from  its  composition,  as  it  increases  in  quantity  during  the  first  few 
days  of  lactation,  is  constantly  increasing  in  nutritive  properties.  The 
differences  in  the  composition  of  the  milk,  taken  from  month  to  month 
during  the  entire  period  of  lactation,  are  not  so  distinctly  marked.  It 
is  difficult,  indeed,  to  indicate  any  constant  variations  of  sufficient  im- 
portance to  lead  to  the  view  that  the  milk  varies  much  in  its  nutritive 
properties  at  different  times  during  the  ordinary  period  of  lactation. 
The  differences  between  the  milk  of  primiparse  and  multiparas  are 
slight  and  unimportant.  As  a  rule,  however,  the  milk  of  primiparae 
approaches  more  nearly  the  normal  standard. 

In  normal  lactation  there  is  no  marked  and  constant  difference  in 
composition  between  milk  that  has  been  secreted  in-  great  abundance 
and  milk  produced  in  comparatively  small  quantity ;  and  the  difference 
between  the  liquid  first  drawn  from  the  breast  and  that  taken  when  the 
ducts  are  nearly  empty,  which  is  observed  in  the  milk  of  the  cow,  has 
not  been  noted  in  human  milk. 

Colostrum 

Near  the  end  of  utero-gestation,  during  a  period  which  varies  con- 
siderably in  different  women  and  has  not  been  accurately  determined, 
a  small  quantity  of  a  thickish  stringy  liquid  frequently  may  be  drawn 
from  the  mammary  glands.  This  bears  little  resemblance  to  perfectly- 
formed  milk.  It  is  small  in  quantity  and  usually  is  more  abundant  in 
multiparas  than  in  primiparae.  This  liquid,  as  well  as  that  secreted  for 
the  first  few  days  after  delivery,  is  called  colostrum.  It  is  yellowish, 
semiopaque,  of  a  distinctly  alkaline  reaction  and  is  somewhat  mucilagi- 
nous in  consistence.  Its  specific  gravity  is  considerably  above  that  of  the 
ordinary  milk,  being  between  1040  and  1060.  As  lactation  progresses, 
the  character  of  the  secretion  rapidly  changes,  until  the  liquid  becomes 
filled  with  true  milk-globules  and  assumes  the  characters  of  ordinary 
milk. 

The  opacity  of  the  colostrum  is  due  to  the  presence  of  a  number  of 
different  corpuscular  elements.  Milk-globules,  variable  in  size  and 
number,  are  to  be  found  in  the  secretion  from  the  first.     These,  how- 


302 


SECRETION 


ever,  do  not  exist  in  sufficient  quantity  to  render  the  liquid  very  opaque, 
and  they  frequently  are  aggregated  in  rounded  or  irregular  masses,  held 
together,  apparently,  by  some  glutinous  matter.  Peculiar  corpuscles, 
supposed  to  be  characteristic  of  the  colostrum,  always  exist  in  this  secre- 
tion.    These  are  known  as  colustrum-corpuscles.     They  are  spherical, 

varying  in  size  between  osVo  ^^"^  soo  °^  ^^  ^^*^^  (^o  ^^^  5°  ^)'  ^^^ 
sometimes  pale,  but  more  frequently  quite  granular,  and  they  contain 
very  often  a  large  number  of  fatty  particles.  They  behave  in  all 
respects    like    leucocytes    and    are    described    as    a    variety    of    these 

bodies.  Many  of  them  are  precisely 
like  the  leucocytes  found  in  the  blood 
and  lymph.  In  addition  to  these  cor- 
puscular elements,  a  small  quantity  of 
mucin  frequently  may  be  observed  in 
the  colostrum  on  microscopical  ex- 
amination. 

On  the  addition  of  ether  to  a 
specimen  of  colostrum  under  the  mi- 
croscope, most  of  the  fatty  particles, 
both  within  and  without  the  colostrum- 
corpuscles,  are  dissolved.  Ammonia 
added  to  the  liquid  renders  it  stringy, 
and  sometimes  the  entire  mass  as- 
sumes a  gelatinous  consistence. 

In  its  composition,  colostrum  pre- 
sents many  points  of  difference  from 
true  milk.  It  is  sweeter  to  the  taste 
and  contains  a  greater  proportion  of 
The  proportion  of  fat  is  at  least  equal 
to  the  proportion  in  the  milk  and  usually  is  greater.  Instead  of  casein, 
colostrum  contains  a  large  proportion  of  serum-albumin ;  and  as  the 
character  of  the  secretion  changes,  the  albumin  gradually  becomes 
reduced  in  quantity  and  casein  takes  its  place. 

The  following  may  be  taken  as  the  ordinary  composition  of  colostrum 
of  the  human  female  (Clemm):  — 


Fig.  64.  —  Colostrum  from  a  healthy  lying-in 
woman  twelve  hours  after  delivery  ,x  40o(Funke). 

The  smaller  globules  are  globules  of  milk. 
The  larger  globules,  a,  a,  filled  with  granules, 
are  colostrum-corpuscles.  As  lactation  ad- 
vances, the  colostrum-corpuscles  gradually  dis- 
appear, and  the  milk-globules  become  more 
abundant,  smaller  and  more  nearly  uniform  in 
size. 

sugar  and  of  the  inorganic  salts. 


COMPOSITION   OF   COLOSTRUM 

Water 945  24 

Albumin,  and  salts  insoluble  in  alcohol       ......  29.81 

Butter 7.07 

Sugar  of  milk,  extractive  matters  and  salts  soluble  in  alcohol       .         .  17-27 

Loss           ............  0.61 


1000.00 


COLOSTRUM  303 

Colostrum  ordinarily  decomposes  more  readily  than  milk  and  rapidly 
takes  on  putrefactive  changes.  If  allowed  to  stand  for  twelve  to  twenty- 
four  hours,  it  separates  into  a  thick,  opaque,  yellowish  cream  and  a 
serous  liquid.  In  an  observation  by  Astley  Cooper,  nine  measures  of 
colostrum,  taken  soon  after  parturition,  after  twenty-four  hours  of 
repose,  gave  six  parts  of  cream  to  three  of  milk. 

The  peculiar  constitution  of  colostrum,  particularly  the  presence  of 
an  excess  of  sugar  and  inorganic  salts,  renders  it  somewhat  laxative  in 
its  effects,  and  it  is  supposed  to  be  useful,  during  the  first  few  days 
after  delivery,  in  assisting  to  relieve  the  infant  of  the  accumulation  of 
meconium. 

As  the  quantity  of  colostrum  that  may  be  pressed  from  the  mam- 
mary glands  during  the  later  periods  of  utero-gestation,  particularly 
the  last  month,  is  variable,  it  becomes  an  important  question  to  deter- 
mine whether  this  secretion  has  any  relation  to  the  quantity  of  milk 
that  may  be  expected  after  delivery.  This  question  has  been  studied 
by  Donne,  who  arrived  at  the  following  conclusions  :  — 

In  women  in  whom  the  secretion  of  colostrum  is  almost  absent,  the 
liquid  being  in  exceedingly  small  quantity,  viscid,  and  containing  hardly 
any  corpuscular  elements,  there  is  hardly  any  milk  produced  after 
delivery. 

In  women  who,  before  delivery,  present  a  moderate  quantity  of 
colostrum,  containing  very  few  milk-globules  and  a  number  of  colos- 
trum-corpuscles, after  delivery  the  milk  will  be  scanty  or  it  may  be 
abundant,  but  it  is  always  of  poor  quality. 

When  the  quantity  of  colostrum  produced  is  considerable,  the  secre- 
tion being  quite  fluid  and  rich  in  corpuscular  elements,  particularly 
milk-globules,  the  milk  after  delivery  is  always  abundant  and  of  good 
quality. 

From  this,  it  would  seem  that  the  production  of  colostrum  is  an 
indication  of  the  proper  development  of  the  mammary  glands ;  and  the 
early  production  of  fatty  granules,  which  are  first  formed  by  the  cells 
fining  the  secreting  vesicles,  indicates  the  probable  activity  in  the  secre- 
tion of  milk  after  lactation  shall  have  become  fully  established. 

The  secretion  of  the  mammary  glands  preserves  the  characters  of 
colostrum  until  toward  the  end  of  the  so-called  milk-fever,  when  the 
colostrum-corpuscles  rapidly  diminish  in  number,  and  the  milk-globules 
become  more  abundant,  regular  and  uniform  in  size.  It  may  be  stated 
in  general  terms  that  the  secretion  of  milk  becomes  fully  established 
and  all  the  characters  of  the  colostrum  disappear  between  the  eighth 
and  tenth  days  after  delivery.  A  few  colostrum-corpuscles  and  masses 
of  agglutinated  milk-globules  may  sometimes  be  discovered  after  the 


304  SECRETION 

tenth  day,  but  they  are  rare.     After  the  fifteenth  day,  the  milk  does 
not  sensibly  change  in  microscopical  or  chemical  characters. 


Lacteal  Secretion  in  the  Newly-Born 

In  infants  of  both  sexes  there  usually  is  a  certain  quantity  of  secre- 
tion from  the  mammary  glands,  beginning  at  birth  or  two  or  three  days 
after  and  continuing  sometimes  for  two  or  three  weeks.  The  quantity 
of  liquid  that  may  be  pressed  out  at  the  nipples  at  this  time  is  variable. 
Sometimes  only  a  few  drops  can  be  obtained,  but  occasionally  it  amounts 
to  one  or  two  drachms  (3.7  or  7.4  grams).  Although  it  is  impossible  to 
indicate  the  object  of  this  secretion,  which  takes  place  when  the  glands 
are  in  a  rudimentary  condition,  it  has  been  so  often  observed  and  de- 
scribed by  physiologists,  that  there  can  be  no  doubt  in  regard  to  the 
nature  of  the  liquid  and  the  fact  that  the  secretion  is  almost  always 
produced  in  greater  or  less  quantity. 


COMPOSITION   OF  THE   MILK   OF  THE   INFANT  (GUBLER) 

Water 894.00 

Casein 26.40 

Sugar  of  milk         .         .  •      .         .         .         .         .         .         .         .         .  62.20 

Butter 14.00 

Earthy  phosphates         ..........  1.20 

Soluble  salts  (with  a  small  quantity  of  insoluble  phosphates)       .         .  2.20 

1000.00 

This  secretion  does  not  differ  much  in  its  composition  from  ordinary 
milk.  The  proportion  of  butter  is  less,  but  the  proportion  of  sugar  is 
greater  and  the  quantity  of  casein  is  nearly  the  same. 

Of  the  other  liquids  classed  as  secretions,  the  saliva,  gastric  juice, 
pancreatic  juice  and  the  intestinal  secretions  have  already  been  described 
in  connection  with  the  physiology  of  digestion.  The  physiology  of  the 
lachrymal  secretion  will  be  taken  up  in  connection  with  the  eye,  and  the 
bile  will  be  treated  of  fully  under  the  head  of  excretion. 


CHAPTER    XII 

EXCRETION    BY    THE    SKIX 

Physiological  anatomy  of  the  skin —  Layers  of  the  skin  —  The  corium,  or  true  ^kin  — The  epi- 
dermis —  Physiological  anatomy  of  the  nails  —  Physiological  anatomy  of  the  hairs  —  Roots 
of  the  hairs,  and  hair-follicles  —  Growth  of  the  hairs  —  Sudden  blanching  of  the  hair  — 
Uses  of  the  hairs  —  Perspiration  —  Quantity  of  cutaneous  exhalation  —  Properties  and 
composition  of  the  sweat. 

Physiological  Anatomy  of  the  Skin 

The  skin  is  one  of  the  most  complex  and  important  structures  in  the 
body  and  has  a  variety  of  uses.  In  the  first  place,  it  forms  a  protec- 
tive covering  for  subjacent  parts.  It  is  quite  thick  over  the  parts  most 
subject  to  pressure  and  friction,  is  elastic  over  movable  parts  and  those 
liable  to  variations  in  size,  and  in  many  situations  is  covered  with  hair. 
The  skin  and  its  appendages  are  imperfect  conductors  of  caloric,  are 
capable  of  resisting  very  considerable  variations  in  temperature,  and 
they  thus  tend  to  maintain  the  normal  standard  of  the  animal  heat.  As 
an  organ  of  sensibility,  the  skin  has  important  uses,  being  abundantl}' 
supplied  with  sensory  nerves,  some  of  which  present  an  arrangement 
peculiarly  adapted  to  the  nice  appreciation  of  tactile  impressions.  The 
skin  assists  in  preserving  the  external  forms  of  the  muscles.  It  also 
relieves  the  abrupt  projections  and  depressions  of  the  general  surface 
and  gives  roundness  and  grace  to  the  contours  of  the  body.  In  some 
parts  it  is  closely  attached  to  the  subjacent  structures,  while  in  others 
it  is  less  adherent  and  rests  on  a  layer  of  adipose  tissue. 

The  skin  is  important  as  an  organ  of  excretion  ;  and  although  the 
quantity  of  excrementitious  matter  exhaled  from  it  is  not  large,  the 
evaporation  of  water  from  the  general  surface  is  considerable  and  is  sub- 
ject to  such  modifications  as  may  become  necessary  from  the  varied 
conditions  of  the  animal  temperature.  Thus,  while  the  skin  protects 
the  body  from  external  influences,  its  office  is  important  in  regulating 
the  heat  that  is  produced  as  one  of  the  phenomena  attendant  on  the 
general  process  of  nutrition. 

Extent  and  Thickness  of  the  Skm.  — -Without  detailing  the  measure- 
ments of  different  parts,  it  may  be  stated  in  general  terms  that  the 
cutaneous  surface  in  a  good-sized  man  is  equal  to  a  Httle  more  than 
sixteen  square  feet  (15,000  square  centimeters);  and  in  men  of  more 


3o6  EXCRETION 

than  ordinary  size,  it  may  extend  to  twenty-one  or  twenty-two  square 
feet  (2  square  meters).  In  women  of  medium  size,  the  surface  is 
equal  to  about  twelve  and  a  half  square  feet  ( 1 1,500  square  centimeters). 
The  true  skin  is  ^^2  ^^  1  ^^  ^^  ^^^^  (^-^  ^^  3-^  millimeters)  in  thickness ; 
but  in  certain  parts,  particularly  in  the  external  auditory  meatus,  the  Hps 
and  the  glans  penis,  it  frequently  measures  not  more  than  jlo  of  an  inch 
(0.254  millimeter). 

Layers  of  the  Skin.  —  The  skin  is  naturally  divided  into  two  principal 
layers,  which  may  be  readily  separated  from  each  other  by  maceration. 
These  are  the  true  skin  —  cutis  vera,  derma,  or  corium  —  and  the  epi- 
dermis, cuticle,  or  scarf-skin.  The  true  skin  is  more  or  less  closely 
attached  to  subjacent  parts  by  a  fibrous  structure  called  the  subcuta- 
neous areolar  tissue,  in  the  meshes  of  which  there  usually  is  a  certain 
quantity  of  adipose  tissue.  This  layer  is  sometimes  described  under 
the  name  of  the  panniculus  adiposus.  The  thickness  of  the  adipose 
layer  varies  in  different  parts  of  the  general  surface  and  in  different 
persons.  There  is  no  fat  beneath  the  skin  of  the  eyelids,  the  upper  and 
outer  part  of  the  ear,  the  penis  and  the  scrotum.  Beneath  the  skin  of 
the  cranium,  the  nose,  the  neck,  the  dorsum  of  the  hand  and  foot,  the 
knee  and  the  elbow,  the  fatty  layer  is  about  y^^  o^  ^^  \xvz\i  (2.1  milli- 
meters) in  thickness.  In  other  parts  it  usually  measures  \  to  \  of  an 
inch  (4.2  to  12.7  millimeters).  In  very  fat  persons  it  may  measure  an 
inch  (25.4  millimeters)  or  more.  On  the  head  and  the  neck,  in  the 
human  subject,  are  muscles  attached  more  or  less  closely  to  the  skin. 
These  are  capable  of  moving  the  skin  to  a  slight  extent.  Muscles  of 
this  kind  are  largely  developed  and  quite  extensively  distributed  in  some 
of  the  lower  animals. 

There  is  no  sharply-defined  line  of  demarcation  between  the  cutis 
and  the  subcutaneous  areolar  tissue ;  and  the  under  surface  of  the  skin 
is  irregular,  from  the  presence  of  fibres  that  are  divided  necessarily  in 
detaching  it  from  the  subjacent  structures.  The  fibres  which  enter  into 
the  composition  of  the  skin  become  looser  in  their  arrangement  near  its 
under  surface,  the  change  taking  place  rather  abruptly,  until  they  present 
large  alveoli,  which  usually  contain  a  certain  quantity  of  adipose  tissue. 

The  layer  called  the  true  skin  is  subdivided  into  a  deep,  reticulated, 
or  fibrous  layer,  and  a  superficial  portion,  called  the  papillary  layer. 
The  epidermis  also  is  divided  into  two  layers,  as  follows :  an  external 
layer,  called  the  horny  layer;  and  an  internal  layer,  called  the  Mal- 
pighian,  or  the  mucous  layer,  which  is  in  contact  with  the  papillary 
layer  of  the  corium. 

TJic  Coruim,  or  True  Skin.  —  The  reticulated  and  the  papillary 
layers  of   the    true    skin  are  quite  distinct.     The  lower  stratum  —  the 


PHYSIOLOGICAL   ANATOMY    OF    THE    SKIN  307 

reticulated  layer  —  is  much  thicker  than  the  papillary  layer  and  is 
dense,  resisting,  quite  elastic  and  slightly  contractile.  It  is  composed 
of  bundles  of  fibrous  tissue,  interlacing  with  each  other  in  every  direc- 
tion, usually  at  acute  angles.  Distributed  throughout  this  layer  are 
found  anastomosing  elastic  fibres  of  the  small  variety,  and  with  them  a 
number  of  non-striated  muscular  fibres.  This  layer  contains  in  addition 
a  considerable  quantity  of  amorphous  matter,  which  serves  to  hold  the 
fibres  together.  The  muscular  fibres  are  particularly  abundant  about 
the  hair-follicles  and  the  sebaceous  glands  connected  with  them,  and 
their  arrangement  is  such  that  when  they  are  excited  to  contraction  by 
cold  or  by  electricity,  the  follicles  are  drawn  up,  projecting  on  the 
general  surface  and  producing  the  appearance  known  as  "goose-flesh." 
Contraction  of  these  fibres  is  especially  marked  about  the  nipple,  pro- 
ducing the  so-called  erection  of  this  organ,  and  about  the  scrotum  and 
penis,  wrinkling  the  skin  of  these  parts.  The  peculiar  arrangement  of 
the  little  muscles  around  the  hair-follicles,  forming  little  bands  attached 
to  the  surface  of  the  true  skin  and  the  base  of  the  follicles,  explains 
fully  the  manner  in  which  the  "goose-flesh"  is  produced  (see  Fig. 
67,  page  312). 

The  papillary  layer  of  the  skin  passes  insensibly  into  the  subjacent 
structure  without  any  marked  line  of  division.  It  is  composed  chiefly 
of  amorphous  matter  like  that  which  exists  in  the  reticulated  layer.  The 
papillae  themselves  appear  to  be  simple  elevations  of  this  amorphous 
matter,  although  they  contain  a  few  fibres  and  connective-tissue  nuclei. 

As  regards  form,  the  papillae  may  be  divided  into  two  varieties :  the 
simple  and  the  compound.  The  simple  papillae  are  conical,  rounded  or 
club-shaped  elevations  of  the  amorphous  matter  and  are  irregularly  dis- 
tributed on  the  general  surface.  The  smallest  are  j^  to  ^^  of  an  inch 
(36  to  62/jl)  in  length  and  are  found  chiefly  on  the  face.  The  largest 
are  on  the  palms  of  the  hands,  the  soles  of  the  feet  and  the  nipple. 
These  measure  o^o"  ^^  2^0"  °^  ^n  inch  (100  to  125/i).  Large  papillae, 
regularly  arranged  in  a  longitudinal  direction,  are  found  beneath  the 
nails.  The  regular  curved  lines  observed  on  the  palms  of  the  hands 
and  the  soles  of  the  feet,  particularly  the  palmar  surfaces  of  the  last 
phalanges,  are  formed  by  double  rows  of  compound  papillae,  which 
present  two,  three  or  four  elevations  attached  to  a  single  base.  In  the 
centre  of  each  of  these  double  rows  of  papillae,  is  a  fine  and  shallow 
groove,  in  which  are  found  the  orifices  of  the  sudoriferous  ducts. 

The  papillae  are  abundantly  supplied  with  bloodvessels  terminating 
in  looped  capillary  plexuses  and  with  nerves.  The  termination  of  the 
nerves  is  peculiar  and  will  be  fully  described  in  connection  with  the 
organs  of  touch.     The  arrangement  of  the  lymphatics,  which  are  very 


3o8  EXCRETION 

abundant  in  the  skin,  has  already  been  indicated  in  the  general  descrip- 
tion of  the  lymphatic  system. 

TJie  Epider'mis  and  its  Appendages.  —  The  epidermis,  or  external 
layer  of  the  skin,  is  composed  of  cells.  It  has  neither  bloodvessels, 
nerves  nor  lymphatics.  Its  external  surface  is  marked  with  shallow 
grooves,  which  correspond  to  the  deep  furrows  between  the  papillae  of 
the  derma.  Its  internal  surface  is  applied  directly  to  the  papillary  layer 
of  the  true  skin  and  follows  closely  all  its  inequalities.  This  portion  of  the 
skin  is  subdivided  into  two  layers.  The  internal  layer  is  called  the  rete 
mucosum,  or  the  Malpighian  layer,  and  the  external  is  called  the  horny 
layer.     These  layers  present  certain  important  distinctive  characters. 

The  Malpighian  layer  is  composed  of  a  stratum  of  prismoidal  nu- 
cleated cells,  containing  pigmentary  matter,  and  a  number  of  layers 
of  rounded  cells  without  pigment.  The  upper  layers  of  cells  are  semi- 
transparent  and  nearly  colorless ;  and  it  is  the  pigmentary  layer  chiefly 
that  gives  to  the  skin  its  characteristic  color.  All  the  epidermic  cells  are 
somewhat  colored  in  the  dark  races,  but  the  upper  layers  contain  no 
pigmentary  granules.  The  thickness  of  the  rete  mucosum  is  ^yo  ^  to  y^^ 
of  an  inch  (15  to  333  a^)- 

The  horny  layer  is  composed  of  strata  of  hard  flattened  cells,  irregu- 
larly polygonal  in  shape  and  usually  without  nuclei.  The  deeper  cells 
are  thicker  and  more  rounded  than  those  of  the  superficial  layers,  are 
polygonal  in  form  and  their  borders  present  a  great  number  of  short 
protoplasmic  spines.  These  are  called  prickle-cells.  There  is  constantly 
more  or  less  desquamation  of  the  epidermis,  particularly  of  the  horny 
layer,  and  the  cells  are  regenerated  from  the  subjacent  parts. 

Physiological  Anatomy  of  the  Nails.  — The  nails  are  situated  on  the 
dorsal  surfaces  of  the  distal  phalanges  of  the  fingers  and  toes.  They 
serve  to  protect  these  parts,  and  in  the  fingers,  they  are  quite  important 
in  prehension.  The  general  appearance  of  the  nails  is  sufficiently 
familiar.  In  their  description  anatomists  have  distinguished  a  root,  a 
body  and  a  free  border. 

The  root  of  the  nail  is  thin  and  soft,  terminating  in  rather  a  jagged 
edge,  which  is  turned  slightly  upward  and  is  received  into  a  fold  of  the 
skin  extending  around  the  nail  to  its  free  edge.  The  length  of  the  root 
varies  with  the  size  of  the  nail,  but  it  usually  is  one-fourth  to  one-third 
of  the  length  of  the  body. 

The  body  of  the  nail  extends  from  the  fold  of  skin  covering  the  root 
to  the  free  border.  This  portion  of  the  nail,  with  the  root,  is  closely 
adherent  by  its  under  surface  to  the  true  skin.  It  is  marked  by  fine  but 
distinct  longitudinal  striae  and  very  faint  transverse  lines.  It  usually 
presents  a  reddish   color  on   account  of  the  great  vascularity  of  the 


PHYSIOLOGICAL    ANATOMY  OF   THE   NAILS 


309 


subjacent  structure.  At  the  posterior  part,  is  a  whitish  portion,  of  a  semi- 
lunar shape,  called  the  lunula,  which  has  this  appearance  simply  from 
the  fact  that  the  corium  in  this  part  is  less  vascular  and  the  papillae  are 
not  so  regular  as  in  the  rest  of  the  body.  The  skin  beneath  the  root 
and  body  of  the  nail  is  called  the  matrix.  It  presents  highly  vascular 
papillae  arranged  in  longitudinal  rows,  and  it  receives  into  its  grooves 
corresponding  ridges  on  the  under  surface  of  the  nail. 

On  examining  the  nail  in  a  longitudinal  section,  the  horny  layer  is 
found  to  increase  progressively  in  thickness  from  the  root  to  near  the  free 
border.  Examined  in  transverse  section,  the  nail  will  also  be  found  much 
thicker  in  the  central  portion  than  near  the  edge,  and  that  part  which  is 
received  into  the  lateral  portions  of  the  fold  becomes  thin  like  the  rest 
of  the  root.     The  nail  becomes  thinner  at  and  near  the  free  border. 


9      1      5  106    2  7     3     « 


"       ■  712 


Fig.  65. — Anatomy  of  the  nails  (Sappey). 

A,  nail  in  situ :  i,  cutaneous  fold  covering  the  root  of  the  nail ;  2,  section  of  this  fold,  turned  back 
to  show  the  root  of  the  nail ;  3,  lunula ;  4,  nail.  B,  concave  or  adherent  surface  of  the  nail :  i,  border 
of  the  root;  2,  lunula  and  root ;  3,  body;  4,  free  border.  C,  longitudinal  section  of  the  nail :  1,2,  epi- 
dermis; 3,  superficial  layer  of  the  nail ;  4,  epidermis  of  the  pulp  of  the  finger;  5,  6,  true  skin  ;  7, 11,  bed 
of  the  nail ;  8,  Malpighian  layer  of  the  pulp  of  the  finger;  9,  10,  true  skin  on  the  dorsal  surface  of  the 
finger ;  12,  true  skin  of  the  pulp  of  the  finger ;   13,  last  phalanx  of  the  finger. 

The  two  layers  correspond  to  the  Malpighian  and  the  horny  layers  of 
the  epidermis,  although  they  are  more  distinct.  The  Malpighian  layer 
is  applied  directly  to  the  ridges  of  the  bed  of  the  nail  and  presents 
ridges  much  less  strongly  marked  than  those  of  the  underlying  true 
skin.  This  layer  is  rather  thinner  than  the  horny  layer,  is  whitish  in 
color  and  is  composed  of  elongated  prismoidal  nucleated  cells  arranged 
perpendicularly  to  the  matrix. 

The  horny  layer  —  which  constitutes  the  true  nail  —  is  applied  by  its 
under  surface  directly  to  the  ridges  of  the  Malpighian  layer.  It  is  com- 
posed of  strata  of  flattened  nucleated  cells  which  can  not  be  isolated 
without  the  use  of  reagents.  After  boiling  in  a  dilute  solution  of  sodium 
or  potassium  hydrate,  it  becomes  evident  that  here,  as  in  the  horny  layer 
of  the  epidermis,  the  lower  cells  are  rounded  and  those  nearer  the 
surface  are  flattened.  The  thickness  of  this  layer  varies  while  that  of 
the  Malpighian  layer  is  nearly  uniform.  This  layer  is  constantly  grow- 
ing, and  it  constitutes  the  entire  substance  of  the  free  borders  of  the  nails. 


310 


EXCRETION 


The  connections  of  the  nails  with  the  true  skin  resemble  those  of  the 
epidermis  ;  but  the  relations  of  these  structures  to  the  epidermis  itself 
are  somewhat  peculiar.  Before  the  fourth  month  of  foetal  life,  the  epi- 
dermis covering  the  dorsal  surfaces  of  the  last  phalanges  of  the  fingers 
and  toes  does  not  present  any  marked  peculiarities ;  but  at  about  the 

fourth  month,  the  hard  cells 
of  the  horny  layer  of  the  nails 
make  their  appearance  be- 
tween the  Malpighian  and 
the  horny  layers  of  the  epi- 
dermis, and  at  the  same  time 
the  Malpighian  layer  beneath 
this  plate,  which  is  destined  to 
become  the  Malpighian  layer 
of  the  nails,  is  thickened  and 
the  cells  assume  a  more  elon- 
gated form.  The  horny  layer 
of  the  nails  constantly  thickens 
from  this  time ;  but  until  the 
end  of  the  fifth  month,  it  is 
covered  with  the  horny  layer 
of  the  epidermis.  After  the 
fifth  month,  the  epidermis 
breaks  away  and  disappears 
from  the  surface ;  and  at  the 
seventh  month,  the  nails  begin 
to  increase  in  length.  Thus, 
at  one  time  the  nails  are  actu- 
ally included  between  the  two 
layers  of  the  epidermis ;  but 
after  they  have  become  devel- 
oped, they  simply  are  covered 
at  their  roots  by  a  narrow 
border  of  the  horny  layer.  The  nails  are  therefore  to  be  regarded  as 
modifications  of  the  horny  layer  of  the  epidermis,  possessing  certain 
anatomical  and  chemical  peculiarities.  The  Malpighian  layer  of  the  nails 
is  continuous  with  the  corresponding  layer  of  the  epidermis,  but  the 
horny  layers  are  distinct. 

Physiological  Anatomy  of  the  Hairs.  —  Hairs,  varying  greatly  in  size, 
cover  nearly  every  portion  of  the  cutaneous  surface.  The  only  parts  in 
which  they  are  not  found  are  the  palms  of  the  hands  and  soles  of  the 
feet,  the  palmar  surfaces  of  the  fingers  and  toes,  the  dorsal  surfaces  of 


IP 


lk!.if.''jrM 


Fig.  66.  —  Section  of  the  nail  (Sappey). 

A,  section  of  the  nail:  i,  i,  superficial  layer;  2,  deep 
layer ;  3,  3,  4,  4,  section  of  the  grooves  on  the  attached  sur- 
face ;  5,  5,  union  of  the  superficial  with  the  deep  layer ; 
6,  dark  line  between  the  two  layers. 

B,  cells  of  the  superficial  layer,  lateral  view. 

C,  cells  of  the  superficial  layer,  flat  view. 

D,  cells  of  the  deep  layer. 


PHYSIOLOGICAL    ANATOMY    OF    THE    HAIRS  311 

the  last  phalanges  of  the  fingers  and  toes,  the  lips,  the  upper  eyelids, 
the  lining  of  the  prepuce,  and  the  glans  penis.  Some  of  the  hairs  are 
long,  others  are  short  and  stiff,  and  others  are  fine  and  downy.  These 
differences  have  led  to  a  division  of  the  hairs  into  three  varieties  :  — 

The  first  variety  includes  the  long  soft  hairs,  found  on  the  head,  on 
the  face  in  the  male  adult,  around  the  genital  organs  and  under  the  arms 
in  both  the  male  and  the  female,  and  sometimes  on  the  breast  and  over 
the  general  surface  of  the  body  and  extremities,  particularly  in  the  male. 

The  second  variety,  the  short  stiff  hairs,  is  found  just  within  the 
nostrils,  on  the  edges  of  the  eyelids  and  on  the  eyebrows. 

The  third  variety,  the  short,  soft,  downy  hairs,  is  found  on  parts  of 
the  general  surface  not  provided  with  the  long  hairs,  and  in  the  carun- 
cula  lachrvmalis.  In  earlv  life  and  ordinarilv  in  the  female  at  all  agfes, 
the  trunk  and  extremities  are  covered  with  downy  hairs  ;  but  in  the  adult 
male,  these  frequently  become  developed  into  long  soft  hairs. 

The  hairs  usually  are  set  obliquely  in  the  skin  and  take  a  definite 
direction  as  they  lie  on  the  surface.  On  the  head  and  face,  and,  indeed, 
the  entire  surface  of  the  body,  the  general  course  of  the  hairs  mav  be 
followed  out;  and  they  present  currents  or  sweeps  that  have  nearly 
always  the  same  directions. 

The  diameter  and  length  of  the  hairs  are  variable  in  different  per- 
sons, especially  in  the  long  soft  hairs  of  the  head  and  beard.  It  may 
be  stated  in  general  terms  that  the  long  hairs  attain  the  length  of  twenty 
inches  to  three  feet  ( 500  to  900  millimeters)  in  women,  and  considerably 
less  in  men.  Like  the  nails,  the  hair,  when  left  to  itself,  attains  in  three 
or  four  years  a  definite  length,  but  when  it  is  habituallv  cut  it  grows 
constantly.  The  short  stiff  hairs  are  ^  to  i-  of  an  inch  (6.4  to  12.7  milli- 
meters) in  length.  The  soft  downy  hairs  measure  ordinarilv  -^  to  I  of 
an  inch  (2.1  to  12.7  millimeters)  in  length. 

Of  the  long  hairs,  the  finest  are  on  the  head,  where  thev  average 
about  ^^^  of  an  inch  (64  fj.)  in  diameter.  The  hair  ordinarily  is  coarser 
in  women  than  in  men.  Dark  hair  usually  is  coarser  than  light  hair; 
and  on  the  same  head  the  extremes  of  variation  are  sometirnes  observed. 
The  hairs  of  the  beard  and  the  long  hairs  of  the  body  are  coarser  than 
the  hairs  of  the  head.  The  average  number  of  hairs  on  a  square  inch 
of  the  scalp  is  about  looo  (155  in  a  square  centimeter)  and  the  number 
on  the  head,  about  120,000  (Wilson). 

In  a  normal  condition  the  hairs  are  elastic  and  may  be  stretched  to 
one-fifth  or  one-third  more  than  their  original  length.  Their  strength 
varies  with  their  thickness,  but  an  ordinary  hair  from  the  head  will  bear 
a  weight  of  six  to  seven  ounces  (170  to  200  grams).  A  well-known  prop- 
erty of  the  hair  is  that  of  becoming  strongly  electric  by  friction  ;  and  this 


31 


EXCRETION 


is  particularly  marked  when  the  weather  is  cold  and  dry.  The  electricity 
thus  excited  is  negative.     Sections  of  the  shaft  of  the  hairs  show  that 

they  are  oval,  but  their  shape  is  va- 
riable, straight  hairs  being  nearly 
round  while  curled  hairs  are  quite 
flat.  Another  peculiarity  of  the 
hairs  is  that  they  are  hygrometric. 
They  readily  absorb  moisture  and 
become  sensibly  elongated,  a  prop- 
erty that  has  been  made  use  of 
by  physicists  in  the  construction  of 
hygrometers. 

Roots  of  the  Hairs,  and  Hair- 
follicles.  —  The  roots  of  the  hairs 
are  embedded  in  follicular  open- 
ings in  the  skin,  which  differ  in 
the  different  varieties  only  in  the 
depth  to  which  they  penetrate  the 
cutaneous  structure.  In  the  downy 
hairs,  the  roots  pass  into  the  super- 
ficial layers  only  of  the  true  skin  ; 
but  in  the  thicker  hairs,  the  roots 
pass  through  the  skin  and  penetrate 
the  subcutaneous  cellulo-adipose 
tissue. 

The  root  of  the  hair  is  softer, 
rounder  and  a  little  larger  than  the 
shaft.  It  becomes  enlarged  into  a 
rounded  bulb  at  the  bottom  of  the 
follicle,  and  rests  on  a  fungiform 
papilla,  constricted  at  its  base,  to 
which  the  hair  is  closely  attached. 

The  hair-follicles  are  tubular 
inversions  of  the  structures  that 
compose  the  corium,  and  their 
walls  present  three  membranes. 
Their  length  is  -^^  to  \  of  an  inch 

licle;  II,  simple  sebaceous  gland;  12,  opening  of  (3. 1  tO  6.4  millimeters).  The  mcm- 
the  hair-follicle.  ^  ^  ' 

brane  that  forms  the  external  coat 
of  the  follicles  is  composed  of  inelastic  fibres  usually  arranged  longi- 
tudinally. It  is  provided  with  bloodvessels,  a  few  nerves  and  some 
connective-tissue  elements,  but  no  elastic  tissue.     This  is  the  thickest 


Fig.  67.  —  Hair  and  hair-follicle  (Sappey). 

I,  root  of  the  hair;  2,  bulb  of  the  hair;  3,  in- 
ternal root-sheath  ;  4,  external  root-sheath  ;  5,  mem- 
brane of  the  hair-follicle  (the  internal,  amorphous 
membrane  of  the  follicle  is  very  delicate  and  is  not 
represented  in  the  figure)  ;  6,  external  membrane 
of  the  follicle  ;  7,  7,  muscular  bands  attached  to  the 
follicle ;  8,  8,  extremities  of  these  bands  passing  to 
the  skin;  9,  compound  sebaceous  gland,  with  its 
duct  (10)  opening  into  the  upper  third  of  the  fol- 


STRUCTURE   OF   THE   HAIRS 


313 


of  the  three  membranes  and  is  closely  connected  with  the  corium.  Next 
to  this,  is  a  fibrous  membrane  composed  of  fusiform  nucleated  fibres 
arranged  transversely.  These  resemble  non-striated  muscular  fibres. 
The  internal  membrane  is  structureless  and  cor- 
responds to  the  amorphous  layer  of  the  true  skin. 
The  papilla  at  the  bottom  of  the  hair-sac  varies 
in  size  with  the  size  of  the  hairs  and  is  connected 
with. the  fibrous  layers  of  the  walls  of  the  follicle. 
It  is  composed  of  amorphous  matter,  with  a  few 
granules  and  nuclei,  and  it  probably  contains 
bloodvessels  and  nerves,  although  these  are  not 
very  distinct. 

The  investment  of  the  root  of  the  hair  pre- 
sents two  distinct  layers  called  the  external  and 
internal  root-sheaths.  The  external  root-sheath 
is  three  or  four  times  as  thick  as  the  inner  mem- 
brane, and  it  corresponds  exactly  to  the  Malpi- 
ghian  layer  of  the  epidermis.  This  sheath  is 
continuous  with  the  bulb  of  the  hair.  The  in- 
ternal root-sheath  is  a  transparent  membrane  com- 
posed of  flattened  cells,  usually  without  nuclei. 
This  extends  from  the  bottom  of  the  hair-follicle 
and  covers  the  lower  two-thirds  of  the  root  (see 
Plate  VI). 

Structure  of  the  Hairs.  —  The  different  varie- 
ties of  hairs  present  certain  peculiarities  in  their 
anatomy,  but  they  are  all  composed  of  a  fibrous 
structure,  forming  the  greater  part  of  their  sub- 
stance, covered  by  a  thin  layer  of  imbricated  cells. 
In  the  short  stiff  hairs  and  in  the  long  white 
hairs,  there  is  a  distinct  medullary  substance ; 
but  this  is  wanting  in  the  downy  hairs  and  is 
indistinct  in  many  of  the  long  dark  hairs. 

The  fibrous  substance  of  the  hairs  is  com- 
posed of  hard,  elongated,  longitudinal  fibres, 
which  can  not  be  isolated  without  the  aid  of 
reagents 


Fig.  68.  —  Root  of  the  hair 
(Sappey). 

I,  root  of  the  hair;  2,  hair- 
bulb  ;  3,  papilla  of  the  follicle  ; 
4,  opening  of  the  follicle  ;  5,  5, 
internal  root-sheath  ;  6,  exter- 
nal  root-sheath  ;     7,  7,  seba- 

They  may  be  separated,  however,  by  ceous  glands;  8,  8,  excretory 

,    ,        .  .  ,         ,  ,  ducts  of  the  sebaceous  glands. 

maceration  m  warm   sulphuric  acid,  when  they 

present  themselves  in  the  form  of  dark  irregular  spindle-shaped  plates. 
These  contain  pigmentary  matter  of  various  shades  of  color,  occasional 
cavities  filled  with  air  and  a  few  nuclei.  The  pigment  may  be  of  any 
shade  between  a  light  yellow  and  an  intense  black;  and  it  is  this  sub- 


314  EXCRETION 

stance  that  gives  to  the  hair  the  variety  in  color  observed  in  different 
persons.  In  the  lower  part  of  the  root  the  fibres  are  much  shorter,  and 
at  the  bulb  they  are  transformed  into  the  soft  rounded  cells  found  in 
this  situation  and  covering  the  papilla. 

The  epidermis  of  the  hair  is  thin  and  is  composed  of  flattened 
quadrangular  plates,  overlying  each  other  from  below  upward.  These 
scales,  or  plates,  are  without  nuclei,  and  they  exist  in  a  single  layer  over 
the  shaft  of  the  hair  and  the  upper  part  of  its  root ;  but  in  the  Ipwer 
part  of  the  root,  the  cells  are  thicker,  softer,  frequently  are  nucleated, 
and  they  exist  in  two  layers. 

The  medulla  is  found  in  the  short  stiff  hairs,  and  it  is  often  quite 
distinct  in  the  long  white  hairs  of  the  head.  It  occupies  one-fourth  to 
one-third  of  the  diameter  of  the  hair.  The  medulla  can  be  traced  from 
just  above  the  bulb  to  near  the  pointed  extremity  of  the  hair.  It  is 
composed  of  small,  rounded,  nucleated  cells,  which  often  contain 
dark  granules  of  pigmentary  matter.  Mixed  with  these  cells  are  air- 
globules  ;  and  frequently  the  cells  are  interrupted  for  a  short  distance 
and  the  space  is  filled  with  air.  The  medulla  likewise  contains  a  gluti- 
nous substance  between  the  cells  and  surrounding  the  air-globules  (see 
Plate  VII,  Fig.  i,  for  transverse  sections  of  hairs). 

Grozvth  of  the  Hairs.  —  Although  not  provided  with  blood  and 
devoid  of  sensibility,  the  hairs  are  connected  with  vascular  parts  and 
are  nourished  by  imbibition  from  the  papillae.  Each  hair  is  first  de- 
veloped in  a  closed  sac,  and  at  about  the  sixth  month  of  intra-uterine 
life,  its  pointed  extremity  perforates  the  epidermis.  These  first-formed 
hairs  are  afterward  shed,  like  the  milk-teeth,  being  pushed  out  by  new 
hairs  from  below,  which  latter  arise  from  a  second  and  more  deeply 
seated  papilla.  The  shedding  of  the  hairs  usually  takes  place,  between 
the  second  and  the  eighth  month  after  birth. 

The  differences  in  the  color  of  the  hair  depend  on  differences  in  the 
quantity  and  the  tint  of  the  pigmentary  matter  ;  and  in  old  age  the  hair 
becomes  white  or  gray  from  a  blanching  of  the  cortex  and  medulla. 

Sudden  Blanching  of  the  Hair. — There  are  a  few  instances  on 
record  in  which  sudden  blanching  of  the  hair  has  been  observed  and 
the  causes  of  this  remarkable  change  fully  investigated.  One  of  these 
cases  has  been  reported  by  Landois.  In  this  instance  the  blanching 
of  the  hair  occurred  in  a  hospital  in  a  single  night,  while  the  patient, 
who  had  an  acute  attack  of  delirium  tremens,  was  under  the  daily  obser- 
vation of  the  visiting  physician.  The  microscopical  examinations  by 
Landois  and  others  leave  no  doubt  as  to  the  cause  of  the  white  color  of 
the  hair  in  cases  of  sudden  blanching  ;  and  the  fact  of  the  occurrence 
of  this  phenomenon  can  no  longer  be  called  in  question.    All  are  agreed 


PERSPIRATION 


315 


that  there  is  no  diminution  in  the  pigment,  but  that  the  greater  part  of 
the  medulla  becomes  filled  with  air,  small  globules  being  also  found  in 
the  cortical  substance.  The  hair  in  these  cases  presents  a  marked 
contrast  with  hair  that  has  gradually  become  gray  from  old  age,  when 
there  is  always  a  loss  of  pigment  in  the  cortex  and  medulla.  How  the 
air  finds  its  way  into  the  hair  in  sudden  blanching,  it  is  difficult  to 
understand ;  and  the  views  that  have  been  expressed  on  this  subject  by 
different  authors  are  entirely  theoretical. 

The  fact  that  the  hair  may  become  white  or  gray  in  the  course  of  a 
few  hours  renders  it  probable  that  many  of  the  cases  reported  on  unsci- 
entific authority  actually  occurred  ;  and  these  have  all  been  supposed 
to  be  connected  with  intense  grief  or  terror.  The  terror  was  very 
marked  in  the  case  reported  by  Landois.  In  the  great  majority  of 
recorded  observations,  the  sudden  blanching  of  the  hair  has  been  appar- 
ently connected  with  intense  niental  emotion ;  but  this  is  all  that  can 
be  said  on  the  subject  of  causation,  and  the  mechanism  of  the  change 
is  not  understood. 

Uses  of  the  Hair.  —  The  hairs  serve  an  important  purpose  in  the 
protection  of  the  general  surface  and  in  guarding  certain  of  the  orifices 
of  the  body.  The  hair  on  the  head  and  face  protects  from  cold  and 
shields  the  head  from  the  rays  of  the  sun  during  exposure  in  hot  cli- 
mates. Although  the  quantity  of  hair  on  the  general  surface  is  small,  as 
it  is  an  imperfect  conductor  of  caloric,  it  serves  in  a  degree  to  maintain 
the  heat  of  the  body.  It  also  moderates  the  friction  upon  the  surface. 
The  eyebrows  prevent  the  perspiration  from  running  from  the  forehead 
upon  the  lids ;  the  eyelashes  protect  the  surface  of  the  conjunctiva 
from  dust  and  other  foreign  matters  ;  the  mustache  protects  the  lungs 
from  dust,  which  is  very  important  in  persons  exposed  to  dust  in  long 
journeys  or  in  their  daily  work ;  and  the  short  stiff  hairs  at  the  open- 
ings of  the  ears  and  nose  protect  these  orifices.  It  is  difficult  to  assign 
any  special  oflfice  to  the  hairs  in  some  other  situations,  but  their  general 
uses  are  sufificiently  evident. 

Perspiration 

In  the  fullest  acceptation  of  the  term,  perspiration  embraces  the 
entire  action  of  the  skin  as  an  excreting  organ  and  includes  the  exhala- 
tion of  carbon  dioxide  as  well  as  of  watery  vapor  and  organic  matters. 
The  office  of  the  skin  as  an  eliminator  is  important ;  but  the  quantity  of 
excrementitious  matters  with  the  properties  of  which  physiologists  are 
well  acquainted,  such  as  carbon  dioxide  and  urea,  thrown  off  from  the 
general  surface,  is  small  as  compared  with  what  is  exhaled  by  the  lungs 
and  discharged  by  the  kidneys.     If  the  surface  of  the  body  is  covered 


3i6 


EXCRETION 


with  an  impermeable  coating,  death  occurs  in  a  very  short  time,  with 
great  reduction  in  the  body-temperature  due  to  excessive  radiation  from 
the  varnished  surface,  the  temperature  being  reduced  to  about  70°  Fahr. 
(21°  C.)-  Warm-blooded  animals  die  usually  when  more  than  one-half 
of  the  general  surface  has  been  varnished.  Rabbits  die  when  one- 
fourth  of  the  surface  has  been  covered  with  an  impermeable  coating 
(Laschkewitsch).  Valentin  and  Laschkewitsch  found  that  when  the 
temperature  was  kept  at  about  the  normal  standard  by  artificial  means, 
no  morbid  symptoms  were  developed. 

Sudoriparous  Glands.  —  With  few  exceptions,  all  parts  of  the  skin 
are  provided  with  sudoriparous  glands.  They  are  not  found,  however, 
in  the  skin  covering  the  concave  surface  of  the  concha  of  the  ear,  the 
glans  penis,  the  inner  lamella  of  the  prepuce  and,  unless  the  ceruminous 

glands  are  regarded  as  sudoriparous  or- 
gans, in  the  external  auditory  meatus. 

On  examining  the  surface  of  the  skin 
with  a  low  magnifying  power,  especially 
on  the  palms  of  the  hands  and  the  soles 
of  the  feet,  the  openings  of  the  sudorifer- 
ous ducts  may  be  seen  in  the  middle  of 
the  papillary  ridges,  forming  a  regular 
line  in  the  shallow  groove  between  the 
two  rows  of  papillae.  The  tubes  always 
open  on  the  surface  obliquely.  In  a  thin 
section  of  the  skin,  the  ducts  are  seen 
passing  through  the  different  layers  and 
terminating  in  rounded  convoluted  coils 
in  the  subcutaneous  structure.  These 
Httle  rounded  or  ovoid  bodies,  which  are 
the  sudoriparous,  or  sweat-producing  structures,  may  be  seen  attached 
to  the  under  surface  of  the  skin  after  it  has  been  removed  from  the  sub- 
jacent parts  by  maceration.  A  perspiratory  gland  consists,  indeed,  of  a 
simple  tube,  presenting  a  coiled  mass,  the  sudoriparous  portion,  beneath 
the  skin,  and  a  tube  of  greater  or  less  length  in  proportion  to  the 
thickness  of  the  cutaneous  layers,  which  is  the  excretory  duct,  or  the 
sudoriferous  portion. 

The  glandular  coils  are  y^-^  to  2V  of  an  inch  (0.2  to  i  millimeter)  in 
diameter  ;  the  smallest  coils  being  found  beneath  the  skin  of  the  penis, 
the  scrotum,  the  eyelids,  the  nose  and  the  convex  surface  of  the  concha  of 
the  ear,  and  the  largest,  on  the  areola  of  the  nipple  and  on  the  perineum. 
Very  large  glands  are  found  mixed  with  smaller  glands  in  the  axilla,  and 
these  produce  a  peculiar  secretion.     The  coiled  portion  of  the  tube  is 


Fig.  69.  —  Surface  of  the  palm  of  the 
hand,  a  portion  of  the  skin  about  one-half 
an  inch  (12.5  millimeters)  square,  x  3I 
(Sappey). 

I,  I,  I,  I,  openings  of  the  sudoriferous 
ducts ;  2,  2,  2,  2,  grooves  between  the 
papillae  of  the  skin. 


SUDORIPAROUS    GLANDS  317 

about  3^0  of  an  inch  (0.07  inillimeter)  in  diameter,  and  presents  six  to 
twelve  turns.  It  consists  of  a  sharply-defined  strong  external  mem- 
brane, which  is  very  transparent,  uniformly  granular  and  sometimes  in- 
distinctly striated.  The  tube  is  of  uniform  diameter  throughout  the  coil 
and  terminates  in  a  very  slightly-dilated,  rounded,  blind  extremity.  It 
is  filled  with  epithelium  in  the  form  of  finely-granular  matter,  usually 
not  segmented  into  cells,  and  is  provided  with  small  oval  nuclei.  The 
glandular  mass  is  surrounded  with  a  plexus  of  capillary  bloodvessels, 
which  send  a  few  small  branches  between  the  convolutions  of  the  coil. 
Sometimes  the  coil  is  enclosed  in  a  delicate  fibrous  envelope  (see 
Plate  VII,  Fig.  2). 

The  excretory  duct  is  simply  a  continuation  of  the  glandular  coil. 
Its  course  through  the  layers  of  the  true  skin  is  nearly  straight.  It  then 
passes  into  the  epidermis,  between  the  papillae  of  the  corium,  and  pre- 
sents, in  this  layer,  a  number  of  spiral  turns.  The  spirals  vary  in 
number  according  to  the  thickness  of  the  epidermis.  Six  to  ten  are 
found  in  the  palms  of  the  hands,  and  twelve  to  fifteen  in  the  soles  of  the 
feet.  As  it  emerges  from  the  glandular  coil,  the  excretory  duct  is  some- 
what narrower  than  the  tube  in  the  secreting  portion  ;  but  as  it  passes 
through  the  epidermis  it  again  becomes  larger.  It  possesses  the  same 
external  membrane  as  the  glandular  coil  and  is  lined  usually  by  two 
layers  of  cells. 

In  a  section  of  the  skin  and  the  subcutaneous  tissue,  involving 
several  of  the  sudoriparous  glands  with  their  ducts,  it  is  seen  that  the 
glandular  coils  nearly  always  are  situated  at  different  planes  beneath  the 
skin. 

Sudoriparous  glands  in  the  axilla  have  been  described  which  do  not 
differ  so  much  from  the  glands  in  other  parts  in  their  anatomy  as  in  the 
character  of  their  secretion.  The  coil  in  these  glands  is  much  larger 
than  in  other  parts,  measuring  gV  to  ^^  ^^  ^"^  i^^^  (i  to  2  millimeters) ; 
the  walls  of  the  tube  are  thicker,  and  they  present  an  investment  of 
fibrous  tissue  with  an  internal  layer  of  longitudinal  non-striated  muscu- 
lar fibres ;  and  finally,  the  tubes  of  the  coil  itself  are  lined  with  cells  of 
epithelium.  These  glands  are  abundant  in  the  axilla,  forming  a  continu- 
ous layer  beneath  the  skin.  Mixed  with  these  are  a  few  glands  of  the 
ordinary  variety. 

Estimates  have  been  made  of  the  number  of  sudoriparous  glands  in 
the  body  and  the  probable  extent  of  the  exhalant  surface  of  the  skin, 
but  they  are  to  be  taken  as  approximate.  Krause  found  great  differ- 
ences in  the  number  of  perspiratory  openings  in  different  portions  of  the 
skin ;  but  taking  an  average  for  the  entire  surface,  it  was  estimated  that 
the  entire  number  of  perspiratory  glands  is  2,381,248  ;   and  assuming 


3i8  EXCRETION 

that  each  coil  when  unravelled  measures  about  ^^g  of  an  inch  (1.8  milli- 
meter), the  entire  length  of  the  secreting  tubes  is  about  2\  miles  (3I 
kilometers).  It  must  be  remembered,  however,  that  the  length  of  the 
secreting  coil  only  is  given  and  that  the  excretory  ducts  are  not  included. 

Mcchanisvi  of  the  Secretion  of  Siveat. — The  action  of  the  skin  as  a 
glandular  organ  is  continuous  and  not  intermittent ;  but  under  ordinary 
conditions  the  sweat  is  exhaled  from  the  general  surface  in  the  form  of 
vapor.  In  regard  to  the  mechanism  of  its  separation  from  the  blood, 
nothing  is  to  be  said  in  addition  to  the  general  remarks  on  the  subject 
of  secretion  ;  and  it  is  probable  that  the  epithelium  of  the  secreting  coils 
is  the  active  agent  in  the  selection  of  the  peculiar  matters  which  enter 
into  its  composition.  There  are  no  examples  of  the  separation  by 
glandular  organs  of  vapor  from  the  blood,  and  the  perspiration  is  se- 
creted as  a  Hquid,  which  becomes  vaporous  as  it  is  discharged  upon  the 
surface. 

The  influence  of  the  nervous  system  on  the  secretion  of  sweat  is  im- 
portant. It  is  well  known,  for  example,  that  an  abundant  production  of 
perspiration  frequently  is  the  result  of  mental  emotions.  Bernard  has 
shown  that  the  nervous  influence  may  be  exerted  through  the  sympa- 
thetic system.  He  divided  the  sympathetic  in  the  neck  of  a  horse, 
producing  as  a  consequence  an  elevation  in  temperature  and  an  increase 
in  the  arterial  pressure  in  the  part  supplied  with  branches  of  the  nerve. 
He  found,  also,  that  the  skin  of  the  part  became  covered  with  a  copious 
perspiration.  On  stimulating  the  divided  extremity  of  the  nerve,  the 
secretion  of  sweat  was  arrested.  The  local  secretion  of  sweat  after 
division  of  the  sympathetic  in  the  neck  of  the  horse  was  first  observed 
by  Dupuy  in  18 16. 

The  stimulation  as  well  as  the  division  of  certain  nerves  induces  local 
secretion  of  sweat,  but  this  nearly  always  is  associated  with  dilatation  of 
the  bloodvessels  of  the  part ;  still,  sweat  frequently  is  secreted  when  the 
surface  is  pale  and  bloodless,  showing  that  dilatation  of  the  bloodvessels 
is  not  an  indispensable  condition.  The  action  of  so-called  vaso-dilator 
nerves  will  be  treated  of  in  connection  with  the  physiology  of  the 
nervous  system.  In  experiments  on  the  cat,  excito-secretory  fibres  have 
been  found  to  exist  in  the  cerebro-spinal  nerves  going  to  the  anterior 
extremities.  The  fibres  for  the  posterior  extremities  are  in  the  sheath 
of  the  sciatic  nerve.  In  all  instances  the  action  of  these  nerves  is  direct 
and  not  reflex.  Experiments  on  the  cat  have  been  quite  satisfactory,  as 
this  animal  sweats  only  on  the  soles  of  the  feet  and  the  secretion  can 
readily  be  observed. 

The  so-called  sweat-centres  are  in  the  lower  part  of  the  dorsal  region 
of  the  spinal  cord,  for  the  posterior  extremities,  and  in  the  lower  part  of 


QUANTITY    OF    CUTANEOUS    EXHALATION  319 

the  cervical  region  of  the  cord,  for  the  anterior  extremities.  According 
to  Adamkiewicz,  these  centres  are  subordinate  to  the  principal  swea"t- 
centre,  which  is  situated  in  the  bulb.  Ott  has  collected  a  number  of 
cases  of  disease  of  the  cord  in  the  human  subject  which  go  far  to  con- 
firm the  results  of  experiments  on  the  inferior  animals  in  regard  to  the 
action  of  excito-secretory  nerves  and  sweat-centres. 

When  the  skin  is  in  a  normal  condition,  after  exercise  or  whenever 
there  is  a  tendency  to  elevation  of  the  animal  temperature,  there  is 
a  determination  of  blood  to  the  surface,  accompanied  with  an  increase 
in  the  secretion  of  sweat.  This  is  the  case  when  the  body  is  exposed 
to  a  high  temperature;  and  it  is  by  an  increase  in  the  transpiration 
from  the  surface  that  the  heat  of  the  body  is  kept  down  to  a  normal 
standard. 

Quantity  of  Cutaneous  ExJialation.  —  The  quantity  of  cutaneous  ex- 
halation is  subject  to  variations,  depending  on  conditions  of  temperature 
and  moisture,  exercise,  the  quantity  and  character  of  the  ingesta  etc. 
Most  of  these  variations  relate  to  the  action  of  the  skin  in  regulating  the 
temperature  of  the  body ;  and  it  is  probable  that  the  ehmination  of  ex- 
crementitious  matters  by  the  skin  is  not  subject,  under  normal  condi- 
tions, to  the  same  modifications,  although  experiments  on  this  point  are 
wanting.  When  there  is  such  a  wide  range  of  variation  in  different  in- 
dividuals and  in  the  same  person  under  different  conditions  of  season, 
climate  etc.,  it  is  possible  to  give  only  approximate  estimates  of  the 
quantity  of  sweat  secreted  and  exhaled  in  the  twenty-four  hours.  It  is 
assumed,  however,  that  the  average  quantity  is  nearly  two  pounds,  or 
about  900  grams. 

Under  violent  and  prolonged  exercise,  the  loss  of  weight  by  exhala- 
tion from  the  skin  and  lungs  may  become  very  considerable.  It  is 
stated  by  Maclaren,  the  author  of  a  work  on  training,  that  in  one  hour's 
energetic  fencing,  the  loss  by  perspiration  and  respiration,  taking  the 
average  of  six  consecutive  days,  was  forty  ounces  (1130  grams),  with  a 
range  of  variation  of  eight  ounces  (227  grams). 

When  the  body  is  exposed  to  a  high  temperature,  the  exhalation 
from  the  surface  is  largely  increased ;  and  it  is  by  this  rapid  evapora- 
tion that  persons  have  been  able  to  endure  for  several  minutes  a  dr}' 
heat  considerably  exceeding  that  of  boiling  water.  Southwood  Smith 
made  a  series  of  observations  in  regard  to  this  point  on  men  employed 
about  the  furnaces  of  gas-works  and  exposed  to  intense  heat ;  and  he 
found  that  in  an  hour  the  loss  of  weight  was  two  to  four  pounds  (907 
to  1 8 14  grams),  chiefly  by  exhalation  of  watery  vapor  from  the  skin. 
In  such  instances  the  loss  of  water  by  transpiration  is  compensated  by 
the  ingestion  of  large  quantities  of  liquid. 


320 


EXCRETION 


Properties  aiid  Compositio7i  of  the  Szvcat.  —  An  analysis  of  the  sweat 
was  made  by  Favre  in  1853.  After  taking  every  precaution  to  obtain 
the  secretion  in  a  perfectly  pure  state,  he  collected  a  very  large  quan- 
tity, nearly  thirty  pints  (14  liters),  the  result  of  six  transpirations  from 
one  person,  which  he  assumed  to  represent  about  the  average  in  compo- 
sition. The  liquid  was  perfectly  limpid,  colorless,  and  of  a  feeble  but 
characteristic  odor.  Almost  all  observers  have  found  the  reaction  of 
the  sweat  to  be  acid ;  but  it  readily  becomes  alkaline  on  being  subjected 
to  evaporation,  showing  that  it  contains  some  of  the  volatile  acids. 
Favre  found  that  the  liquid  collected  during  the  first  half-hour  of  the 
observation  was  acid ;  during  the  second  half-hour  it  was  neutral  or 
feebly  alkaline  ;  and  during  the  third  half-hour,  it  was  constantly  alka- 
line.    The  specific  gravity  of  the  sweat  is  1003  to  1004. 


COMPOSITION   OF  THE   SWEAT    (FAVRE) 


Water 

99-5573 

Urea 

0.043 

Fatty  matters        ..... 

0.014 

Alkaline  lactates  ..... 

0-317 

Alkaline  sudorates        .... 

1.562 

Sodium  chloride. 

2.230 

Potassium  chloride. 

0.244 

Alkaline  sulphates. 

■  soluble  in  water 

0.012 

Alkaline  phosphates, 

a  trace 

Alkaline  albuminates,  . 

0.005 

Alkaline  earthy  phosphates  (soluble  in  acidulated  water) 

a  trace 

Epidermic  debris  (insoluble)       ..... 

a  trace 

1 000.000 

The  sweat  is  exhaled  usually  in  the  form  of  vapor,  when  it  is  known 
as  insensible  perspiration.  When  from  any  cause  it  collects  on  the  sur- 
face, in  the  form  of  a  liquid,  it  is  called  sensible  perspiration. 

The  peculiar  constituents  of  the  sweat  are  the  following :  The 
neutral  fats  probably  are  derived  in  great  part  from  the  sebaceous 
glands,  although  certain  fats,  palmitin  and  stearin,  have  been  found  in 
the  secretion  of  the  palms  of  the  hands,  which  contain  no  sebaceous 
glands.  The  volatile  fatty  acids  are  formic,  butyric,  caproic,  capric, 
acetic  etc.,  some  of  which  exist  also  in  milk.  These  give  to  the  sweat 
its  peculiar  odor.  Urea  is  always  present  in  small  quantity,  and  its 
proportion  may  be  largely  increased  when  there  is  a  deficiency  in 
elimination  by  the  kidneys.  It  is  a  matter,  also,  of  common  as  well 
as  of  scientific  observation  that  the  sweat  is  more  abundant  when 
the  kidneys  are  comparatively  inactive,  and  vice  versa.     Usually,  how- 


PECULIARITIES    OF   THE    SWEAT    IN    CERTAIN    PARTS  32 1 

ever,  when  conditions  operate  to  increase  the  quantity  of  sweat,  the 
quantity  of  urine  is  proportionally  diminished.  The  skin  is  undoubtedly 
an  important  organ  of  excretion,  and  it  may  eliminate  excrementitious 
matters  of  a  character  as  yet  unknown.  In  regard  to  the  inorganic 
constituents  of  the  sweat,  there  is  no  great  interest  attached  to  any  but 
the  sodium  chloride,  which  exists  in  a  proportion  many  times  greater 
than  that  of  all  the  other  inorganic  salts  combined. 

Peculiarities  of  the  Szveat  in  Certain  Parts.  —  In  the  axilla,  the 
inguino-scrotal  region  in  the  male  and  the  inguino-vulvar  region  in 
the  female,  and  between  the  toes,  the  sweat  always  has  a  peculiar 
odor,  more  or  less  marked,  which  in  some  persons  is  excessively  dis- 
agreeable. Whenever  the  secretion  has  an  odor  of  this  kind  its  reaction 
is  distinctly  alkaline ;  and  its  peculiar  characters  are  due  to  a  mixture 
of  the  secretion  of  the  other  follicles  found  in  these  situations.  Some- 
times the  sweat  about  the  nose  has  an  alkaline  reaction.  In  the  axillary 
region  the  secretion  frequently  has  a  yellowish  color,  which  may  stain 
the  clothing. 


CHAPTER   XIII 

EXCRETION    BY    THE    KIDNEYS 

Physiological  anatomy  of  the  kidneys  —  Pyramidal  substance  —  Cortical  substance  —  Tubes  of 
the  cortical  substance  —  Narrow  tubes  of  Henle  —  Distribution  of  bloodvessels  in  the  kid- 
ney—  Mechanism  of  the  production  and  discharge  of  urine  —  Influence  of  blood-pressure, 
the  nervous  system  etc.,  on  the  secretion  of  urine  —  Physiological  anatomy  of  the  urinary 
passages  —  Mechanism  of  the  discharge  of  urine — Properties  and  composition  of  the  urine 

—  Urea  —  Origin  of  urea  —  Influence  of  the  ingesta  on  the  composition  of  the  urine  and  on 
the  discharge  of  nitrogen  —  Influence  of  muscular  exercise  on  the  discharge  of  nitrogen  — 
Uric  acid  and  its  compounds — Hippuric  acid,  hippurates  and  lactates  —  Calcium  oxalate 

—  Xanthin,  hypoxanthin,  leucin,  tyrosin  and  taurin  —  Fatty  matters —  Inorganic  constitu- 
ents of  the  urine  —  Chlorides  —  Sulphates  —  Phosphates  —  Water  as  a  product  of  excretion 

—  Variations  in  the  composition  of  the  urine  —  Variations  with  age  and  sex  —  Influence 
of  mental  exertion  —  Internal  secretion —  Work  of  the  kidneys. 

Physiological  Anatomy  of  the  Kidneys 

The  kidneys  are  symmetrical  organs,  situated  in  the  lumbar  region, 
beneath  the  peritoneum,  invested  with  a  proper  fibrous  coat,  called  the 
capsule,  and  always  surrounded  with  more  or  less  adipose  tissue.  They 
extend  usually  from  the  eleventh  or  twelfth  rib  downward  to  near  the 
crest  of  the  ilium,  and  the  right  is  always  a  little  lower  than  the  left. 
In  shape  the  kidney  is  appropriately  compared  to  a  bean;  and  the  con- 
cavity—  the  deep,  central  portion  of  which  is  called  the  hilum — looks 
inward  toward  the  spinal  column.  The  weight  of  each  kidney  is  four 
to  six  ounces  (113  to  170  grams),  usually  about  half  an  ounce  (14  grams) 
less  in  the  female  than  in  the  male.  The  left  kidney  is  nearly  always  a 
little  heavier  than  the  right. 

External  to  the  proper  coat  of  the  kidney,  is  a  certain  quantity  of 
adipose  tissue  enclosed  in  a  loose  fibrous  structure.  This  is  sometimes 
called  the  adipose  capsule ;  but  the  proper  coat  consists  of  a  close  net- 
work of  ordinary  fibrous  tissue,  interlacing  with  small  elastic  fibres. 
This  coat  is  thin  and  smooth  and  may  readily  be  removed  from  the 
surface  of  the  organ.  At  the  hilum  it  is  continued  inward  to  line  the 
pelvis  of  the  kidney,  covering  the  calices  and  bloodvessels. 

The  kidney  in  a  vertical  section  presents  a  cavity  at  the  hilum, 
bounded  internally  by  the  dilated  origin  of  the  ureter.  This  is  called 
the  pelvis.  It  is  lined  with  a  smooth  membrane,  which  is  simply  a 
continuation  of  the  proper  coat  of  the  kidney  and  which  forms  little 
cylinders,  called    calices,  into  which    the    apices    of    the  pyramids  are 

322 


PHYSIOLOGICAL   ANATOMY    OF    THE    KIDNEYS 


323 


received.  Some  of  the  calices  receive  the  apex  of  a  single  pyramid, 
while  others  are  larger  and  receive  two  or  three.  The  calices  unite 
into  three  short,  funnel-shaped  tubes,  called  infundibula,  corresponding 
respectively  to  the  superior,  middle  and  inferior  portions  of  the  kidney. 
These  finally  open  into  the  common  cavity,  the  pelvis.  The  substance 
of  the  kidney  is  composed  of  two  distinct  portions,  called  respectively 
the  cortical  substance  and  the  medullary,  or  pyramidal  substance. 

The  cortical  substance  is  reddish 
and  granular,  rather  softer  than  the 
pyramidal  substance,  and  is  about 
one-sixth  of  an  inch  (4.2  millimeters) 
in  thickness.  This  occupies  the  ex- 
terior of  the  kidney  and  sends  little 
prolongations,  called  the  columns 
of  Bertin,  between  the  pyramids. 
The  surface  of  the  kidney  is  marked 
by  little  polygonal  divisions,  giving 
it  a  lobulated  appearance.  This, 
however,   is   due    mainly  to  the  ar- 


rangement of  the  superficial  blood- 
vessels. The  medullary  substance 
is  arranged  in  the  form  of  pyramids, 
sometimes  called  the  pyramids  of 
Malpighi,  twelve,  fifteen  or  eighteen 
in  number,  their  bases  presenting 
toward  the  cortical  substance  and 
their  apices  being  received  into  the 
calices,  at  the  pelvis.  Ferrein  sub- 
divided the  pyramids  of  Malpighi 
into    smaller    pyramids,  called    the  P'^hi,  5.  s.  s,s,  5.5.  apices  of  the  pyramids,  sur- 

"■^  '  rounded  by  the  cahces;  6,  6,  columns  of  Bertm ; 

pyramids    of    Ferrein,   each    contain-    7.  Pe'vls  of  the  kidney;  8,  upper  extremity  of  the 

ing  about  one  hundred  tubes  radiat- 
ing from  the  openings  at  the  apices  of  the  pyramids  toward  their  bases. 
The  tubes  composing  these  pyramids  pass  into  the  cortical  substance, 
forming  corresponding  pyramids  of  convoluted  tubes,  thus  dividing  this 
portion  of  the  kidney  into  lobules  more  or  less  distinct. 

The  medullary  substance  is  firm,  of  a  darker  red  color  than  the 
cortical  substance,  and  is  marked  by  tolerably  distinct  strias  that  take 
a  nearly  straight  course  from  the  bases  to  the  apices  of  the  pyramids. 
As  these  striae  indicate  the  direction  of  the  tubes  that  constitute  the 
greatest  part  of  the  medullary  substance,  this  is  sometimes  called  the 
tubular  portion  of  the  kidney. 


Fig.  70 


Longitiidiiial    section    of  the   kidney 
(Sappey). 

I,  I,  2,  2,  3,  3,  3,  4,  4,  4,  4,  pyramids  of  Mai- 


324 


EXCRETION 


From  the  arrangement  of  the  secreting  portion  of  the  kidneys,  these 
organs  are  classed  as  tubular  glands,  presenting  a  system  of  tubes,  or 
canals,  some  of  which  are  supposed  simply  to  carry  off  the  urine,  while 
others  separate  the  excrementitious  constituents  of  the  urine  from  the 
blood.     It  is  difficult  to  determine  precisely  where  the  secreting  tubes 


Pig.  71.  — Longitudinal  section  of  the  pyramidal 
substance  of  the  kidney  ofthefcetus  (Sappey). 

I,  trunk  of  a  large  uriniferous  tube ;  2,  2,  pri- 
mary branches  of  this  tube;  3,  3,  3,  secondary 
branches;  4,  4,  5,  5,  6,  6,  7,  7,  7,  7,  branches  be- 
coming smaller  and  smallt-r;  8,  8,  8,  8,  loops  of 
the  tubes  of  Henle. 


4* 


<<^ 


'>^' 


m 


■1 


y 


\  L 


Fig.  72. —  Longitudinal  section  of  the  cortical  sub- 
stance of  the  same  kidney  (Sappey) . 

I,  I,  limit  of  the  cortical  substance  and  base 
of  the  pyramids  ;  2,  2,  2,  tubes  passing  toward  the 
surface  of  the  kidney;  3,  3,  3,  8,  8,  8.  convoluted 
tubes  ;  4,  4,  4,  4,  5,  Malpighian  bodies ;  6,  6,  artery, 
with  its  branches  (7,  7,  7)  ;  9,  9,  fibrous  covering 
of  the  kidney. 


merge  into  the  excretory  ducts ;  but  it  is  a  common  idea,  which  prob- 
ably is  correct,  that  the  cortical  substance  is  the  active  portion,  while 
the  tubes  of  the  pyramidal  portion  simply  carry  off  the  excretion. 

Pyramidal  Substance.  —  Each  papilla,  as  it  projects  into  the  pelvis 
of  the  kidney,  presents  ten  to  twenty-five  openings,  -^q  ^^  eV  ^^  ^"^  ^^^'^ 
(85  to  425  IX)  in  diameter.     The  tubes  leading  from  the  pelvis  immedi- 


PHYSIOLOGICAL   ANATOMY   OF   THE   KIDNEYS 


325 


ately  divide  at  very  acute  angles,  usually  dichotomously,  until  a  bundle 
of  tubes  arises,  as  it  were,  from  each  opening.  These  bundles  constitute 
the  pyramids  of  Ferrein.  In  their  course  the  tubes  are  shghtly  wavy 
and  are  nearly  parallel  with  each  other.  These  are  called  the  straight 
(collecting)  tubes  of  the  kidney,  or  the  tubes  of  BelHni.  They  extend 
from  the  apices  of  the  pyramids  to  their  bases  and  pass  then  into  the 
cortical  substance.  The  pyramids  contain,  in  addition  to  the  straight 
tubes,  a  delicate  fibrous  matrix  and  bloodvessels,  which  latter  usually 
pass  beyond  the  pyramids,  to  be  finally  distributed  in  the  cortical  sub- 
stance. Small  tubes,  continuous  with  the  convoluted  tubes  of  the 
cortical  substance,  dip  down  into  the  pyramids,  returning  to  the  cortical 
substance  in  the  form  of  loops. 
The  tubes  of  the  pyramidal 
substance  are  composed  of  a 
strong  structureless  basement- 
membrane  lined  with  granular 
nucleated  cells.     They  measure 

300  ^°  20^0  *^f  ^^  ^^*^^  (^5  ^0 
127  /w)  in  diameter  at  the  apices, 

and  near  the  bases  of  the  pyra- 
mids their  diameter  is  about  g^^- 
of  an  inch  (42  fx). 

The  cells  lining  the  straight 
tubes  exist  in  a  single  layer  ap- 
plied to  the  basement-membrane. 
They  are  thick  and  irregularly 
polygonal  in  shape,  with  abun-  ^ig-73-^ 
dant  albuminous  granules.  They 
present  one,  and  occasionally,  though  rarely,  two  granular  nuclei,  with 
one  or  two  nucleoli.  They  readily  undergo  alteration  and  are  seen  in 
their  normal  condition  only  in  a  perfectly  fresh  healthy  kidney.     Their 

The  calibre  of  the  tubes  is 

^     .  Ao  or  8^0  of  an 

inch  (28  or  30  fi). 

Cortical  Substance.  —  In  the  cortical  portion  of  the  kidney  are  found 
tubes,  differing  somewhat  from  the  tubes  of  the  pyramidal  portion  in 
their  size  and  in  the  character  of  their  epithelial  lining,  and  presenting 
a  marked  difference  in  their  direction.  These  tubes  are  rather  larger 
than  the  tubes  of  the  pyramidal  substance,  and  are  convoluted,  inter- 
lacing with  each  other  in  every  direction.  Scattered  pretty  uniformly 
throughout  this  portion  of  the  kidney,  are  rounded  or  ovoid  bodies, 
about  four  times  the  diameter  of  the  convoluted  tubes,  known  as  the 


Collecting  tubes  of  the  kidney,  X  130,  hema- 
toxylin and  eosin  (Author's  collection). 


diameter  is  about  Y5V0  of  an  inch  (17  /u-). 

reduced  by  the  thickness  of  their  lining  epithelium  to  ^-^^  .^x  -g  q-q 


326  EXCRETION 

Malpighian  bodies.  These  are  simply  flask-like  terminal  dilatations  of 
the  tubes  themselves  (see  Plate  \'II,  Fig.  4). 

The  cortical  portion  of  the  kidney  presents  a  delicate  fibrous  matrix, 
which  forms  a  support  for  the  secreting  portion  and  its  bloodvessels. 
The  tubes  of  the  cortical  substance  present  considerable  differences  in 
size,  and  three  well-defined  varieties  can  be  distinguished :  — 

I.  The  first  convoluted  tubes,  directly  connected  with  the  ]\Ial- 
pighian  bodies.  2.  Small  tubes,  continuous  with  the  convoluted  tubes, 
dipping  down  into  the  pyramids  and  returning  to  the  cortical  portion 
in  the  form  of  loops.  3.  The  second  convoluted  tubes,  forming  a  plexus 
connecting  the  different  kinds  of  tubes  with  each  other  and  finally  with 
the  straight  tubes  of  the  jn'ramidal  portion. 

In  tracing  out  the  course  of  the  tubes,  it  will  be  found  most  con- 
venient to  begin  with  a  description  of  the  Malpighian  bodies  and  to 
follow  the  tubes  from  these  bodies  to  their  connections  with  the  straight 
tubes  of  the  pyramidal  substance. 

MalpigJiiaji  Bodies.  — These  are  ovoid  or  rounded  terminal  dilatations 
of  the  first  convoluted  tubes  and  are  c,\-^  to  yj-o  °^  "^^^  inch  ( 100  to  250  /i) 
in  diameter.  They  are  composed  of  a  membrane,  which  is  continuous 
with  the  external  membrane  of  the  convoluted  tubes,  and  is  of  the  same 
homogeneous  character,  but  somewhat  thicker.  This  envelope,  called 
the  capsule  of  M tiller  or  of  Bowman,  encloses  a  mass  of  convoluted 
bloodvessels  and  is  lined  with  a  layer  of  nucleated  epithelial  cells.  In 
addition  to  the  cells  lining  the  capsule,  there  are  other  cells,  which  are 
applied  to  the  bloodvessels. 

The  cells  attached  to  the  capsule  of  Miiller  are  smaller  and  more 
transparent  than  those  lining  the  convoluted  tubes.  They  are  ovoid, 
nucleated  and  finely  granular.  The  cells  covering  the  vessels,  however, 
are  larger  and  more  opaque,  and  they  resemble  the  epithelium  lining 
the  tubes.  They  measure  -j^Vo  ^o  TnVir  of  an  inch  (16  to  25  /i,)  in 
diameter,  by  about  o -Vo  ^f  an  inch  ( 10  fi)  in  thickness. 

Tubes  of  the  Cortical  Substance.  —  Passing  from  the  IMalpighian 
bodies  the  tubes  present  first  a  short  constricted  portion,  called  the 
neck  of  the  capsule,  which  soon  dilates  to  the  diameter  of  about  5^  of 
an  inch  (50  /x),  when  their  course  becomes  quite  intricate  and  convoluted. 
These  are  what  are  known  as  the  first  convoluted  tubes.  The  mem- 
brane of  these  tubes  is  transparent  and  homogeneous,  but  quite  firm 
and  resisting.  It  is  lined  throughout  with  a  single  layer  of  epithelial 
cells,  ^4^0  0  ^o  loVo  of  a"  ^^^^  (^^^  ^o  25  \i)  in  diameter,  somewhat  larger, 
therefore,  than  the  cells  lining  the  straight  tubes.  The  cells  lining  the 
convoluted  tubes  present  two  tolerably  distinct  portions.  The  inner 
portion  or  zone,  which  is  next  the  lumen  of  the  tube,  is  finely  granular, 


PHYSIOLOGICAL   ANATOMY    OF    THE    KIDNEYS 


327 


with  sometimes  a  few  small  oil-globules.  The  outer  zone  presents  little 
fibrils  or  rods,  which  are  perpendicular  to  the  tubular  membrane.  These 
are  called  "rodded"  cells,  and  a  similar  appearance  is   presented  by 


Fig.  74.  —  Diagram  of  the  structure  of  the  kidney  (Landois). 

I.  Bloodvessels  and  tubes  (semidiagrammatic)  :  A,  capillaries  of  the  cortical  substance;  B,  capil- 
laries of  the  medullary  substance;  i,  artery  penetrating  a  Malpighian  body;  2,  vein  emerging  from  a 
Malpighian  body;  R,  arterioias  rectae ;  C,  venae  rectas;  /',  V,  interlobular  veins ;  5',  slellate  veins; 
I,  I,  capsules  of  Miiller;  X,  X,  first  convoluted  tubes;  T,  T,  T,  tubes  of  Henle;  ^V,  A',  A",  ^N',  second 
convoluted  tubes;  O,  O,  straight  tubes;  O,  opening  into  the  pelvis  of  the  kidney.  II.  Malpighian 
body  :  A,  artery  ;  E,  vein  ;  C.  capillaries  ;  K,  epithelium  of  the  capsule  ;  //,  beginning  of  a  convoluted 
tube.  III.  Rodded  cells  from  a  convoluted  tube  :  i,  view  from  the  surface  ;  2,  side  view  (  G,  granular 
zone).  IV.  Cells  lining  the  tubes  of  Henle.  V.  Cells  lining  the  second  convoluted  tubes.  VI.  Sec- 
tion of  a  straight  tube. 


328  EXCRETION 

some  of  the  cells  of  the  pancreas  and  of  the  salivary  glands.  The 
nucleus  usually  is  situated  between  the  granular  and  the  rodded  zones. 

The  pyramids  of  Ferrein  extend  into  the  cortical  substance  to  form 
what  are  known  as  the  medullary  rays.  The  spaces  between  the  medul- 
lary rays  constitute  the  labyrinth.  The  division  between  the  cortical 
and  the  medullary  substance  is  known  as  the  boundary  zone. 

The  greatest  part  of  the  solid  excrementitious  constituents  of  the 
urine,  such  as  urea  and  the  urates,  is  separated  from  the  blood  by  the 
cells  of  the  convoluted  tubes  of  the  cortical  substance  and  perhaps 
by  the  dilated  portions  of  the  tubes  of  Henle,  while  the  water  and  a 
certain  portion  of  the  inorganic  salts  of  the  urine  transude  through  the 
bloodvessels  in  the  Malpighian  bodies. 

Narroiv  Tubes  of  Hcnlc. — The  convoluted  tubes  above  described, 
after  a  tortuous  course  in  the  cortical  substance,  become  continuous, 
near  the  pyramids,  with  the  tubes  of  much  smaller  diameter,  which  form 
loops  extending  to  a  greater  or  less  depth  into  the  pyramids.  The  loops 
formed  by  these  canals  (the  narrow  tubes  of  Henle)  are  nearly  parallel 
with  the  tubes  of  Bellini  and  are  much  greater  in  number  near  the  bases 
of  the  pyramids  than  toward  the  apices.  The  diameter  of  these  tubes 
is  variable,  and  they  present  enlargements  at  irregular  intervals  in  their 
course.  The  narrow  portions  are  about  ooVo  ^^  ^'^  inch  ( 12  /w.)  in  diame- 
ter, and  the  wide  portions,  about  twice  this  size.  The  narrow  portion  is 
lined  with  small  clear  cells  with  very  prominent  nuclei.  The  wider  por- 
tions are  lined  with  larger,  granular  cells.  Near  the  bases  of  the  pyra- 
mids the  wide  portion  sometimes  forms  the  loop,  but  near  the  apices  the 
loop  is  always  narrow.  The  difference  in  the  size  of  the  epithelium  is 
such  that  while  the  diameter  of  the  tube  is  variable  its  calibre  remains 
nearly  uniform.  The  membrane  of  these  tubes  is  quite  thick,  thicker, 
even,  than  the  membrane  of  the  tubes  of  Bellini. 

After  the  narrow  tubes  of  Henle  have  returned  to  the  cortical  sub- 
stance, they  communicate  with  a  system  of  canals,  3o\)o  to  -^-^-^-^  of  an 
inch  (21  to  25/x)  in  diameter,  with  very  thin  walls,  lined  by  rodded 
epithelium.  These  are  known  as  the  second  convoluted  tubes.  They 
take  an  irregular  and  somewhat  angular  course  between  the  first  con- 
voluted tubes  and  finally  empty  into  the  branches  of  the  straight  tubes 
of  Bellini,  thus  establishing  a  communication  between  the  tubes  coming 
from  the  Malpighian  bodies  and  the  tubes  of  the  pyramidal  substance. 
They  are  sometimes  called  the  intermediate  tubes,  or  the  canals  of  com- 
munication. 

The  tubes  into  which  the  second  convoluted  tubes  open  join  with 
others,  usually,  two  by  two,  and  then  pass  in  a  nearly  straight  direc- 
tion into  the  pyramids,  where  they  continue  to  unite  with  each  other  in 


PHYSIOLOGICAL    ANATOMY   OF    THE    KIDNEYS  329 

their  course,  becoming  reduced  in  number  until  they  open  at  the  apices 
of  the  pyramids  into  the  infundibula  and  the  pelvis  of  the  kidney. 

Distribution  nf  Bloodvessels  i}i  the  Kieliiey.  —  The  renal  arterv,  which 
is  quite  voluminous  in  proportion  to  the  size  of  the  kidnev,  enters  at 
the  hilum  and  divides  into  four  branches.  A  number  of  smaller 
branches  penetrate  between  the  pyramids  and  ramify  in  the  columns 
of  cortical  substance  that  occupy  the  spaces  between  the  pvramids 
(columns  of  Bertin).  The  main  vessels,  which  usually  are  two  in  num- 
ber, occupy  the  centre  of  the  columns  of  Bertin,  sending  off  in  their 
course  at  short  intervals  regular  branches  on  either  side  toward  the 
pyramids.  When  these  branches  reach  the  boundarv  of  the  cortical 
substance  they  turn  upward  and  follow  the  periphery  of  the  pvramid 
to  its  base.  Here  the  vessels  form  an  arched  anastomosing  plexus,  the 
arterial  arcade,  situated  between  the  rounded  base  of  the  pvramid  and 
the  cortical  substance.  This  plexus  presents  a  convexitv  looking  toward 
the  cortical  substance,  and  a  conca\'ity,  toward  the  pyramid.  It  is  so 
arranged  that  the  interstices  are  just  large  enough  to  admit  the  collec- 
tions of  tubes  that  form  the  pyramids  of  Ferrein. 

From  the  arterial  arcade,  branches  are  given  off  in  two  opposite 
directions.  From  its  concavity,  small  branches,  measuring  at  first 
T2V0  ^o  ToT  °^  ^^  \riz\\  (21  to  34  A^j  in  diameter,  pass  downward 
toward  the  papillae,  giving  off  small  ramifications  at  verv  acute  angles 
and  becoming  reduced  in  size  to  about  0-5^  of  ^n  inch  (lO//).  These 
vessels,  called  the  arteriolas  rect«,  surround  the  straight  tubes  and  pass 
into  capillaries  in  the  substance  of  the  pyramids  and  at  their  apices. 

From  the  convex  surface  of  the  arterial  arcade,  branches  are  given 
off  at  nearly  right  angles.  These  pass  into  the  cortical  substance, 
breaking  up  into  a  number  of  little  arterial  twigs,  -^h^'^  ^o  6T0  ^^  ^^ 
inch  (17  to  40  IX)  in  diameter,  each  one  of  which  penetrates  a  Mal- 
pighian  body  at  a  point  opposite  the  neck  of  the  capsule.  Once  within 
the  capsule,  the  arteriole  breaks  up  into  five  to  eight  branches,  which 
then  divide  dichotomously  into  vessels  measuring  g-gVo"  ^o  ToVo"  ^^  ^^ 
inch  (8  to  17  ix)  in  diameter,  arranged  in  the  form  of  coils  and  loops, 
constituting  a  dense  rounded  mass  (the  Malpighian  coil,  or  glomerulus), 
filling  the  capsule.  These  vessels  break  up  into  capillaries  without 
anastomoses  (see  Plate  VII,  Fig.  4). 

The  blood  is  collected  from  the  vessels  of  the  Malpighian  bodies  bv 
a  vein,  which  passes  out  of  the  capsule  by  the  side  of  the  arteriole  and, 
with  veins  from  other  glomeruli,  forms  a  plexus  closely  surrounding  the 
convoluted  tubes.  This  is  a  true  plexus,  the  branches  anastomosing 
freely  in -every  direction;  and  the  distribution  of  vessels  in  this  part 
resembles  essentiallv  the  vascular  arrangement  in  most  of  the  glands. 


330 


EXCRETION 


Bowman  called  the  branches  which  connect  together  the  vessels  of  the 
Malpighian  tuft  and  the  capillary  plexus  surrounding  the  tubes,  the 
portal  system  of  the  kidney.  These  intermediate  vessels  form  a  coarse 
plexus  surrounding  the  prolongations  of  the  pyramids  of  Ferrein  into 
the  cortical  substance. 

The  renal,  or  emulgent  vein  takes  its  origin  in  part  from  the  capil- 
larv  plexus  surrounding  the  convoluted  tubes  and  in  part  from  vessels 
distributed  in  the  pyramidal  substance.  A  few  branches  come  from 
vessels  in  the  envelopes  of  the  kidney,  but  these  are  comparatively 
unimportant.  The  plexus  surrounding  the  convoluted  tubes  empties 
into  venous  radicles  which  pass  to  the  surface  of  the  kidney,  and  these 
present  a  number  of  little  radiating  groups,  each  converging  toward  a 
central  vessel.  This  arrangement  gives  to  the  vessels  under  the  fibrous 
envelope  of  the  kidney  a  peculiar  stellate  appearance,  forming  what  are 
called  the  stars  of  Verheyn.  The  large  trunks  which  form  the  centres 
of  these  stars  then  pass  through  the  cortical  substance  to  the  rounded 
bases  of  the  pyramids,  where  they  form  a  vaulted  venous  plexus  cor- 
responding to  the  arterial  plexus  already  described.  The  vessels  dis- 
tributed on  the  straight  tubes  of  the  pyramidal  substance  form  a  loose 
plexus  around  these  tubes,  except  at  the  papillae,  where  the  network  is 
much  closer.  They  then  pass  into  the  plexus  at  the  bases  of  the  pyra- 
mids to  join  with  the  veins  from  the  cortical  substance.  From  this 
plexus  a  number  of  larger  trunks  arise  and  pass  toward  the  hilum,  in 
the  axis  of  the  interpyramidal  substance,  enveloped  in  a  sheath  with 
the  arteries.  Passing  to  the  pelvis  of  the  kidney,  the  veins  converge 
into  three  or  four  branches,  which  unite  to  form  the  renal  vein.  A 
preparation  of  all  the  vessels  of  the  kidneys  shows  that  the  veins  are 
much  more  voluminous  than  the  arteries  (see  Frontispiece j. 

The  capsule  of  the  kidney  has  a  lymphatic  plexus  connected  with 
lymph-spaces  below  ;  and  lymph-spaces,  in  the  form  of  large  slits,  exist 
between  and  around  the  convoluted  tubes. 

The  nerv'es  are  abundant  and  are  derived  from  the  solar  plexus,  their 
filaments  following  the  renal  artery  in  its  distribution  in  the  interior  of 
the  orsfan  and  ramifving  on  the  walls  of  the  vessels. 


Mechanism  of  the  Production  and  Discharge  of  Urine 

The  most  important  constituent  of  the  urine  is  urea  —  CO(N  1^2)2  — 
a  crystallizable  nitrogenous  substance,  which  is  discharged  by  the  skin 
as  well  as  by  the  kidneys.  This  has  long  been  recognized  as  an  excre- 
mentitious  substance  ;  but  the  first  observations  that  gave  a  definite  idea 
of  the  mechanism  of  its  production  were  made  by  Prevost  and  Dumas 


MECHANISM   OF  THE   PRODUCTION   OF   URINE  331 

in  1 82 1.  At  the  time  these  experiments  were  made,  chemists  were  not 
able  to  detect  urea  in  the  normal  blood ;  but  Prevost  and  Dumas  extir- 
pated the  kidneys  from  living  animals  —  dogs  and  cats  —  and  found  urea 
in  the  blood  after  certain  nervous  symptoms  had  developed.  For  the 
first  two  or  three  days  after  the  operation  there  were  no  marked  symp- 
toms ;  but  stupor  and  other  evidences  of  nervous  disturbance  finally 
supervened,  when  the  presence  of  urea  in  the  blood  could  easily  be 
determined.  These  observations  were  confirmed  and  extended  by 
Segalas  and  Vauquelin  in  1822.  Since  that  time,  as  the  processes  for 
the  determination  of  urea  in  the  animal  liquids  have  been  improved,  this 
substance  has  been  detected  in  normal  blood.  Picard  (1856;  estimated 
and  compared  the  proportions  of  urea  in  the  renal  artery  and  the  renal 
vein  and  found  that  the  quantity  in  the  blood  was  diminished  by  about 
one-half  in  its  passage  through  the  kidneys.  Still  later,  urea  was  found 
in  the  lymph  and  chyle,  in  larger  quantity,  even,  than  in  the  blood 
(Wurtz).  It  has  been  ascertained  that  urea  is  an  active  diuretic  when 
injected  in  small  quantity  into  the  veins  of  a  healthy  animal,  and  is 
promptly  eliminated.  When  injected  into  the  vascular  system  of  a 
nephrotomized  animal,  however,  it  produces  death  in  a  very  short  time, 
with  characteristic  symptoms. 

From  a  review  of  the  important  facts  bearing  on  the  question 
under  consideration,  there  seems  to  be  no  valid  ground  for  a  change 
in  the  ideas  of  physiologists  concerning  the  mode  of  elimination  of  urea 
and  other  important  excrementitious  constituents  of  the  urine.  There 
is  every  reason  to  suppose  that  these  substances  are  produced  in 
various  tissues  and  organs  of  the  body  during  the  process  of  katabolism, 
are  taken  up  by  the  lymph  and  the  blood  and  are  separated  from  the 
blood  by  the  kidneys.  Urea,  however,  probably  is  formed  almost  ex- 
clusively in  the  liver  from  substances  of  a  like  nature,  the  final  process 
of  oxidation  taking  place  in  this  organ.  The  mechanism  of  this  will  be 
described  farther  on. 

Extirpation  of  one  kidney  from  a  living  animal  is  not  necessarily 
fatal.  When  the  operation  is  carefully  performed,  the  wound  usually 
heals  without  difficulty,  and  in  most  instances  the  remaining  kidney 
seems  sufficient  for  the  elimination  of  urine  for  an  indefinite  period.  In 
a  large  number  of  experiments,  the  animals  killed  long  after  the  wound 
had  healed  presented  no  marked  symptoms  of  retention  of  excrementi- 
tious matters  in  the  blood,  except  in  one  or  two  instances.  It  is  a 
noticeable  fact,  however,  that  in  many  instances  they  showed  a  change 
in  disposition,  and  the  appetite  became  voracious  and  unnatural.  These 
animals  would  sometimes  eat  feces,  the  flesh  of  dogs  etc.,  and,  in 
short,  presented   certain  of  the   phenomena  frequently  observed  after 


332 


EXCRETION 


extirpation  of  the  spleen  (Flint).  After  extirpation  of  one  kidney,  it 
has  been  observed  that  the  remaining  kidney  increases  in  weight,  al- 
though investigations  have  shown  that  this  is  due  mainly  to  an  increase 
in  the  quantity  of  blood,  lymph  and  urinary  matters,  and  not  to  a  new 
development  of  renal  structure. 

Influence  of  Dlood-pressjire,  the  Nervous  System  etc.,  on  the  Secretion 
of  Urine.  —  There  are  many  instances  in  which  marked  and  sudden 
modifications  in  the  action  of  the  kidneys  take  place  under  the  influence 
of  fear,  anxiety,  hysteria  etc.,  which  must  operate  through  the  nervous 
system.  Although  little  is  known  of  the  final  distribution  of  the  nerves 
in  the  kidney,  it  has  been  ascertained  that  here,  as  elsewhere,  vasomotor 
nerves  are  distributed  to  the  walls  of  the  bloodvessels,  and  they  are 
capable  of  modifying  the  quantity  and  the  pressure  of  blood  in  these 
organs. 

It  may  be  stated  as  a  general  proposition,  that  an  increase  in  the 
pressure  of  blood  in  the  kidneys  increases  the  flow  of  urine,  and  that 
when  the  blood-pressure  is  lowered,  the  flow  of  urine  is  correspond- 
ingly diminished.  This  will  in  a  measure  account  for  the  increase  in 
the  flow  of  urine  during  digestion  ;  but  it  can  not  serve  to  explain  all  the 
modifications  that  may  take  place  in  the  action  of  the  kidneys. 

Inasmuch  as  the  excrementitious  matters  eliminated  by  the  kidneys 
are  being  constantly  produced  in  the  tissues  by  the  process  of  katabo- 
lism,  the  formation  of  urine  is  constant,  presenting,  in  this  regard,  a 
marked  contrast  with  the  intermittent  flow  of  most  of  the  secretions 
proper  as  distinguished  from  the  excretions.  It  was  noted  by  Erichsen, 
in  a  case  of  extroversion  of  the  bladder,  and  it  has  been  further  shown 
by  experiments  on  dogs,  that  there  is  an  alternation  in  the  action  of  the 
kidneys  on  the  two  sides.  Bernard  exposed  the  ureters  in  a  living  ani- 
mal and  fixed  a  small  silver  tube  in  each,  so  that  the  secretion  from 
either  kidney  could  be  readily  observed ;  and  he  noted  that  a  large 
quantity  of  liquid  was  discharged  from  one  side  for  fifteen  to  thirty 
minutes,  while  the  flow  from  the  other  side  was  shght  and  in  some 
instances  was  arrested.  The  flow  then  began  with  activity  on  the  other 
side,  while  the  discharge  from  the  opposite  ureter  was  diminished  or 
arrested. 

Physiological  Ajiatomy  of  the  Urinary  Passages.  —  The  excretory 
ducts  of  the  kidneys — the  ureters  —  begin  each  by  a  funnel-shaped 
portion,  which  is  applied  to  the  kidney  at  the  hilum.  The  ureters 
themselves  are  membranous  tubes  of  about  the  diameter  of  a  goose- 
quill,  becoming  much  reduced  in  calibre  as  they  penetrate  the  coats  of 
the  bladder.  They  are  sixteen  to  eighteen  inches  (40  to  46  centimeters) 
in  length,  and  pass  from  the  kidneys  to  the  bladder,  behind  the  peri- 


PHYSIOLOGICAL  ANATOMY    OF    THE    URINARY    PASSAGES       333 

toneum.  They  have  three  distinct  coats  :  an  external  coat,  composed  of 
ordinary  fibrous  tissue  with  small  elastic  fibres  ;  a  middle  coat,  composed 
of  non-striated  muscular  fibres ;  and  a  mucous  coat. 

The  external  coat  requires  no  special  description.  It  is  prolonged 
into  the  calices  and  is  continuous  with  the  fibrous  coat  of  the  kidney. 

The  fibres  of  the  muscular  coat,  in  the  greatest  part  of  the  length 
of  the  ureters,  interlace  with  each  other  in  every  direction  and  are  not 
arranged  in  distinct  layers  ;  but  near  the  bladder,  is  an  internal  layer, 
in  which  the  direction  of  the  fibres  is  longitudinal. 

The  mucous  lining  is  thin,  smooth  and  without  follicular  glands. 
It  is  thrown  into  narrow  longitudinal  folds,  when  the  tube  is  flaccid, 
which  are  easily  effaced  by  distention.  The  epithelium  exists  in  several 
layers  and  is  remarkable  for  the  irregular  shape  of  the  cells.  These 
present,  usually,  dark  granules  and  one  or  two  clear  nuclei  with  distinct 
nucleoli.  Some  of  the  cells  are  flattened,  some  are  rounded,  and  some 
are  caudate  with  one  or  two  prolongations. 

Passing  to  the  base  of  the  bladder,  the  ureters  become  constricted, 
penetrate  the  coats  of  this  organ  obliquely,  their  course  in  its  walls 
being  a  little  less  than  an  inch  (25  millimeters)  in  length.  This  valvular 
opening  allows  the  free  passage  of  the  urine  from  the  ureters,  but  com- 
pression or  distention  of  the  bladder  closes  the  orifices  and  opposes  a 
return  of  the  liquid. 

The  bladder,  which  serves  as  a  reserv^oir  for  the  urine,  varies  in  its 
relations  to  the  pelvic  and  abdominal  organs  as  it  is  empty  or  more  or 
less  distended.  When  empty,  it  lies  deeply  in  the  pelvic  cavity  and  is 
then  a  small  sac  of  an  irregularly-triangular  form.  As  it  becomes  filled, 
it  assumes  a  globular  or  ovoid  form,  rises  up  in  the  pelvic  cavity,  and 
when  excessively  distended,  it  may  extend  partly  into  the  abdomen. 
When  the  urine  is  voided  at  normal  intervals,  the  bladder,  when  filled, 
contains  about  a  pint  (nearly  500  cubic  centimeters)  of  liquid  ;  but  under 
pathological  conditions  it  may  become  distended  so  as  to  contain  ten  or 
twelve  pints  (about  4  or  5  liters),  and  in  some  instances  of  obstruction 
it  has  been  found  to  contain  even  more.  The  bladder  usually  is  more 
capacious  in  the  female  than  in  the  male. 

The  coats  of  the  bladder  are  three  in  number.  The  external  coat 
is  simply  a  reflection  of  the  peritoneum,  covering  the  posterior  portion 
completely,  from  the  openings  of  the  ureters  to  the  summit,  about  one- 
third  of  the  lateral  portion  and  a  small  part  of  the  anterior  portion. 

The  middle  or  muscular  coat  consists  of  non-striated  fibres,  arranged 
in  three  tolerably  distinct  layers  :  The  external  muscular  layer  is  com- 
posed of  longitudinal  fibres,  which  arise  from  parts  adjacent  to  the 
neck,  and  pass  anteriorly,  posteriorly  and  laterallv  over  the  organ,  so 


334  EXCRETION 

that  when  they  contract  they  diminish  its  capacity  chiefly  by  shorten- 
ing its  vertical  diameter.  The  fibres  of  the  external  layer  are  of  a 
pinkish  hue,  being  much  more  highly  colored  than  the  other  layers. 
The  middle  layer  is  formed  of  circular  fibres,  arranged,  on  the  anterior 
surface  of  the  bladder,  in  distinct  bands  at  right  angles  to  the  superfi- 
cial fibres.  They  are  thinner  and  less  strongly  marked  on  the  posterior 
and  lateral  surfaces.  The  internal  layer  is  composed  of  pale  fibres 
arranged  in  longitudinal  fasciculi,  the  anterior  and  lateral  bundles  anas- 
tomosing with  each  other,  as  they  descend  toward  the  neck  of  the 
bladder,  by  oblique  bands  of  communication,  and  the  posterior  bundles 
interlacing  in  every  direction,  forming  an  irregular  plexus.  Here  they 
are  not  to  be  distinguished  from  the  fibres  of  the  middle  layer.  This  is 
sometimes  called  the  plexiform  layer ;  and  it  gives  to  the  interior  of  the 
bladder  its  reticulated  appearance.  This  layer  is  continuous  with  the 
muscular  fibres  of  the  urachus,  the  ureters  and  the  urethra. 

The  sphincter  vesicae  is  a  band  of  non-striated  fibres,  about  half  an 
inch  (12.7  millimeters)  in  breadth  and  one-eighth  of  an  inch  (3.2  milli- 
meters) in  thickness,  embracing  the  neck  of  the  bladder  and  the  poste- 
rior half  of  the  prostatic  portion  of  the  urethra.  The  tonic  contraction 
of  these  fibres  prevents  the  discharge  of  urine,  and  during  the  ejacula- 
tion of  semen,  it  offers  an  obstruction  to  its  passage  into  the  bladder. 

The  mucous  membrane  of  the  bladder  is  smooth,  rather  pale,  thick, 
and  loosely  adherent  to  the  submucous  tissue,  except  over  the  corpus 
trigonum.  The  epithelium  is  stratified  and  presents  the  same  diversity 
in  form  as  that  observed  in  the  pelvis  of  the  kidney  and  the  ureters. 
In  the  neck  and  fundus  of  the  bladder,  are  a  few  mucous  glands,  some 
in  the  form  of  simple  follicles  and  others  collected  to  form  glands  of 
the  simple  racemose  variety. 

The  corpus  trigonum  is  a  triangular  body  lying  just  beneath  the 
mucous  membrane  at  the  base  of  the  bladder  and  extending  from  the 
urethra  in  front  to  the  openings  of  the  ureters.  It  is  composed  of 
ordinary  fibrous  tissue  with  a  few  elastic  and  muscular  fibres.  At  the 
opening  of  the  urethra,  it  presents  a  small  projecting  fold  of  mucous 
membrane,  which  is  sometimes  called  the  uvula  vesicae.  Over  the  sur- 
face of  the  trigone,  the  mucous  membrane  is  closely  adherent,  and  it  is 
not  thrown  into  folds  even  when  the  bladder  is  entirely  empty. 

The  bloodvessels  going  to  the  bladder  are  finally  distributed  to  its 
mucous  membrane.  They  are  not  abundant  except  at  the  fundus, 
where  the  mucous  membrane  is  very  vascular.  Lymphatics  are 
found  in  the  walls  of  the  bladder.  The  nerves  of  the  bladder  are 
derived  from  the  hypogastric  plexus. 

The  urethra  is  provided  with  muscular  fibres,  and  it  is  lined  by  a 


MECHANISM    OF   THE    DISCHARGE    OF   URINE  335 

mucous  membrane,  the  anatomy  of  which  will  be  more  fully  considered 
in  connection  with  embryology.  In  the  female  the  epithelium  of  the 
urethra  is  hke  that  of  the  bladder.  In  the  male  the  epithelial  cells  are 
small,  pale  and  of  the  columnar  variety. 

Mechanism  of  the  Discharge  of  Urine. — In  the  human  subject,  the 
urine  is  discharged  into  the  pelves  of  the  kidneys  and  the  ureters  by 
pressure  due  to  the  act  of  separation  of  liquid  from  the  blood.  Once 
discharged  into  the  ureters,  the  course  of  the  urine  is  determined  in 
part  by  the  vis  a  tergo,  and  in  part,  probably,  by  the  action  of  the  mus- 
cular coats  of  these  canals. 

When  the  urine  has  accumulated  in  certain  quantity  in  the  bladder, 
a  peculiar  sensation  is  felt  which  leads  to  the  act  for  its  expulsion.  The 
intervals  at  which  it  is  experienced  are  variable.  The  urine  usually  is 
voided  before  retiring  to  rest,  on  rising  in  the  morning,  and  two  or  three 
times,  in  addition,  during  the  day.  The  frequency  of  micturition,  how- 
ever, depends  on  habit,  on  the  quantity  of  liquids  ingested  and  on 
the  degree  of  activity  of  the  skin. 

Evacuation  of  the  bladder  is  accompHshed  by  the  muscular  walls  of 
the  organ  itself,  aided  by  contractions  of  the  diaphragm  and  the  abdomi- 
nal muscles  with  certain  muscles  which  operate  on  the  urethra,  and 
it  is  accompanied  by  relaxation  of  the  sphincter  vesic£e.  This  act  is  at 
first  voluntary,  but  once  begun,  it  may  be  continued  by  the  involuntary 
contraction  of  the  bladder  alone.  During  the  first  part  of  the  process, 
the  distended  bladder  is  compressed  by  contraction  of  the  diaphragm 
and  the  abdominal  muscles  ;  and  this  after  a  time  excites  the  action  of 
the  bladder  itself.  A  certain  time  usually  elapses  then  before  the  urine 
begins  to  flow.  When  the  bladder  contracts,  aided  by  the  muscles  of 
the  abdomen  and  the  diaphragm^  the  resistance  of  the  sphincter  is  over- 
come and  a  jet  of  urine  flows  from  the  urethra.  All  voluntary  action 
may  then  cease  for  a  time,  and  the  bladder  will  nearly  empty  itself ;  but 
the  force  of  the  jet  may  be  increased  by  voluntary  effort. 

Toward  the  end  of  the  expulsive  act,  when  the  quantity  of  liquid 
remaining  in  the  bladder  is  small,  the  diaphragm  and  the  abdominal 
muscles  are  again  called  into  action,  and  there  is  a  convulsive  inter- 
rupted discharge  of  the  small  quantity  of  urine  that  remains.  At  this 
time  the  impulse  from  the  bladder,  and,  indeed,  the  influence  of  the 
abdominal  muscles  and  diaphragm,  are  very  slight,  and  the  flow  of  urine 
along  the  urethra  is  aided  by  the  contractions  of  its  muscular  walls  and 
the  action  of  certain  of  the  perineal  muscles,  the  most  efficient  being 
the  accelerator  urinas;  but  with  all  this  muscular  action,  a  few  drops 
of  urine  remain  in  the  male  urethra  after  the  act  of  urination  has  been 
accomplished.     The  process  of  evacuation  of  urine  in  the  female  is  essen- 


336  EXCRETION 

tially  the  same  as  in  the  male,  with  the  exception  of  the  slight  modifica- 
tions due  to  differences  in  the  direction  and  length  of  the  urethra. 

According  to  Budge,  the  influence  of  the  nervous  system  on  the 
bladder  operates  through  the  sympathetic ;  and  he  has  described  a 
centre  in  the  spinal  cord,  which  presides  over  the  contractions  of  the 
lower  part  of  the  intestinal  canal,  the  bladder  and  the  vasa  deferentia. 
This  is  called  the  genito  spinal  centre,  and  it  has  been  located,  in  experi- 
ments on  rabbits,  in  the  spinal  cord,  at  a  point  opposite  the  fourth 
lumbar  vertebra.  From  this  centre  the  nervous  filaments  pass  through 
the  sympathetic  nerve,  communicating  with  the  ganghon  which  corre- 
sponds to  the  fifth  lumbar  vertebra. 

Properties  and  Composition  of  the  Urine 

The  color  of  the  urine  in  the  human  subject  is  quite  variable  within 
the  limits  of  health  and  depends  to  a  considerable  extent  on  the  char- 
acter of  food,  the  quantity  of  drink  and  the  activity  of  the  skin.  As  a 
rule  the  color  is  yellowish  or  amber,  with  more  or  less  of  a  reddish  tint. 
The  liquid  is  perfectly  transparent,  free  from  viscidity,  and  exhales, 
when  first  passed,  a  peculiar  aromatic  odor  that  is  not  disagreeable. 
Soon  after  the  urine  cools,  it  loses  this  peculiar  odor  and  has  an  odor 
known  as  urinous.  This  odor  remains  until  the  liquid  begins  to  undergo 
decomposition.  The  color  and  odor  of  the  urine  usually  are  modified  by 
the  same  physiological  conditions.  When  the  urine  contains  a  large 
proportion  of  solid  matters,  the  color  is  more  intense  and  the  urinous 
odor  is  more  penetrating ;  and  when  its  quantity  is  increased  by  an  ex- 
cess of  water,  the  specific  gravity  is  low,  the  color  is  pale  and  the  odor  is 
faint.  The  first  urine  passed  in  the  morning,  immediately  after  rising, 
usually  is  more  intense  in  color  than  that  passed  during  the  day  and 
contains  a  relatively  larger  proportion  of  solids  in  solution. 

The  temperature  of  the  urine  at  the  moment  of  its  emission,  under 
physiological  conditions,  varies  but  a  small  fraction  of  a  degree  from 
ioo°  Fahr.  (37.78°  C). 

In  estimating  the  total  quantity  of  urine  discharged  in  the  twenty- 
four  hours,  it  is  important  to  take  into  consideration  the  specific  gravity 
as  an  indication  of  the  amount  of  solid  matter  excreted  by  the  kidneys. 
Variations  in  quantity  constantly  occur  in  health,  depending  on  the 
proportion  of  water ;  but  the  quantity  of  solid  matters  excreted  usually 
is  more  nearly  uniform.  It  must  also  be  taken  into  account  that 
differences  in  climate,  habits  of  life  etc.,  in  different  countries,  have  an 
important  influence  on  the  daily  quantity  of  urine.  Parkes  collected 
the  results  of  twenty-six  series  of  observations  made  in  America,  Eng- 


PROPERTIES    AND    COMPOSITION    OF   THE   URINE  337 

land,  France  and  Germany,  and  found  the  average  daily  quantity  of 
urine  in  healthy  male  adults,  between  twenty  and  forty  years  of  age,  to  be 
fifty-two  and  a  half  fluidounces  (1552.6  cubic  centimeters),  the  average 
quantity  per  hour  being  two  and  one-tenth  fluidounces  (62  cubic  centi- 
meters). The  extremes  were  thirty-five  ounces  and  eighty-one  ounces 
(1035  and  2395  cubic  centimeters).  The  average  quantity  may  be 
assumed  to  be  about  fifty-one  fluidounces  (1500  cubic  centimeters). 
The  normal  range  of  variation  is  between  thirty  and  sixty  ounces  (about 
900  and  1775  cubic  centimeters).  The  conditions  which  lead  to  a  dimi- 
nution in  the  quantity  of  urine  usually  are  more  efficient  in  their  opera- 
tion than  those  which  tend  to  an  increase ;  and  the  range  below  the 
normal  standard  is  rather  wider  than  it  is  above.  More  urine  usually 
is  secreted  during  the  day  than  at  night.  The  quantity  of  water  dis- 
charged by  the  kidneys  in  the  twenty -four  hours  is  a  little  greater  in 
the  female  than  in  the  male ;  but  in  the  female  the  specific  gravity  is 
lower,  and  the  quantity  of  solid  constituents  is  relatively  and  absolutely 
less. 

The  specific  gravity  of  the  urine  should  be  estimated  in  connection 
with  the  absolute  quantity  in  the  twenty-four  hours.  Those  who  assume 
that  the  daily  quantity  is  about  fifty-one  ounces  (1500  cubic  centimeters), 
give  the  ordinary  specific  gravity  of  the  mixed  urine  of  the  twenty-four 
hours  as  about  1020.  The  specific  gravity  is  Hable  to  the  same  varia- 
tions as  the  proportion  of  water,  and  the  density  is  increased  as  the 
water  is  diminished.  The  ordinary  range  of  variation  in  specific  gravity 
is  between  1015  and  1025  ;  but  without  positively  indicating  a  pathologi- 
cal condition,  it  may  temporarily  be  as  low  as  1005  or  as  high  as  1030. 

The  reaction  of  the  urine  is  acid  in  the  carnivora  and  alkaline  in 
the  herbivora.  In  the  human  subject  it  usually  is  acid  at  the  moment 
of  its  discharge  from  the  bladder ;  although  at  certain  times  of  the  day 
it  may  be  neutral  or  feebly  alkaline,  the  reaction  depending  on  the 
character  of  food.  The  acidity  may  be  measured  by  neutralizing  the 
urine  with  an  alkali  in  a  solution  that  has  previously  been  graduated 
with  a  solution  of  oxalic  acid  of  known  strength ;  and  the  degree  of 
acidity  usually  is  expressed  as  equivalent  to  so  many  grains  of  crystal- 
lized oxalic  acid. 

The  total  quantity  of  acid  in  the  urine  of  the  twenty-four  hours  in 
a  healthy  adult  male  is  equal  to  between  thirty  and  sixty  grains  (2  and 
4  grams)  of  oxalic  acid.  The  hourly  quantity  in  the  observations  of 
Vogel  was  equal,  in  round  numbers,  to  between  one  and  a  half  and  three 
grains  (o. i  and  0.2  gram)  of  acid.  The  proportion  of  acid  was  found  to 
be  variable  in  the  same  person  at  different  times  of  the  day.  The  urine 
contains  no  free  acid,  but  its  acidity  under  an  animal  or  a  mixed  diet 


338 


EXCRETION 


depends  on  the   presence  of  acid  salts,  the   principal  salt  being  acid 
sodium  phosphate,  with  possibly  a  little  acid  calcium  phosphate. 


COMPOSITION   OF  THE   HUMAN   URINE 

Water  (in  24  hours,  27  to  50  fluidounces,  800  to  1480  cubic  centimeters 

—  Becquerel) 967.47  to  940.36 

Urea  (in  24  hours,  355  to  463  grains,  23  to  30  grams — Robin) 15.00  to     23.00 

Uric  acid accidental,  or  traces 

Sodium  urate,  neutral  and  acid 


Ammonium  urate,  neutral  and  acid 

small  quantity) 
Potassium  urate 
Calcium  urate 
Magnesium  urate 
Sodium  hippurate 
Potassium  hippurate 
Calcium  hippurate 
Sodium  lactate 
Potassium  lactate 
Calcium  lactate 
Creatin 
Crealinin 


(in 


(In  24  hours,  6  to  9  grains, 

0.39  to  0.58  gram,  of  uric  acid  — 

•  Becquerel — or  9  to  14  grains,  0.58 

I  to  0.9  gram,  of  urates,  estimated 

as  neutral  urate  of  soda)    .     .     . 

(In  24  hours,  about  7.5  grains,  0.486  gram,  of 
hippuric  acid — Thudichum — equivalent  to  about 
8.7  grains,  0.566  gram,  of  sodium  hippurate)    , 


1. 00  to 


1.60 


(Daily  quantity  not  estimated) 


(In  24  hours,  about  1 1.5  grains,  0.745  gram, 
of  both  —  Thudichum) 


Sodium  sulphate 
Potassium  sulphate 
Calcium  sulphate  (traces) 


Calcium  oxalate  (daily  quantity  not  estimated) traces 

Xanthin 

Palmitin,  olein  and  other  fatty  matters , 

Sodium  chloride  (in  24  hours,  about  154  grains,  10  grams — Robin)    .     ,     . 

Potassium  chloride 

Ammonium  chloride 

(In  24  hours,  23  to  38  grains,  1.5  to  2.5 
grams,  of  sulphuric  acid  —  Thudichum.  About 
equal  parts  of  sodium  sulphate  and  potassium 
sulphate  —  Robin  —  equivalent  to  22.5  to  37.5 
grains,  1.45  to  2.43  grams  of  each)      .... 

Potassium  indoxyl-sulphate  (indican) 

Sodium  phosphate,  neutral 

Sodium  phosphate,  acid 

Magnesium  phosphate  (in  24  hours,  7.7  to  11.8  grains,  0.5  to  0.768  gram  — 
Neubauer) 

Calcium  phosiihate,  acid        |       (In    24    hours,   4.7   to   5.7   grains,   0.307   to 

Calcium  phosphate,  basic      )  0.372  gram  —  Neubauer) 

Ammonio-magnesian  phosphate  (daily  quantity  not  estimated) 

(Daily  excretion  of  phosphoric  acid,  about  56  grains,  3.629  grams  — 
Thudichum.) 

Silicic  acid 

Urochrome  ) 

Mucus  from  the  bladder    ! 

Proportion  of  solid  constituents,  32.63  to  59.89  parts  per  1000. 


1. 00  to 

1.40 

1.50  to 

2.60 

1.60  to 

3.00 

■aces  to 

1. 10 

not  estimated. 

o.io  to 

0.20 

3.00  to 

8.00 

traces 

i       (Daily  quantity  not  estimated) 


1.50  to       2.20 


3.00  to       7.00 

not  estimated. 

2.50  to       4.30 
0.50  to        1. 00 


0.20  to 

1.30 

1.50  to 

2.40 

0.03  to 

0.04 

O.IO   to 

0.50 

1000.00      1000.00 

Gases  of  the  Urine. 

Oxygen  in  solution 

Nitrogen  in  solution 

Carbon  dioxide  in  solution 


(Parts  per  1000,  in  volume) 


0.90  to        1. 00 

7.00  to     10.00 

.45  to     50.00 


UREA  339 

Composition  of  the  Urine.  —  Regarding  the  excrementitioiis  constitu- 
ents of  the  urine  as  a  measure,  to  a  certain  extent,  of  the  general 
processes  of  katabolism,  it  is  more  important  to  recognize  the  quantities 
of  these  products  discharged  in  a  definite  time  than  to  learn  simply  their 
proportions  in  the  urine ;  and  in  the  preceding  table  of  composition  of 
the  urine,  the  absolute  quantities  of  its  different  constituents  excreted 
in  twenty-four  hours  have  been  given  when  practicable. 

Urea.  —  As  regards  quantity,  and  probably  as  a  measure  of  the 
activity  of  the  process  of  proteid  katabolism,  urea  —  CO(NH2)2  —  is 
the  most  important  of  the  urinary  constituents.  Regarding  the  daily 
excretion  of  urea  as  a  measure  of  the  physiological  wear  of  certain 
tissues,  its  consideration  would  come  properly  under  the  head  of  nu- 
trition, in  connection  with  other  substances  known  to  be  products  of 
katabolism ;  but  it  is  convenient  to  treat  of  its  general  physiological 
properties  and  some  of  its  variations  in  common  with  other  excrementi- 
tious  matters  separated  by  the  kidneys,  in  connection  with  the  composi- 
tion of  the  urine. 

The  formula  for  urea,  showing  the  presence  of  a  large  proportion  of 
nitrogen,  would  lead  to  the  supposition  that  this  substance  is  one  of  the 
products  of  the  wear  of  the  nitrogenous  constituents  of  the  body.  It  is 
found,  under  normal  conditions,  in  the  urine,  the  lymph  and  chyle,  the 
blood,  the  sweat,  the  vitreous  humor  and  a  trace  in  the  saliva.  Its 
presence  has  been  demonstrated,  also,  in  the  substance  of  the  healthy 
liver  in  both  carnivorous  and  herbivorous  animals ;  and  it  has  been 
found  in  minute  quantity  in  the  muscular  juice. 

Urea  has  been  produced  synthetically  by  combining  ammonium 
sulphate  with  potassium.  The  products  of  this  combination  are  potas- 
sium sulphate,  with  cyanic  acid  and  ammonium  in  a  form  to  consti- 
tute urea.  Ammonium  cyan  ate  is  isomeric  with  urea,  and  the  change 
is  effected  by  a  rearrangement  of  its  elements.  It  has  long  been  known 
that  urea  is  readily  convertible  into  ammonium  carbonate  ;  and  ammo- 
nium carbonate,  when  heated  in  sealed  tubes  to  the  temperature  at  which 
urea  begins  to  decompose,  is  converted  into  urea. 

Urea  may  readily  be  extracted  from  the  urine  by  processes  fully 
described  in  works  on  physiological  chemistry ;  and  its  proportion 
may  now  easily  be  estimated  by  the  various  methods  of  volumetric 
analysis.  It  is  not  so  easy,  however,  to  separate  it  from  the  blood  or 
from  the  substance  of  any  of  the  tissues,  on  account  of  the  difficulty  in 
getting  rid  of  other  organic  matters  and  the  readiness  with  which  it 
undergoes  decomposition. 

When  pure,  urea  crystallizes  in  the  form  of  long,  four-sided,  colorless 
and  transparent  prisms,  which  are  without  odor,  neutral,  and  in  taste 


340  EXCRETION 

resemble  saltpetre.  These  crystals  are  very  soluble  in  water  and  in 
alcohol  but  are  insoluble  in  ether.  In  its  behavior  with  reagents,  urea 
acts  as  a  base,  combining  readily  with  certain  acids,  particularly  nitric 
and  oxalic.  It  also  forms  combinations  with  certain  salts,  such  as  mer- 
curic oxide,  sodium  chloride  etc.  It  exists  in  the  economy  in  a  state  of 
watery  solution,  with  perhaps  a  small  portion  modified  by  the  presence 
of  sodium  chloride. 

Origin  of  Urea.  —  It  is  now  admitted  by  physiologists  that  urea  is  not 
formed  in  the  kidneys  but  preexists  in  the  blood.  It  finds  its  way  into 
the  blood,  in  part  directly  from  the  tissues,  and  in  part  from  the  lymph, 
which  contains  a  greater  proportion  of  urea  than  is  found  in  the  blood 
itself.  The  principal  seat  of  its  formation,  however,  is  the  liver,  although 
it  is  produced  in  other  organs  in  small  quantity.  The  quantity  of  urea 
in  the  blood  is  kept  down  by  the  eliminating  action  of  the  kidneys.  In 
certain  cases  of  structural  diseases  of  the  liver,  the  excretion  of  urea  is 
much  diminished,  and  it  may,  indeed,  disappear  from  the  urine. 

Proteids,  in  the  metabolic  processes  that  result  in  the  change  of  the 
albuminous  constituents  of  the  tissues  into  urea,  are  supposed  to  un- 
dergo the  following  changes.  The  carbon  molecules  are  oxidized  into 
carbon  dioxide,  nitrogen  is  split  off  as  ammonia  (NHg),  and  the  two 
combine  to  form  ammonium  carbonate.  In  the  liver,  ammonium  car- 
bonate loses  one  molecule  of  water  and  is  converted  into  ammonium  car- 
bamate. This  loses  a  second  molecule  of  water  and  is  converted  into 
carbamid  (urea).  Carbamic  acid  in  a  free  state  is  unknown ;  but  it 
exists  as  ammonium  carbamate  in  commercial  ammonium  carbonate. 

Assuming  that  urea  is  the  most  abundant  and  important  of  the  ni- 
trogenous excrementitious  products  —  which  is  fully  justified  by  physio- 
logical facts  —  it  is  difficult  to  avoid  the  conclusion  that  this  substance 
represents,  to  a  great  extent,  the  katabolism  of  the  nitrogenous  parts  of 
the  tissues  and  necessarily  the  physiological  wear  of  the  muscular  sub- 
stance. The  fact  that  urea  exists  in  very  minute  quantity  in  the  muscles 
—  some  chemists  state  that  it  is  absent  —  probably  is  due  to  its  constant 
removal  by  the  blood  and  lymph. 

Uric  acid,  creatin,  creatinin,  xanthin,  hypoxanthin,  leucin,  tyrosin 
and  some  other  analogous  substances  are  to  be  regarded  as  formations 
antecedent  to  urea,  urea  being  the  final  and  perfect  excrementitious 
product  of  the  liver. 

Influence  of  Ingesta  on  the  Compositioji  of  the  Urine  and  on  the  Elimi- 
nation of  Nitrogen.  —  Water  and  other  liquid  ingesta  usually  increase 
the  proportion  of  water  in  the  urine  and  diminish  its  specific  gravity. 
This  is  so  marked  after  the  ingestion  of  large  quantities  of  liquids,  that 
the  urine  passed  under  these  conditions  is  sometimes  spoken  of  as  the 


ELLAIIXATIOX    OF    NITROGEN  34I 

urina  potus ;  but  when  an  excess  of  water  has  been  taken  for  purposes 
of  experiment,  the  diet  being  carefully  regulated,  the  absolute  quantity 
of  soUd  matters  excreted  is  considerably  increased.  This  is  particularly 
marked  as  regards  urea,  but  it  is  noticeable  in  the  sulphates  and  phos- 
phates, though  not  to  any  great  extent  in  the  chlorides.  The  results  of 
experiments  on  this  point  seem  to  show  that  water  taken  in  excess 
increases  the  activity  of  katabolism. 

-  The  ordinary  meals  increase  the  solid  constituents  of  the  urine,  the 
most  constant  and  uniform  increase  being  in  the  proportion  of  urea. 
This,  however,  depends  to  a  great  extent  on  the  kind  of  food  taken. 
The  increase  usually  is  noted  during  the  first  hour  after  a  meal  and 
attains  its  maximum  at  the  third  or  fourth  hour.  The  inorganic  matters 
are  increased  as  well  as  the  excrementitious  substances  proper.  The 
urine  passed  after  taking  food  has  been  called  urina  cibi,  under  the  idea 
that  it  is  to  be  distinguished  from  the  urine  supposed  to  be  derived 
exclusively  from  katabolism,  which  is  called  the  urina  sanguinis. 

It  is  an  important  question,  to  determine  the  influence  of  different 
kinds  of  food  on  the  composition  of  the  urine,  particularly  the  compara- 
tive effects  of  a  nitrogenous  and  a  non-nitrogenous  diet.  Lehmann 
made  a  number  of  observations  on  this  point,  and  his  results  have  been 
confirmed  by  many  other  physiologists.  Without  discussing  fully  all 
these  observations,  it  is  sufficient  to  state  that  the  ingestion  of  an  excess 
of  nitrogenous  food  always  produced  a  great  increase  in  the  proportion 
of  the  nitrogenous  constituents  of  the  urine,  particularly  urea.  On  a 
non-nitrogenous  diet,  the  proportion  of  urea  was  found  to  be  diminished 
more  than  one-half.  The  general  results  of  the  experiments  of  Lehmann 
are  embodied  in  the  following  quotation:  — 

"  My  experiments  show  that  the  amount  of  urea  which  is  excreted 
is  extremely  dependent  on  the  nature  of  the  food  which  has  been  pre- 
Wously  taken.  On  a  purely  animal  diet,  or  on  food  very  rich  in  nitrogen, 
there  were  often  two-fifths  more  urea  excreted  than  on  a  mixed  diet ; 
while,  on  a  mixed  diet,  there  was  almost  one-third  more  than  on  a  purely 
vegetable  diet ;  while,  finally,  on  a  non-nitrogenous  diet,  the  amount  of 
urea  was  less  than  half  the  quantity  excreted  during  an  ordinary  mixed 
diet." 

The  influence  of  food  is  not  confined  to  the  period  when  any  particu- 
lar kind  of  food  is  taken,  but  is  continued  for  many  hours  after  a  return 
to  the  ordinary  diet. 

In  regard  to  the  influence  of  food  on  the  inorganic  constituents  of 
the  urine,  it  may  be  stated  in  general  terms  that  the  ingestion  of 
mineral  substances  increases  their  proportion  in  the  excretions. 

There  are  certain  articles  which,  when  taken  into  the  svstem,  the 


342 


EXCRETION 


diet  being  regular,  seem  to  retard  the  process  of  katabolism  ;  or  at  least 
they  diminish,  in  a  marked  manner,  the  quantity  of  matters  excreted, 
particularly  urea.  Alcohol  has  a  decided  influence  of  this  kind.  Its 
action  may  be  modified  by  the  presence  of  salts  and  other  matters  in  dif- 
ferent alcoholic  beverages,  but  in  nearly  all  direct  experiments,  alcohol 
either  taken  under  normal  conditions  of  diet,  when  the  diet  is  deficient 
or  when  it  is  in  excess,  diminishes  the  excretion  of  urea.  The  same  may 
be  stated  in  general  terms  of  tea  and  coffee. 

Influence  of  Muscular  Exercise  on  the  Elimination  of  Nitrogen.  —  In 
all  observations  on  the  influence  of  muscular  exercise  on  the  elimi- 
nation of  nitrogen,  account  should  be  taken  of  the  influence  of  diet; 
and  those  observations  are  most  valuable  which  have  given  the  propor- 
tion of  nitrogen  eliminated  to  the  nitrogen  of  food.  The  observations 
of  Fick  and  Wislicenus  (1866)  showed  a  diminution  in  the  elimination  of 
nitrogen  during  work  ;  but  during  the  time  of  the  muscular  work,  no 
nitrogenous  food  was  taken.  The  same  conditions  obtained  in  certain 
of  the  observations  of  Parkes.  In  a  series  of  observations  made  in  1880 
(FHnt),  on  a  man  who  walked  317^  miles  (about  510  kilometers)  in  five 
consecutive  days,  the  diet  was  normal,  and  the  proportionate  quantity  of 
nitrogen  was  calculated  for  three  periods  of  five  days  each,  with  the  fol- 
lowing results :  — 

For  the  five  days  before  the  walk,  with  an  average  exercise  of 
about  eight  miles  (13  kilometers)  daily,  the  nitrogen  eUminated  was 
92.82  parts  for  100  parts  of  nitrogen  ingested.  For  the  five  days  of  the 
walk,  for  every  hundred  parts  of  nitrogen  ingested,  there  were  discharged 
1 53.99  parts.  For  the  five  days  after  the  walk,  when  there  was  hardly 
any  exercise,  for  every  hundred  parts  of  nitrogen  ingested,  there  were 
discharged  84.63  parts.  During  the  walk,  the  nitrogen  excreted  was  in 
direct  ratio  to  the  amount  of  work  ;  and  the  excess  of  nitrogen  eliminated 
over  the  nitrogen  of  food  almost  exactly  corresponded  to  a  calculation  of 
the  nitrogen  of  the  muscular  tissue  consumed,  as  estimated  from  the  loss 
of  weight  of  the  body.  In  1876,  a  similar  series  of  observations  was 
made  on  the  same  man  by  Pavy.  In  these  observations  he  walked  450 
miles  (724.21  kilometers)  in  six  consecutive  days.  During  this  period 
the  proportionate  elimination  of  nitrogen  was  increased,  but  not  to  the 
extent  observed  in  1870.  Similar  results  —  although  the  experiments 
were  made  on  a  less  extended  scale  —  were  obtained  by  North  in  1878. 
These  observations  are  opposed  to  the  views  of  many  physiologists, 
since  the  experiments  of  Fick  and  Wislicenus,  who  regard  the  elimina- 
tion of  nitrogen  under  ordinary  conditions  as  dependent  mainly  on  the 
diet  and  not  upon  the  muscular  work  performed.  The  observations  of 
Voit,  indeed,  are  favorable  to  this  view. 


URIC   ACID   AND    ITS    COMPOUNDS  343 

Notwithstanding  the  results  obtained  by  Fick  and  WisHcenus,  Frank- 
land,  Haughton,  Voit,  and  others,  the  fact  remains  that  severe  and  pro- 
longed muscular  work  increases  the  elimination  of  nitrogen  over  and 
above  the  quantity  to  be  accounted  for  by  the  nitrogenous  food  taken. 
Actual  observations  (Flint,  Pavy  and  others)  are  conclusive  as  regards 
this  simple  fact ;  but  it  is  well  known  that  muscular  exercise  largely 
increases  the  elimination  of  carbon  dioxide  and  the  consumption  of 
oxygen.  In  exercise  so  violent  as  to  produce  dyspnoea,  the  distress  in 
breathing  probably  is  due  to  the  impossibihty  of  supplying  by  the  lungs 
sufficient  oxygen  to  meet  the  increased  demand  on  the  part  of  the  mus- 
cular system,  and  the  possible  amount  of  muscular  work  is  thereby 
limited. 

The  observations  and  conclusions  of  Oppenheim  (1880)  go  far  to 
harmonize  the  results  obtained  by  different  experimenters.  Oppenheim 
concludes  that  muscular  work,  when  not  carried  to  the  extent  of  pro- 
ducing shortness  of  breath  or  when  moderate  and  extending  over  a  con- 
siderable length  of  time,  does  not  increase  the  ehmination  of  urea ;  but 
that  even  less  work,  when  violent  and  attended  with  shortness  of  breath, 
increases  the  discharge  of  urea.  According  to  this  view,  moderate 
work  draws  on  the  oxygen  supplied  to  the  body  and  at  once  largely 
increases  the  elimination  of  carbon  dioxide ;  but  the  less  active  processes 
which  result  in  the  production  of  urea  are  not  so  promptly  affected. 
Violent  muscular  work,  however,  or  work  which  is  excessively  prolonged, 
consumes  those  parts  of  the  tissues  the  kataboHsm  of  which  is  repre- 
sented by  the  discharge  of  urea.  This  view,  if  accepted,  harmonizes 
the  apparently  contradictory  experiments  on  the  influence  of  muscu- 
lar work  on  the  elimination  of  nitrogen. 

The  daily  quantity  of  urea  excreted  is  subject  to  considerable  varia- 
tions. It  is  given  in  the  table  as  355  to  463  grains  (23  to  30  grams). 
This  is  less  than  the  estimates  frequently  given ;  but  when  the  quan- 
tity has  been  very  large,  it  has  depended  on  an  unusual  amount  of 
nitrogenous  food,  or  the  weight  of  the  body  has  been  above  the  average. 
Parkes  has  given  the  results  of  twenty-five  different  series  of  observations 
on  this  point.  The  lowest  estimate  was  286.1  grains  (18.24  grams),  and 
the  highest,  688.4  grains  (44.61  grams). 

Uric  Acid  and  its  Compounds.  — Uric  acid  (C5H4N4O3)  seldom  if 
ever  exists  in  a  free  state  in  normal  urine.  It  is  very  insoluble,  re- 
quiring fourteen  to  fifteen  thousand  times  its  volume  of  cold  water  or 
eighteen  to  nineteen  hundred  parts  of  boiling  water  for  its  solution.  Its 
presence  uncombined  in  the  urine  must  be  regarded  as  a  pathological 
condition. 

In  normal   urine,  uric   acid  is  combined  with  sodium,  ammonium, 


344 


EXCRETION 


potassium,  calcium  and  magnesium.  Of  these  combinations,  the  sodium 
urate  and  ammonium  urate  are  by  far  the  most  important,  and  they  con- 
stitute a  great  proportion  of  the  urates,  potassium,  calcium  and  magne- 
sium urates  existing  only  in  minute  traces.  Sodium  urate  is  much  more 
abundant  than  ammonium  urate.  The  union  of  uric  acid  with  the  bases 
is  verv  feeble.  If  from  any  cause  the  urine  becomes  excessively  acid 
after  its  emission,  a  deposit  of  uric  acid  is  Hkely  to  occur.  The  addi- 
tion of  a  very  small  quantity  of  almost  any  acid  is  sufficient  to  decom- 
pose the  urates,  when  the  uric  acid  appears  after  a  few  hours,  in  a 
crystalline  form. 

Uric  acid,  probably  in  combination  with  bases,  is  always  found  in  the 
substance  of  the  liver  in  large  quantity.  The  urates  also  exist  in  the 
blood  in  small  quantity  and  pass  ready-formed  into  the  urine.  The  fact 
that  the  urates  exist  in  the  liver  has  led  to  the  opinion  that  this  organ  is 
the  principal  seat  of  the  formation  of  uric  acid  (Meissner).  However 
this  may  be,  uric  acid  certainly  is  not  formed  in  the  kidneys  but  is 
simply  separated  by  these  organs  from  the  blood.  Meissner  did  not 
succeed  in  finding  uric  acid  in  the  muscular  tissue,  although  the  speci- 
mens were  taken  from  animals  in  which  he  had  found  large  quantities  in 
the  liver.  The  urates,  particularly  sodium  urate,  are  products  of  katabo- 
lism  of  the  proteid  constituents  of  the  body. 

The  daily  excretion  of  uric  acid,  given  in  the  table,  is  six  to  nine 
grains  (0.39  to  0.58  gram),  the  equivalent  of  nine  to  fourteen  grains 
(0.58  to  0.9  gram)  of  urates  estimated  as  neutral  sodium  urate.  Like 
urea,  the  proportion  of  urates  in  the  urine  is  subject  to  certain  physio- 
logical variations. 

Hipptiric  Acid,  Hippiiratcs  and  Lactates.  —  The  compounds  of  hip- 
puric  acid  (C9H9NO3),  which  are  so  abundant  in  the  urine  of  the  her- 
bivora,  are  now  known  to  be  constant  constituents  of  human  urine. 
Hippuric  acid  is  always  to  be  found  in  the  urine  of  children,  but  it  is 
sometimes  absent  temporarily  in  the  adult.  The  hippurates  have  been 
detected  in  the  blood  of  the  ox  and  have  since  been  found  in  the 
blood  of  the  human  subject.  There  can  be  scarcely  any  doubt  that 
they  pass  ready-formed  from  the  blood  into  the  urine.  As  to  the 
exact  mode  of  origin  of  the  hippurates,  there  is  even  less  information 
than  in  regard  to  the  origin  of  the  other  urinary  constituents  already 
considered.  Experiments  have  shown  that  the  proportion  of  hippuric 
acid  in  the  urine  is  greatest  after  taking  vegetable  food  ;  but  it  is  found 
after  a  purely  animal  diet,  and  probably  it  also  exists  during  fasting. 
The  daily  excretion  of  hippuric  acid  is  about  7.5  grains  (0.486  gram), 
which  is  equivalent  to  about  Z.J  grains  (0.566  gram)  of  sodium  hip- 
p  urate. 


CREATIN    AND    CREATININ 


345 


Hippuric  acid  itself,  unlike  uric  acid,  is  soluble  in  water  and  in  a 
mixture  of  hydrochloric  acid.  It  requires  six  hundred  parts  of  cold 
water  for  its  solution,  but  a  much  smaller  proportion  of  warm  water. 
Under  pathological  conditions  it  is  sometimes  found  free  in  solution  in 
the  urine. 

Sodium,  potassium  and  calcium  lactates  exist  in  considerable  quan- 
tity in  normal  urine.  They  are  derived  immediately  from  the  blood, 
passing  ready-formed  into  the  urine,  where  they  exist  in  simple  watery 
solution.  The  lactates  are  formed  in  the  muscles,  in  the  substance  of 
which  .they  can  readily  be  detected.  Physiologists  have  little  positive 
information  in  regard  to  the  precise  mode  of  formation  of  these  salts. 
It  is  probable,  however,  that  the  lactic  acid  is  the  result  of  transforma- 
tion of  glucose.  The  lactic  acid  contained  in  the  lactates  extracted  from 
the  muscular  substance  is  not  identical  with  the  acid  resulting  from  the 
transformation  of  the  sugars.  The  former  have  been  called  sarcolactates, 
and  they  contain  one  molecule  of  water  less  than  the  ordinary  lactates. 
The  compounds  of  lactic  acid  in  the  urine  are  in  the  form  of  sarcolac- 
tates. 

Creatin  and  Creatinin.  —  CreatinfC^HgNgOg)  and  creatininfC^H^NgO) 
probably  are  identical  in  their  relations  to  the  general  process  of  ka- 
tabolism,  for  one  is  easily  converted  into  the  other,  out  of  the  body,  by 
very  simple  chemical  means ;  and  there  is  every  reason  to  suppose  that 
in  the  organism  they  are  the  products  of  physiological  wear  of  the  same 
tissue  or  tissues.  These  substances  have  been  found  in  the  urine,  blood, 
muscular  tissue  and  brain.  By  certain  chemical  manipulations,  both 
creatin  and  creatinin  may  be  converted  into  urea.  These  substances 
are  now  regarded  as  excrementitious  matters,  taken  from  the  tissues  by 
the  blood,  to  be  eliminated  by  the  kidneys. 

Creatin  has  a  bitter  taste,  is  quite  soluble  in  cold  water  (one  part 
in  seventy-five),  and  is  much  more  soluble  in  hot  water,  from  which  it 
separates  in  a  crystalhne  form  on  cooling.  It  is  slightly  soluble  in  alco- 
hol and  is  insoluble  in  ether.  A  watery  solution  of  creatin  is  neutral. 
It  does  not  readily  form  combinations  as  a  base ;  but  it  has  lately  been 
made  to  form  crystalline  compounds  with  some  of  the  strong  mineral 
acids  —  nitric,  hydrochloric  or  sulphuric.  When  boiled  for  a  long  time 
with  barium  hydrate,  it  is  changed  into  urea  and  sarcosin.  When  boiled 
with  the  strong  acids,  creatin  loses  a  molecule  of  water  and  is  converted 
into  creatinin.  This  change  takes  place  readily  in  decomposing  urine, 
which  contains  neither  urea  nor  creatin  but  a  large  quantity  of  creatinin, 
when  far  advanced  in  putrefaction. 

Creatinin  is  more  soluble  than  creatin,  and  its  watery  solution  has 
a  strongly  alkaline  reaction.     It  is   dissolved  by  eleven  parts  of  cold 


346  EXCRETION 

water  and  is  even  more  soluble  in  boiling  water.  It  is  slightly  soluble 
in  ether  and  is  dissolved  by  one  hundred  parts  of  alcohol.  This  sub- 
stance is  one  of  the  strongest  of  the  organic  bases,  readily  forming 
crystalline  combinations  with  a  number  of  acids.  According  to  Thudi- 
chum,  creatin  is  the  original  excrementitious  substance  produced  in  the 
muscular  substance,  and  creatinin  is  formed  in  the  blood  by  a  trans- 
formation of  a  portion  of  the  creatin,  somewhere  between  the  muscles 
and  the  kidneys ;  "  for,  in  the  muscle,  creatin  has  by  far  the  preponder- 
ance over  creatinin  ;  in  the  urine,  creatinin  over  creatin."  The  fact  that 
creatin  has  been  found  in  the  brain  would  lead  to  the  supposition  that 
it  is  also  one  of  the  products  of  katabolism  of  nervous  tissue. 

The  average  daily  excretion  of  creatin  and  creatinin  has  been  esti- 
mated at  about  1 1.5  grains  (0.745  gram).  Of  this,  Thudichum  estimated 
that  4.5  grains  (0.292  gram)  consisted  of  creatin,  and  7  grains  (0.453 
gram)  of  creatinin. 

Calcium  Oxalate.  —  Calcium  oxalate  (oxalic  acid,C2H204)  is  not  con- 
stantly present  in  normal  human  urine,  although  it  may  exist  in  certain 
quantity  without  indicating  any  pathological  condition.  It  is  exceed- 
ingly insoluble,  and  the  appearance  of  its  crystals,  which  commonly  are 
in  the  form  of  small  regular  octahedra,  is  quite  characteristic.  A  small 
quantity  may  be  retained  in  solution  by  the  acid  sodium  phosphate  in 
the  urine.  Calcium  oxalate  may  find  its  way  out  of  the  system  by  the 
kidneys  after  it  has  been  taken  with  vegetable  food  or  with  certain 
medicinal  substances.  The  ordinary  rhubarb,  or  pie-plant,  contains  a 
large  quantity  of  calcium  oxalate,  which,  when  this  article  is  taken, 
passes  into  the  urine.  It  is  probable,  however,  that  a  certain  quantity 
is  formed  in  the  organism. 

XantJiin,  HypoxantJiin,  Leucin,  Tyrosui  and  Tauriti.  —  Traces  of 
xanthin  (C5H4N4O2)  have  been  found  in  the  normal  human  urine,  but 
its  proportion  has  not  been  estimated  and  observers  are  as  yet  but  im- 
perfectly acquainted  with  its  physiological  relations.  It  has  been  found 
in  the  liver,  spleen,  thymus,  pancreas,  muscles  and  brain.  It  is  insol- 
uble in  water  but  is  soluble  in  both  acid  and  alkaline  liquids.  Hypo- 
xanthin  (C5H4N4O)  has  not  been  found  in  normal  urine,  although  it 
exists  in  the  muscles,  liver,  spleen  and  thymus.  Leucin  (CgHjgN02) 
exists  in  the  pancreas,  salivary  glands,  thyroid,  thymus,  suprarenal  cap- 
sules, lymphatic  glands,  liver,  lungs,  kidneys  and  the  gray  substance  of 
the  brain.  It  has  not  been  detected  in  the  normal  urine.  The  same 
remarks  apply  to  tyrosin  (CgH^^NOg),  although  it  is  not  so  exten- 
sively distributed  in  the  economy,  to  taurin  (C2H7NO3S)  and  to  cystin 
(C3HyNS02).  The  last  two,  however,  contain  sulphur,  and  they  may 
have  peculiar  physiological  and  pathological  relations  that  are  not  at 
present  understood. 


INORGANIC   CONSTITUENTS    OF   THE    URINE  347 

Fatty  Matters.  —  Fat  and  fatty  acids  are  said  to  exist  in  the  normal 
urine  in  certain  quantity.  Their  proportion,  however,  is  small,  and  the 
mere  fact  of  their  presence,  only,  is  of  physiological  interest. 

Inorga7iic  Co^istitiients  of  the  Uj'ine.  — It  is  by  the  kidneys  that  the 
greatest  quantity  and  variety  of  inorganic  salts  are  discharged  from  the 
organism  ;  and  it  is  probable  that  even  now  physiological  chemists  are 
not  acquainted  with  the  exact  proportion  and  condition  of  all  the 
.constituents  of  this  class  found  in  the  urine.  In  all  the  processes  of 
nutrition  it  is  found  that  the  inorganic  constituents  of  the  blood  and 
tissues  accompany  the  organic  matters  in  their  various  transformations, 
although  they  are  themselves  unchanged.  Indeed,  the  condition  of 
union  of  inorganic  with  organic  matters  is  so  intimate  that  they  can  not 
be  completely  separated  without  incineration.  In  view  of  these  facts, 
it  is  evident  that  a  certain  proportion,  at  least,  of  the  inorganic  salts  of 
the  urine  is  derived  from  the  tissues,  of  which,  in  combination  with 
organic  matters,  they  have  formed  a  constituent  part.  As  the  kidneys 
frequently  eliminate  from  the  blood  foreign  matters  taken  into  the 
system,  and  are  capable  sometimes  of  throwing  off  an  excess  of  the 
normal  constituents  which  may  be  introduced  into  the  circulation,  it  can 
readily  be  understood  how  a  large  proportion  of  some  of  the  inorganic 
constituents  of  the  urine  may  be  derived  from  food. 

CJilorides.  —  Almost  all  the  chlorin  in  the  urine  is  in  the  form  of 
sodium  chloride,  the  quantity  of  potassium  chloride  being  insignificant 
and  not  of  any  special  physiological  importance.  By  reference  to  the 
table  of  the  composition  of  the  urine,  it  is  seen  that  the  proportion  of 
sodium  chloride  is  subject  to  great  variations,  the  range  being  between 
three  and  eight  parts  per  thousand.  This  at  once  suggests  the  idea 
that  the  quantity  excreted  is  dependent  to  a  considerable  extent  on  the 
quantity  taken  in  with  the  food ;  and,  indeed,  it  has  been  shown  by 
direct  observations  that  this  is  the  fact.  The  proportion  of  sodium 
chloride  in  the  blood  seems  to  be  tolerably  constant;  and  any  excess 
that  may  be  introduced  is  thrown  off  chiefly  by  the  kidneys.  As  the 
chlorides  are  deposited  with  the  organic  matters  in  all  the  acts  of  nutri- 
tion, they  are  found  to  be  eliminated  constantly  with  the  products  of 
katabolism  of  the  nitrogenous  parts,  and  their  absence  from  the  food 
does  not  completely  arrest  their  discharge  in  the  urine.  By  suppressing 
salt  in  the  food,  its  daily  excretion  may  be  reduced  to  between  thirty 
and  forty-five  grains  (1.9  and  2.9  grams).  This  quantity  is  less  than 
that  ordinarily  contained  in  the  ingesta,  and  under  these  conditions  there 
is  a  gradual  diminution  in  the  general  nutritive  activity.  In  nearly  all 
acute  febrile  disorders,  the  chlorin  in  the  urine  rapidly  diminishes  and 
frequently  is  reduced  to  one-hundredth  of  the  normal  proportion.     The 


348 


EXCRETION 


quantity  rapidly  returns  to  the  normal  standard  during  convalescence. 
Most  of  the  chlorides  of  the  urine  are  in  simple  watery  solution ;  but 
a  certain  proportion  of  sodium  chloride  exists  in  combination  with 
urea. 

The  daily  eHmination  of  sodium  chloride  is  about  one  hundred  and 
fifty-four  grains  (lo  grams).  The  great  variations  in  its  proportion  in 
the  urine,  under  different  conditions  of  alimentation,  etc.,  will  explain 
the  differences  in  the  estimates  given  by  various  authorities. 

Sulphates.  —  In  normal  urine  the  sulphates  are  in  the  form  of  salts 
of  potassium  and  of  sodium.  It  is  probable  that  these  in  great  part 
pass  into  the  urine  with  the  products  of  proteid  katabolism  and  are 
unimportant.  A  certain  proportion  of  the  sulphates,  however  —  about 
ten  per  cent  —  is  in  a  pecuhar  form  of  combination  with  putrefactive 
products  from  the  large  intestine,  notably  indol,  phenol,  cresol  and 
skatol.  These  organic  matters  are  in  part  absorbed  by  the  blood  and  in 
part  discharged  in  the  feces.  That  portion  absorbed  by  the  blood  is 
carried  to  the  liver  and  there  combines  with  sulphates,  forming  the  so- 
called  conjugate,  or  ethereal  sulphates.  These  sulphates  are  not  toxic, 
like  the  organic  matters  with  which  they  are  united,  and  they  are  elimi- 
nated from  the  blood  by  the  kidneys.  One  of  the  chief  products  of 
this  kind  is  potassium  indoxyl-sulphate.  This  may  be  made  to  yield 
indigo  by  treatment  with  certain  reagents  and  is  called  indican.  The 
urinary  indican  is  supposed  to  represent  putrefactive  processes  in  the 
large  intestine. 

Although  urinary  indican  is  of  ten.  found  in  disease,  when  present  in 
what  may  be  called  normal  urine  it  exists  in  very  small  quantity.  It 
has  been  estimated,  however,  that  Jg  to  ^  of  a  grain  (0.005  to  0.02  gram) 
is  discharged  in  twenty-four  hours  (Jaffe).  It  is  unfortunate  that  this 
product  is  called  indican,  as  it  is  likely  to  be  confounded  with  vegetable 
indican  (QeHgiNOj^),  which  is  a  glucoside.  The  formula  for  indoxyl- 
sulphuric  acid  is  C8H7NSO4.     Urinary  indican  is  C8H7NSO4K. 

Phosphates.  —  The  urine  contains  phosphates  in  a  variety  of  forms  ; 
but  inasmuch  as  it  is  not  known  that  any  one  of  the  different  combina- 
tions possesses  peculiar  relations  to  the  processes  of  katabolism,  as 
distinguished  from  the  other  phosphates,  the  phosphatic  salts  may  be 
considered  together. 

The  phosphates  exist  constantly  in  the  urine  and  are  derived  in  part 
from  food  and  in  part  from  the  tissues.  Like  other  inorganic  matters, 
they  are  associated  with  the  nitrogenous  constituents  of  the  organism, 
and  when  these  are  changed  into  excrementitious  substances  and  are 
separated  from  the  blood  by  the  kidneys,  they  pass  with  them  and  are 
discharged  from  the  body. 


INORGANIC    CONSTITUENTS    OF    THE    URINE  349 

It  is  a  question  of  some  importance  to  consider  how  far  the  phos- 
phates are  derived  from  the  tissues  and  what  proportion  comes  directly 
from  food.  All  observ^ers  agree  that  the  quantity  of  phosphates  in  the 
urine  is  in  direct  relation  to  the  proportion  in  food,  and  that  an  excess 
of  phosphates  taken  into  the  stomach  is  immediately  thrown  off  by  the 
kidneys.  It  is  a  famihar  fact,  indeed,  that  the  phosphates  are  deficient 
and  the  carbonates  predominate  in  the  urine  of  the  herbivora,  while  the 
reverse  obtains  in  the  carnivora,  and  that  variations,  in  this  respect,  in 
the  urine  may  be  produced  by  feeding  animals  with  different  kinds  of 
food.  Deprivation  of  food  diminishes  the  quantity  of  phosphates  in  the 
urine,  but  a  certain  proportion  is  discharged  that  is  derived  exclusively 
from  the  tissues. 

In  connection  with  the  fact  that  phosphorus  exists  in  considerable 
quantity  in  the  ner\'ous  matter,  it  has  been  assumed  that  mental  exer- 
tion is  attended  with  an  increase  in  the  elimination  of  phosphates ;  and 
this  has  been  advanced  to  support  the  view  that  these  salts  are  specially 
derived  from  katabolism  of  the  brain-substance.  Experiments  show 
that  it  is  not  alone  the  phosphates  that  are  increased  in  quantity  by 
mental  work,  but  urea,  the  chlorides,  sulphates  and  inorganic  matters 
generally ;  and  in  point  of  fact,  physiological  conditions  that  increase 
the  proportion  of  nitrogenous  excrementitious  matters  increase  as  well 
the  elimination  of  inorganic  salts.  It  can  not  be  assumed,  therefore, 
that  the  discharge  of  phosphates  is  specially  connected  with  the  activity 
of  the  brain.  Little  has  been  learned  on  this  point  from  pathology ;  for 
although  many  observations  have  been  made  on  the  excretion  of  phos- 
phoric acid  in  disease  —  Vogel  having  made  about  one  thousand  dif- 
ferent analyses  in  various  affections  —  no  definite  results  have  been 
obtained.  From  these  facts  it  is  seen  that  there  is  no  physiological 
reason  why  the  elimination  of  the  phosphates  should  be  specially  con- 
nected with  the  katabolism  of  any  particular  tissue  or  organ,  espe- 
cially as  these  salts  in  some  form  are  universally  distributed  in  the 
organism. 

Obsen-^ations  have  been  made  on  the  hourly  variations  in  the  dis- 
charge of  phosphoric  acid  at  different  times  of  the  day  ;  but  these  do 
not  appear  to  bear  any  definite  relation  to  known  physiological  condi- 
tions, not  even  to  the  process  of  digestion. 

Of  the  different  phosphatic  salts  of  the  urine,  the  most  important 
are  those  in  which  the  acid  is  combined  with  sodium.  These  exist  in 
the  form  of  the  neutral  and  acid  phosphates.  The  acid  salt  is  sup- 
posed to  be  the  source  of  the  acidity  of  the  urine  at  the  moment  of 
its  emission.  The  so-called  neutral  salt  is  slightly  alkaline.  The  pro- 
portion of  the  sodium  phosphates  in  the  urine  is  larger  than  that  of  any 


350 


EXCRETION 


of  the  other  phosphatic  salts,  but  the  daily  quantity  excreted  has  not 
been  estimated.  There  exists  in  the  urine  a  small  quantity  of  the 
ammonio-magnesian  phosphate,  but  it  never  in  health  is  in  sufficient 
quantity  to  form  a  crystalline  deposit.  The  daily  excretion  of  the  phos- 
phates is  subject  to  great  variations,  but  the  average  quantity  of  phos- 
phoric acid  excreted  daily  may  be  estimated  at  about  fifty-six  grains 
(3.629  grams). 

The  urine  contains,  in  addition  to  the  inorganic  salts  that  have  been 
mentioned,  a  small  quantity  of  silicic  acid ;  but  so  far  as  is  known,  this 
has  no  physiological  importance. 

Coloring  Matter  and  Mnais.  —  The  peculiar  color  of  the  urine  is  due 
mainly  to  the  presence  of  a  nitrogenous  substance  called  urochrome. 
Normal  urine,  however,  contains  a  number  of  pigments.  A  substance 
called  urobilin,  although  its  proportion  is  very  small,  is  the  pigment  that 
has  been  most  carefully  studied.  This  is  supposed  to  result  from  a 
transformation  of  a  certain  quantity  of  stercobilin  that  is  taken  up  by 
the  blood  from  the  intestinal  tract  and  is  separated  from  the  blood  by 
the  kidneys.  After  this,  however,  most  of  the  urobilin  is  thought  to  be 
converted  into  urochrome.  The  sum  of  definite  knowledge  in  regard  to 
the  urinary  pigments  is  small ;  and  the  physiological  relations  of  these 
substances  are  not  understood  and  may  be  unimportant.  It  is  sufficient 
to  state  here  that  the  color  of  normal  urine  is  due  to  a  mixture  of  color- 
ing matters,  the  most  important  being  urochrome.  All  these  matters 
are  originally  iron-free  derivatives  of  hemoglobin. 

Normal  urine  always  contains  a  small  quantity  of  mucus,  with  more 
or  less  epithelium  from  the  urinary  passages  and  a  few  leucocytes. 
These  form  a  faint  cloud  in  the  lower  strata  of  healthy  urine  after  a  few 
hours'  repose.  The  properties  of  the  different  kinds  of  mucus  have 
already  been  considered.  An  important  peculiarity,  however,  of  the 
mucus  contained  in  normal  urine  is  that  it  does  not  excite  decomposi- 
tion of  urea  and  that  the  urine  may  remain  for  a  long  time  in  the  bladder 
without  undergoing  putrefactive  changes. 

Gases  of  the  Urine.  —  In  the  process  of  separation  of  the  urine  from 
the  blood  by  the  kidneys,  certain  gases  in  solution  are  removed.  By 
using  the  method  employed  by  Magnus  in  estimating  the  gases  of  the 
blood,  Morin  was  able  to  extract  about  two  and  a  half  volumes 
of  gas  from  a  hundred  parts  of  urine.  He  ascertained,  however,  that 
a  certain  quantity  of  gas  remained  in  the  urine  and  could  not  be 
extracted  by  the  ordinary  process.  This  was  about  one-fifth  of  the 
whole  volume  of  gas.  Adding  this  to  the  quantity  of  gas  extracted,  he 
obtained  the  following  proportions  to  one  liter  of  urine,  in  cubic  cen- 
timeters (one  part  per  thousand  in  volume) :  — 


WATER   AS    A   PRODUCT    OF   EXCRETION  351 

Oxygen 0.824 

Nitrogen 9-589 

Carbon  dioxide 19.620 

The  proportion  of  these  gases  was  found  by  Morin  to  be  subject  to  cer- 
tain variations.  For  example,  after  the  ingestion  of  a  considerable 
quantity  of  water  or  any  other  liquid,  the  proportion  of  oxygen  was  con- 
siderably increased  (from  0.824  to  1.024),  and  the  carbon  dioxide  was 
diminished  more  than  one-half.  The  most  important  variations,  how- 
ever, were  in  connection  with  muscular  exercise.  After  walking  a  long 
distance,  the  exercise  being  taken  both  before  and  after  eating,  the  quan- 
tity of  carbon  dioxide  was  found  to  be  double  that  contained  in  the  urine 
after  repose.  The  proportion  of  oxygen  was  slightly  diminished  and 
the  nitrogen  was  somewhat  increased ;  but  the  variations  of  these  gases 
were  insignificant. 

It  is  not  probable  that  the  kidneys  are  important  as  eliminators  of 
carbon  dioxide,  but  the  presence  of  this  gas  in  the  urine  assists  in  the 
solution  of  some  of  its  saline  constituents,  notably  the  phosphates. 

Water  as  a  Product  of  Excretion.  —  It  has  been  shown  by  indirect 
observations  that  a  large  proportion  of  the  hydrogen  introduced  as  an 
ingredient  of  food,  about  eighty-five  per  cent,  is  not  accounted  for  by 
the  hydrogen  of  the  excreta.  Direct  observations  have  shown,  also, 
that  under  certain  conditions  an  excess  of  water  over  that  introduced 
with  food  and  drink  is  discharged  from  the  body.  One  of  these  con- 
ditions is  abstinence  from  food  (Flint,  1878).  The  elimination  of  water 
is  much  increased  by  muscular  work  (Pettenkofer  and  Voit,  1868  ;  Flint, 
1879).  These  facts  point  to  the  actual  production  of  water  in  the  body 
by  a  union  of  oxygen  with  hydrogen. 

While  it  is  not  certain  that  water  is  constantly  produced  in  the  body, 
there  can  be  no  doubt  in  regard  to  its  formation  under  some  conditions, 
and  the  oxidation  of  hydrogen  is  important  as  one  of  the  factors  in  the 
production  of  animal  heat.  If  a  certain  proportion  of  the  water  dis- 
charged by  the  lungs,  skin  and  kidneys  is  to  be  regarded  as  a  product 
of  oxidation  within  the  body,  the  relations  which  it  bears  to  nutrition 
probably  are  the  same  as  those  of  some  of  the  excretions,  especially 
carbon '  dioxide,  and  are  subject  to  nearly  the  same  laws.  It  has  not 
been  shown,  however,  that  water  is  produced  constantly,  like  the  sub- 
stances commonly  regarded  as  true  excretions ;  and  it  gives  rise  to  no 
direct  toxic  phenomena  when  retained  in  the  system  or  when  its  produc- 
tion is  diminished  pathologically.  Water  also  has  important  physio- 
logical uses,  particularly  as  a  solvent.  Still,  carbon  dioxide,  with  which 
water  may  be  compared  as  regards  its  mode  of  production,  is  not  in 
itself  poisonous,  its  retention  in  the  blood  simply  interfering  with  the 


352  EXCRETION 

absorption  of  oxygen  ;  and  carbon  dioxide  probably  is  useful  in  increas- 
ing the  solvent  properties  of  the  liquids  of  the  organism. 

Vanations  in  the  Composition  of  the  Urine.  —  The  urine  not  only 
represents,  in  its  varied  constituents,  a  great  part  of  the  physiological 
disintegration  of  the  organism,  but  it  contains  matters  evidently  derived 
from  food.  Its  constitution  is  varying  with  different  conditions  of 
nutrition,  with  exercise,  bodily  and  mental,  with  sleep,  age,  sex,  diet, 
respiratory  activity,  the  quantity  of  cutaneous  exhalation,  and,  indeed, 
with  every  condition  that  affects  any  part  of  the  system.  There  is  no 
liquid  in  the  body  that  presents  such  a  variety  of  constituents  as  a  con- 
stant condition,  but  in  which  the  proportion  of  these  constituents  is  so 
variable.  It  is  for  this  reason  that  in  the  table  of  the  composition  of 
the  urine,  the  ordinary  limits  of  variation  of  its  different  constituents 
have  been  given ;  and  it  has  been  found  necessary,  in  treating  of  the 
individual  excrementitious  products,  to  refer  to  some  of  the  variations 
in  their  proportion  in  the  urine. 

Variations  with  Age  and  Sex. — There  are  decided  differences  in 
the  composition  of  the  urine  at  different  periods  of  life  and  in  the  sexes. 
These  undoubtedly  depend  in  part  on  the  different  conditions  of  nutri- 
tion and  exercise  and  in  part  on  differences  in  the  food.  Although  the 
quantities  of  excrementitious  matters  present  great  variations,  their 
relations  to  the  organism  are  not  materially  modified,  except,  perhaps, 
at  an  early  age ;  and  the  influence  of  sex  and  age  operates  merely  as 
these  conditions  affect  the  diet  and  the  general  habits  of  Hfe. 

It  has  been  stated  that  urea  does  not  exist  in  the  urine  of  the  foetus ; 
but  in  a  specimen  of  urine  taken  from  a  stillborn  child  delivered  with 
forceps,  examined  by  Elliot  and  Isaacs,  the  presence  of  urea  was  deter- 
mined. Beale  found  urea  in  a  specimen  taken  at  the  seventh  month. 
Observations  on  children  between  the  ages  of  three  and  seven  have 
shown  that  at  this  period  of  life,  the  urea  excreted  in  proportion  to 
the  weight  of  the  body  is  about  double  the  quantity  excreted  by  the 
adult. 

There  are  not  many  definite  observations  on  record  in  regard  to  the 
composition  of  the  urine  in  the  later  periods  of  life.  It  has  been  shown, 
however,  that  there  is  a  decided  diminution  at  this  time  in  the  excretion 
of  urea,  and  that  the  absolute  quantity  of  urine  is  somewhat  less. 

The  absolute  quantity  of  solids  excreted  is  less  in  women  than  in 
men,  and  the  same  is  true  of  the  quantity  in  proportion  to  the  weight 
of  the  body ;  still,  the  differences  are  not  very  marked,  and  the  pro- 
portion of  the  urinary  constituents  being  subject  to  modifications  from 
the  same  causes  as  in  men,  the  small  deficiency,  in  the  few  direct  obser- 
vations on  record,  may  be  in  part  if  not  entirely  explained  by  the  fact 


VARIATIONS    IN   THE    COMPOSITION    OF    THE    URINE  353 

that  women  usually  perform  less  mental  and  physical  work  than  men 
and  that  their  digestive  system  is  not  so  active. 

Variations  at  Different  Seasons  and  at  Different  Periods  of  the  Day. 
—  The  changes  in  the  quantity  and  composition  of  the  urine  that  may 
be  referred  directly  to  conditions  of  digestion,  temperature,  sleep,  exer- 
cise etc.,  have  long  been  recognized  by  physiologists ;  but  it  is  difficult 
so  to  separate  these  influences  that  the  true  modifying  value  of  each 
can  be  fully  appreciated.  For  example,  there  is  nothing  which  pro- 
duces such  marked  variations  in  the  composition  of  the  urine  as  diges- 
tion. Under  strictly  physiological  conditions,  the  modifying  influence 
of  digestion  must  always  complicate  observations  on  the  effects  of 
exercise,  sleep,  season,  period  of  the  day  etc. ;  and  the  urine  is  con- 
tinually varying  in  health,  with  the  physiological  modifications  in  the 
different  processes  and  conditions  of  life. 

At  different  seasons  of  the  year  and  in  different  climates,  the  urine 
presents  certain  variations  in  its  quantity  and  composition.  It  seems 
necessary  that  a  tolerably  definite  quantity  of  water  should  be  dis- 
charged from  the  body  at  all  times ;  and  when  the  temperature  or  the 
hygrometric  condition  of  the  atmosphere  is  favorable  to  the  action  of 
the  skin,  as  in  a  warm,  dry  climate,  the  quantity  of  water  in  the  urine 
is  diminished  and  its  proportion  of  solid  matters  is  correspondingly 
increased.  On  the  other  hand,  the  reverse  obtains  when  the  action 
of  the  skin  is  diminished  from  any  cause. 

At  different  times  of  the  day  the  urine  presents  certain  important 
variations.  It  is  evident  that  the  specific  gravity  must  vary  with  the 
relative  proportions  of  water  and  solid  constituents.  The  urine  first 
discharged  in  the  morning  is  dense  and  highly  colored ;  that  passed 
during  the  forenoon  is  pale  and  of  a  low  specific  gravity ;  and  in  the 
afternoon  and  evening  it  is  again  deeply  colored  and  its  specific  gravity 
is  increased.  Its  acidity  is  also  subject  to  certain  variations,  which  have 
already  been  mentioned. 

Influence  of  Mental  Exertion.  —  Although  the  influence  of  mental 
exertion  on  the  composition  of  the  urine  has  not  been  very  closely, 
studied,  the  results  of  the  investigations  that  have  been  made  are  in 
many  regards  quite  satisfactory.  It  is  a  matter  of  common  remark  that 
the  secretion  of  urine  often  is  modified  to  a  considerable  extent  through 
the  nervous  system.  Fear,  anger  and  various  violent  emotions  some- 
times produce  a  sudden  and  copious  secretion  of  urine  containing  a 
large  proportion  of  water,  and  this  is  often  observed  in  cases  of  hysteria. 
Intense  mental  exertion  will  occasionally  produce  the  same  result. 

Internal  Secretion.  —  It  is  possible  that  the  kidneys  are  the  seat  of 
an  internal  secretion  analogous  to  the  internal  secretion  of  the  supra- 


354  EXCRETION 

renal  capsules.  Some  observers,  indeed,  have  extracted  from  the  kid- 
neys a  substance  (renin)  that  produces  an  elevation  of  blood-pressure 
when  injected  into  the  tissues  or  bloodvessels  of  living  animals,  by 
exciting  the  vasomotor  centres.  Renal  extract  has  also  been  employed 
in  the  treatment  of  uremia,  it  was  thought  with  favorable  results.  The 
entire  question,  however,  demands  further  investigation. 

Wor^  of  the  Kidney.  —  The  work  of  the  kidney,  as  regards  the 
separation  of  water  from  the  blood-plasma,  has  been  estimated  by 
comparing  the  osmotic  pressure  of  the  urine  with  that  of  the  blood- 
plasma,  expressed  in  percentage  solutions  of  sodium  chloride.  In  a 
typical  experiment  by  Dreser,  two  hundred  cubic  centimeters  (about 
6|  fluidounces)  of  urine  were  secreted  during  the  night,  with  a  pres- 
sure equal  to  a  four  per  cent  solution  of  sodium  chloride.  Compared 
with  the  blood-plasma,  with  a  pressure  equal  to  a  0.92  per  cent  solution 
of  sodium  chloride,  the  difference  (equal  to  a  3.08  per  cent  solution  of 
sodium  chloride)  is  equivalent  to  267.88  foot-pounds  (thirty-seven  kilo- 
grammeters).  It  must  be  admitted,  however,  that  this  view  in  regard 
to  the  actual  work  of  the  kidneys  in  separating  from  the  blood  a  given 
volume  of  a  liquid  of  a  certain  osmotic  pressure  is  in  some  degree 
speculative.  It  is  not  certain  that  the  laws  of  osmosis  can  be  applied 
to  the  processes  of  secretion  absolutely  and  without  reserve,  taking  no 
account  of  a  cell-action,  with  the  exact  nature  of  which  physiologists  are 
not  acquainted. 


CHAPTER  XIV 

USES    OF    THE    LIVER  — DUCTLESS    GLANDS 

Physiological  anatomy  of  the  liver — Branches  of  the  portal  vein,  the  hepatic  artery  and  the 
hepatic  duct  —  Interlobular  vessels  —  Structure  of  a  lobule — Arrangement  of  the  bile- 
ducts  in  the  lobules  —  Anatomy  of  the  excretory  passages  —  Gall-bladder,  cystic  and  com- 
mon ducts  —  Chemistry  of  the  liver  —  Nerves  and  lymphatics  of  the  liver —  Mechanism  of 
the  secretion  of  bile  —  Quantity  of  bile  —  Uses  of  the  bile  —  Properties  and  composition  of 
the  bile — Biliary  salts — Cholesterin  and  stercorin — Bilirubin — Tests  for  bile  —  Excre- 
tory action  of  the  liver  —  Origin  of  cholesterin  —  Formation  of  glycogen  in  the  liver 

Conditions  that  influence  the  quantity  of  sugar  in  the  blood  —  Ductless  glands  and  internal 
secretion  —  Suprarenal  capsules  —  Cortical  substance  —  Medullary  substance — Vessels  and 
nerves  —  Chemistry  of  the  suprarenal  capsules  —  Addison's  disease  —  The  spleen  —  Fibrous 
structure  —  Malpighian  bodies  —  Spleen-pulp  —  Bloodvessels,  nerves  and  lymphatics  — 
Chemical  constitution  —  Variations  in  volume  —  Extirpation  —  Thyroid  gland  —  Structure 
—  Vessels  and  nerves  —  Myxoedema  —  Thymus  gland  —  Pituitary  body  and  pineal  gland  — 
Acromegaly  and  giantism  —  Internal  secretion  by  the  testes  and  ovaries. 

Physiological  Anatomy  of  the  Liver 

In  regard  to  the  descriptive  anatomy  of  the  liver,  it  is  sufficient  to 
state  that  it  is  situated  just  below  the  diaphragm,  in  the  right  hypochon- 
driac region  and  is  the  largest  gland  in  the  body,  weighing,  when  moder- 
ately filled  with  blood,  about  four  and  a  half  pounds  (2  kilograms).  Its 
weight  is  somewhat  variable,  but  in  a  person  of  ordinary  adipose  develop- 
ment, its  proportion  to  the  weight  of  the  body  is  about  as  one  to  thirty- 
two.  In  early  life  the  liver  is  relatively  larger,  its  proportion  to  the 
weight  of  the  body  in  the  newborn  child  being  as  one  to  eighteen 
or  twenty. 

The  liver  is  covered  externally  with  peritoneum,  folds  or  dupHcatures 
of  this  membrane  passing  from  the  surface  of  the  organ  to  the  adjacent 
parts.  These  constitute  four  of  the  so-called  ligaments  that  hold  the 
liver  in  place.  The  proper  coat  is  a  thin  but  dense  and  resisting  fibrous 
structure,  adherent  to  the  substance  of  the  organ,  but  detached  without 
much  difficulty,  and  very  closely  united  to  the  peritoneum.  This  mem- 
brane is  of  variable  thickness  at  different  parts  of  the  liver,  being  espe- 
cially thin  in  the  groove  for  the  vena  cava.  At  the  transverse  fissure 
it  surrounds  the  duct,  bloodvessels  and  nerves,  and  it  penetrates  the 
substance  of  the  organ  in  the  form  of  a  vagina,  or  sheath,  investing 
the  vessels  and  branching  with  them.  This  membrane,  as  it  ramifies  in 
the  substance  of  the  liver,  is  called   the  capsule  of  GHsson.     It  will 

355 


356  USES    OF    THE    LIVER  — DUCTLESS   GLANDS 

be  more  fully  described  in  connection  with  the  arrangement  and  dis- 
tribution of  the  hepatic  vessels. 

The  substance  of  the  liver  is  made  up  of  lobules  of  an  irregularly- 
ovoid  or  rounded  form  and  about  ^^  of  an  inch  ( i  miUimeter)  in  diameter. 
The  space  which  separates  these  lobules  is  about  one-quarter  of  the 
diameter  of  the  lobule  and  is  occupied  by  the  bloodvessels,  nerves  and 
ramifications  of  the  hepatic  duct.  In  certain  animals,  the  pig  and  the 
polar  bear,  the  division  of  the  hepatic  substance  can  readily  be  made 
out  with  the  naked  eye ;  but  in  man  and  in  most  of  the  mammalia,  the 
lobules  are  not  so  distinct,  although  their  arrangement  is  essentially 
the  same.  The  lobules  are  intimately  connected  with  each  other,  and 
branches  going  to  a  number  of  different  lobules  are  given  off  from  the 
same  interlobular  vessels ;  but  they  are  sufficiently  distinct  to  represent, 
each  one,  the  general  anatomy  of  the  secreting  portion. 

At  the  transverse  fissure,  the  portal  vein,  having  collected  the  blood 
from  the  abdominal  organs,  and  the  hepatic  artery,  which  is  a  branch  of 
the  coeliac  axis,  penetrate  the  substance  of  the  liver,  with  the  hepatic 
duct,  nerves  and  lymphatics,  all  enveloped  in  the  fibrous  vagina,  or 
sheath.  The  portal  vein  is  by  far  the  larger  of  the  two  bloodvessels ; 
and  its  calibre  may  be  roughly  estimated  as  eight  to  ten  times  that 
of  the  artery. 

The  vagina,  or  capsule  of  Ghsson,  is  composed  of  fibrous  tissue  in 
the  form  of  a  dense  membrane,  closely  adherent  to  the  adjacent  struc- 
ture of  the  liver,  and  enveloping  the  vessels  and  nerves,  to  which  it  is 
attached  by  loose  areolar  tissue.  The  attachment  of  the  bloodvessels 
to  the  sheath  is  so  loose  that  the  branches  of  the  portal  vein  are  col- 
lapsed when  not  filled  with  blood  ;  presenting  a  striking  contrast  to  the 
hepatic  veins,  which  are  closely  adherent  to  the  substance  of  the  liver 
and  remain  open  when  they  are  cut  across.  This  sheath  is  prolonged 
over  the  vessels  as  they  branch  and  follows  them  in  their  subdivisions. 
It  varies  considerably  in  thickness  in  different  animals.  In  man  and  in 
the  mammalia  generally,  it  is  rather  thin,  becoming  more  and  more 
delicate  as  the  vessels  subdivide.  It  is  lost  before  the  vessels  are  dis- 
tributed between  the  lobules. 

The  vessels  distributed  in  the  liver  are  the  following:  — 

The  portal  vein,  the  hepatic  artery  and  the  hepatic  duct,  passing 
in  at  the  transverse  fissure,  to  be  distributed  in  the  lobules.  The  blood- 
vessels are  continuous  in  the  lobules  with  the  radicles  of  the  hepatic 
veins.    The  duct  is  to  be  followed  to  its  branches  of  origin  in  the  lobules. 

The  hepatic  veins ;  vessels  that  originate  in  the  lobules,  and  collect 
the  blood  distributed  in  their  substance  by  branches  of  the  portal  vein 
and  of  the  hepatic  artery. 


PHYSIOLOGICAL   ANATOAIY    OF    THE    LIVER  357 

Branches  of  the  Portal  Vein,  tJie  Hepatic  Artery  and  the  Hepatic  Duct. 
—  These  vessels  follow  out  the  branches  of  the  capsule  of  Glisson,  become 
smaller  and  smaller,  and  they  finally  pass  directly  between  the  lobules.  In 
their  course,  however,  they  send  off  lateral  branches  to  the  sheath,  form- 
ing the  so-called  vaginal  plexus.  The  arrangement  of  the  vessels  in 
the  sheath  is  not  in  the  form  of  a  true  anastomosing  plexus,  although 
branches  pass  from  this  so-called  vaginal  plexus  between  the  lobules. 
These  vessels  do  not  anastomose  or  communicate  with  each  other  in  the 
sheath. 

The  portal  vein  does  not  present  any  important  peculiarity  in  its 
course  from  the  transverse  fissure  to  the  interlobular  spaces.  It  sub- 
divides, enclosed  in  its  sheath,  until  its  small  branches  go  directly 
between  the  lobules;  and  in  its  course  it  sends  branches  to  the  sheath 
(vaginal  vessels),  which  afterward  go  between  the  lobules.  The  hepatic 
artery  has  three  sets  of  branches.  As  soon  as  it  enters  the  sheath  with 
the  other  vessels,  it  sends  off  minute  branches  (vasa  vasorum)  to  the 
walls  of  the  portal  vein,  to  the  larger  branches  of  the  artery  itself,  to 
the  walls  of  the  hepatic  veins,  and  a  rich  network  of  vessels  to  the 
hepatic  duct.  In  its  course  the  hepatic  artery  also  sends  branches 
to  the  capsule  of  Glisson  (capsular  branches),  which,  with  branches  of 
the  portal  vein,  go  to  form  the  so-called  vaginal  plexus.  From  these 
vessels  a  few  arterial  branches  are  given  off,  which  pass  between  the 
lobules.  The  hepatic  artery  can  not  be  followed  beyond  the  interlobular 
vessels.  The  terminal  branches  of  the  hepatic  artery  are  not  directly 
connected  with  the  radicles  of  the  hepatic  veins,  but  they  empty  into 
small  branches  of  the  portal  vein  within  the  capsule  of  Glisson. 

Interlobular  Vessels.  —  Branches  of  the  portal  vein,  coming  from  the 
terminal  ramifications  of  the  vessel  within  the  capsule  and  from  the 
branches  in  the  walls  of  the  capsule,  are  distributed  between  the  lobules, 
constituting  the  greatest  part  of  the  so-called  interlobular  plexus.  These 
are  situated  between  the  lobules  and  surround  them  ;  each  vessel,  how- 
ever, giving  off  branches  to  two  or  three  lobules,  and  never  to  one 
alone.  They  do  not  anastomose  and  consequently  are  not  in  the  form 
of  a  true  plexus.  The  diameter  of  the  interlobular  vessels  varies  between 
l^^-Q  and  y|-Q  of  an  inch  (17  and  34  ^l).  In  this  distribution,  the  blood- 
vessels are  followed  by  branches  of  the  duct,  which  are  much  fewer 
and  smaller,  measuring  only  w^x^  of  an  inch  (10  /i),  and  some,  even, 
have  been  measured  that  are  not  more  than  goVo"  ^^  ^^  ^'^"^^  (8  jU.)  in 
diameter. 

Lobular  Vessels.  — ■  From  the  interlobular  veins  eight  or  ten  branches 
are  given  off  which  penetrate  the  lobule.  As  the  interlobular  vessels 
ramify  between  different  lobules,  each  one  sends  branches  into  two  and 


358 


USES    OF   THE   LIVER  — DUCTLESS    GLANDS 


sometimes  three  of  these  lobules ;  so  that,  so  far  as  vascular  supply- 
is  concerned,  the  lobular  divisions  of  the  liver  are  never  absolutely 
distinct. 

After  passing  from  the  interlobular  plexus  into  the  lobules,  the 
vessels  immediately  break  up  into  an  elongated  network  of  capillaries, 
■3Fo"o  ^o  22V0  ^^  ^^  ^"^^  (8  to  II  fi)  in  diameter,  which  occupy  the 
lobules  with  a  true  plexus.  These  vessels  are  very  abundant.  The 
blood,  having  been  distributed  in  the  lobules  by  this  lobular  plexus,  is 
collected  by  three  or  four  venous  radicles  into  a  single  central  vessel 
situated  in  the  long  axis  of  the  lobule,  called  the  intralobular  vein.  A 
single  lobule,  surrounded  by  interlobular  vessels,  showing  the  lobular 
capillary  plexus,  and  the  central  vein  (the  intralobular  vein)  cut  across, 

is  represented  in  Fig.  75 


and  Plate  VII,  Fig.  5. 

Intralobular  Veins.  — 
The  capillaries  of  the 
lobules  converge  into 
three  or  four  venous 
radicles  (2,  2,  2,  2,  in  Fig. 
75)  which  empty  into  a 
central  vessel.  This  is 
the  intralobular  vein.  If 
a  liver  is  carefully  in- 
jected from  the  hepatic 
veins,  and  if  sections 
are  made  in  various  di- 
rections, it  will  be  seen 
that  the  intralobular 
veins  follow  the  long 
axes  of  the  lobules,  re- 
ceiving vessels  in  their 
course,  until  they  empty  into  a  larger  vessel  situated  at  what  may  be 
called  the  base  of  the  lobules.  These  latter  are  the  sublobular  veins. 
They  collect  the  blood,  in  the  manner  just  described,  from  all  parts  of 
the  liver,  unite  with  others,  becoming  larger  and  larger,  until  finally 
they  form  the  three  hepatic  veins,  which  discharge  the  blood  from  the 
liver  into  the  vena  cava  ascendens. 

The  hepatic  veins  differ  somewhat  in  their  structure  from  other 
veins.  Their  walls  are  thinner  than  those  of  the  portal  veins,  they  are 
not  enclosed  in  a  sheath  and  they  are  closely  adherent  to  the  hepatic 
tissue.  It  has  also  been  noted  that  the  hepatic  veins  possess  a  well- 
marked  muscular  tunic,  very  thin  in  man  but  well  developed  in  the  pig, 


^iS-  75- —  Transverse  section  of  a  single  hepatic  lobule  (Sappey). 

I,  intralobular  vein,  cut  across ;  2,  2,  2,  2,  afferent  branches  of 
the  intralobular  vein;  3,  3,  3,  3,  3,  3,  3,  3,  3,  interlobular  branches 
of  the  portal  vein,  with  its  capillary  branches,  forming  the  lobular 
plexus,  extending  to  the  radicles  of  the  intralobular  vein. 


PHYSIOLOGICAL   ANATOMY   OF   THE   LIVER 


359 


the  ox  and  the  horse,  and  composed  of  non-striated  muscular  fibres 
interlacing  with  each  other  in  every  direction. 

In  addition  to  the  bloodvessels  just  described,  the  liver  receives 
venous  blood  from  vessels  that  have  been  called  accessory  portal  veins, 
coming  from  the  gastro-hepatic  omentum,  the  surface  of  the  gall- 
bladder, the  diaphragm  and  from  the  anterior  abdominal  walls.  These 
vessels  penetrate  at  different  points  on  the  surface  of  the  liver,  and  they 
may  serve  as  derivatives  when  the  circulation  through  the  portal  vein  is 
obstructed. 

Stnictjire  of  a  Lobule  of  the  Liver.  —  Each  hepatic  lobule,  bounded 
and  more  or  less  distinctly  separated  from  the  others  by  the  interlobular 
vessels,  contains  bloodvessels,  radicles  of  the  hepatic  ducts  and  the 
so-called  hepatic  cells.  The  arrangement  of  the  bloodvessels  has  just 
been  described;  but  in  all  preparations  made  by  artificial  injection,  the 
space  occupied  by  the  bloodvessels  is  exaggerated  by  excessive  disten- 
tion, and  the  difficulties  in  the  study  of  the  relations  of  the  ducts  and 
the  liver-cells  are  thereby  much  increased. 

Liver-cells.  —  If  a  scraping  from  the  cut  surface  of  a  fresh  liver  is 
examined  with  a  moderately  high  magnifying  power,  the  field  of  view 
will  be  found  filled  with  rounded,  ovoid  or  irregularly-polygonal  cells, 
measuring  ygVo  to  io^q-  of  an  inch  (i6  to  25  ^i)  in  diameter.  In  their 
natural  condition  they  are  more  frequently  ovoid  than  polygonal ;  and 
when  they  have  the  latter  form  the  corners  are  always  rounded.  These 
cells  present  one  and  occasionally  two  nuclei,  sometimes  with  and  some- 
times without  nucleoli.  The  presence  of  small  pigmentary  granules 
gives  to  the  cells  a  peculiar  and  characteristic  appearance ;  and  in  addi- 
tion, nearly  all  contain  a  few  granules  or  small  globules  of  fat.  Some- 
times the  fatty  and  pigmentary  granules  are  so  abundant  as  to  obscure 
the  nuclei.  The  cells  also  contain  more  or  less  glycogen  in  the  form  of 
granules  surrounding  the  nuclei.  As  regards  intimate  structure,  the 
liver-cells  present  a  delicate  honeycomb  network  in  the  meshes  of  which 
are  contained  the  granules  just  described.  They  have  no  distinct  cell- 
walls,  and  they  adhere  together  by  portions  of  their  surface  so  as  to 
form  rows,  or  columns  radiating  from  the  centre  of  each  lobule  (see 
Plate  VII,  Fig.  6). 

Arrangement  of  the  Bile-diicts  in  the  T^obnles. — In  the  substance 
of  the  lobules  is  a  fine  and  regular  network  of  vessels  of  nearly  uniform 
size,  about  j^q^qq  of  an  inch  (2  or  3  ^)  in  diameter,  which  surround  the 
liver-cells,  each  cell  lying  in  a  space  bounded  by  inosculating  branches 
of  these  canals.  This  plexus  is  independent  of  the  bloodvessels,  and 
it  seems  to  enclose  in  its  meshes  each  individual  cell,  extending  from  the 
periphery  of  the  lobule  to  the  intralobular  vein.     These  canals  or  inter- 


36o 


USES    OF   THE   LIVER  — DUCTLESS    GLANDS 


spaces  between  the  liver-cells  in  the  lobules  open  into  the  interlobular 
hepatic  ducts.  It  is  still  a  question  whether  these  passages  are  simple 
spaces  between  the  cells  or  true  vessels  lined  with  a  membrane. 

Anatomy  of  the  Excretory  Biliaiy  Passages.  —  Between  the  lobules 
the  ducts  are  very  small,  the  smallest  measuring  about  3  J-q  of  an  inch 
(8  \i)  in  diameter.  They  are  composed  of  a  delicate  membrane  lined 
with  epithelium.  The  ducts  larger  than  Y2V0  °^  ^'^  m<z\i  (about  20  \i) 
have  a  fibrous  coat,  formed  of  inelastic  with  a  few  elastic  elements,  and 
in  the  larger  ducts,  there  are  in  addition  a  few  non-striated  muscular 
fibres.     The  epithelium  lining  these  ducts  is  of  the  columnar  variety, 

the  cells  gradually  under- 
going a  transition  from 
the  pavement  form  as  the 
ducts  increase  in  size.  In 
the  largest  ducts  there  is 
a  distinct  mucous  mem- 
brane with  mucous  glands. 
Throughout  the  extent 
of  the  biliary  passages, 
from  the  interlobular 
canals  to  the  ductus  chole- 
dochus,  are  little  utricular 
or  racemose  glands,  vary- 
ing in  size  in  different  por- 
tions of  the  liver.  These 
are  situated  at  short  in- 
tervals at  the  sides  of  the 
canals.  The  glands  con- 
nected with  the  smallest 
injected  liver  ducts  are  simple  follicles, 
TOO  to  ^^0  of  an  inch  (31 
to  62  \x)  long.  The  larger  glands  are  formed  of  groups  of  these  follicles, 
and  they  measure  2^0^  or  -^-^  of  an  inch  (100  or  250  11)  in  diameter.  The 
glands  are  found  connected  with  the  ducts  ramifying  in  the  substance 
of  the  liver  only,  and  they  do  not  exist  in  the  hepatic,  cystic  and  com- 
mon ducts.  They  are  composed  of  a  homogeneous  membrane  lined 
with  small  pale  cells  of  epithelium.  If  the  ducts  in  the  substance  of  the 
liver  are  isolated,  they  are  found  covered  with  these  little  groups  of 
follicles  and  have  the  appearance  of  an  ordinary  racemose  gland,  except 
that  the  acini  are  relatively  small  and  scattered.  This  appearance  is 
represented  in  Fig.  yy. 

The  excretory  biliary  ducts,  from  the  interlobular  vessels  to  the  point 


Fig.  76.  —  Bile-capillaries  between  the  liver-cells 
of  the  rabbit,  x  500  (Pfeiffer). 


PHYSIOLOGICAL   ANATOMY    OF   THE    LIVER 


361 


of  emergence  of  the  hepatic  duct,  present  frequent  anastomoses  with 
each  other  in  their  course. 

Vasa  Aberrantia.  —  In  the  Kvers  of  old  persons,  and  occasionally  in 
the  adult,  certain  vessels  are  observed  ramifying  on  the  surface  of  the 
liver  but  always  opening  into  the  biliary  ducts,  which  have  been  called 
vasa  aberrantia.  These  are  not  found  in  the  foetus  or  in  children. 
They  are  appendages  of  the  excretory  system  of  the  Hver,  and  are 
analogous  in  their  structure  to  the  ducts,  but  are  apparently  hyper- 
trophied,  with  thickened  fibrous  walls,  and  present  in  their  course 
irregular  constrictions  not  found  in  the  normal  ducts.  The  racemose 
glands  attached  to  them  are  always  much  atrophied. 


Fig.  77.  —  Racemose  glands  attached  to  the  biliary  ducts  of  the  pig,  x  18  (Sappey). 

I,  I,  branch  of  an  hepatic  duct,  with  the  surface  almost  entirely  covered  with  racemose  glands 
opening  into  its  cavity;  2,  branch  in  which  the  glands  are  smaller  and  less  abundant ;  3,  3,  3,  branches 
of  the  duct  with  still  simpler  glands  ;  4,  4, 4,  4,  biliary  ducts  with  simple  follicles  attached  ;  5,  5,  5,  5,  the 
same,  with  fewer  follicles ;  6,  6,  6,  6,  6,  anastomoses  in  arches;  7,  7,  7,  angular  anastomoses  ;  8,  8,  8,  8, 
anastomoses  by  transverse  branches. 

Gall-bladder,  Hepatic,  Cystic  and  Common  Ducts.  —  The  hepatic  duct 
is  formed  by  the  union  of  two  ducts,  one  from  the  right  and  the  other 
from  the  left  lobe  of  the  liver.  It  is  about  an  inch  and  a  half  (38  milli- 
meters) in  length  and  joins  at  an  acute  angle  with  the  cystic  duct  to 
form  the  ductus  communis  choledochus.  The  common  duct  is  about 
three  inches  {jG  milhmeters)  in  length,  of  the  diameter  of  a  goose-quill 
and  opens  into  the  descending  portion  of  the  duodenum.  It  passes 
obHquely  through  the  coats  of  the  intestine  and  opens  into  its  cavity 
in  connection  with  the  principal  pancreatic  duct.  The  cystic  duct  is 
about  an  inch  (25  miUimeters)  in  length  and  is  the  smallest  of  the  three 
canals.     The  structure  of   these  ducts  is  essentially  the   same.     They 


362 


USES    OF   THE    LIVER  — DUCTLESS    GLANDS 


have  a  proper  coat  formed  of  ordinary  fibrous  tissue,  a  few  elastic 
fibres  and  non-striated  muscular  fibres.  The  muscular  tissue  is  not 
sufficiently  distinct  to  form  a  separate  coat.  The  mucous  membrane  is 
always  found  tinged  yellow  with  the  bile,  even  in  living  animals.  It 
presents  a  large  number  of  minute  excavations  and  is  covered  with  cells 
of  columnar  epithelium.  This  membrane  contains  a  large  number  of 
mucous  glands. 

The  gall-bladder  is  an  ovoid  or  pear-shaped  sac,  about  four  inches 
(lo  centimeters)  in  length,  one  inch  (25  millimeters)  in  breadth  at  its 


6   25  ^'^ 


Fig.  78. —  Gall-bladder,  hepatic,  cystic  atid  common  ducts  (Sappey). 

I,  2,  3,  duodenum  ;  4, 4,  5,  6,  7,  7,  8,  pancreas  and  pancreatic  ducts ;  9,  10, 11,  12,  13,  liver ;  14,  gall- 
bladder ;  15,  hepatic  duct;  16,  cystic  duct ;  17,  common  duct ;  18,  portal  vein;  19,  branch  from  the 
coeliac  axis  ;  20,  hepatic  artery  ;  21,  coronary  artery  of  the  stomach  ;  22,  cardiac  portion  of  the  stomach  ; 
23,  splenic  artery;  24,  spleen  ;  25,  left  kidney;  26,  right  kidney;  27,  superior  mesenteric  artery  and 
vein  ;  28,  inferior  vena  cava. 


widest  portion,  and  capable  of  holding  an  ounce  to  an  ounce  and  a  half 
(30  to  45  cubic  centimeters)  of  fluid.  Its  fundus  is  covered  entirely 
with  peritoneum  but  this  membrane  passes  only  over  the  lower  surface 
of  its  body. 

The  proper  coat  of  the  gall-bladder  is  composed  of  ordinary  fibrous 
tissue  with  a  few  elastic  fibres.  In  some  of  the  lower  animals  there  is  a 
distinct  muscular  coat,  but  a  few  scattered  fibres  only  are  found  in  the 
human  subject.  The  mucous  coat  is  of  a  yellowish  color,  with  very 
small  interlacing  folds  that  are  very  vascular.  The  mucous  membrane 
of  the  gall-bladder  has  a  general  lining  of  columnar  epithelium  with  a 


SECRETION    AND    DISCHARGE    OF   BILE  363 

few  goblet-cells.  In  the  gall-bladder  are  found  small  racemose  glands 
formed  of  four  to  eight  foUicles  lodged  in  the  submucous  structure. 
These  are  essentially  the  same  as  the  glands  opening  into  the  ducts  in 
the  substance  of  the  liver  and  secrete  a  mucus  that  is  mixed  with  the 
bile. 

Nerves  ajid  LynipJiatics  of  tJie  Liver.  —  The  nerves  of  the  liver  are 
derived  from  the  pneumogastric,  the  phrenic,  and  the  solar  plexus  of 
the  sympathetic.  The  branches  of  the  left  pneumogastric  penetrate 
■with  the  portal  vein,  while  the  branches  from  the  right  pneumogastric, 
the  phrenic  and  the  sympathetic,  surround  the  hepatic  artery  and  the 
hepatic  duct.  All  these  nerves  penetrate  at  the  transverse  fissure  and 
follow  the  bloodvessels  in  their  distribution.  They  have  not  been 
traced  beyond  the  final  ramifications  of  the  capsule  of  Glisson  and  their 
exact  mode  of  termination  is  unknown. 

The  lymphatics  of  the  liver  are  very  abundant.  They  are  divided 
into  two  layers;  the  superficial  layer,  situated  just  beneath  the  serous 
membrane,  and  the  deep  layer.  The  superficial  lymphatics  from  the 
under  surface  of  the  liver  and  that  portion  of  the  deep  lymphatics  which 
follows  the  hepatic  veins  out  of  the  liver  pass  through  the  diaphragm 
and  are  connected  with  the  thoracic  glands.  Some  of  the  lymphatics 
from  the  superior,  or  convex  surface  join  the  deep  vessels  that  emerge 
at  the  transverse  fissure  and  pass  into  glands  below  the  diaphragm, 
while  others  pass  into  the  thoracic  cavity. 

The  mode  of  origin  of  the  lymphatics  is  peculiar.  The  superficial 
lymphatics  are  subperitoneal  and  are  connected  with  spaces  or  canals 
in  the  general  connective  tissue  of  the  liver.  The  deep  lymphatics  are 
supposed  to  originate  by  perivascular  canals  surrounding  the  blood- 
vessels of  the  lobules,  which  are  connected  with  vessels  in  the  walls  of 
small  branches  of  the  hepatic  and  portal  veins,  afterward  surrounding 
the  larger  vessels. 

Chemistry  of  the  Liver.  —  As  regards  the  chemistry  of  the  liver,  little 
has  been  ascertained  that  is  of  much  physiological  importance.  The 
liver-cells  contain  globulins,  nucleo-proteids,  cholesterin,  urea,  uric  acid, 
xanthin,  hypoxanthin  and  sometimes  leucin  and  tyrosin.  In  addition, 
a  nitrogenous  substance  (CiQjH^ggNjSPgO^g)  containing  phosphorus  has 
been  found.  This  has  been  called  jecorin  (Drechsel),  although  it  is 
not  confined  to  the  liver  but  exists  in  the  spleen,  brain,  muscle  and  some 
other  tissues.     In  most  of  its  properties  it  resembles  lecithin. 

Mechanism  of  the  Secretion  and  Discharge  of  Bile.  —  In  its  anatomy 
the  liver  differs  greatly  from  other  glandular  organs,  both  secretory  and 
excretory.  The  liver-cells  are  not  enclosed  in  ducts,  but  are  surrounded 
with  a  plexus  of  small  vessels  or   spaces  that  receive  the  bile  as  it  is 


364  USES    OF   THE    LIVER  — DUCTLESS   GLANDS 

formed.  The  liver,  also,  is  supplied  with  both  venous  and  arterial  blood, 
the  venous  blood  largely  predominating.  In  addition  it  is  now  recog- 
nized that  the  bile  is  necessary  to  intestinal  digestion,  that  it  contains 
excrementitious  matters  and  that  the  cells  constantly  produce  glycogen. 
The  liver  produces  urea,  which  is  excreted,  however,  chiefly  by  the 
kidneys.  It  also  effects  certain  important  changes  in  digested  and 
foreign  matters  that  are  absorbed  from  the  alimentary  canal. 

As  regards  the  bile,  the  only  view  that  is  consistent  with  actual 
knowledge  is  that  this  secretion  is  produced  by  the  liver-cells  and  is 
taken  up  by  the  plexus  of  canals  that  surrounds  these  cells.  The 
little  glandular  organs  attached  to  the  larger  branches  of  the  duct  secrete 
mucus  that  gives  the  viscidity  observed  in  the  bile  of  some  animals. 
The  bile,  indeed,  is  viscid  in  different  animals  in  proportion  to  the 
development  of  these  mucous  glands ;  and  in  the  rabbit,  in  which  the 
glands  do  not  exist,  the  bile  has  no  viscidity. 

Of  course  the  circulation  of  blood  in  the  liver  is  a  condition  neces- 
sary to  the  secretion  of  bile.  As  regards  the  question  of  the  production 
of  bile  from  venous  or  arterial  blood,  it  has  been  shown  that  the  mate- 
rials out  of  which  the  bile  is  formed  may  be  supplied  by  either  the 
hepatic  artery  or  the  portal  vein.  Bile  is  secreted  after  the  hepatic 
artery  has  been  tied,  and  also  after  the  portal  vein  has  been  gradually 
obliterated,  the  hepatic  artery  being  intact.  Bile  is  produced  in  the 
liver  from  the  blood  distributed  in  its  substance  by  the  portal  vein  and 
the  hepatic  artery,  and  not  from  the  blood  of  either  of  these  vessels 
exclusively ;  and  bile  may  continue  to  be  secreted,  if  either  one  of  these 
vessels  is  obliterated,  provided  the  supply  of  blood  be  sufficient. 

The  influence  of  the  nervous  system  on  the  secretion  of  bile  has  been 
little  studied ;  and  the  question  is  one  of  some  difficulty  and  obscurity. 
The  liver  is  supplied  abundantly  with  nerves,  both  cerebro-spinal  and 
sympathetic,  and  some  observations  have  been  made  on  the  influence 
of  the  nerves  on  its  glycogenic  action  ;  but  in  regard  to  the  secretion  of 
bile,  there  is  little  to  be  said  beyond  what  has  already  been  stated  con- 
cerning the  influence  of  the  nervous  system  on  other  secretions. 

The  bile  is  discharged  through  the  hepatic  ducts  like  the  secretion 
of  any  other  gland.  During  digestion  the  liquid  accumulated  in  the 
gall-bladder  passes  into  the  ductus  communis,  in  part  by  contractions 
of  its  walls,  and  in  part,  probably,  by  compression  exerted  by  the  dis- 
tended and  congested  digestive  organs  adjacent  to  it.  It  seems  that  this 
secretion  —  which  necessarily  is  produced  by  the  liver  without  intermis- 
sion, separating  from  the  blood  certain  excrementitious  matters  —  is  re- 
tained in  the  gall-bladder  for  use  during  digestion. 

Quantity  of  Bile.  —  The  estimates  of  the  daily  quantity  of  bile  in  the 


PROPERTIES   AND    COMPOSITION    OF   THE    BILE  365 

human  subject  must  be  merely  approximate ;  and  the  ideas  of  physiolo- 
gists on  this  point  are  derived  chiefly  from  experiments  on  the  inferior 
animals.  There  are  great  variations  in  the  daily  quantity  in  different 
classes  of  animals,  the  quantity  in  the  carnivora  being  the  smallest. 
Applying  the  results  of  experiments  on  the  lower  animals  to  the  human 
subject,  and  assuming  that  the  amount  is  about  equal  to  the  quantity 
secreted  by  the  carnivora,  the  daily  secretion  in  a  man  weighing  one 
hundred  and  forty  pounds  (63.5  kilograms)  would  be  about  two  and  a 
half  pounds  (11 34  grams). 

Uses  of  the  Bile 

The  uses  of  the  bile  in  digestion  have  already  been  fully  described ; 
but  before  considering  its  characters  as  an  excretion,  it  will  be  necessary 
to  study  its  general  properties  and  composition. 

Properties  and  Composition  of  the  Bile.  —  The  secretion  as  it  comes 
directly  from  the  liver  is  somewhat  viscid ;  but  after  it  has  passed  into 
the  gall-bladder,  its  viscidity  is  much  increased  by  a  further  admixture 
of  mucus. 

The  color  of  the  bile  is  very  variable  within  the  limits  of  health.  It 
may  be  of  any  shade  between  a  dark  yellowish  green  and  a  reddish 
brown.  It  is  semitransparent  except  when  the  color  is  very  dark.  In 
different  classes  of  animals  the  variations  in  color  are  considerable. 
In  the  pig  it  is  bright  yellow  ;  in  the  dog  it  is  dark  brown ;  and  in  the 
ox  it  is  greenish  yellow.  As  a  rule  the  bile  is  dark  green  in  the  car- 
nivora and  greenish  yellow  in  the  herbivora. 

The  specific  gravity  of  human  bile  from  the  gall-bladder  is  1026  to 
1032.  When  perfectly  fresh  it  is  almost  inodorous  but  it  readily  under- 
goes putrefactive  changes.  It  has  a  disagreeable  and  bitter  taste.  It 
is  not  coagulated  by  heat.  When  mixed  with  water  and  shaken,  it 
becomes  frothy,  probably  on  account  of  the  tenacious  mucus  and  its 
saponaceous  constituents. 

It  usually  is  stated  that  the  bile  is  alkaline.  This  is  true  of  the 
liquid  discharged  from  the  hepatic  duct,  although  the  alkalinity  is  not 
strongly  marked  ;  but  the  reaction  varies  after  it  has  passed  into  the 
gall-bladder.  In  the  hepatic  ducts  the  reaction  always  is  alkaline ;  and 
there  are  no  observations  on  human  bile  that  show  that  it  is  not  alkaline 
in  all  the  biliary  passages. 

The  epithelium  of  the  biliary  passages  is  strongly  tinged  with  yellow 
even  in  living  animals.  This  is  due  to  the  facility  with  which  the  color- 
ing matter  of  the  bile  stains  the  animal  tissues. 

Perfectly  normal  and  fresh  bile,  examined  with  the  microscope,  pre- 
sents a  certain  quantity  of  mucus,  the  characters  of  which  have  already 


366 


USES    OF   THE    LIVER  — DUCTLESS    GLANDS 


been  described.  There  are  no  formed  anatomical  elements  character- 
istic of  this  secretion.  The  fatty  and  coloring  matters  are  in  solution 
and  not  in  the  form  of  globules  or  granules. 


COMPOSITION   OF   HUMAN 


Water  . 

Sodium  taurocholate 

Sodium  glycocliolate 

Cholesterin    . 

Bilirubin 

Lecithin 

Palmitin,  olein  and  traces  of  soaps 

Cholin  . 

Sodium  chloride    . 

Sodium  phosphate 

Potassium  phosphate 

Calcium  phosphate 

Magnesium  phosphate 

Salts  of  iron 

Salts  of  manganese 

Silicic  acid    . 

Mucin    . 

Loss 


BILE 

:robin) 

.       916  GO    to    819.00 

56.50  to  106.00 

traces. 

0.62  to       2.66 

14.00  to     30.00 

3.20  to     31.00 

traces. 

2.77  to       3.50 

1.60  to       2.50 

0.75  to       1.50 

0.50  to       1.35 

0.45  to       0.80 

0.15  to       0.30 

traces  to       0.12 

0.03  to       0.06 

traces. 

3.43  to       1.21 

1000.00       1000.00 

The  bile  contains  no  coagulable  organic  matters  except  mucin,  and 
all  its  constituents  simply  are  solids  in  solution.  The  quantity  of  solid 
matter  is  large  and  the  proportion  of  water  is  relatively  small.  Among 
the  inorganic  salts,  sodium  chloride  exists  in  considerable  quantity,  with 
a  large  proportion  of  phosphates.  There  exist,  also,  salts  of  iron  and 
of  manganese,  with  a  small  quantity  of  silicic  acid. 

The  fatty  and  saponaceous  constituents  of  the  bile  demand  hardly 
any  more  extended  consideration.  A  small  quantity  of  palmitin  and 
olein  are  held  in  solution,  partly  by  the  soaps,  but  chiefly  by  the  sodium 
taurocholate.  The  fats  sometimes  exist  in  larger  quantity,  when  they 
may  be  discovered  in  the  form  of  globules.  The  proportion  of  soaps 
is  small.  Lecithin  (C44HgQNP09)  is  a  neutral  fatty  substance  extracted 
from  the  bile,  and  maybe  decomposed  into  phosphoric  acid  and  glycerin. 
Cholin  (C5H15NO2)  is  found  in  the  bile  in  minute  quantity,  and  when 
present,  it  is  supposed  to  be  one  of  the  decomposition-products  of  lecithin. 

Biliary  Salts.  —  In  human  bile  the  characteristic  biliary  salt  is  a 
combination  of  taurocholic  acid  (C26H45NSO)  with  sodium.  A  small 
quantity  of  sodium  exists  in  combination  with  glycocholic  acid 
(C26H43NOg).  Sodium  glycocholate  exists  in  quantity  in  ox-gall.  Both 
these  salts  may  be  precipitated  from  an  alcohohc  extract  of  bile  by  an 


CHOLESTERIN  367 

excess  of  ether.  The  taurocholate  is  precipitated  in  the  form  of  dark 
resinous  drops  which  crystallize  with  difficulty.  The  glycocholate  is 
readily  crystallizable.  The  biliary  salts  are  very  soluble  in  water  and 
in  alcohol.     Their  reaction  is  neutral. 

There  can  be  no  doubt  that  the  biliary  salts  are  products  of  secre- 
tion and  are  formed  in  the  substance  of  the  liver.  In  no  instance  have 
they  been  discovered  in  the  blood  in  health ;  and  although  they  present 
certain  points  of  resemblance  with  some  of  the  constituents  of  the  urine, 
they  are  not  found  in  the  excreta,  except  in  very  rare  instances  in  the 
urine.  There  is  no  reason,  therefore,  for  supposing  that  these  salts  are 
products  of  katabolism.  Once  discharged  into  the  intestine,  they  undergo 
certain  changes  and  can  no  longer  be  recognized  by  the  usual  tests  ;  but 
experiments  have  shown  that,  changed  or  unchanged,  they  are  absorbed 
with  the  products  of  digestion.  They  probably  are  concerned  in  the 
digestive  action  of  the  bile. 

Cholesterin.  —  Cholesterin  (C27H4QO)  is  a  normal  constituent  of  vari- 
ous of  the  tissues  and  liquids  of  the  body.  Most  authors  state  that  it 
is  found  in  the  bile,  blood,  liver,  nervous  tissue,  crystalline  lens,  meco- 
nium and  fecal  matter.  It  is  to  be  found  in  all  these  situations,  with 
the  exception  of  the  feces,  where  it  does  not  exist  normally,  being  trans- 
formed into  stercorin  in  its  passage  down  the  intestinal  canal. 

In  the  liquids  of  the  body  cholesterin  exists  in  solution  ;  but  by  virtue 
of  what  constituents  it  is  held  in  this  condition  is  a  question  not  entirely 
settled.  It  is  stated  that  the  bihary  salts  have  the  power  of  holding 
cholesterin  in  solution  in  the  bile,  and  that  the  small  quantity  of  fatty 
acids  contained  in  the  blood  also  holds  it  in  solution ;  but  direct  experi- 
ments on  this  point  are  wanting.  In  the  nervous  tissue  and  in  the  crys- 
talline lens,  it  is  united  with  the  other  substances  that  go  to  make  up 
these  parts.  After  it  is  discharged  into  the  intestinal  canal,  when  it  is 
not  changed  into  stercorin  it  is  to  be  found  in  a  crystalline  form,  as  in 
the  meconium  and  in  the  feces  of  certain  animals  in  hibernation.  In 
pathological  fluids  and  in  tumors,  it  is  found  in  a  crystalline  form  and 
may  be  detected  by  microscopical  examination. 

Cholesterin  is  a  monatomic  alcohol.  It  is  neutral,  inodorous,  crys- 
tallizable, insoluble  in  water,  soluble  in  ether,  and  very  soluble  in  hot 
alcohol  though  sparingly  soluble  in  cold  alcohol.  It  is  inflammable  and 
burns  with  a  bright  flame.  When  treated  with  strong  sulphuric  acid 
it  strikes  a  peculiar  red  color.  It  may  easily  and  certainly  be  recognized 
under  the  microscope  by  the  form  of  its  crystals.  These  are  rectangular 
or  rhomboidal,  very  thin  and  transparent,  of  variable  size,  with  distinct 
and  usually  regular  borders,  and  frequently  arranged  in  layers  with 
the  borders  of  the  lower  strata  showing  through  those  which  are  super- 


368  USES    OF   THE    LIVER  — DUCTLESS    GLANDS 

imposed.  The  plates  of  cholesterin  often  show  a  cleavage  at  one  corner, 
the  lines  running  parallel  to  the  borders.  Frequently  the  plates  are 
rectangular  and  sometimes  they  are  lozenge-shaped. 

The  proportion  of  cholesterin  in  the  bile  usually  is  estimated  at  0.62 
to  2.66  parts  per  thousand.  In  a  single  examination  of  the  human  bile, 
however,  the  proportion  was  o.6i8  of  a  part  per  thousand  (Flint). 

Bilirubm. — The  coloring  matter  of  the  bile,  bilirubin  (CggHggN^Og), 
bears  a  certain  resemblance  to  the  coloring  matter  of  the  blood  and  is 
supposed  to  be  formed  from  it  in  the  liver.  It  gives  to  the  bile  its 
peculiar  tint  and  has  the  property  of  coloring  the  tissues  with  which  it 
comes  in  contact.  Whenever  the  flow  of  bile  is  obstructed  for  any  con- 
siderable time,  the  coloring  matter  is  absorbed  by  the  blood  and  can 
readily  be  detected  in  the  serum  and  in  the  urine.  It  also  colors  the  skin 
and  the  conjunctiva.  It  is  soluble  in  chloroform,  by  which  it  is  dis- 
tinguished from  biliverdin,  and  forms  soluble  combinations  with  alkalies, 
in  which  form  it  is  thought  to  exist  in  the  bile.  It  probably  is  formed 
in  the  liver  from  the  hemoglobin  of  the  red  blood-corpuscles.  When 
exposed  to  the  air  or  to  the  influence  of  certain  oxidizing  agents,  it 
assumes  a  greenish  color  and  is  changed  into  biliverdin.  It  is  unneces- 
sary to  follow  the  various  other  changes  produced  by  spontaneous 
decomposition  or  by  the  action  of  reagents. 

Tests  for  Bile.  —  A  simple  test  for  bile-pigment  is  the  following  : 
A  ten  per  cent  solution  of  iodin  in  alcohol  is  floated  on  the  suspected 
solution  in  a  test  tube.  If  the  coloring  matter  of  bile  is  present,  a  green 
ring  will  appear  between  the  two  liquids. 

A  delicate  test  for  the  biliary  salts  in  a  clear  solution  not  containing 
albumin  is  what  is  known  as  Pettenkofer's  test :  To  the  suspected  liquid 
are  added  a  few  drops  of  a  strong  solution  of  cane-sugar.  Sulphuric 
acid  is  then  slowly  added,  to  the  extent  of  about  two-thirds  of  the  bulk 
of  the  liquid.  It  is  recommended  to  add  the  acid  slowly  so  that  the 
temperature  shall  be  but  little  raised.  If  a  large  quantity  of  the  biliary 
salts  is  present,  a  red  color  shows  itself  almost  immediately  at  the  bot- 
tom of  the  test  tube,  and  this  soon  extends  through  the  entire  liquid, 
rapidly  deepening  until  it  becomes  dark  lake  or  purple.  If  the  biliary 
matter  exists  in  small  proportion,  it  may  be  several  minutes  before  a 
red  color  makes  its  appearance,  and  the  change  to  a  purple  is  corre- 
spondingly slow,  the  whole  process  occupying  fifteen  to  twenty  minutes. 

Excretory  Action  of  the  Liver 

Although  the  liver  produces  a  greater  or  less  quantity  of  urea,  this 
substance  is  discharged  from  the  body  chiefly  in  the  urine  and  mere 


ORIGIN   OF    CHOLESTERIN  369 

traces  exist  in  the  bile.  The  excretory  action  of  the  liver  will  be  con- 
sidered, in  this  connection,  with  reference  to  the  bile  itself.  At  the 
present  day  it  is  admitted  that  the  bile  is  an  excretion  as  well  as  a 
secretion ;  and  this  question  has  been  fully  discussed  in  connection 
with  the  physiology  of  digestion.  The  constant  and  invariable  pres- 
ence of  cholesterin  in  the  bile  assimilates  it  in  every  regard  to  the 
excretions,  of  which  the  urine  may  be  taken  as  the  type.  Cholesterin 
always  exists  in  the  blood  and  in  certain  of  the  tissues  of  the  body.  It 
is  not  produced  in  the  substance  of  the  liver,  but  is  merely  separated 
from  the  blood  by  this  organ.  It  is  constantly  passed  into  the  intestine, 
and  is  discharged,  although  in  a  modified  form,  in  the  feces.  Physiolo- 
gists know  of  no  office  which  it  has  to  perform  in  the  economy,  any 
more  than  urea  or  any  other  of  the  excrementitious  constituents  of  the 
urine.  It  accumulates  in  the  blood  in  certain  cases  of  organic  disease 
of  the  liver  and  gives  rise  to  grave  nervous  symptoms. 

Origin  of  Cholesterin.  —  Cholesterin  exists  in  largest  quantity  in  the 
substance  of  the  brain  and  nerves.  It  is  also  found  in  the  substance  of 
the  liver  —  probably  in  the  bile  contained  in  this  organ  —  the  crystalline 
lens  and  the  spleen  ;  but  with  these  exceptions,  it  is  found  only  in  the 
nervous  tissue  and  blood.  It  is  either  deposited  in  the  nervous  matter 
from  the  blood  or  it  is  formed  in  the  brain  and  taken  up  by  the  blood. 
This  is  a  question,  however,  that  can  be  settled  experimentally. 

In  a  series  of  experiments  made  in  1862,  it  was  invariably  found  that 
the  proportion  of  cholesterin  in  the  blood  of  the  internal  jugular  vein 
and  the  femoral  vein  was  greater  than  in  the  arterial  blood.  In  experi- 
ments made  on  dogs  not  etherized,  the  blood  of  the  jugular  vein  con- 
tained, in  one  instance  23.3  and  in  another  59.8  per  cent  more  choles- 
terin than  the  arterial  blood  of  the  same  animals.  The  blood  of  the 
femoral  vein  contained  about  6.3  per  cent  more  cholesterin  than  arterial 
blood.  In  three  cases  of  hemiplegia,  cholesterin  was  found  in  normal 
quantity  in  blood  taken  from  the  arm  of  the  sound  side,  while  blood 
from  the  paralyzed  side  contained  no  cholesterin  (Flint). 

These  observations  point  to  the  production  of  cholesterin  in  the 
tissues  ;  and  the  fact  of  its  existence,  under  normal  conditions,  in  the 
nervous  tissue  renders  it  probable  that  the  chief  seat  of  its  formation  is 
the  substance  of  the  nerve-centres  and  nerves.  The  question  of  its 
production  in  the  spleen  is  one  that  has  not  been  investigated. 

In  another  series  of  experiments,  it  was  shown  that  the  blood  lost 
cholesterin  in  passing  through  the  liver.  In  one  observ^ation  it  was 
found  that  the  arterial  blood  lost  a  little  more  than  23  per  cent  and  the 
portal  blood  about  4 J  per  cent,  in  passing  through  the  liver  (Flint). 

The  portal  blood,  as  it  goes  to  the  liver,  contains  but  a  small  per- 


370  USES    OF   THE    LIVER  — DUCTLESS    GLANDS 

centage  of  cholesterin  over  the  blood  of  the  hepatic  veins,  while  the 
percentage  in  the  arterial  blood  is  large.  The  arterial  blood  is  the 
mixed  blood  of  the  entire  system  ;  and  as  it  probably  passes  through  no 
organ  which  diminishes  its  cholesterin  before  it  goes  to  the  liver,  it  con- 
tains a  quantity  of  this  substance  which  must  be  removed.  The  portal 
blood,  coming  from  a  limited  part  of  the  system,  contains  less  choles- 
terin, although  it  gives  up  a  certain  quantity.  In  the  circulation  in  the 
liver,  the  portal  system  largely  predominates  and  is  necessary  to  other 
important  actions  of  this  organ,  such  as  the  production  of  glycogen  ; 
but  soon  after  the  portal  vein  enters  the  liver,  its  blood  becomes  mixed 
with  that  from  the  hepatic  artery,  and  from  this  mixture  the  cholesterin 
is  separated.  It  is  necessary  only  that  blood  containing  a  certain  quan- 
tity of  cholesterin,  should  come  in  contact  with  the  bile-secreting  cells  in 
order  that  this  substance  shall  be  separated.  The  fact  that  it  is  elimi- 
nated by  the  liver  is  proved  with  much  less  difficulty  than  that  it  is  formed 
in  the  nervous  system.  In  fact,  its  presence  in  the  bile,  and  the  neces- 
sity of  its  constant  removal  from  the  blood,  consequent  on  its  constant 
formation  and  absorption,  are  almost  sufficient  in  themselves  to  warrant 
the  conclusion  that  it  is  eliminated  by  the  liver. 

In  treating  of  the  composition  of  the  feces,  the  changes  which  the 
cholesterin  of  the  bile  undergoes  in  its  passages  down  the  intestinal 
canal  have  been  fully  considered.  But  one  examination  only  was  made 
of  the  quantity  of  stercorin  contained  in  the  daily  fecal  evacuation ;  and 
assuming  that  the  quantity  of  cholesterin  excreted  by  the  liver  is  equal 
to  the  stercorin  found  in  the  evacuations,  the  quantity  in  twenty-four 
hours  is  about  ten  and  a  half  grains  (0.68  gram).  This  corresponds  with 
the  estimates  of  the  daily  quantity  of  cholesterin  excreted,  calculated 
from  its  proportion  in  the  bile  and  the  estimated  daily  quantity  of  bile 
produced  by  the  liver. 

To  complete  the  chain  of  the  evidence  leading  to  the  conclusion  that 
cholesterin  is  an  excrementitious  product  formed  in  certain  of  the  tis- 
sues and  eliminated  by  the  liver,  it  is  necessary  only  to  show  that  it 
may  accumulate  in  the  blood  when  the  eliminating  action  of  the  liver  is 
interrupted. 

In  a  case  of  simple  jaundice  frorn  duodenitis,  in  which  there  was  no 
great  disturbance  of  the  system,  a  specimen  of  blood  taken  from  the 
arm  presented  evidences  of  the  coloring  matter  of  the  bile,  but  the 
proportion  of  cholesterin  was  not  increased,  being  only  0.508  of  a  part 
per  thousand.  The  feces  contained  a  large  proportion  of  saponifiable 
fat  but  no  cholesterin  or  stercorin. 

In  a  case  of  cirrhosis  with  jaundice,  there  was  ascites,  with  great 
general  prostration.     This  patient  died  a  few  days  after  the  blood  and 


ORIGIN    OF   CHOLESTERIN  371 

feces  had  been  examined,  and  the  liver  was  found  in  a  condition  of 
cirrhosis,  with  the  liver-cells  shrunken  and  the  gall-bladder  contracted. 
In  this  case  the  blood  contained  1.85  of  a  part  of  cholesterin  per  thou- 
sand, more  than  double  the  largest  quantity  found  in  health.  The  feces 
contained  a  small  quantity  of  stercorin. 

Inasmuch  as  cases  frequently  present  themselves  in  which  there  are 
evidences  of  cirrhosis  of  the  liver  with  little  if  any  constitutional  dis- 
turbance, while  others  are  attended  with  grave  nervous  symptoms,  it 
seemed  an  interesting  question  to  determine  whether  it  were  possible 
for  cholesterin  to  accumulate  in  the  blood  without  the  ordinary  evidences 
of  jaundice.  An  opportunity  occurred  to  examine  the  blood  in  two 
strongly-contrasted  cases  of  cirrhosis,  in  neither  of  which  was  there 
jaundice.  One  of  these  patients  had  been  tapped  repeatedly — -about 
thirty  times  —  but  the  ascites  was  the  only  troublesome  symptom  and 
the  general  health  was  little  impaired.  In  this  case  the  proportion  of 
cholesterin  in  the  blood  was  only  0.246  of  a  part  per  thousand,  consider- 
ably below  the  quantity  ordinarily  found  in  health.  The  other  patient 
had  cirrhosis,  but  he  was  confined  to  the  bed  and  was  very  feeble. 
The  proportion  of  cholesterin  in  the  blood  in  this  case  was  0.922  of  a 
part  per  thousand,  a  little  above  the  largest  proportion  found  in  health. 
A  few  other  pathological  observations  of  this  kind  are  on  record.  Picot, 
in  1872,  reported  a  fatal  case  of  "  grave  jaundice,"  in  which  he  deter- 
mined a  great  increase  in  the  quantity  of  cholesterin  in  the  blood,  the 
proportion  being  1.804  P^r  thousand. 

It  is  probable  that  organic  disease  of  the  liver,  accompanied  with 
grave  symptoms  affecting  usually  the  nervous  system,  does  not  differ 
in  its  pathology  from  cases  of  simple  jaundice  in  the  fact  of  retention  of 
the  biliary  salts  in  the  blood  ;  but  these  grave  symptoms,  it  is  more  than 
probable,  are  due  to  a  deficiency  in  the  elimination  of  cholesterin  and  its 
consequent  accumulation  in  the  system.  This  condition  may  be  char- 
acterized by  the  name  cholesteremia,  a  term  expressing  a  pathological 
condition,  but  at  the  same  time  indicating  the  physiological  relations  of 
cholesterin. 

Koloman  Miiller,  in  1873,  succeeded  in  injecting  cholesterin  into  the 
bloodvessels  without  producing  any.  effects  due  to  mechanical  obstruc- 
tion of  the  circulation.  He  made  a  preparation  by  rubbing  cholesterin 
with  glycerin  and  mixing  the  mass  with  soap  and  water.  He  injected 
into  the  veins  of  dogs  2.16  fluidounces  (about  64  cubic  centimeters)  of 
this  solution,  containing  about  69  grains  (4.5  grams)  of  cholesterin.  In 
five  experiments  of  this  kind,  he  produced  a  complete  representation  of 
the  phenomena  of  "  grave  jaundice." 

In  view  of  all  these  facts,  an  excretory  action  of  the  liver,  involving 


372  USES    OF   THE    LIVER  —  DUCTLESS   GLANDS 

the  separation  of  cholesterin  from  the  blood  and  its  discharge  in  the 
feces  in  the  form  of  stercorin,  may  be  regarded  as  estabhshed,  as  well 
as  the  existence  of  cholesteremia  as  a  definite  pathological  condition 
(Flint,  1862). 

Formation  of  Glycogen  in  the  Liver 

In  addition  to  the  uses  of  the  liver  already  described,  this  organ  con- 
stantly contains  in  health  a  substance  resembling  starch,  called  glyco- 
gen, which  is  converted  into  glucose  and  is  carried  into  the  circulation 
by  the  hepatic  veins. 

Glycogen  belongs  to  the  class  of  carbohydrates,  is  isomeric  with 
starch  and  is  readily  converted  into  glucose.  In  nearly  all  regards  it  has 
the  properties  of  starch,  but  it  gives  a  deep  red  color  with  iodin  instead 
of  a  blue.  In  the  liver-cells  it  exists  in  the  form  of  amorphous  granules 
surrounding  the  nuclei.  It  may  be  extracted  from  a  decoction  of  the 
liver-substance,  precipitating  the  albuminous  matters  by  adding  alter- 
nately dilute  hydrochloric  acid  and  potassio-mercuric  iodide,  filtering  and 
treating  the  filtrate  with  an  excess  of  alcohol.  The  alcoholic  precipitate, 
washed  with  alcohol  and  dried  rapidly,  is  in  the  form  of  a  white  powder 
that  will  keep  indefinitely.  In  the  adult,  glycogen  is  most  abundant 
in  the  liver ;  but  it  has  been  found  in  small  quantity  in  the  muscular 
substance,  in  cartilage  and  in  certain  cells  in  process  of  development. 
In  the  early  months  of  foetal  life  it  exists  in  nearly  all  the  tissues  and 
is  found,  also,  in  cells  attached  to  the  villi  of  the  placenta. 

The  most  important  of  the  conditions  that  influence  the  quantity  of 
glycogen  in  the  liver  relate  to  ahmentation  and  digestion.  The  liver 
always  contains  more  glycogen  during  digestion  than  fasting.  After  a 
few  days  of  starvation,  glycogen  may  almost  or  quite  disappear  from 
the  liver.  This  also  occurs  in  animals  fed  for  a  time  exclusively  with 
fats,  and  the  quantity  is  diminished  by  a  purely  albuminous  diet  as  con- 
trasted with  a  mixed  diet.  Still,  glycogen  is  invariably  present  in  the 
livers  of  healthy  carnivorous  animals  that  have  always  been  fed  with 
meat  alone. 

A  great  increase  in  the  quantity  of  glycogen  in  the  liver  is  produced 
by  feeding  animals  largely  with  carbohydrates.  Not  only  are  the  starches 
apparently  stored  up  for  a  time  in  the  form  of  glycogen  in  the  liver,  but 
sugars  undergo  a  change  into  glycogen,  which  accumulates  in  the  liver. 
This  is  to  be  expected,  as  the  starches  are  changed  into  sugar  before 
they  are  absorbed  and  all  the  carbohydrates  behave  in  the  same  way  as 
regards  general  nutrition. 

So  far  as  regards  the  influence  of  alimentation  on  the  formation  of 
glycogen,  it  seems  probable  that  in  the  herbivora  and  in  man,  the  chief 


FORMATION    OF   GLYCOGEN    IN    THE    LIVER  373 

source  of  hepatic  glycogen  is  the  class  of  alimentary  substances  called 
carbohydrates ;  but  the  fact  that  glycogen  exists  in  the  livers  of  the 
carnivora,  and  probably  in  man,  under  a  nitrogenous  diet,  shows  that 
the  liver  is  capable  of  forming  glycogen  from  albuminous  matters. 

Change  of  Glycogen  into  Sugar.  —  It  is  almost  certain  that  the  liver 
does  not  contain  sugar  during  life.  Many  years  ago  (1858)  this  fact 
was  recognized  by  Pavy,  and  it  has  since  been  confirmed  by  other  physi- 
ologists. Pavy,  however,  assumed  that  there  was  no  such  thing  as 
sugar-formation  by  the  Hver,  under  absolutely  normal  conditions.  He 
regarded  the  sugar  found  in  the  substance  of  the  liver  and  in  the  blood 
of  the  hepatic  veins  as  due  to  post-mortem  action,  and  his  obser\'ations 
seemed  to  be  directly  opposed  to  those  of  Bernard.  The  views  of  these 
two  observers  and  their  followers  seemed  to  be  harmonized  by  a  series 
of  experiments  made  in  1868.  If  the  abdomen  of  a  dog,  perfectly  quiet 
and  not  under  the  influence  of  an  anesthetic,  is  opened,  and  a  portion 
of  the  liver  excised,  rinsed  in  cold  water,  and  rapidly  cut  up  into  boiling 
water,  the  extract  will  show  no  reaction  with  FehHng's  test  for  sugar. 
In  one  experiment,  in  which  twenty-eight  seconds  elapsed  between  the 
time  of  opening  the  abdomen  and  the  action  of  the  boiling  water,  the 
reaction  with  Fehling's  test  was  doubtful.  In  an  experiment  in  which 
the  time  was  only  ten  seconds,  there  was  no  trace  of  sugar  in  the  extract 
from  the  liver  (Flint).  All  observers  are  now  agreed  that  sugar  is 
formed  in  the  liver  very  rapidly  after  death. 

If  the  view  is  correct  —  that  the  glycogen  of  the  liver  is  being  con- 
stantly transformed  into  sugar  during  life,  and  that  this  sugar  is  carried 
away  in  the  blood-current,  as  fast  as  it  is  formed  —  sugar  would  not 
necessarily  be  contained  in  the  liver  under  normal  conditions  ;  and  there 
is  no  actual  antagonism  between  the  results  obtained  by  Bernard  and  the 
fact  that  sugar  itself  is  not  a  normal  constituent  of  the  liver,  as  is  asserted 
by  Pavy,  McDonnell,  Meissner,  Ritter  and  others. 

If  the  liver  is  washed  by  means  of  a  stream  of  water  passed  through 
its  vessels  until  it  is  free  from  sugar  and  is  then  kept  at  the  temperature 
of  the  body  for  a  few  hours,  sugar  will  reappear  in  abundance.  This  is 
due  to  a  conversion  of  the  glycogen  of  the  Hver  into  sugar  by  a  ferment, 
which  has  been  extracted  and  isolated  by  a  process  analogous  to  that 
by  which  similar  ferments  have  been  extracted  from  the  saliva  and  the 
pancreatic  juice.  This  ferment  probably  exists  originally  in  the  liver 
and  does  not  appear  first  in  the  blood. 

The  question  of  the  transformation  of  glycogen  into  sugar  during  life 
depends  on  the  comparative  quantities  of  sugar  in  the  blood  going  to  and 
coming  from  the  liver.  Sugar  is  found  in  quantity  in  the  blood  of  the 
hepatic  veins  taken  immediately  after  death  and  exists  in  blood  drawn 


374  USES   OF   THE    LIVER —  DUCTLESS    GLANDS 

during  life  by  a  catheter  introduced  into  the  right  cavities  of  the  heart ; 
while  in  the  carnivora,  under  a  purely  animal  diet,  no  sugar  is  contained 
in  the  blood  of  the  portal  system.  The  normal  blood  contains,  perhaps, 
a  small  quantity  of  sugar  —  0.5  to  i  part  per  thousand  —  but  the  pro- 
portion is  always  greater  in  the  blood  of  the  hepatic  veins. 

The  characters  of  animal  sugar  do  not  materially  differ  from  those 
of  glucose,  except  that  it  ferments  more  readily  and  is  destroyed  in  the 
system  with  great  facility.  This  property  of  the  sugar  resulting  from 
the  glycogen  formed  in  the  liver  probably  is  of  great  importance.  The 
sugar  which  results  from  digestion  is  all  carried  to  the  liver.  Here  it  is 
changed  into  glycogen ;  and  it  is  probable  that  without  this  change  into 
glycogen  and  its  subsequent  transformation  into  what  is  called  liver- 
sugar,  it  is  not  perfectly  adapted  to  the  purposes  of  nutrition. 

The  sugar  discharged  into  the  venous  system  by  the  hepatic  veins 
usually  is  lost  in  the  passage  of  the  blood  through  the  lungs.  The  ques- 
tion of  the  final  destination  of  sugar  will  be  taken  up  again  in  connec- 
tion with  the  physiology  of  nutrition. 

Conditions  that  influence  the  Quantity  of  Sugar  iji  the  Blood.  —  It  is 
probable  that  disturbances  of  the  circulation  in  the  liver  are  the  most 
important  conditions  influencing  the  discharge  of  sugar  by  the  hepatic 
veins,  and  these  operate  mainly  through  the  nervous  system. 

A  notable  experiment  on  the  influence  of  the  nervous  system  on  the 
liver  is  the  one  in  which  artificial  diabetes  is  produced  by  stimulation  of 
the  floor  of  the  fourth  ventricle  (Bernard).  This  operation  is  not  dif- 
ficult. The  instrument  used  is  a  delicate  stilet,  with  a  flat  cutting  ex- 
tremity and  a  small  projecting  point  about  ^V  o^  ^^  i^'^ch  (i  miUimeter) 
long.  In  performing  the  operation  on  a  rabbit,  the  head  of  the  animal 
is  firmly  held  in  the  left  hand,  and  the  skull  is  penetrated  in  the  median 
line,  just  behind  the  superior  occipital  protuberance.  This  can  easily  be 
done  by  a  few  lateral  movements  of  the  instrument.  Once  within  the 
cranium,  the  instrument  is  passed  obliquely  downward  and  forward,  so 
as  to  cross  an  imaginary  line  drawn  between  the  two  auditory  canals, 
until  its  point  reaches  the  basilar  process  of  the  occipital  bone.  The 
point  then  penetrates  the  medulla  oblongata,  between  the  roots  of  the 
auditory  nerves  and  the  pneumogastrics,  and  its  projection  serves  to 
protect  the  nervous  centre  from  more  serious  injury  from  the  cutting 
edge.  The  instrument  is  then  carefully  withdrawn  and  the  operation  is 
completed.  This  experiment  is  almost  painless,  and  it  is  not  desirable 
to  administer  an  anesthetic,  as  this,  in  itself,  would  disturb  the  glyco- 
genic process.  The  urine  may  be  obtained  before  the  operation,  by  press- 
ing the  lower  part  of  the  abdomen,  taking  care  not  to  allow  the  bladder 
to  pass  up  above  the  point  of  pressure,  and  it  will  be  found  turbid,  alka- 


INTERNAL    SECRETION 


375 


line  and  without  sugar.  In  one  or  two  hours  after  the  operation,  the 
urine  will  have  become  clear  and  acid,  and  it  will  react  readily  with  any 
of  the  copper  tests.  When  this  operation  is  performed  without  injuring 
the  adjacent  organs,  the  presence  of  sugar  in  the  urine  is  temporary; 
and  the  next  day  the  secretion  will  have  returned  to  its  normal  condition. 
The  production  of  glycosuria  in  this  way,  in  animals,  is  important  in  its 
relations  to  certain  cases  of  diabetes  in  the  human  subject,  in  which 
the  affection  is  traumatic  and  directly  attributable  to  injury  near  the 
bulb.  The  irritation  is  not  conveyed  through  the  pneumogastric 
nerves,  for  the  experiment  succeeds  after  both  of  these  nerves  have  been 
divided  ;  nevertheless,  the  pneumogastrics  have  an  important  influence 
on  glycogenesis.  If  both  nerves  are  divided  in  the  neck,  in  a  few  hours 
or  days,  depending  on  the  length  of  time  that  the  animal  survives  the 
operation,  no  sugar  is  to  be  found  in  the  liver,  and  there  is  reason  to 
believe  that  the  glycogenic  action  has  been  arrested.  After  division  of 
the  nerves  in  the  neck,  stimulation  of  their  peripheral  ends  does  not 
affect  the  production  of  sugar ;  but  stimulation  of  the  central  ends  pro- 
duces an  impression  that  is  conveyed  to  the  nerve-centre,  is  reflected  to 
the  liver  and  gives  rise  to  an  increased  production  of  sugar.  It  reaches 
the  hver  probably  through  the  sympathetic  system. 

It  has  been  obser\^ed  that  the  inhalation  of  anesthetics  and  irritat- 
ing vapors  produces  temporary  glycosuria;  and  this  has  been  attributed 
to  an  irritation  conveyed  by  the  pneumogastrics  to  the  nerve-centre, 
and  reflected,  in  the  form  of  a  stimulus,  to  the  liver.  It  is  for  this 
reason  that  the  administration  of  anesthetics  should  be  avoided  in 
experiments  on  glycogenic  action. 

In  addition  to  the  varied  uses  of  the  liver  that  have  been  described, 
it  is  thought  that  this  organ  either  arrests  or  in  some  way  influences  the 
condition  of  certain  foreign  and  poisonous  substances  absorbed  from 
the  alimentary  canal ;  but  a  study  of  this  action  does  not  properly 
belong  to  physiology. 

Ductless    Glands  and  Internal  Secretion 

Certain  organs  in  the  body,  with  a  structure  resembling,  in  some 
respects,  the  true  glands,  but  without  excretory  ducts,  have  long  been 
the  subject  of  physiological  speculation  ;  and  the  most  extravagant 
notions  concerning  their  uses  prevailed  in  the  early  history  of  physi- 
ology. The  discovery  of  the  action  of  the  liver  in  modifying  the  com- 
position of  the  blood  passing  through  its  substance  foreshadowed  the 
probable  mode  of  action  of  the  ductless  glands  ;  for  so  far  as  the  pro- 
duction of  glycogen  is  concerned,  the  liver  belongs  to  this  class.    Indeed, 


Ije  USES    OF   THE    LIVER  — DUCTLESS    GLANDS 

the  supposition  that  the  ductless  glands  effect  certain  changes  in 
the  blood  is  now  regarded  by  physiologists  as  the  most  reasonable  of  the 
many  theories  that  have  been  entertained  concerning  their  uses  in  the 
economy.  Under  this  idea,  these  organs  have  been  called  blood-glands 
or  vascular  glands,  and  their  action  is  now  known  as  internal  secretion. 
Under  the  head  of  ductless  glands,  are  classed  the  suprarenal  capsules, 
the  spleen,  the  thyroid  gland,  the  thymus,  and  sometimes  the  pituitary 
body  and  the  pineal  gland. 

Suprarenal  Capsules 

The  suprarenal  capsules,  or  adrenals,  as  their  name  implies,  are 
situated  above  the  kidneys.  They  are  small  triangular  flattened  bodies, 
situated  behind  the  peritoneum  and  capping  the  kidneys  at  the  anterior 
portion  of  their  superior  ends.  The  left  capsule  is  a  little  larger  than 
the  right  and  is  rather  semilunar  in  form,  the  right  being  more  nearly 
triangular.  Their  size  and  weight  are  variable  in  different  individuals. 
It  may  be  stated  as  an  average  that  each  capsule  weighs  about  one 
hundred  grains  (6.5  grams).  The  capsules  are  about  an  inch  and  a  half 
(38  millimeters)  in  length,  a  little  less  in  width,  and  about  one-fourth 
of  an  inch  (6.4  millimeters)  in  thickness. 

The  weight  of  the  capsules,  in  proportion  to  the  weight  of  the 
kidneys,  presents  great  variations  at  different  periods  of  life.  They 
are  relatively  much  larger  in  the  foetus  than  after  birth.  They  are 
easily  distinguished  in  the  foetus  of  two  months ;  at  the  end  of  the 
third  month  they  are  a  little  larger  and  heavier  than  the  kidneys ; 
they  are  equal  in  size  to  the  kidneys  —  though  a  little  lighter  —  at  four 
months;  and  at  the  beginning  of  the  sixth  month  they  are  to  the 
kidneys  as  two  to  five.  In  the  foetus  at  term  the  proportion  is  as  one 
to  three,  and  in  the  adult,  as  one  to  twenty-three  (see  Plate  XVI,  Fig.  3). 

The  color  of  the  capsules  is  whitish  yellow.  They  are  completely 
covered  by  a  thin  fibrous  coat  which  penetrates  their  interior  in  the 
form  of  trabeculae.  On  section  they  present  a  cortical  and  a  medul- 
lary substance.  The  cortex  is  yellowish  and  o\  to  ^V  of  an  inch  (i  to 
2  millimeters)  in  thickness.  It  surrounds  the  capsule  completely  and 
.constitutes  about  two-thirds  of  its  substance.  The  medullary  substance 
is  whitish,  very  vascular,  and  is  remarkably  prone  to  decomposition,  so 
that  it  is  desirable  to  study  the  anatomy  of  these  bodies  in  specimens 
that  are  perfectly  fresh. 

Cortical  Substance.  —  The  cortical  substance  is  divided  into  two  layers. 
The  external  layer  is  pale  yellow  and  is  composed  of  closed  vesicles, 
rounded  or  ovoid  in  form,  containing  an  albuminous  liquid,  cells,  nuclei 
and  fatty  globules.     This  layer  is  very  thin.     The  greater  part  of  the 


SUPRARENAL    CAPSULES  377 

cortical  substance  is  of  a  reddish  brown  color  and  is  composed  either  of 
closed  tubes  containing  cells  or  of  columns  of  cells  surrounded  with 
delicate  fibrous  trabeculae.  On  making  thin  sections  through  the  corti- 
cal substance  previously  hardened  in  chromic  acid  and  rendered  clear 
by  glycerin,  rows  of  cells  are  seen,  arranged  with  great  regularity,  and 
extending,  apparently,  from  the  investing  membrane  to  the  medullary 
substance.  The  cells  appear  to  be  enclosed  in  tubes  measuring  yoVo  ^° 
g^Q-  of  an  inch  (25  to  80  jx)  in  diameter.  They  are  granular,  with  a 
distinct  nucleus  and  nucleolus  and  a  variable  number  of  oil-globules. 
They  measure  ^7^50^  to  ygVo  °^  ^^  mch  (14  to  25  jjl)  in  diameter.  Be- 
tween the  rows  of  cells  of  the  cortical  substance  are  bands  of  fibrous 
tissue  connected  with  the  investing  membrane  of  the  capsule. 

Medullary  Substance.  —  The  medullary  substance  is  much  paler  and 
more  transparent  than  the  cortex.  In  its  centre  are  openings  that  mark 
the  passage  of  its  venous  sinuses.  It  is  penetrated  in  every  direction 
by  delicate  bands  of  fibrous  tissue,  which  enclose  bloodvessels,  nerves 
and  elongated  closed  vesicles  containing  cells,  nuclei  and  granular  mat- 
ter. These  vesicles,  which  are  -g^^  of  an  inch  (0.32  millimeters)  long 
and  about  -^\-^  of  an  inch  (64  ii)  broad,  have  been  demonstrated  in  the 
ox  and  in  the  human  subject.  The  cells  in  the  human  subject  are  y^o" 
to  Y2V0  ^^  "^^  inch  (15  to  20 /u.)  in  diameter.  They  are  isolated  with 
difficulty  and  are  irregular  in  form.  The  nuclei  measure  about  2"5Vo  °^ 
an  inch  (10  yn).  The  medullary  substance  is  peculiarly  rich  in  vessels 
and  nerves  (see  Plate  IX,  Fig.  i). 

Vessels  and  Nerves.  —  The  bloodvessels  going  to  the  suprarenal 
capsules  are  very  abundant  and  are  derived  from  the  aorta,  the  phrenic 
artery,  the  coeliac  axis  and  the  renal  artery.  Sometimes  as  many  as 
twenty  distinct  vessels  penetrate  each  capsule.  In  the  cortical  substance 
the  capillaries  are  arranged  in  elongated  meshes,  anastomosing  freely 
and  surrounding  but  not  penetrating  the  tubes.  In  the  medullary  sub- 
stance the  meshes  are  more  rounded,  and  here  the  vessels  form  a  rich 
capillary  plexus.  Two  large  veins  pass  out,  to  empty  on  the  right 
side  into  the  vena  cava,  and  on  the  left,  into  the  renal  vein.  Other 
smaller  veins  empty  into  the  vena  cava,  the  renal  and  the  phrenic 
veins. 

The  nerves  are  abundant  and  are  derived  from  the  semilunar 
ganglia,  the  renal  plexus,  the  pneumogastric  and  the  phrenic.  The 
nerves  probably  pass  directly  to  the  medullary  substance,  but  here  their 
mode  of  distribution  is  unknown.  In  the  medullary  substance,  however, 
there  are  two  ganglia  situated  close  to  the  central  vein. 

Nothing  is  known  of  lymphatics  in  the  suprarenal  capsules,  and  the 
existence  of  such  vessels  is  doubtful. 


3/8  USES    OF   THE    LIVER  — DUCTLESS   GLANDS 

Chemistry  of  the  Suprarenal  Capsules.  —  Vulpian  has  described 
(1856),  in  the  medullary  portion  of  the  suprarenal  capsules,  a  peculiar 
substance,  soluble  in  water  and  in  alcohol,  which  gave  a  greenish 
reaction  with  the  salts  of  iron  and  a  peculiar  rose  tint  on  the  addition 
of  iodin.  He  could  not  determine  the  same  reaction  with  extracts 
from  any  other  parts.  Later,  in  conjunction  with  Cloez,  he  discovered 
hippuric  and  taurocholic  acid  in  the  capsules  of  certain  of  the  herbivora. 
These  bodies  contain  in  addition,  leucin,  hypoxanthin,  taurin,  fats  and 
inorganic  salts,  the  latter  chiefly  phosphates  and  salts  of  potassium. 

It  has  lately  been  observed  that  extracts  of  the  medullary  substance 
of  the  suprarenal  capsules  when  injected  into  the  bloodvessels  produce 
slowing  of  the  heart  with  great  increase  in  the  blood-pressure.  This 
occurs  in  animals  under  normal  conditions ;  but  after  division  of  the 
pneumogastrics,  the  effect  is  an  acceleration  of  the  heart's  action,  with 
a  still  greater  increase  in  blood-pressure.  This  peculiar  action  is  diffi- 
cult to  explain ;  but  the  fact  that  the  same  results  follow  the  use  of 
extracts  from  the  blood  of  the  adrenal  veins  shows  that  the  gland  is  the 
seat  of  an  internal  secretion.  It  is  probable,  however,  that  the  increase 
in  blood-pressure  is  due  to  a  direct  action  on  the  muscular  coats  of  the 
bloodvessels,  as  it  occurs  after  destruction  of  the  vasomotor  centres. 
The  active  substance  has  been  isolated  and  is  described  under  the  name 
of  epinephr'in,  with  the  formula  C17H15NO4.  This  probably  is  the 
active  principle  of  the  adrenalin  now  often  used  in  therapeutics. 

The  suprarenal  capsules  seem  to  be  essential  to  Hfe.  In  Addison's 
disease,  a  disorder  attended  with  bronzing  of  the  skin  and  serious  and 
finally  fatal  disorder  of  nutrition,  there  usually  is  disorganization  of  the 
suprarenal  capsules,  but  this  is  not  invariable.  It  has  not  been  estab- 
lished, however,  that  disorganization  of  the  capsules  stands  always  in  a 
causative  relation  to  the  discoloration  of  the  skin  or  to  the  constitutional 
disturbance.  Investigations  into  diseased  conditions  have  developed 
little  of  importance  concerning  the  physiology  of  these  organs. 

The  Spleen 

The  spleen  is  situated  in  the  left  hypochondriac  region,  next  the 
cardiac  extremity  of  the  stomach.  Its  color  is  a  dark  bluish  red  and 
its  consistence  is  rather  soft  and  friable.  It  is  shaped  somewhat  Hke 
the  tongue  of  a  dog,  presenting  above,  a  rather  thickened  extremity, 
which  is  in  relation  with  the  diaphragm,  and  below,  a  pointed  extremity, 
in  relation  with  the  transverse  colon.  Its  external  surface  is  convex. 
Its  internal  surface  is  concave,  presenting  a  vertical  fissure,  the  hilum, 
which  gives  passage  to  the  vessels  and  nerves.    It  is  connected  with  the 


THE    SPLEEN  379 

stomach  by  the  gastro-splenic  omentum  and  is  still  further  fixed  by  a 
fold  of  peritoneum  passing  to  the  diaphragm.  It  is  about  five  inches 
(127  millimeters)  in  length,  three  to  four  inches  (75  to  100  miUimeters) 
in  breadth  and  a  little  more  than  an  inch  (25.4  millimeters)  in  thickness. 
Its  weight  is  six  to  seven  ounces  (170  to  198  grams).  In  the  adult  it 
attains  its  maximum  of  development,  and  it  diminishes  slightly  in  size 
and  weight  in  old  age.  In  early  life  it  bears  about  the  same  relation  to 
the  weight  of  the  body  as  in  the  adult. 

The  external  coat  of  the  spleen  is  the  peritoneum,  which  is  closely 
adherent  to  the  subjacent  fibrous  structure.  The  proper  coat  is  dense 
and  resisting;  but  in  the  human  subject  it  is  quite  thin  and  somewhat 
translucent.  It  is  composed  of  ordinary  fibrous  tissue  mixed  with 
abundant  small  fibres  of  elastic  tissue  and  a  few  non-striated  muscular 
fibres. 

At  the  hilum  the  fibrous  coat  penetrates  the  substance  of  the  spleen 
in  the  form  of  sheaths  for  the  vessels  and  nerves.  The  number  of  the 
sheaths  in  the  spleen  is  equal  to  the  number  of  arteries  that  penetrate 
the  organ.  This  membrane  is  sometimes  called  the  capsule  of  Alalpighi. 
The  fibrous  sheaths  are  closely  adherent  to  the  surrounding  substance, 
but  they  are-  united  to  the  vessels  by  a  loose  fibrous  network.  They 
follow  the  vessels  in  their  ramifications  to  the  smallest  branches  and  are 
lost  in  the  spleen-pulp.  Between  the  sheath  and  the  outer  coat  are  bands, 
or  trabeculas,  presenting  the  same  structure  as  the  fibrous  coat.  The 
presence  of  elastic  fibres  in  the  trabeculae  can  easily  be  demonstrated ; 
and  this  kind  of  tissue  is  very  abundant  in  the  herbivora.  In  the  car- 
nivora  the  muscular  tissue  is  particularly  abundant  and  can  readily  be 
demonstrated ;  but  in  man  this  is  not  so  easy,  and  the  fibres  are  less 
abundant.  These  peculiarities  in  the  fibrous  structure  are  important  in 
their  relations  to  certain  physiological  changes  in  the  size  of  the  spleen. 
Its  contractility  may  be  demonstrated  in  the  dog  by  the  application  of  a 
faradic  current  to  the  nerves  as  they  enter  at  the  hilum.  This  is  followed 
by  a  prompt  and  energetic  contraction  of  the  organ.  Contractions  may 
be  produced,  though  they  are  much  more  feeble,  by  applying  the  cur- 
rent directly  to  the  spleen. 

The  substance  of  the  spleen  is  soft  and  friable ;  and  a  portion  of  it, 
the  spleen-pulp,  may  be  pressed  out  with  the  fingers  or  even  washed 
away  by  a  stream  of  water.  Aside  from  the  vessels  and  nerves,  it 
presents  for  study:  i,  an  arrangement  of  fibrous  bands,  or  trabeculae, 
by  which  it  is  divided  into  communicating  spaces ;  2,  closed  vesicles, 
called  Malpighian  bodies,  attached  to  the  walls  of  the  bloodvessels ; 
3,  a  soft,  reddish  substance,  containing  large  numbers  of  cells  and  free 
nuclei,  called  spleen-pulp. 


38o  USES    OF    THE    LIVER  — DUCTLESS    GLANDS 

Fibi'OJis  Structure  of  the  Spleen  ( Trabecules).  —  From  the  internal 
face  of  the  investing  membrane  of  the  spleen  and  from  the  fibrous 
sheaths  of  the  vessels  (capsule  of  Malpighi)  are  bands,  or  trabeculae, 
which,  by  their  interlacement,  divide  the  substance  of  the  organ  into 
irregularly-shaped  communicating  cavities.  These  bands  are  2V  ^^  ylg- 
of  an  inch  (i  to  1.7  millimeter)  broad,  and  are  composed,  like  the 
proper  coat,  of  ordinary  fibrous  tissue  with  elastic  fibres  and  probably  a 
few  non-striated  muscular  fibres.  They  pass  off  from  the  capsule  of 
Malpighi  and  the  fibrous  coat  at  right  angles,  soon  branch,  interlace  and 
unite  with  each  other,  becoming  smaller  and  smaller,  until  they  measure 
sio  ^^  eV  ^^  ^^  ^""^^  (^°-^  ^o  ^-42  millimeter).  This  fibrous  network 
serves  as  a  support  for  the  softer  parts. 

MalpigJiiau  Bodies.  —  These  bodies  are  sometimes  called  splenic 
corpuscles  or  glands.  They  are  rounded  or  slightly  ovoid,  about  -^-^  of 
an  inch  (0.5  millimeter)  in  diameter,  and  are  filled  with  what  are 
thought  to  be  lymph-corpuscles,  and  free  nuclei.  The  Malpighian 
bodies  have  no  investing  membrane.  With  this  difference,  they  resem- 
ble in  structure  the  solitary  glands  of  the  intestine.  Both  the  cells  and 
the  free  nuclei  of  the  splenic  corpuscles  bear  a  close  resemblance  to 
cells  and  nuclei  found  in  the  spleen-pulp.  The  corpuscles  are  sur- 
rounded with  bloodvessels  —  which  send  branches  into  the  interior,  to 
form  a  delicate  capillary  plexus  —  and  with  what  is  thought  to  be  a 
lymphatic  space  or  sinus. 

The  number  of  the  Malpighian  corpuscles  in  a  spleen  of  ordinary 
size  has  been  estimated  at  about  ten  thousand.  They  are  readily  made 
out  in  the  ox  and  sheep,  but  frequently  are  not  to  be  discovered  in  the 
human  subject.  The  occasional  absence  of  these  bodies  constitutes 
another  point  of  resemblance  to  the  solitary  glands  of  the  small  intestine. 

The  Malpighian  bodies  are  attached  to  arteries  measuring  gL  to  ^^ 
of  an  inch  (0.32  to  0.42  millimeter)  or  less  in  diameter,  i  hey  arc 
often  found  in  the  notch  formed  by  the  branching  of  an  artery,  but  they 
usually  lie  by  the  sides  of  the  vessel  (see  Plate  IX,  Fig.  3). 

Spleen-piilp.  —  The  spleen-pulp  is  a  dark,  reddish,  semifluid  sub- 
stance, its  color  varying  in  intensity  in  different  specimens.  It  is  so 
soft  that  it  may  be  washed  by  a  stream  of  water  from  a  thin  section, 
and  it  readily  decomposes,  becoming  then  nearly  liquid.  It  is  contained 
in  the  cavities  bounded  by  the  fibrous  trabeculae,  and  it  contains  itself 
microscopic  bands  of  fibres  arranged  in  the  same  way.  It  surrounds  the 
Malpighian  bodies  and  contains  the  terminal  branches  of  the  blood- 
vessels, nerves  and  lymphatics.  On  microscopical  examination,  it 
presents  free  nuclei  and  cells  like  those  described  in  the  Malpighian 
bodies;    but  the  nuclei  are  here  relatively  much  more  abundant.     In 


BLOODVESSELS,  NERVES  AND  LYMPHATICS  OF  THE  SPLEEN     38 1 

addition  are  found  red  blood-corpuscles,  some  natural  in  form  and  size 
and  others  more  or  less  altered,  with  pigmentary  granules,  both  free 
and  enclosed  in  cells. 

Bloodvessels,  Nerves  and  Lymphatics  of  the  Spleen.  —  The  quantity 
of  blood  which  the  spleen  receives  is  large  in  proportion  to  the  size  of 
the  organ.  The  splenic  artery  is  the  largest  branch  of  the  coeliac  axis. 
It  is  a  vessel  of  considerable  length  and  is  remarkable  for  its  tortuous 
course.  It  gives  off  several  branches  to  the  adjacent  viscera,  and  as  it 
passes  to  the  hilum,  it  divides  into  three  or  four  branches,  which  again 
divide  so  as  to  form  six  to  ten  vessels.  These  penetrate  the  substance 
of  the  spleen,  enveloped  in  fibrous  sheaths  with  the  veins,  nerves 
and  lymphatics.  In  the  substance  of  the  spleen  the  arteries  branch 
rather  peculiarly,  giving  off  many  small  ramifications  in  their  course, 
usually  at  right  angles  to  the  parent  trunk.  These  are  accompanied  by 
the  veins  until  they  are  reduced  to  g^^-  or  ^^  of  an  inch  (0.32  or  0.42 
millimeter)  in  diameter.  The  two  classes  of  vessels  then  separate,  and 
the  arteries  have  attached  to  them  the  corpuscles  of  Malpighi.  It  is 
also  a  noticeable  fact  that  the  arteries  passing  in  at  the  hilum  have  no 
inosculations  with  each  other  in  the  substance  of  the  spleen,  so  that  the 
organ  is  divided  up  into  six  to  ten  vascular  compartments. 

The  veins  join  the  small  branches  of  the  arteries  in  the  spleen-pulp 
and  pass  out  of  the  spleen  in  the  same  sheath.  They  anastomose  quite 
freely  in  their  larger  as  well  as  their  smaller  branches.  Their  calibre 
is  estimated  as  about  twice  that  of  the  arteries.  The  estimates  which 
have  put  the  calibre  of  the  veins  at  four  or  five  times  that  of  the  arteries 
probably  are  exaggerated.  The  number  of  veins  emerging  from  the 
spleen  is  equal  to  the  number  of  arteries  of  supply. 

By  most  anatomists  two  sets  of  lymphatic  vessels  have  been  recog- 
nized, the  superficial  and  the  deep.  The  superficial  lymphatics  are  in 
the  investing  membrane  of  the  spleen  and  probably  are  connected  with 
the  deep  lymphatics.  The  origin  of  the  deep  vessels  is  somewhat  ob- 
scure. Lymphatic  spaces,  with  anastomosing  venous  spaces  or  sinuses, 
however,  surround  the  Malpighian  bodies  and  permeate  the  spleen-pulp. 
It  is  probable  that  lymph  and  blood  are  mixed  in  these  sinuses  (see 
Plate  IX,  Fig.  2).  At  the  hilum  the  deep  lymphatics  are  joined  by 
vessels  from  the  surface.  The  vessels,  numbering  five  or  six,  then 
pass  into  small  lymphatic  glands  and  empty  into  the  thoracic  duct 
opposite  the  eleventh  or  twelfth  dorsal  vertebra.  No  lymphatic  vessels 
have  been  observed  going  to  the  spleen. 

The  nerves  of  the  spleen  are  derived  from  the  solar  plexus.  They 
follow  the  vessels  in  their  distribution  and  are  enclosed  with  them  in  the 
capsule  of  Malpighi.     They  are  distributed    ultimately  in   the  spleen- 


382  USES    OF   THE    LIVER  — DUCTLESS    GLANDS 

pulp,  but  nothing  definite  is  known  of  their  mode  of  termination. 
When  these  nerves  are  stimulated,  the  non-striated  muscles  in  the  sub- 
stance of  the  spleen  are  thrown  into  contraction. 

Some  Points  in  tJie  Chemical  Co7istitntion  of  the  Spleen.  ■ —  Little  has 
been  learned  in  regard  to  the  probable  uses  of  the  spleen  from  analyses 
of  its  substance;  and  it  would  therefore  be  out  of  place  to  discuss  its 
chemical  constitution  very  fully.  Cholesterin  has  been  found  constantly 
and  in  considerable  quantity,  and  the  same  may  be  said  of  uric  acid. 
In  addition,  chemists  have  extracted  from  the  substance  of  the  spleen 
various  proteids,  hypoxanthin,  leucin,  tyrosin,  lecithin,  jecorin,  a  peculiar 
crystallizable  substance  called,  by  Scherer,  lienin,  crystals  of  hematoi- 
din,  lactic  acid,  acetic  acid,  butyric  acid,  inosite,  amyloid  matter  and 
some  indefinite  fatty  matters. 

Variations  in  the  Volume  of  the  Spleen.  —  One  of  the  theories  in 
regard  to  the  uses  of  the  spleen,  which  merits  some  consideration,  is 
that  it  serves  as  a  diverticulum  for  the  blood  when  there  is  a  tendency 
to  congestion  of  the  other  abdominal  viscera. 

It  has  been  shown  that  the  spleen  becomes  enlarged  in  dogs  four  or 
five  hours  after  feeding,  that  its  enlargement  is  at  its  maximum  at  about 
the  fifth  hour  and  that  it  gradually  diminishes  to  its  original  size  during 
the  succeeding  twelve  hours ;  but  it  is  not  apparent  how  far  these 
changes  are  important  or  essential  to  normal  digestion  and  absorption. 
Experiments  have  shown  that  animals  may  live,  digest,  and  absorb 
alimentary  matters  after  the  spleen  has  been  removed,  and  this  has 
been  observed  even  in  the  human  subject.  In  view  of  these  facts,  it 
can  not  be  assumed  that  the  office  of  the  spleen  as  a  diverticulum  for  the 
blood  is  essential  to  the  proper  action  of  the  other  abdominal  organs. 

Changes  in  the  volume  of  the  spleen  may  be  produced  by  operating 
on  the  nervous  system,  chiefly  through  the  vasomotor  nerves.  Section 
of  the  nerves  at  the  hilum  increases  the  size  of  the  spleen  by  increasing 
the  quantity  of  blood ;  and  stimulation  of  these  nerves  produces  con- 
traction of  the  spleen.  It  is  said  that  stimulation  of  the  bulb  dimin- 
ishes the  size  of  the  spleen,  and  that  the  same  result  can  be  produced 
by  reflex  action,  stimulating  the  central  ends  of  the  pneumogastrics  or 
of  various  sensory  nerves,  provided  the  splanchnic  nerves  be  intact. 
Starting  from  the  bulb,  the  nerve-fibres  that  influence  the  size  of  the 
spleen  pass  down  the  spinal  cord  to  the  lower  dorsal  region,  enter  the 
semilunar  ganglion  by  the  left  splanchnic  and  are  distributed  to 
the  spleen  through  the  splenic  plexus. 

Rhythmical  contraction  of  the  spleen,  occurring  about  once  a 
minute,  has  been  observed  in  dogs  and  cats  (Roy)  and  was  supposed 
to  assist  the  circulation    in  this  organ  ;  but  there  is   no  evidence  that 


EXTIRPATION    OF   THE    SPLEEN  383 

this  takes  place  in  the  human  subject,  and  the  movements  are  so  slow 
and  inefficient  that  it  does  not  appear  that  they  can  either  promote  or 
retard  the  flow  of  blood. 

Extirpatioji  of  the  Spleen.  —  Removal  of  the  spleen  is  an  old  and 
a  very  common  experiment.  In  the  works  of  Malpighi  (1687)  is 
an  account  of  an  experiment  on  a  dog,  in  which  the  spleen  was  de- 
stroyed and  the  operation  was  followed  by  no  serious  results.  Since 
then  it  has  been  removed  so  often  and  the  experiments  have  been 
so  often  negative  in  their  results  that  it  is  hardly  necessary  to  cite  au- 
thorities on  the  subject.  There  are  many  instances,  also,  in  which  it  has 
been  in  part  or  entirely  removed  from  the  human  subject,  which  it  is  un- 
necessary to  refer  to  in  detail.  One  of  the  phenomena  following  extir- 
pation of  the  spleen  is  a  modification  of  the  appetite.  Great  voracity  in 
animals  after  removal  of  the  spleen  was  noted  by  the  earlier  observers. 
Later  experimenters  have  observed  this  change  in  the  appetite  and  have 
noted  that  digestion  and  assimilation  do  not  appear  to  be  disturbed,  the 
animals  becoming  unusually  fat. 

In  the  following  observation  these  phenomena  were  well  marked :  — 

The  spleen  was  removed  from  a  young  dog  weighing  twenty-two 
pounds  (about  10  kilograms).  Before  the  operation  the  dog  presented 
nothing  unusual,  either  in  his  appetite  or  disposition.  The  wound 
healed  rapidly,  and  after  recovery  had  taken  place,  the  animal  was  fed 
moderately  once  a  day.  It  was  noticed,  however,  that  the  appetite  was 
voracious.  The  dog  became  so  irritable  and  ferocious  that  it  was  dan- 
gerous to  approach  him,  and  it  became  necessary  to  separate  him  from 
the  other  animals  in  the  laboratory.  He  would  eat  refuse  from  the 
dissecting-room,  the  flesh  of  dogs,  feces  etc.  About  six  weeks  after 
the  operation,  having  been  well  fed  twenty-four  hours  before,  the  dog 
ate  at  one  time  a  little  more  than  four  pounds  (1814  grams)  of  beef- 
heart,  nearly  one-fifth  of  his  weight.  This  he  digested  well,  and  the 
appetite  was  undiminished  on  the  following  day.  The  dog  had  a 
remarkably  sleek  and  well-nourished  appearance  (Flint,  1861). 

The  above  is  a  striking  example  of  the  change  in  the  appetite  and 
disposition  of  animals  after  extirpation  of  the  spleen;  but  these  results 
are  by  no  means  invariable.  In  many  instances  of  removal  of  the  spleen 
from  dogs,  the  animals  were  kept  for  several  months  and  nothing 
unusual  was  observed.  On  the  other  hand,  the  change  in  disposition 
and  the  development  of  an  unnatural  appetite  were  observed  in  animals 
after  removal  of  one  kidney.  These  effects  were  also  marked  in  an 
animal  with  biliary  fistula  that  lived  for  thirty-eight  days.  In  the  latter 
instance,  the  voracity  could  be  accounted  for  by  the  disturbance  in 
digestion  and  assimilation  produced  by  shutting  off  the  bile  from  the 


384  USES    OF   THE    LIVER  — DUCTLESS    GLANDS 

intestine ;  but  these  phenomena  occurring  after  removal  of  one  kidney 
are  not  so  readily  explained. 

Cases  are  on  record  of  congenital  absence  of  the  spleen  in  the 
human  subject,  in  which  no  special  phenomena  had  been  observed  dur- 
ing life. 

Aside  from  certain  uses  connected  with  changes  in  its  volume,  it  is 
certain  that  the  spleen  has  an  important  relation  to  the  development  of 
blood-corpuscles,  both  white  and  red.  In  certain  cases  of  leucocythe- 
mia,  the  spleen  is  in  a  condition  of  hyperplastic  enlargement.  The 
blood  coming  from  the  spleen  is  peculiarly  rich  in  leucocytes,  but  the 
proportion  of  its  red  corpuscles  is  diminished.  It  may  be  that  the  spleen 
destroys  a  certain  number  of  red  corpuscles,  the  coloring  matter  being 
changed  into  other  pigmentary  matters,  and  that  it  also  produces  new 
red  corpuscles.  After  removal  of  the  spleen,  the  red  blood-corpuscles 
are  diminished  in  number  and  the  proportion  of  leucocytes  is  increased. 
This  condition  continues  for  about  six  months ;  but  after  that  time,  in 
dogs,  the  marrow  of  the  long  bones,  which  normally  is  yellow,  becomes 
red,  assuming  the  character  of  the  marrow  concerned  in  the  formation 
of  blood-corpuscles.  Temporary  diminution  of  red  corpuscles  and 
increase  of  leucocytes  have  been  observed  in  the  blood  in  cases  of 
extirpation  of  the  spleen  in  the  human  subject.  Whatever  uses  the 
spleen  has  in  connection  with  the  development  of  red  and  of  white 
blood-corpuscles  it  shares  with  the  red  marrow  of  the  bones  and  the 
so-called  lymphatic  glands. 

A  theory  has  been  proposed  that  the  cells  of  the  Malpighian  bodies 
of  the  spleen  act  as  phagocytes  and  destroy  certain  pathogenic  bac- 
teria (Metschnikoff).  This  notion  was  based  on  experiments  on  mon- 
keys with  the  spirillum  of  relapsing  fever ;  but  the  original  observations 
were  not  fully  confirmed  by  other  investigators.  As  the  result  of  care- 
ful experiments  on  rabbits,  Melkinow-Raswedenkow  drew  the  conclu- 
sion that  while  removal  of  the  spleen  diminishes  the  power  of  resistance 
to  certain  infections,  the  structures  in  this  organ  do  not  act  as  phagocytes 
and  destroy  micro-organisms.  This  question,  however,  belongs  to  pathol- 
ogy rather  than  to  physiology. 

The  production,  in  the  spleen,  of  a  kinase,  which  converts  trypsin- 
ogen  into  trypsin,  has  already  been  mentioned  in  connection  with  the 
pancreatic  secretion. 

Thyroid  Gland 

The  thyroid  gland  is  attached  to  the  lower  part  of  the  larynx  and 
follows  it  in  its  movements.  Its  color  is  brownish  red.  The  anterior 
face  is  convex  and  is  covered  by  certain  of  the  muscles  of  the  neck. 


THYROID    GLAND  385 

The  posterior  surface  is  concave  and  is  applied  to  the  larynx  and  trachea. 
It  presents  two  lateral  lobes,  each  with  a  rounded  thickened  base  below 
and  a  long  pointed  extremity  extending  upward,  the  lobes  being  con- 
nected by  an  isthmus  (see  Fig.  79,  page  388).  Each  of  these  lobes  is 
about  two  inches  (50  millimeters;  in  length,  three-quarters  of  an  inch 
(19  millimeters)  in  breadth,  and  about  the  sam'e  in  thickness  at  its  thick- 
est portion.  The  isthmus  connects  the  lower  portion  of  the  lateral  lobes, 
covers  the  second  and  third  tracheal  rings  and  is  about  half  an  inch 
(12  millimeters;  wide  and  one-third  of  an  inch  (8.5  millimeters;  thick. 
From  the  left  side  of  the  isthmus,  and  sometimes  from  the  left  lobe,  is 
a  portion  projecting  upward,  called  the  pyramid.  The  weight  of  the 
thyroid  gland  is  350  to  380  grains  (22  to  24  grams;.  Its  weight  in  pro- 
portion to  the  weight  of  the  adjacent  organs  does  not  vary  with  age. 
It  is  a  little  larger  and  more  prominent  in  the  female  than  in  the  male. 

Structure  of  the  Thyroid  Gland.  —  The  thyroid  gland  is  covered  with 
a  thin  but  resisting  coat  of  ordinary  fibrous  tissue  which  is  loosely  con- 
nected with  the  surrounding  parts.  From  the  internal  surface  of  this 
membrane  are  fibrous  bands,  or  trabeculae,  giving  off,  as  they  pass 
through  the  gland,  secondary  trabeculas  and  then  subdividing  until 
they  become  of  microscopic  size.  By  this  arrangement  the  gland  is 
divided  up  into  small  communicating  cavities.  The  trabeculae  contain 
many  small  elastic  fibres.  Throughout  the  substance  of  the  gland, 
lodged  in  the  meshes  of  the  trabeculae,  are  rounded  or  ovoid  closed 
vesicles,  measuring  g^nj  to  ^\-^  of  an  inch  (^40  to  100  ^i).  These  are 
formed  of  a  structureless  membrane  and  are  lined  with  a  single  layer 
of  pale  granular  nucleated  cells,  giyVo  to  2T1V1T  of  an  inch  f8  to  12  ix) 
in  diameter.  The  layer  of  cells  sometimes  lines  the  vesicle  completelv, 
sometimes  it  is  incomplete  and  sometimes  it  is  wanting.  The  contents 
of  the  vesicles  are  a  clear,  yellowish,  slightly  viscid,  colloid  sub- 
stance, with  a  few  granules,  pale  cells,  and  nuclei.  The  vesicles  are 
arranged  in  the  form  of  lobules,  and  between  them  are  the  great  veins 
(see  Plate  IX,  Fig.  4;. 

Four  small  bodies,  two  on  either  side,  He  posteriorly  to  the  thvroid. 
These  are  called  parathyroids.  Sometimes  two  are  enclosed  in  the  thy- 
roid itself.  They  are  composed  mainly  of  cells  resembling  epithelium 
but  present  no  acinous  vesicles.  Accessory  thyroids  in  the  neck  and 
sometimes  extending  into  the  thorax  have  also  been  described.  These 
structures,  however,  have  little  more  than  an  anatomical  interest,  except 
that  extirpation  of  the  parathyroids  may  be  followed  bv  nearlv  all  the 
phenomena  resulting  from  removal  of  the  thyroid,  and  when  death  does 
not  follow  thyroidectomy,  this  result  is  supposed  to  be  due  to  the  existence 
of  accessory  thyroids. 


386  USES    OF   THE    LIVER  — DUCTLESS    GLANDS 

Vessels  and  Nerves.  —  The  bloodvessels  of  the  thyroid  gland  are 
very  abundant,  this  organ  being  supplied  by  the  superior  and  inferior 
thyroid  arteries  with  sometimes  a  branch  from  the  innominata.  The 
arteries  break  up  into  a  close  capillary  plexus,  surrounding  the  vesicles 
with  a  rich  network,  but  never  penetrating  their  interior.  The  veins 
are  large,  and  like  the  hepatic  veins,  they  are  so  closely  adherent  to  the 
surrounding  tissue  that  they  do  not  collapse  when  cut  across.  The 
veins  emerging  from  the  gland  form  a  plexus  over  its  surface  and  the 
surface  of  the  trachea,  and  they  then  go  to  form  the  superior,  middle 
and  inferior  thyroid  veins.  The  nerves  are  derived  from  the  pneumo- 
gastrics  and  from  the  cervical  sympathetic  ganglia.  The  lymphatics 
are  abundant  but  difficult  to  inject.  The  exact  distribution  of  the  nerves 
and  the  origin  of  the  lymphatics  are  not  well  understood. 

Nearly  all  that  is  known  in  regard  to  the  chemical  constitution  of 
the  thyroid  may  be  embodied  in  the  statement  that  it  contains  leucin, 
xanthin,  lactic  acid,  succinic  acid  and  some  volatile  fatty  acids.  Recently, 
however,  a  substance  called  iodothyrin  has  been  extracted,  which  contains 
nearly  ten  per  cent  of  iodin  in  combination  with  proteids.  It  is  prob- 
able that  this  is  the  active  principle  of  thyroid  extract,  now  often  used 
in  therapeutics.  The  blood  of  the  thyroid  veins  has  been  analyzed,  but 
the  changes  in  its  composition  in  passing  through  the  gland  are  slight 
and  indefinite.  "It  has  been  said  that  one  of  the  uses  of  the  thyroid  is 
to  regulate  the  blood-circulation  in  the  brain,  but  the  observations  in 
support  of  this  view  are  not  satisfactory. 

Myxccdcvm.  —  Important  clinical  facts  have  been  developed  showing 
a  connection  between  the  thyroid  gland  and  a  disease  characterized  by 
infiltration  of  the  connective  tissues  with  a  gelatinous  substance  con- 
taining mucin.  This  disease  has  been  described  by  Ord  under  the 
name  of  myxoedema.  It  is  attended  with  marked  impairment  of  the 
mental  faculties  and  a  condition  like  cretinism.  This  usually  is  asso- 
ciated with  disease  of  the  thyroid  gland. 

Complete  excision  of  the  thyroid  gland  in  the  human  subject  has 
been  followed  by  the  peculiar  mental  condition  characteristic  of  cretin- 
ism. In  the  lower  animals  the  operation  of  complete  extirpation  is  fatal. 
The  experiments  of  Horsley  on  dogs  and  monkeys  show  great  differences 
in  the  results,  depending  on  age.  In  young  animals  death  usually  occurs 
in  a  few  days,  while  old  animals  survive  the  operation  four,  five  or  six 
months.  So  far  as  could  be  ascertained  from  these  experiments  on  the 
lower  animals  —  dogs  and  monkeys  —  the  conditions,  including  the 
mental  phenomena,  resembled  those  observed  in  cases  of  myxoedema 
in  the  human  .subject.  The  animals  operated  on  were  found  to  be 
exceedingly  sensitive  to  cold ;  but  when  put  in  a  hot-air  bath  at  a  tern- 


THYMUS    GLAND        "  387 

perature  of  105°  Fahr.  (40.5°  C.)  after  the  general  symptoms  made  their 
appearance,  they  could  be  kept  alive  for  several  months.  Recent 
experiments  on  animals  (Lanz)  and  observations  on  the  human  subject 
(Halsted)  seem  to  show  that  the  thyroid  has  some  relation  to  the 
generative  function,  its  absence  or  disease  greatly  impairing  fecundity 
and  sexual  activity. 

It  is  difficult  to  draw  from  these  various  observations  absolutely 
definite  conclusions  in  regard  to  the  physiological  relations  of  the 
thyroid.  This  organ  seems  essential  to  life  and  its  removal  profoundly 
affects  the  general  processes  of  nutrition.  It  influences  the  quantitv  of 
mucin  in  the  body,  but  precisely  in  what  way  it  is  difficult  to  determine. 

Thymus  Gland 

In  its  anatomy  the  thymus  resembles  the  ductless  glands,  but  its  office, 
whatever  this  may  be,  is  confined  to  early  life.  In  the  adult  the  organ 
is  wanting,  traces,  only,  of  fibrous  tissue,  with  a  little  fat,  existing  after 
puberty,  in  the  situation  previously  occupied  by  the  gland.  As  there 
never  has  been  a  plausible  theory,  even,  of  the  uses  of  this  organ,  the 
existence  of  which  is  confined  to  the  first  two  or  three  years  of  life,  it 
seems  necessary  to  give  only  a  brief  sketch  of  its  structure. 

The  thymus  appears  at  about  the  third  month  of  foetal  life  and  grad- 
ually increases  in  size  until  near  the  end  of  the  second  year.  It  then 
undergoes  atroph}'  and  disappears  almost  entirely  at  the  age  of  puberty. 
It  is  situated  partly  in  the  thorax  and  partly  in  the  neck.  The  thoracic 
portion  is  in  the  anterior  mediastinum,  resting  on  the  pericardium  and 
extending  as  low  as  the  fourth  costal  cartilage.  The  cervical  portion 
extends  upward  as  far  as  the  lower  border  of  the  thyroid.  The  whole 
gland  is  about  two  inches  (50.8  millimeters)  in  length,  an  inch  and  a 
half  (38  millimeters)  broad  at  its  lower  portion,  and  about  one-quarter 
of  an  inch  (6.4  millimeters)  thick.  Its  color  is  grayish  with  a  slightly 
rosy  tint.  It  usually  is  in  the  form  of  two  lateral  lobes  lying  in  apposi- 
tion in  the  median  line,  although  sometimes  there  exists  but  a  single 
lobe.  It  is  composed  of  a  number  of  lobules  held  together  by  connec- 
tive tissue. 

The  proper  coat  of  the  thymus  is  a  delicate  fibrous  membrane  sending 
processes  into  the  interior  of  the  organ.  Its  fibrous  structure,  however, 
is  loose,  so  that  the  lobules  can  be  separated  with  little  difficulty.  Por- 
tions of  the  gland  may  be,  as  it  were,  unravelled,  by  loosening  the 
interstitial  fibrous  tissue  ;  and  in  this  way  it  is  found  to  be  composed 
of  little  lobular  masses  attached  to  a  continuous  cord.  This  arrange- 
ment is  more  distinct  in  the  inferior  animals  of  lar^e  size  than  in  man. 


388 


USES    OF   THE    LIVER  — DUCTLESS    GLANDS 


The  lobules  are  composed  of  rounded  vesicles,  ten  to  fifteen  in  number 
and  ylg  to  ^Q  of  an  inch  (200  to  600  /x)  in  diameter.  The  walls  of  these 
vesicles  are  thin,  finely  granular  and  fragile.  The  vesicles  contain  a 
small  quantity  of  an  albuminous  liquid,  with  cells  and  free  nuclei.  The 
cells  are  small  and  transparent,  and  the  nuclei  are  spherical,  relatively 
large,  containing  one  to  three  nucleoli.      The  free  nuclei  are  rounded 

A  B  C 


Fig.  79. —  Thyroid  and  thy fitus  glands  (Sappey). 

A.  I,  right  lobe  of  the  thymus ;  2,  left  lobe  ;  3,  groove  between  the  two  lobes ;  4,  lungs,  the  anterior 
borders  raised  to  show  the  thymus  ;  5,  terminal  branch  of  the  internal  mammary  vein  ;  6,  thyroid  gland  ; 
7,  median  inferior  thyroid  veins;  8,  lateral  inferior  thyroid  veins;  9,  common  carotid  artery;  10,  in- 
ternal jugular  vein;  11,  pneumogastric  nerve.  B,  right  lobe  of  the  thymus  with  the  investing  mem- 
brane removed:  i,  upper  extremity  of  the  lobe;  2,  lower  extremity;  3,  external  border;  4,  internal 
border.  C,  arrangement  of  the  lobules  of  the  same  lobe,  around  the  central  cord :  i,  upper  extremity 
of  the  lobe;  2,  lower  extremity;  3,  3,  3,  lobules;  4,  4,  central  cord. 

and  contain  several  distinct  nucleoli.  Histologists  describe  a  cortex 
and  a  medullary  portion.  In  the  latter  are  small  masses  of  imbricated 
epithelium,  known  as  the  concentric  corpuscles  of  Hassall  (see  Plate 
IX,  Fig.  5). 

The  bloodvessels  of  the  thymus  are  abundant,  but  their  calibre  is 
small  and  the  gland  is  not  very  vascular.     They  are  derived    chiefly 


PITUITARY   BODY   AND    PINEAL    GLAND  389 

from  the  internal  mammary  artery,  a  few  coming  from  the  inferior 
thyroid,  with  occasional  branches  from  the  superior  diaphragmatic  or 
the  pericardial.  They  pass  between  the  lobules,  surround  and  penetrate 
the  vesicles  and  form  a  capillary  plexus  in  their  interior.  The  vesicles 
in  this  respect  bear  a  certain  resemblance  to  the  closed  follicles  of  the 
intestine.  The  veins  are  abundant,  but  they  do  not  follow  the  course  of 
the  arteries.  The  principal  vein  emerges  at  about  the  centre  of  the 
gland  posteriorly  and  empties  into  the  left  brachio-cephalic.  Other  small 
veins  empty  into  the  internal  mammary,  the  superior  diaphragmatic 
and  the  pericardial.  A  few  nervous  filaments  from  the  sympathetic 
surround  the  principal  thymic  artery  and  penetrate  the  gland.  Their 
ultimate  distribution  is  uncertain.     The  lymphatics  are  very  abundant. 

As  regards  chemical  constitution,  it  may  be  stated  in  general  terms 
that  the  thymus  contains  matters  of  about  the  same  character  as  those 
found  in  the  other  ductless  glands. 

Inasmuch  as  the  thymus  is  peculiar  to  early  life,  the  most  important 
points  in  its  anatomical  history  relate  to  its  mode  of  development.  This, 
however,  does  not  present  any  great  physiological  interest  and  is  fully 
treated  of  in  works  on  anatomy. 

Little  that  is  definite  can  be  said  in  regard  to  the  physiology  of 
the  thymus.  In  some  recent  experiments  on  Guinea  pigs  (Paton 
and  Goodall,  1904)  it  was  found  that  removal  of  the  thymus  soon 
after  birth  was  not  followed  by  any  marked  effects  on  the  growth  of  the 
animals ;  but  it  seemed  to  diminish  the  resistance  to  the  toxins  of 
staphylococci  and  streptococci.  The  operation  had  no  effect  on  the 
resistance  to  diphtheria.  Later  observations  by  Henderson  showed  that 
"castration  in  cattle  causes  a  persistent  growth  and  a  retarded  atrophy 
of  the  thymus  gland";  and  a  similar  effect  was  noted  in  Guinea  pigs 
and  rabbits.  "  In  bulls  and  unspayed  heifers  the  normal  atrophy  of 
the  thymus  which  begins  after  the  period  of  puberty  is  greatly  accel- 
erated when  the  bulls  have  been  used  for  breeding  and  when  the 
heifers  have  been  pregnant  for  several  months."  The  exact  signifi- 
cance of  these  experimental  results  is  not  apparent. 

Pituitary  Body  and  Pineal  Gland 

These  little  bodies,  situated  at  the  base  of  the  brain,  are  quite  vas- 
cular, contain  closed  vesicles  and  but  few  nervous  elements  and  are 
sometimes  classed  with  the  ductless  glands.  Physiologists  have  no 
definite  idea  of  their  uses. 

The  pituitary  body,  sometimes  called  the  hypophysis,  is  of  an  ovoid 
form,  a  reddish  gray  color,  weighs  five  to  ten  grains  (0.324  to  0.648 


390  USES    OF   THE   LIVER  — DUCTLESS    GLANDS 

gram),  and  is  situated  on  the  sella  Turcica  of  the  sphenoid  bone.  It  is 
said  to  be  larger  in  the  foetus  than  in  the  adult,  and  in  foetal  life  it  has  a 
cavity  communicating  with  the  third  ventricle.  This  little  body  has 
been  studied  by  Grandry,  in  connection  with  the  suprarenal  capsules. 
He  regarded  it  as  composed  essentially  of  closed  vesicles,  with  fibres  of 
connective  tissue  and  bloodvessels.  The  vesicles  are  formed  of  a  trans- 
parent membrane,  containing  irregularly-polygonal  nucleated  cells  and 
free  nuclei.  The  nuclei  are  distinct,  with  a  well-marked  nucleolus. 
Capillary  vessels  surround  these  vesicles  without  penetrating  them. 
Grandry  did  not  observe  either  nerve-cells  or  fibres  between  the  vesicles. 

The  pineal  gland  is  situated  just  behind  the  posterior  commissure  of 
the  brain,  between  the  nates,  and  is  enclosed  in  the  velum  interpositum. 
It  is  of  a  conical  shape,  one-third  of  an  inch  (8.5  millimeters)  in  length 
and  of  nearly  the  color  of  the  pituitary  body.  It  is  connected  with 
the  base  of  the  brain  by  several  delicate  commissural  peduncles.  It 
presents  a  small  cavity  at  its  base,  and  frequently  it  contains  in  its  sub- 
stance little  calcareous  masses  composed  of  calcium  phosphate,  cal- 
cium carbonate,  ammonio-magnesian  phosphate  and  a  small  quantity 
of  organic  matter.  It  is  covered  with  a  fibrous  envelope  which  sends 
processes  into  its  interior.  As  the  result  of  the  researches  of  Grandry, 
it  has  been  found  to  present  a  cortical  substance,  analogous  in  structure 
to  the  pituitary  body,  and  a  central  portion,  composed  of  the  ordinary 
nervous  elements  found  in  the  gray  matter  of  the  brain.  Its  structure 
is  very  like  that  of  the  medullary  portion  of  the  suprarenal  capsules. 

Acromegaly  and  Giantism.  —  Disease  of  the  pituitary  body,  espe- 
cially in  adult  life,  is  attended  with  great  enlargement  of  the  bones  of 
the  extremities  and  the  features  of  the  face,  or  what  is  known  as 
acromegaly.  When  the  disease  occurs  in  early  life,  as  development 
progresses  there  is  a  condition  known  as  giantism,  the  individual  some- 
times reaching  an  enormous  stature.  That  there  is  some  relation 
between  the  pituitary  body  and  acromegaly  and  giantism,  there  can 
be  no  doubt ;  but  the  nature  of  this  relation  is  obscure.  In  some  cases 
of  acromegaly,  improvement  has  been  noted  following  the  exhibition  of 
extract  of  the  normal  pituitary  body. 

Internal  Secretion  by  the  Testes  and  Ovaries.  —  As  early  as  1889, 
Brown-Sequard  described  an  internal  secretion  by  the  testes,  and  others 
have  included  in  their  investigations  the  ovaries.  While  it  is  by  no 
means  certain  or  even  reasonably  probable,  notwithstanding  the  redun- 
dant literature  on  the  subject,  that  testicular  extracts  increase  mental  and 
physical  vigor  in  the  male  or  that  ovarian  extracts  have  similar  effects 
on  the  female,  these  early  experiments  have  the  merit  of  having  practi- 
cally inaugurated  important  observations  on  the  internal  secretions  of 


INTERNAL   SECRETION    BY   THE    TESTES    AND    OVARIES       391 

Other  organs,  although  they  led  at  first  to  certain  therapeutic  extrava- 
gancies. It  is  not  to  be  understood,  however,  from  this  comment,  that 
future  researches  may  not  show  important  functions  belonging  to  the 
sexual  organs,  in  addition  to  their  well-known  action  in  reproduction. 

As  regards  the  ovaries,  it  has  been  conjectured  that  they  have  an 
internal  secretion  which  may  have  a  general  influence  on  the  organism  ; 
but  although  ovariectomy  has  lately  become  frequent,  sufficient  time  has 
not  elapsed  to  warrant  definite  conclusions  concerning  the  remote  effects 
of  this  operation.  The  testicles  present  a  vascular  areolar  tissue  which 
passes  from  the  fibrous  structure  between  the  seminiferous  tubes.  In 
this  tissue  are  cytoplasmic  cells  with  some  fatty  and  pigmentary  gran- 
ules ;  and  this  structure  is  now  called  the  interstitial  gland  of  the  testis. 
Some  late  researches  seem  to  show  that  these  cells  have  a  function 
resembling  internal  secretion  ;  but  their  action  is  obscure,  and  it  has  not 
been  shown  that  they  furnish  an  extract  producing  any  well-defined 
results  when  administered  by  subcutaneous  injection  or  by  the  mouth. 

Internal  secretion  by  the  pancreas  and  kidneys  has  already  been 
considered  in  connection  with  the  other  and  more  famihar  functions  of 
these  organs. 


CHAPTER   XV 

METABOLISM  — NUTRITION  — ANIMAL   HEAT   AND   FORCE 

Action  of  glandular  cells  —  Metabolism,  anabolism  and  katabolism  —  General  nutrition  — 
Luxus-consumption  —  Isodynamic  values  of  foods  —  Animal  heat  and  force — -Limits  of 
variations  in  the  normal  temperature  in  man  —  Variations  in  different  parts  of  the  body 

—  Variations  at  different  periods  of  life  —  Variations  at  different  times  of  the  day — Influ- 
ence of  exercise  etc.,  on  the  heat  of  the  body  —  Influence  of  the  nervous  system  on  the 
production  of  animal  heat  (heat-centres)  —  Mechanism  of  the   production  of  animal  heat 

—  Equalization  of  the  animal  temperature  —  Relations  of  heat  to  force. 

Metabolism,  Anabolism  and  Katabolism 

The  constant  change  going  on  in  the  constituents  of  the  body  is 
called  metabolism.  A  part  of  this  process  consists  in  a  repair  of  the 
tissues  and  is  known  as  anabolism.  This  repair  is  made  necessary  by 
a  constant  change  of  the  constituents  of  the  organism  into  effete 
matters.     This   change  is  called  katabolism. 

In  the  changes  that  are  involved  in  metabolism,  inorganic  as  well  as 
organic  matters  participate.  Organic  matters,  indeed,  are  never  free 
from  inorganic  substances ;  and  the  latter  accompany  organic  matters 
in  the  changes  incident  to  nutrition.  The  organic  constituents  of  the 
body  are  almost  all  included  in  the  proteids. 

The  inorganic  matters  number  about  twenty-one.  The  most  impor- 
tant of  these  is  water.  This  is  found  in  all  tissues  without  exception. 
It  is  discharged  from  the  body  as  water  and  is  useful  in  carrying  off 
effete  matters  in  solution.  It  is  introduced  in  all  forms  of  food  and 
drink.  In  addition,  it  is  formed  in  the  body  by  the  union  of  hydrogen 
with  oxygen,  this  process  contributing  to  the  production  of  animal  heat 
and  force.  The  water  thus  formed  and  discharged  from  the  body  may 
properly  be  regarded  as  an  excretion. 

Many  saline  compounds  exist  in  the  body  in  solution  in  water. 
These  are  essential  to  nutrition.  They  are  introduced  from  without, 
exist  in  the  body  united  with  organic  matters  and  are  discharged  in 
the  form  in  which  they  entered. 

Proteids,  as  proteids,  are  not  discharged  from  the  body  in  health. 
They  are  converted  into  excrementitious  matters  and  as  such  form  part 

392 


METABOLISM,    ANABOLISM    AND    KATABOLISM  393 

of  the  excretions.  The  twenty-one  inorganic  matters  belong  to  a  class 
of  substances  that  pass  through  the  body  unchanged. 

The  carbohydrates  undergo  important  changes  in  the  body.  They 
are  oxidized  and  converted  into  carbon  dioxide  and  water,  contributing 
to  the  production  of  animal  heat  and  force.  Oxidation  of  the  carbo- 
hydrates is  one  of  the  sources  of  water  produced  in  the  economy. 

The  probable  mechanism  of  the  transformation  of  the  carbohydrates 
by  oxidation  into  carbon  dioxide  and  water  was  foreshadowed  by  Ford, 
an  American  physician,  in  1872.  This  observer  obtained  a  small  quan- 
tity of  alcohol  from  the  blood  of  the  ox,  which  he  assumed  was  derived 
from  the  carbohydrates.  The  results  of  these  experiments,  however, 
were  not  confirmed  by  certain  German  physiologists  and  were  dis- 
credited; but  recently  (1904),  Stolaska  has  extracted  from  the  blood 
of  the  ox,  the  heart  of  the  dog  and  the  pancreas  of  the  pig,  a  glycolytic 
enzyme  capable  of  producing  alcohol.  This  writer  regards  "  alcoholic 
fermentation  as  the  first  stage  of  the  respiratory  process." 

The  modern  trend  of  physiological  opinion  is  toward  the  idea  that 
alcohol,  in  doses  so  small  that  it  may  be  promptly  oxidized,  is  not  harm- 
ful, although,  when  alimentation  is  sufficient,  it  is  unnecessary.  Its  oxi- 
dation produces  energy,  like  the  oxidation  of  so-called  carbonaceous 
foods,  notably  the  carbohydrates.  In  this  connection  a  study  of  diabetes 
mellitus  is  most  instructive.  It  is  thought  by  some  pathologists  that 
this  disorder  is  due,  in  many  instances,  to  absence  of  an  enzyme,  nor- 
mally produced  in  the  pancreas,  that  acts  on  carbohydrates.  It  is 
thought,  also,  that  all  the  energy  due  to  oxidation  of  carbohydrates 
comes  from  the  final  oxidation  of  alcohol  which  results  from  the  action 
of  enzymes  in  the  blood  on  sugar,  and  that  carbohydrates  can  not  be 
utilized  as  producers  of  heat  and  force  in  any  other  way.  All  the  car- 
bohydrates oxidized  in  the  body  pass  into  the  general  circulation  by  the 
hepatic  veins.  As  early  as  1888,  I  wrote  —  "  It  is  reasonable  to  suppose 
that  the  small  quantity  of  sugar  constantly  discharged  into  the  blood  by 
the  liver  is  converted  into  alcohol,  which  is  promptly  oxidized,  being 
converted  into  carbon  dioxide  and  water." 

The  fats  undergo  oxidation  in  the  body  ;  and  this  oxidation  con- 
tributes to  the  production  of  animal  heat  and  force.  As  a  rule  the 
fats  exist  in  the  organism  in  combination  with  each  other  but  are  not 
combined  with  proteids. 

Oxygen  exists  in  the  red  blood-corpuscles  combined  with  hemoglobin. 
Carbon  dioxide  exists  in  solution  in  the  blood,  lymph,  chyle  and  secreted 
liquids.  Nitrogen,  carburetted  hydrogen  and  hydrogen  monosulphide 
exist  in  a  gaseous  state  in  the  alimentary  canal.  A  small  quantity  of 
nitrogen  exists  in  solution  in  the  blood. 


394  GENERAL   NUTRITION 

General  Nutrition' 

A  comparison  of  the  outgo  and  income  of  the  organism  and  estimates 
of  the  quantity  of  food  necessary  for  the  proper  nutrition  of  a  man  of  ordi- 
nary weight  and  under  ordinary  conditions  have  already  been  giyen  in 
the  chapter  treating  of  ahmentation.  It  may  be  stated  here  in  general 
terms  that  ten  to  twelye  ounces  (283.5  to  340.2  grams)  of  carbon,  and 
four  to  fiye  ounces  (113. 4  to  141.75  grams)  of  proteids  are  discharged 
from  the  organism  daily.  To  meet  these  expenditures  exactly  and 
maintain  the  body  in  a  condition  of  physiological  equilibrium  would 
require  the  introduction  of  four  to  fiye  ounces  ( 113. 4  to  141.75  grams) 
of  proteids,  one  and  one-half  ounces  (28.35  to  42.52  grams)  of  fat  and 
sixteen  to  nineteen  ounces  (453.6  to  483.6  grams)  of  carbohydrates. 
Practically,  howeyer,  provision  should  be  made  for  unusual  require- 
ments, and  the  diet  should  be  in  excess  of  what  would  exactly  meet  the 
outgo  of  material. 

Lnxus-Cons7i}iiption.  —  An  illustration  of  the  necessity  of  a  diet  more 
than  sufficient  exactly  to  meet  the  outgo  under  ordinary  conditions  is  to 
be  found  in  what  is  called  luxus-consumption.  By  this  term  it  is  in- 
tended to  indicate  change  in  a  certain  quantity  of  nutritive  matter, 
especially  proteids,  which  does  not  involve  repair  of  tissue.  Voit,  who 
first  described  this  process,  divided  the  proteids  of  the  blood  into  tissue- 
proteids  and  circulating  proteids,  the  latter  representing  the  excess  of 
proteids  over  and  above  actual  nutritive  requirements.  Voit's  theory, 
however,  failed  to  meet  with  general  acceptance,  and  the  expression 
luxus-consumption  is  regarded  as  misleading  and  unscientific ;  but  the 
fact  remains  that  food  taken  in  excess  of  actual  nutritive  requirements 
is  readily  disposed  of  when  it  does  not  remain  in  the  body  in  the  form 
of  fat. 

Isodynamic  Values  of  Foods.  —  The  theory  of  the  isodynamic  values 
of  foods  is  that  proteids,  fats  and  carbohydrates  are  theoretically  inter- 
changeable on  the  basis  of  equal  heat-values  in  oxidation.  This  has  been 
formulated  by  Rubner  into  a  law,  of  which  the  following  is  an  illustration  : 
It  has  been  found  that  one  gram  of  fat  is  equal  in  heat-value  to  about 
two  and  one-quarter  grams  of  proteid  or  carbohydrate.  As  regards  the 
production  of  heat  and  power,  therefore,  fats,  proteids  and  carbohy- 
drates are  interchangeable  in  the  proportion  of  one  part  of  fat  to  two 
and  one-quarter  parts  of  either  proteid  or  carbohydrate.  In  this  theory 
it  is  assumed  that  the  proteids  are  oxidized  into  urea  and  carbon  dioxide, 
and  that  their  heat-value  is  the  same  as  when  they  are  burned  out  of  the 
body.  It  is  probable,  also,  that  isodynamic  substitution  may  include 
alcohol  (Rosemann). 


ANIMAL    HEAT    AND    FORCE  395 

Animal  Heat  and  Force 

The  processes  of  nutrition  in  animals  are  attended  with  the  develop- 
ment and  maintenance  of  a  body-temperature  that  is  more  or  less  inde- 
pendent of  external  conditions.  This  is  true  in  the  lowest  as  well  as 
the  highest  animal  organisms  ;  and  analogous  phenomena  have  been 
observed  in  plants.  In  cold-blooded  animals  nutrition  may  be  sus- 
pended by  a  diminished  external  temperature,  and  certain  of  the  func- 
tions become  temporarily  arrested,  to  be  resumed  when  the  animal  is 
exposed  to  a  greater  heat.  This  is  true,  to  some  extent,  in  certain  warm- 
blooded animals  that  periodically  pass  into  a  condition  of  torpor,  called 
hibernation  ;  but  in  man  and  most  of  the  warm-blooded  animals,  the 
general  temperature  of  the  body  undergoes  but  slight  variations.  Cer- 
tain animals  pass  into  a  condition  analogous  to  hibernation  under  the 
influence  of  the  intense  heat  of  summer  in  tropical  countries.  This 
condition  is  called  estivation.  It  has  been  observed  in  the  tenrec  of 
Madagascar  —  a  kind  of  hedgehog  —  to  continue  for  three  months  dur- 
ing the  hot  season.  The  animal  heat  is  nearly  the  same  in  cold  and 
in  hot  climates  ;  and  if  from  any  cause  the  body  becomes  incapable  of 
keeping  up  its  temperature  when  exposed  to  cold,  or  of  moderating  it 
when  exposed  to  heat,  death  is  the  result. 

Estimated  Qnaiitity  of  Heat  produced  by  the  Body.  —  In  order  to 
express  quantities  of  heat,  it  is  necessary  to  fix  on  some  definite  quantity 
to  be  taken  as  a  heat-unit.  In  what  is  to  follow,  a  heat-unit  is  to  be 
understood  as  the  heat  required  to  raise  the  temperature  of  one  pound 
of  water  one  degree  from  32°  Fahr.  (pound-degree  Fahr. ). 

It  has  been  calculated  that  one  heat-unit  is  equal  to  the  force 
expended  in  raising  one  pound  772  feet  or  772  pounds  one  foot  (Joule). 
The  equivalent  of  heat  in  force  has  been  calculated  by  estimating  the 
heat  produced  by  a  certain  weight  falling  through  a  certain  distance, 
assuming  the  falling  force  to  be  precisely  equal  to  the  force  that  has 
been  used  in  raising  the  weight ;  but  physicists  have  not  actually  suc- 
ceeded in  so  completely  converting  heat  into  force  as  to  raise  one  pound 
Jji  feet  or  772  pounds  one  foot,  by  the  expenditure  of  one  heat-unit. 

The  heat-unit  and  its  equivalent  in  force  are,  of  course,  differently 
expressed  according  to  the  metric  system.  When  heat-units  or  foot- 
pounds are  given  in  the  text,  the  equivalents,  according  to  the  metric 
system,  are  given  in  parentheses.     These  equivalents  are  as  follows  :  — 

A  heat-unit,  according  to  the  metric  system,  or  the  heat  required  to 
raise  the  temperature  of  one  kilo  of  water  one  degree  from  zero  C,  will 
be  designated  as  a  kilo-degree  C.  A  kilo-degree  is  called  a  large  calorie. 
A   gram-degree  —  the  heat  required   to  raise   the  temperature  of  one 


396  GENERAL   NUTRITION 

gram  of  water  one  degree  C. — is  called  a  small  calorie.  One  kilo- 
degree  =  looo  gram-degrees. 

One  pound  degree  =  0.252  kilo-degree  C.  One  kilo-degree  C.  = 
3.96  (nearly  4)  pound-degrees.  A  kilogrammeter  represents  the  force 
required  to  raise  a  weight  of  one  kilogram  one  meter.  One  foot-pound 
=  0.138  kilogrammeter.  One  kilogrammeter  =  7.24  foot-pounds.  One 
pound-degree  =  772  foot-pounds.  One  pound-degree  =  106.6  kilogram- 
meters.  One  kilo-degree  C.  =  422.25  kilogrammeters.  One  kilo-degree 
C.  =  3057  foot-pounds. 

Two  methods  have  been  employed  in  arriving  at  estimates  of  the 
actual  quantity  of  heat  produced  by  the  body  in  a  definite  time :  — 

1.  The  direct  method  consists  in  placing  an  animal  in  a  calorimeter 
and  measuring  the  heat  produced,  making  the  necessary  corrections. 
This  has  repeatedly  been  done,  but  the  results  obtained  have  been 
variable  and  not  entirely  satisfactory.  An  important  element  of  inac- 
curacy in  direct  observations  —  one,  indeed,  which  it  seems  impossible 
to  correct  absolutely  —  is  due  to  the  great  variations  in  heat-produc- 
tion with  digestion,  conditions  of  muscular  repose  or  exercise,  external 
temperature  etc.  Another  source  of  error  is  the  difficulty  in  estimating 
the  heat  lost  by  the  body  and  not  actually  produced  during  the  time  of 
the  observation. 

2.  The  indirect  method  consists  in  estimating  the  heat  represented 
by  oxidation,  calculated  from  the  quantity  of  oxygen  consumed  in  the 
processes  that  result  in  the  production  and  discharge  of  carbon  dioxide, 
water,  urea  etc.  These  estimates  have  been  compared  with  the  calcu- 
lated heat-value  of  the  food  consumed,  and  the  results  very  nearly  cor- 
respond. 

According  to  the  estimates  of  Helmholtz,  Ranke  and  others,  by  the 
indirect  method,  the  heat-production  is  equal  to  about  2.5  heat-units  per 
hour  per  pound-weight  of  the  body  (1.39  kilo-degree  C.  per  kilogram). 
In  a  man  weighing  180.4  pounds  (82  kilograms)  the  heat-production  in 
twenty-four  hours  (Helmholtz)  was  10,818  heat-units  (2732  kilo-degrees 
C).  According  to  this  estimate,  a  man  weighing  140  pounds  (63.5 
kilograms)  would  produce  8400  heat-units  (21 18  kilo-degrees  C.)  in 
twenty-four  hours.  This  would  be  equal  to  6,484,800  foot-pounds,  or 
about  894,500  kilogrammeters. 

A  study  of  this  subject  and  of  the  details  of  observations  both  direct 
and  indirect  has  made  it  evident  that  the  experimental  difficulties 
and  the  unavoidable  elements  of  inaccuracy  are  greater  in  the  direct 
than  in  the  indirect  method.  In  comparing  the  estimates  of  heat  actu- 
ally produced  with  the  heat- value  of  food  —  which,  of  course,  is  the 
ultimate  source  of  heat  and  force  in  the  body  —  the  correspondence  is 


ANIMAL    HEAT    AND    FORCE  397 

much  closer  if  the  indirect  estimates  are  adopted.  It  therefore  seems 
more  in  accordance  with  ascertained  facts  to  adopt  the  indirect  esti- 
mates, although  this  can  not  be  done  without  reserve.  The  heat  pro- 
duced, then,  is  probably  equal  to  about  2.5  heat-units  f  pound-degrees; 
per  hour  per  pound-weight  of  the  body  (nearly  1.4  kilo-degree  C.  per 
kilogram).  This  is  equal  to  about  8400  heat-units,  or  about  2120  kilo- 
degrees  C,  in  twenty-four  hours ;' which  is  equal  to  about  6,500,000 
foot-pounds,  or  about  900,000  kilogrammeters. 

The  normal  variations  in  the  production  of  heat  are  not  absolutely 
and  definitely  represented  by  variations  in  the  actual  temperature  of 
the  body  and  by  the  consumption  of  oxygen.  ^Muscular  work  may 
increase  the  production  of  heat  sixty  per  cent  (Hirn)  while  it  increases 
the  consumption  of  oxygen  about  4;^-  times,  a  large  part  of  the  oxidation 
being  expended  in  the  form  of  work.  The  production  of  heat  is  dimin- 
ished in  fasting  animals  (dogs)  by  nearly  forty-five  per  cent  (Senator;, 
after  deprivation  of  food  for  two  days.  In  old  age  and  in  infancy 
there  is  less  heat  produced  than  in  adult  life.  The  production  of  heat 
is  less  in  females  than  in  males  and  is  less  during  the  night  than  during 
the  day.  These  points  will  be  touched  upon  again,  in  connection  with 
the  normal  variations  in  the  temperature  of  the  body. 

Limits  of  Variation  in  the  Xornial  Temperature  in  Ma^i. — One  of 
the  most  common  methods  of  taking  the  general  temperature  has  been 
to  introduce  a  registering  thermometer  into  the  axilla,  reading  off  the 
degrees  after  the  mercury  has  become  stationary.  Nearly  all  obserA-a- 
tions  made  in  this  way  agree  with  the  results  obtained  by  Gavarret, 
who  estimated  that  the  temperature  in  the  axilla,  in  a  perfectly  healthy 
adult  man,  in  a  temperate  climate,  ranges  between  97.7^  and  99.5'  Fahr. 
(36.5°  and  37.5°  C. ).  Dav}',  from  a  large  number  of  observations  on 
the  temperature  under  the  tongue,  fixed  the  standard,  in  a  temperate 
climate,  at  98^  Fahr.  (36.67^  C).  The  axilla  and  the  tongue,  however, 
being  more  or  less  exposed  to  external  influences,  do  not  exactly  repre- 
sent the  general  heat  of  the  organism ;  but  these  are  the  situations, 
particularly  the  axilla,  in  which  the  temperature  is  most  frequently 
taken.  As  a  standard  for  comparison,  it  may  be  assumed  that  the  most 
common  temperature  in  these  situations  is  98^  Fahr.  (36.67°  C;  subject 
to  variations,  within  the  limits  of  health,  of  about  0.5°  Fahr.  (0.27"  C; 
below  and  1.5°  Fahr.  (0.82''  C.)  above.  • 

J^ariations  with  External  Tcmperatiire.  —  The  general  temperature 
of  the  body  varies,  though  within  restricted  limits,  with  extreme  changes 
in  climate.  The  results  obtained  by  Daw,  in  a  large  number  of  obser- 
vations in  temperate  and  hot  climates,  show  an  elevation  in  the  tropics 
of  0.5°  to  3°  Fahr.  (0.27°  to  1.65^  C.;.     It  is  well  known,  also,  that  the 


398  GENERAL    NUTRITION 

human  body,  the  surface  being  properly  protected,  is  capable  of  endur- 
ing for  some  minutes  a  heat  greater  than  that  of  boihng  water.  Under 
these  conditions  the  body-temperature  is  raised  but  slightly  as  com- 
pared with  the  intense  heat  of  the  surrounding  atmosphere.  In  the 
observations  of  Dobson,  the  temperature  was  raised  to  99.5°  Fahr. 
(37.5°  C.)  in  one  instance,  101.5°  Fahr.  (38.6°  C.)  in  another,  and  102° 
Fahr.  (38.9°  C.)  in  a  third,  when  the  body  was  exposed  to  a  heat  of 
more  than  212°  Fahr.  (100°  C).  Delaroche  and  Berger,  however,  found 
that  the  temperature  in  the  mouth  could  be  increased  by  3°  to  9°  Fahr. 
(1.65°  to  5.05°  C.)  after  sixteen  minutes  of  exposure  to  intense  heat. 
This  was  for  the  external  parts  only  ;  and  it  is  not  probable  that  the 
temperature  of  the  internal  organs  ever  presents  such  wide  variations. 

It  is  difficult  to  estimate  the  temperature  in  persons  exposed  to 
intense  cold,  as  in  Arctic  explorations,  because  care  is  always  taken  to 
protect  the  surface  of  the  body  as  completely  as  possible ;  but  experi- 
ments have  shown  that  the  body-heat  may  be  considerably  reduced,  as 
a  temporary  condition,  without  producing  death.  In  the  latter  part  of 
the  last  century,  Currie  caused  the  temperature  in  a  man  to  fall  15° 
Fahr.  (8.25°  C.)  by  immersion  in  a  cold  bath  ;  but  he  could  not  bring  it 
below  83°  Fahr.  (28.33°  C).  This  extreme  depression,  however,  lasted 
only  two  or  three  minutes,  and  the  temperature  afterward  returned 
to  within  a  few  degrees  of  the  normal  standard.  The  results  of  experi- 
ments show  that  while  the  normal  variations  in  the  temperature  in  the 
human  subject,  even  when  exposed  to  great  climatic  changes,  are 
slight,  usually  not  more  than  2°  Fahr.  (1.1°  C),  the  body  may  be 
exposed  for  a  time  to  excessive  heat  or  cold,  and  the  extreme  limits 
consistent  with  the  preservation  of  life  may  be  reached.  So  far  as  has 
been  ascertained  by  direct  experiment,  these  limits  are  about  83°  and  107° 
Fahr.  (28.33°  and  41.67°  C). 

Variations  in  Differoit  Parts  of  tJic  Body.  —  The  blood  becomes 
slightly  lowered  in  temperature  in  passing  through  the  general  capillary 
circulation,  but  the  difference  is  ordinarily  not  more  than  a  fraction 
of  a  degree.  This  fact  is  not  opposed  to  the  proposition  that  heat  is 
produced  in  greatest  part  in  the  general  capillary  system  as  one  of  the 
results  of  nutritive  action ;  for  the  blood  circulates  with  such  rapidity 
that  the  heat  acquired  in  the  capillaries  of  the  internal  organs,  where 
little  or  none  is  lost,  is  but  slightly  diminished  before  it  passes  into  the 
arteries,  even  in  circulating  through  the  lungs ;  and  cutaneous  evapora- 
tion simply  moderates  the  heat  acquired  in  the  tissues  and  keeps  it  at 
the  proper  standard. 

The  blood  usually  is  0.36°  to  1.8°  Fahr.  (  0.2°  to  1°  C.)  warmer  in  the 
hepatic  veins  than  in  the  aorta.     The  temperature  in  the  hepatic  veins 


ANIMAL    HEAT    AND    FORCE  399 

is  0.18°  to  1.44°  Fahr.  (0.1°  to  0.8°  C.)  higher  than  in  the  portal  veins. 
This  shows  that  the  blood  coming  from  the  liver  is  warmer  than  in  any- 
other  part  of  the  body.  As  regards  the  temperature  of  the  blood  in  the 
two  sides  of  the  heart,  experiments  on  the  lower  animals  have  been 
somewhat  contradictory  ;  but  there  is  no  positive  evidence  of  any  con- 
siderable change  in  the  temperature  of  the  blood  in  passing  through  the 
lungs  in  the  human  subject.  In  the  lower  animals  there  probably 
exist  no  constant  differences  in  temperature  in  the  two  sides  of  the 
heart.  When  the  loss  of  heat  by  the  general  surface  is  active,  as  in 
animals  with  a  slight  covering  of  hair,  the  blood  usually  is  cooler  in  the 
right  cavities  ;  but  in  animals  with  a  thick  covering,  that  probably  lose 
considerable  heat  by  the  pulmonary  surface,  the  blood  is  cooler  in  the 
left  side  of  the  heart. 

Variations  at  Different  Periods  of  Life.  —  The  most  important  vari- 
ations in  the  temperature  of  the  body  at  different  periods  of  life  are 
observed  in  infants  just  after  birth.  The  body  of  the  infant  and  of 
young  mammalia  removed  from  the  mother  presents  a  diminution  in 
temperature  of  1°  to  4°  Fahr.  (0.55°  to  2.2°  C).  In  infancy  the  ability 
to  resist  cold  is  less  than  in  later  years ;  but  after  a  few  days  the  tem- 
perature of  the  child  nearly  reaches  the  standard  in  the  adult,  and  the 
variations  produced  by  external  conditions  are  not  so  great. 

In  certain  animals,  particularly  dogs  and  cats,  that  are  born  with  the 
eyes  closed  and  in  which  the  foramen  ovale  remains  open  for  a  few 
days,  the  temperature  rapidly  diminishes  when  they  are  removed  from 
the  body  of  the  mother,  and  they  then  become  reduced  to  a  condition 
approximating  that  of  cold-blooded  animals ;  but  after  about  fifteen  days 
this  change  in  temperature  can  not  be  effected.  In  dogs  just  born,  the 
temperature  fell,  after  three  or  four  hours'  separation  from  the  mother, 
to  a  point  but  a  few  degrees  above  that  of  the  surrounding  atmosphere 
(W.  F.  Edwards). 

In  adult  hfe  there  does  not  appear  to  be  any  marked  and  constant 
variation  in  the  normal  temperature  ;  but  in  old  age,  while  the  actual 
temperature  of  the  body  is  not  notably  reduced,  the  power  of  resisting 
refrigerating  influences  is  considerably  diminished.  There  are  no 
observations  showing  any  constant  differences  in  the  temperature  of 
the  body  in  the  sexes  ;  and  it  may  be  assumed  that  in  the  female  the 
body-temperature  is  modified  by  the  same  influences  and  in  the  same 
way  as  in  the  male. 

Variations  at  Different  Times  of  the  Day,  etc.  — Although  the  limits 
of  variation  in  the  body-temperature  are  not  very  wide,  certain  fluctua- 
tions are  observed,  depending  on  muscular  repose  or  activity,  diges- 
tion, sleep  etc.      It  has  been  ascertained  that  there  are  two  well-marked 


400  GENERAL    NUTRITION 

periods  in  the  day  when  the  heat  is  at  its  maximum  :  at  eleven  a.m.  and 
four  P.M.  The  fall  in  temperature  during  the  night  takes  place  sleep- 
ing or  waking  ;  and  when  sleep  is  taken  during  the  day,  it  does  not 
disturb  the  period  of  the  maximum,  which  occurs  at  about  four  p.m. 
At  eleven  in  the  morning,  the  body-heat  is  at  one  of  its  periods  of 
maximum  ;  it  gradually  diminishes  for  two  or  three  hours  and  is  raised 
again  to  the  maximum  at  about  four  in  the  afternoon,  when  it  again 
undergoes  diminution  until  the  next  morning.  The  variations  amount 
to  between  i°  and  2.16°  Fahr.  (0.55°  and  1.19°  C).  The  minimum  is 
always  during  the  night. 

The  influence  of  defective  nutrition  or  of  inanition  on  the  heat  of  the 
body  is  very  marked.  In  pigeons  the  extreme  variation  in  temperature 
during  the  day,  under  normal  conditions,  was  found  by  Chossat  to  be 
1.3"  Fahr.  (0.7°  C).  During  the  progress  of  inanition  this  variation  was 
increased  to  5.9°  Fahr.  (3.25"  C.)  with  a  slight  diminution  in  the  absolute 
temperature,  and  the  periods  of  minimum  temperature  were  unusually 
prolonged.  Immediately  preceding  death  from  starvation,  the  diminu- 
tion in  temperature  became  very  rapid,  the  rate  being  7°  to  ii"^  Fahr. 
(3.85°  to  6"  C.)  per  hour.  Death  usually  occurred  when  the  diminution 
had  amounted  to  about  30^  Fahr.  ( 16.5°  C). 

When  the  surrounding  conditions  call  for  the  development  of  an 
unusual  quantity  of  heat,  the  diet  is  modified,  both  as  regards  quantity 
and  kind  of  food  ;  but  when  food  is  taken  in  sufficient  quantity  and  is 
of  a  kind  capable  of  maintaining  proper  nutrition,  its  composition  does 
not  affect  the  general  temperature.  The  temperature  of  the  body,  in- 
deed, seems  to  be  uniform  in  the  same  climate,  even  in  persons  living 
on  entirely  different  kinds  of  food.  Nevertheless,  the  conditions  of 
external  temperature  have  a  remarkable  influence  on  the  diet.  It  is 
well  known  that  in  the  heat  of  summer,  the  quantity  of  meats  and  fat 
taken  is  relatively  small,  and  of  the  succulent  fresh  vegetables  and  fruits, 
large,  as  compared  with  the  diet  in  the  winter ;  but  although  the  pro- 
portion of  carbohydrates  in  many  fresh  vegetables  used  during  a  short 
season  of  the  year  is  not  great,  these  articles  are  also  deficient  in  nitroge- 
nous matters.  During  the  winter  the  ordinary  diet,  composed  of  meat, 
fat,  bread,  potatoes  etc.,  contains  a  large  proportion  of  nitrogenous 
matters  as  well  as  a  considerable  proportion  of  carbohydrates ;  and  in 
the  summer  the  proportion  of  both  these  varieties  of  food  is  reduced, 
the  more  succulent  articles  taking  their  place.  This  is  further  illustrated 
by  a  comparison  of  the  diet  in  the  torrid  or  temperate  and  in  the  frigid 
zones.  It  is  stated  that  the  daily  ration  of  the  Esquimaux  is  twelve 
to  fifteen  pounds  (5.433  to  6.894  kilograms)  of  meat,  about  one-third  of 
which  is  fat.      Hayes  noted  that  with  a  temperature  of —60°  to  —  70° 


ANIMAL    HEAT    AND    FORCE  4OI 

Fahr.  (about  —  5 1""  to  —  57'  C.;,  there  was  a  continual  craving  for  a  strong, 
animal  diet,  particularly  fatty  substances. 

The  influence  of  alcoholic  beverages  on  the  animal  temperature  has 
been  studied  chieiiy  with  reference  to  the  question  of  their  use  in  en- 
abling the  system  to  resist  excessive  cold.  The  testimony  of  scientific 
Arctic  explorers  is  that  the  use  of  alcohol  does  not  enable  men  to  endure 
a  very  low  temperature  for  any  considerable  length  of  time. 

As  a  rule,  when  the  respiratory  activity  is  physiologically  increased 
—  as  it  is  by  exercise,  bodily  or  mental,  ingestion  of  food  or  diminished 
external  temperature  —  the  production  of  heat  in  the  body  is  increased 
correspondingly ;  and  on  the  other  hand,  it  is  diminished  by  conditions 
that  physiologically  decrease  the  absorption  of  oxygen  and  the  exhala- 
tion of  carbon  dioxide.  The  relations  of  animal  heat  to  the  general 
process  of  nutrition  are  most  intimate.  Any  condition  that  increases 
the  activity  of  nutrition  and  of  katabolism,  or  even  anything  that  in- 
creases katabolism  alone,  increases  the  production  of  heat.  The  reverse 
of  this  proposition  is  also  true. 

Notwithstanding  the  fact  that  there  is  a  certain  correspondence 
between  the  activity  of  the  respiratory  processes  and  the  production  of 
heat,  this  is  far  from  absolute.  It  has  been  shown  by  Senator  that 
digestion  increases  heat-production  rather  more  than  it  increases  the 
exhalation  of  carbon  dioxide.  Muscular  work  has  been  found  to  increase 
the  quantity  of  oxygen  consumed  in  much  greater  proportion  than  it 
increased  the  heat-production  (Hirn).  Even  adding  to  the  heat  produced 
the  work,  reduced  to  heat-units,  the  heat-production  was  about  doubled, 
while  the  quantity  of  oxygen  consumed  was  increased  about  four  and 
a  half  times. 

Influence  of  Exercise  etc.,  on  the  Heat  of  the  Body.  —  The  most  nearly 
complete  repose  of  the  muscular  system  is  observed  during  sleep,  when 
hardly  any  of  the  muscles  are  brought  into  action  except  those  concerned 
in  tranquil  respiration.  There  is  always  a  notable  diminution  in  the  gen- 
eral temperature  at  this  time.  In  the  variations  in  the  heat  of  the  body, 
the  minimum  is  always  during  the  night ;  and  this  is  not  entirely  de- 
pendent on  sleep,  for  a  depression  in  temperature  is  always  observed 
at  that  time,  even  when  sleep  is  avoided.  It  is  a  matter  of  common 
observation  that  one  of  the  most  efficient  means  of  resisting  the  depress- 
ing influence  of  cold  is  to  exercise  the  muscles  constantly ;  and  it  is  well 
known  that  after  long  exposure  to  intense  cold,  the  tendency  to  sleep, 
which  becomes  almost  irresistible,  if  yielded  to,  is  followed  by  a  rapid 
loss  of  heat  and  almost  certain  death.  Muscular  work  increases  the 
production  of  heat ;  but  the  variations  in  the  actual  temperature  of  the 
body  in  man,  although  distinct,  are  seldom  considerable,  for  the  reason 


402  GENERAL   NUTRITION 

that  muscular  exercise  usually  is  attended  with  increased  action  of  the 
skin,  which  keeps  the  heat  of  the  body  within  restricted  Hmits.  In  vio- 
lent muscular  exertion,  as  in  fast  running,  the  increased  production 
of  heat  may  be  so  rapid  that  it  can  not  be  entirely  compensated  by 
evaporation  from  the  skin,  and  the  temperature  may  rise  to  104°  Fahr. 
(40°  C).  In  about  an  hour  and  a  half  of  repose  the  temperature  falls 
to  the  normal  standard. 

The  elevation  in  temperature  that  attends  muscular  work  is  produced 
directly  in  the  substance  of  the  muscle  (Becquerel  and  Breschet).  In- 
troducing a  thermo-electric  needle  into  the  biceps  of  a  man  who  used 
the  arm  in  sawing  wood  for  five  minutes,  these  physiologists  noted  an 
elevation  of  temperature  of  nearly  2°  Fahr.  (1°  C). 

Observations  on  the  influence  of  mental  exertion  on  the  temperature 
of  the  body  have  not  been  so  many,  but  they  are,  apparently,  no  less 
exact  in  their  results.  Davy  observed  a  slight  but  constant  elevation 
during  "excited  and  sustained  attention."  Lombard  noted  an  elevation 
of  temperature  in  the  head  during  mental  exertion  of  various  kinds,  but 
it  was  slight,  the  highest  rise  not  exceeding  0.05°  Fahr.  (0.027°  C). 
According  to  Burdach,  the  temperature  of  the  body  is  increased  by  the 
emotions  of  hope,  joy,  anger,  and  all  exciting  passions,  while  it  is  dimin- 
ished by  fear,  fright  and  mental  distress. 

It  is  evident  that  if  animal  heat  be  one  of  the  necessary  attendant 
phenomena  of  nutrition,  it  must  be  greatly  influenced  by  conditions  of 
the  circulation.  It  has  been  a  question,  indeed,  whether  the  modifica- 
tions in  temperature  produced  by  operating  on  the  vasomotor  nerves 
are  not  due  entirely  to  changes  in  the  supply  of  blood.  It  is  certain 
that  whatever  determines  an  increased  supply  of  blood  to  any  part  raises 
the  temperature ;  and  whenever  the  quantity  of  blood  in  any  organ  or 
part  is  considerably  diminished,  the  temperature  is  reduced.  This  fact 
is  illustrated  in  operations  for  the  deligation  of  large  arteries.  It  is 
well  known  that  after  tying  a  large  vessel,  the  utmost  care  is  necessary 
to  keep  up  the  temperature  of  the  part  to  which  its  branches  are  dis- 
tributed, until  the  anastomosing  vessels  become  enlarged  sufficiently  to 
supply  the  quantity  of  blood  necessary  for  normal  nutrition. 

Influence  of  the  Neiiwus  System  on  tJie  Production  of  Animal  Heat 
{Heat-Centres).  — The  local  influences  of  the  vasomotor  nerves  on  calori- 
fication operate  mainly  if  not  entirely  through  changes  in  the  nutrition 
of  parts,  produced  by  variations  in  blood-supply.  These  influences  will 
be  fully  considered  in  connection  with  the  physiology  of  the  nervous 
system. 

The  temperature  of  the  body  may  be  modified  through  the  nervous 
system  by  reflex  action,  and  this  implies  the  existence  of  nerve-centres, 


MECHANISM    OF    THE   PRODUCTION    OF    ANIMAL    HEAT         403 

or  of  a  nerve-centre,  capable  of  influencing  the  general  process  of  calori- 
fication. Experiments  have  been  made,  chiefly  on  parts  of  the  en- 
cephalon,  with  the  view  of  determining  the  existence  and  location  of 
heat-centres.  Ott  describes  four  heat-centres,  irritation  of  which 
by  puncture  increases  the  temperature  of  the  body  in  rabbits  by  several 
degrees  (4°  to  6°  Fahr.,  or  2.2''  to  3.3°  C).  These  four  centres  are  the 
following:  i,  in  front  of  and  beneath  the  corpus  striatum  (Ott);  2,  the 
median  portion  of  the  corpora  striata  and  the  subjacent  parts  ( Aronsohn 
and  Sachs) ;  3,  between  the  corpus  striatum  and  the  optic  thalamus 
(Ott) ;  4,  the  anterior  inner  end  of  the  optic  thalamus  (Ott).  Puncture 
of  these  parts  is  followed  by  rise  in  temperature,  which  continues  for  a 
variable  time  —  two  to  four  days.  A  similar  centre  has  been  described 
as  existing  in  the  dog  in  the  cortex  of  the  anterior  portion  of  the  upper 
surface  of  the  brain  near  the  median  line  (Eulenberg  and  Landois). 
The  conductors  connected  with  these  centres  decussate  and  pass  through 
the  bulb  and  the  spinal  cord.  The  effects  of  puncture  or  stimulation  of 
these  parts  probably  is  inhibitory. 

Mechanism  of  the  Production  of  Animal  Heat 

In  man  and  in  the  warm-blooded  animals  generally,  the  maintenance 
of  the  temperature  of  the  organism  at  a  nearly  fixed  standard  is  a  neces- 
sity of  life ;  and  while  heat  is  generated  with  an  activity  that  is  con- 
stantly varying,  it  is  counterbalanced  by  physiological  loss  of  heat  from 
the  cutaneous  and  respiratory  surfaces.  Variations  in  the  activity  of 
calorification  are  not  to  be  measured  by  corresponding  changes  in  the 
body-temperature,  but  are  to  be  estimated  by  calculating  the  quantity  of 
heat  lost.  The  ability  of  the  human  race  to  live  in  all  climates  is 
explained  by  the  adaptability  of  man  to  different  conditions  of  diet  and 
exercise  and  by  the  power  of  regulating  loss  of  heat  from  the  surface 
by  appropriate  clothing. 

So  far  as  it  is  possible  to  determine  by  experiment,  not  only  is  there 
no  particular  part  or  organ  in  the  body  endowed  with  the  special  office 
of  calorification,  but  every  part  in  which  the  nutritive  forces  are  in 
operation  produces  a  certain  quantity  of  heat ;  and  this  probably  is  true 
of  the  blood-corpuscles  and  other  anatomical  elements  of  this  class. 
The  production  of  heat  in  the  body  is  general  and  is  one  of  the  neces- 
sary results  of  the  process  of  nutrition  ;  but,  with  nutrition,  it  is  subject 
to  local  variations,  as  is  illustrated  in  the  effects  of  operations  on  the 
vasomotor  nerves  and  in  the  phenomena  of  inflammation. 

In  1866  Frankland  made  a  number  of  calculations  of  the  heat-units 
and  the  estimated  force-value  of  various  articles  of  food,  which  are  now 


404 


GENERAL   NUTRITION 


accepted  and  used  by  most  writers  on  subjects  connected  with  the 
theories  of  animal  heat  and  the  source  of  muscular  power.  As  regards 
the  heat  produced  by  the  oxidation  of  these  substances  in  the  body,  if  it 
is  assumed  that  the  same  quantity  of  heat  is  produced  by  the  oxidation, 
under  all  circumstances,  of  a  definite  quantity  of  oxidizable  matter,  it  is 
necessary  simply  to  deduct  from  the  heat-value  of  articles  of  food  the 
heat-value  remaining  in  certain  parts  of  the  food  which  pass  out  of  the 
body  in  an  unoxidized  state.  It  was  in  this  way  that  Frankland  arrived 
at  a  determination  of  the  heat-value  of  articles  of  food  oxidized  in  the 
body. 

The  following  selections  from  Frankland's  table  give  an  idea  of  the 
heat-value  of  different  articles  of  food  oxidized  in  the  body.  In  this 
table  the  heat-units  are  calculated  as  pound-degrees. 


HEAT-VALUE  OF  TEN  GRAINS  OF  THE  MATERIAL  OXIDIZED  INTO  CARBON 
DIOXIDE,   WATER   AND   UREA   IN   THE   ANIMAL   BODY  (FRANKLAND) 


Articles  of  Food 


Heat-units 


Butter 18.68 

Beef-fat  (dry) 23.33 

Lump-sugar 8.61 

Grape-sugar 8.42 

Wheat-flour 9.87 

Bread-crumb 5.52 

Arrowroot 10.06 

Ground  rice 9.52 


Articles  of  Food  Heat-units 

Potatoes 2.56 

Cabbage i-o8 

Milk 1.64 

Egg  (boiled)      .     '. 5.86 

Cheese 1 1.20 

Lean  beef 366 

Ham  (boiled) 4.30 

Mackerel 4.14 


In  the  following,  selected  from  the  table  quoted  by  Chapman,  the 
heat-units  are  calculated  as  kilo-degrees  C. 


HEAT-VALUE   OF   ONE   GRAM   OF  THE  MATERIAL  OXIDIZED  INTO   CARBON 
DIOXIDE,   WATER   AND   UREA   IN  THE   ANIMAL   BODY    (FRANKLAND) 


Articles  of  Food 

Butter  .  .  . 
Beef-fat  (dry) 
Lump-sugar  . 
Grape-sugar  . 
Wheat-flour  . 
Bread-crumb  . 
Arrowroot 
Ground  rice   . 


Heat-units 
7.264 
9.069 
3-348 
3.227 
3.840 
1.450 
3.912 
3.760 


Articles  of  Food  Heat-units 

Potatoes 0.990 

Cabbage 0.420 

Milk 0.620 

Egg  (boiled) 2.280 

"to 


Che 


4.36c 


Lean  beef 1.420 

Ham  (boiled) 1.680 

Mackerel i-6io 


The  heat-value  of  one  gram  of  alcohol  is  equal  to  8.958  heat-units 
(kilo-degrees  C),  or  the  heat-value  of  10  grains  of  alcohol  is  equal  to 
23  heat-units  (pound-degrees  Fahr.). 


MECHANISM    OF    THE    PRODUCTION    OF   ANIMAL    HEAT         405 

As  regards  the  processes  of  combustion  that  take  place  in  the 
living  organism,  the  oxidation  of  the  constituents  of  food  produces  car- 
bon dioxide  and  water  ;  but  it  is  probable  that  the  quantity  of  heat  pro- 
duced bears  a  definite  relation  to  the  total  consumption  of  oxygen,  the 
heat,  so  far  as  this  is  concerned,  being  the  same  whether  the  oxygen 
unite  with  carbon  or  with  hydrogen.  This  relation  between  the  quan- 
tity of  oxygen  consumed  and  the  production  of  heat  seems  to  be  dis- 
turbed by  muscular  work ;  but  it  has  thus  far  been  found  impossible  to 
estimate  accurately  the  quantity  of  heat  represented  by  the  force 
expended  in  muscular  work,  circulation,  respiration  etc. 

The  heat-producing  processes  undoubtedly  are  represented  mainly 
by  the  exhalation  of  carbon  dioxide  and  water  and  to  a  less  degree  by 
the  discharge  of  urea,  the  quantity  of  heat  produced  by  other  chemical 
changes  being  comparatively  small.  It  is  also  true  that  the  fats  are 
much  more  important  factors  in  calorification  than  the  proteids  ;  but 
it  seems  beyond  question  that  there  must  be  heat  evolved  in  the  body 
by  oxidation  of  nitrogenous  matters.  When  the  daily  quantity  of  food 
is  largely  increased  for  the  purpose  of  generating  the  heat  required  in 
excessively  cold  climates,  nitrogenous  matters  are  taken  in  greater 
quantity,  as  well  as  fats,  although  their  increase  is  not  in  the  same 
proportion.  From  these  facts,  and  from  other  considerations  that  have 
already  been  fully  discussed,  it  is  evident  that  the  physiological  meta- 
morphoses of  proteids  have  a  certain  share  in  the  production  of  animal 
heat.  The  carbohydrates  and  fats  are  not  concerned  in  the  building  up 
of  tissues  and  organs,  except  as  fats  are  deposited  in  the  form  of  adi- 
pose tissue.  Their  addition  to  the  food  saves  the  nitrogenous  tissues, 
which  latter  must  be  used  in  heat-production  in  starvation  and  in  a 
restricted  diet  deficient  in  non-nitrogenous  matters.  If  the  non- 
nitrogenous  constituents  of  food  do  not  form  tissue,  are  not  discharged 
from  the  body  and  are  consumed  in  some  of  the  processes  of  nutrition, 
it  would  seem  that  their  change  must  involve  the  production  of  carbon 
dioxide  and  water  and  the  evolution  of  heat. 

Although  it  may  be  assumed  that  the  non-nitrogenous  constituents 
of  food  are  specially  important  in  the  production  of  animal  heat  and 
that  they  are  not  concerned  in  the  repair  of  tissue,  it  must  be  remem- 
bered that  the  body-temperature  may  be  kept  at  the  proper  standard  on 
a  nitrogenous  diet ;  and  it  is  not  possible  to  connect  calorification  exclu- 
sively with  the  consumption  of  any  single  class  of  alimentary  matters. 

The  exact  mechanism  of  the  oxidation-processes  in  the  body  is  not 
understood.  All  physiologists,  however,  are  agreed  that  the  quantity 
of  heat  produced  by  oxidation  is  the  same,  whether  the  combustion  be 
rapid  or  slow.     The  fact  that  fats  are  never  discharged,  but  are  either 


406  GENERAL    NUTRITION 

consumed  entirely  or  are  deposited  in  the  body  as  fat,  leaves  their 
oxidation  and  discharge  as  oxidation-products  the  only  alternative.  The 
oxidation  of  proteids  has  already  been  considered.  As  regards  the  car- 
bohydrates, if  it  can  be  shown  that  alcohol  normally  exists  in  the  blood, 
even  in  very  small  quantity,  the  idea  that  these  matters  are  slowly 
passed  from  the  liver  as  sugar  into  the  general  circulation  and  are  then 
converted  into  alcohol,  which  is  promptly  oxidized,  is  worthy  of  serious 
consideration  (see  page  393).  Such  a  theory  explains  the  destination 
of  the  carbohydrates  and  their  relations  to  calorification.  There  can 
be  no  doubt  that  in  certain  cases  of  fever,  alcohol  administered  in  large 
quantity  may  be  oxidized  and  "  feed "  the  fever,  thereby  saving  con- 
sumption of  tissue. 

In  a  series  of  observations  made  in  1879  (Flint),  it  seemed  impossible 
to  account  for  the  heat  actually  produced  in  the  body  and  expended  as 
force  in  muscular  work  etc.,  by  the  heat-value  of  food  and  of  tissue 
consumed.  The  estimates  of  heat-production,  made  by  the  direct 
method,  were  then  adopted;  but  even  the  indirect  estimates  —  which 
were  much  less- — presented  difficulty,  though  in  a  less  degree.  In 
these  observations  it  was  shown  that  water  was  actually  produced  in  the 
body,  in  quantity  over  and  above  that  contained  in  food  and  drink,  during 
severe  and  prolonged  muscular  work.  It  was  also  shown  that  water 
was  produced  in  considerable  quantity  during  twenty-four  hours  of 
abstinence  from  food.  It  has  been  shown  by  Pettenkofer  and  Voit  that 
"  the  elimination  of  water  is  very  much  increased  by  work,  and  the 
increase  continues  during  the  ensuing  hours  of  sleep."  As  regards  the 
oxidation  of  hydrogen  in  this  formation  of  water,  it  is  probable  that 
the  hydrogen  of  the  tissues  is  used  and  that  the  matter  thus  consumed  is 
supplied  again  to  the  tissues  in  order  to  maintain  the  physiological 
status  of  the  organism.  Adding  the  heat-value  of  the  water  thus  formed 
to  the  heat-value  of  food,  there  is  little  difficulty  in  accounting  for  the 
heat  and  force  actually  produced  and  expended. 

The  demonstration  that  water  is  actually  formed  within  the  organism 
under  certain  conditions  not  only  completes  the  oxidation-theory  of  the 
production  of  animal  heat,  but  it  affords  an  explanation  of  certain  physio- 
logical phenomena  that  have  heretofore  been  obscure.  It  it  well  known, 
for  example,  that  a  proper  system  of  physical  training  will  reduce  the 
fat  of  the  body  to  a  minimum  consistent  with  health  and  strength.  This 
involves  a  diet  containing  a  relatively  small  proportion  of  fat  and  liquids, 
and  regular  muscular  exercise  attended  with  profuse  sweating.  Mus- 
cular work  increases  the  elimination  of  water,  while  it  also  exaggerates 
for  the  time  the  calorific  processes.  Muscular  exercise  undoubtedly 
favors  the  consumption  of  the  non-nitrogenous  parts  of  the  body,  and 


EQUALIZATION    OF    THE   ANIMAL    TEMPERATURE  407 

a  diminution  of  the  supply  of  fats,  carbohydrates  and  water  in  the  food 
prevents,  to  a  certain  extent,  the  new  formation  of  fat.  In  excessive 
muscular  work,  the  production  of  water  is  increased  and  the  circula- 
tion becomes  more  active.  The  volume  of  blood  then  circulating  in  the 
skin  and  passing  through  the  lungs  in  a  given  time  is  relatively  increased, 
and  there  is  an  increased  discharge  of  water  from  these  surfaces.  The 
same  condition  that  produces  an  increased  quantity  of  water  in  the 
body  and  has  a  tendency  to  exaggerate  the  process  of  calorification 
seems  to  produce  also  an  increased  evaporation  from  the  surface,  which 
serves  to  equalize  the  animal  temperature. 

Equalization  of  the  Animal  Temperature.  —  There  is  always  more 
or  less  loss  of  heat  by  evaporation  from  the  general  surface ;  and  when 
the  surrounding  atmosphere  is  very  cold  it  becomes  desirable  to  reduce 
this  loss  to  the  minimum.  This  is  done  by  appropriate  clothing,  which 
certainly  must  be  regarded  as  a  physiological  necessity.  Clothing  pro- 
tects from  excessive  heat  as  well  as  from  cold.  Thin  porous  coverings 
moderate  the  heat  of  the  sun,  equalize  evaporation  and  afford  great 
protection  in  hot  climates.  In  excessive  cold,  clothing  moderates  the 
loss  of  heat  from  the  surface.  When  the  body  is  not  exposed  to 
currents  of  air,  garments  are  useful  chiefly  as  non-conductors,  impris- 
oning many  layers  of  air,  which  are  warmed  by  contact  with  the 
person.  It  is  also  important  to  protect  the  body  from  the  wind,  which 
greatly  increases  the  loss  of  heat  by  evaporation. 

When  from  any  cause  there  is  a  tendency  to  undue  elevation  of  the 
body-heat,  cutaneous  transpiration  is  increased  and  the  temperature  is 
kept  at  the  proper  standard.  This  has  already  been  considered  in  treat- 
ing of  the  action  of  the  skin,  and  facts  were  noted  showing  that  men 
can  work  when  exposed  to  a  heat  much  higher  than  that  of  the  body 
itself.  The  quantity  of  vapor  that  is  lost  under  these  conditions  is  some- 
times very  large.  Tillet  recorded  an  instance  of  a  young  girl  who 
remained  in  an  oven  for  ten  minutes  without  inconvenience,  at  a  tem- 
perature of  324.5°  Fahr.  (162.5°  C).  Blagden,  in  his  noted  experiments 
in  a  heated  room,  made  in  connection  with  Banks,  Solander,  Fordyce 
and  others,  found  in  one  series  of  observations  that  a  temperature  of 
211°  Fahr.  (99.5°  C.)  could  be  easily  borne;  and  at  another  time  the 
heat  was  raised  to  260°  Fahr.  (126.5°  C.).  Under  these  external  condi- 
tions, the  body  is  protected  from  the  radiated  heat  by  clothing,  the  air  is 
perfectly  dry,  and  the  animal  temperature  is  kept  down  by  increased 
evaporation  from  the  surface. 

It  is  a  curious  fact  that  after  exposure  of-  the  body  to  an  intense  dry 
heat  or  to  a  heated  vapor,  as  in  Turkish  or  Russian  baths,  when  the 
general  temperature  is  somewhat  raised  and  the  surface  is  bathed  in 


408  GENERAL    NUTRITION 

perspiration,  a  cold  plunge,  which  checks  the  action  of  the  skin  almost 
immediately,  is  not  injurious  and  is  decidedly  agreeable.  This  presents 
a  striking  contrast  to  the  effects  of  sudden  cold  on  a  system  heated  and 
exhausted  by  long-continued  exertion.  In  the  latter  instance,  when  the 
perspiration  is  suddenly  checked,  serious  disorders  of  nutrition,  with 
inflammation  etc.,  may  supervene.  When  the  skin  acts  to  keep  down 
the  temperature  of  the  body  in  simple  exposure  to  external  heat,  there 
is  no  modification  in  nutrition,  and  the  tendency  to  an  elevation  of  the 
body-temperature  comes  from  causes  entirely  external.  It  is  a  practical 
observation  that  no  ill  effects  are  produced,  under  these  circumstances, 
by  suddenly  changing  the  external  conditions ;  but  when  the  body-heat 
is  raised  by  a  modification  of  the  internal  nutritive  processes,  as  in  pro- 
longed muscular  work,  these  changes  should  not  be  suddenly  arrested ; 
and  a  suppression  of  the  compensative  action  of  the  skin  is  likely  to 
produce  disturbances  in  nutrition,  often  resulting  in  inflammations. 

Relations  of  Heat  to  Force 

Since  the  development  of  the  theory  of  the  conser\'ation  of  forces, 
which  had  its  origin  in  an  essay  published  by  J.  R.  Mayer,  in  1842, 
physiologists  have  applied  the  laws  of  correlation  and  conservation  of 
forces  to  operations  involving  the  production  of  heat  and  the  develop- 
ment and  expenditure  of  force  in  animals.  This  theory,  if  applicable 
to  what  were  formerly  called  vital  operations,  certainly  affords,  in  its 
definite  quantities  of  heat  and  force  as  expressed  in  heat-units  and  foot- 
pounds, a  basis  for  calculating  the  value  of  material  changes  in  the 
body.  Without  discussing  the  purely  physical  questions  involved,  the 
laws  of  correlation  and  conservation  of  forces,  as  they  are  applicable  to 
human  physiology,  may  be  briefly  stated  as  follows  :  — 

Potential  energy  is  something  either  residing  in  or  imparted  to 
matter,  which  is  capable  of  being  converted  directly  or  indirectly  into 
heat.  The  animal  body,  for  example,  is  a  storehouse  of  potential 
energy.  Its  tissues  may  be  made  to  unite  with  oxygen  and  heat  is 
produced.  Any  body  may  have  potential  energy  imparted  to  it.  If  a 
weight  is  raised  to  a  certain  height,  when  the  force  which  has  accom- 
plished this  work  is  exhausted,  the  potential  energy  imparted  to  the 
weight  causes  it  to  fall ;  and  in  this  fall  heat  is  produced.  The  weight 
may  be  supported  at  the  height  to  which  it  has  been  raised  for  an 
indefinite  time ;  but  it  still  possesses  the  potential  energy  that  has  been 
imparted  to  it,  and  when  the  support  is  removed,  this  potential  energy 
is  converted  into  force,  which  may  be  converted  into  heat.  Potential 
energy  may  be  converted  directly  into  heat,  as  when  a  body  is  oxidized. 


RELATIONS    OF   HEAT   TO   FORCE 


409 


It  is  converted  indirectly  into  heat,  when  movement,  falling  or  other 
force  is  produced ;  for  all  force  may  be  converted  into  heat.  The  con- 
version into  heat,  directly  or  indirectly,  affords  a  convenient  measure  of 
potential  energy.  Using  the  example  of  the  change  of  potential  energy 
into  heat  by  oxidation,  the  energy  stored  up  in  matter  is  measured  by 
estimating  the  heat  produced  by  oxidation  as  so  many  heat-units.  Using 
the  example  of  falling  force  imparted  to  a  weight,  the  potential  energy 
imparted  to  the  body  is  estimated  by  calculating  the  heat  produced  by 
the  body  falling. 

If  the  entire  body  of  an  animal  were  to  be  burned  in  a  calorimeter, 
the  heat  produced  would  be  an  exact  measure  of  the  potential  energy 
of  the  tissues  converted  into  heat  by  oxidation.  If  one  could  imagine 
an  animal  perfectly  quiescent,  neither  losing  nor  gaining  weight,  nour- 
ished by  food,  expending  no  force  in  circulation  and  respiration,  but 
supplied  with  oxygen,  the  potential  energy  of  the  food  could  be  meas- 
ured by  the  heat  produced.  In  animal  organisms,  heat  is  produced 
mainly  by  oxidation,  although  other  chemical  processes  contribute  to 
the  production  of  heat  to  some  extent.  The  body  contains  the  potential 
energy  stored  up  in  its  tissues.  The  oxygen  taken  in  by  respiration 
changes  a  certain  part  of  this  potential  energy  into  heat.  If  food  is 
not  supplied  in  adequate  quantity,  the  body  loses  weight  by  this  change 
of  tissue  into  certain  matters,  such  as  carbon  dioxide,  water  and  urea, 
which  are  discharged.  Food  supplies  the  waste  of  tissue  and  is  the 
ultimate  source  of  the  potential  energy  of  the  body.  If  food  is  supplied 
in  excess,  that  which  is  not  in  some  form  discharged  from  the  body 
remains  and  adds  to  the  total  potential  energy  stored  up  in  the  organism. 

Kinetic  energy  is  mechanical  force.  It  is  the  force  of  a  falling  body, 
or  as  regards  animal  mechanics,  it  is  muscular  force  used  in  respiration, 
circulation  or  any  kind  of  muscular  work.  In  physics,  kinetic  energy, 
or  force,  and  heat  are  regarded  as  mutually  convertible.  The  reasoning 
by  which  this  law  was  formulated  is  the  following :  — 

The  force  used  in  raising  a  weight  to  a  certain  height,  which  is 
imparted  to  the  weight  as  potential  energy,  is  precisely  equal  to  the 
force  developed  by  this  body  as  it  falls.  If  this  force  could  be  trans- 
mitted to  another  body  of  equal  weight,  without  any  loss  of  energy  by 
friction,  it  would  raise  the  second  weight  to  an  equal  height.  The 
arbitrary  unit  of  this  force  is  a  foot-pound  or  a  kilogrammeter,  terms 
that  have  already  been  defined.  The  falling  of  a  body  of  a  certain 
weight  through  a  definite  distance  produces  a  definite  quantity  of  heat 
that  itself  is  capable  of  producing  force ;  and  it  is  assumed  that  the  heat 
produced  by  a  faUing  body,  if  absolutely  and  entirely  converted  into 
force,  would  raise  that  body  to  the  height  from  which  it  had  fallen,  or 


4IO  GENERAL   NUTRITION 

would  exactly  equal  the  falling  force.  A  heat-unit  is  therefore  said  to 
be  equal  to  a  definite  number  of  foot-pounds  or  kilogrammeters.  Calcu- 
lations have  been  made  showing  the  conversion  of  foot-pounds  or  kilo- 
grammeters into  heat-units,  but  mechanical  difficulties  have  thus  far 
prevented  the  actual  conversion  of  heat-units  into  their  equivalents  in 
foot-pounds  or  kilogrammeters.  As  a  matter  of  reasoning,  however,  it 
is  assumed  that  if  a  certain  number  of  foot-pounds  or  kilogrammeters 
is  equal  to  a  certain  number  of  heat-units,  the  reverse  of  the  equation  is 
true ;  but  the  application  of  this  law  to  animal  physiology  is  always 
by  a  conversion  of  heat-units  into  foot-pounds  or  kilogrammeters.  The 
experiments  on  which  the  law  rests  have  been  made  by  converting  foot- 
pounds or  kilogrammeters  into  heat-units. 

In  work  by  machinery,  a  large  proportion  of  the  force-value  of  fuel 
is  dissipated  in  the  form  of  heat.  This  is  well  illustrated  by  Landois : 
If  a  steam  engine  burning  a  certain  quantity  of  coal,  but  doing  no  work, 
is  placed  in  a  calorimeter,  the  heat  produced  can  be  measured.  If,  now, 
the  engine  is  made  to  do  a  certain  work,  as  in  raising  a  weight,  the  heat, 
as  measured  by  the  calorimeter,  will  be  less,  and  the  work  done  is  found 
to  be  very  nearly  proportional  to  the  decrease  in  the  measured  heat 
(Hirn).  It  is  estimated  by  Landois,  that  of  the  heat  produced  by  the 
body,  one-fifth  may  be  used  as  work.  In  the  best  steam  engine,  it  is 
possible  to  use  only  one-eighth  as  work,  seven-eighths  being  dissipated 
as  heat. 

Many  elaborate  and  careful  estimates  have  been  made  of  the 
mechanical  work  produced  by  the  human  body.  The  basis  of  such 
calculations  is  more  or  less  indefinite,  and  the  reduction  of  the  work 
to  foot-pounds  or  kilogrammeters  is  difficult  and  inexact.  Even  the 
general  statement,  that  of  the  heat-units  produced  by  the  body,  four- 
fifths  remain  as  heat  and  one-fifth  is  converted  into  work,  must  be 
regarded  as  approximate. 

In  the  application  of  the  law  of  correlation  and  conservation  of  forces 
to  animal  mechanics,  the  matters  consumed  in  the  production  of  heat 
and  force  are  food-stuffs.  These  are  oxidized,  either  directly  or  indi- 
rectly. If  oxidized  indirectly,  it  is  the  substance  of  the  tissues  that  is 
thus  consumed,  the  loss  being  repaired  by  food.  A  certain  proportion 
of  the  heat  produced  is  used  in  maintaining  the  heat  of  the  body ;  an- 
other part  is  dissipated  by  radiation  from  the  general  surface ;  another 
part  is  converted  into  force  and  is  used  by  the  heart  and  the  respiratory 
muscles  ;  and  still  another  part  is  used  in  the  general  work  of  the  mus- 
cular system.     All  this  involves  a  considerable  oxidation  of  matter. 

In  this  connection  it  is  interesting  to  note  again  the  heat-value  of 
different  alimentary  matters  :  — 


RELATIONS  OF  HEAT  TO  FORCE  41 1 

One  gram  of  proteid  =  about  4500  calories  (gram-degrees). 

One  gram  of  fat  =  about  9000  calories  (gram-degrees). 

One  gram  of  carbohydrate  =  about  4000  calories  (gram-degrees). 

In  the  animal  organism,  a  part  of  the  potential  energy  of  the  tissues 
may  be  converted  into  force  by  voluntary  effort.  In  fevers,  an  abnor- 
mally large  proportion  of  the  potential  energy  of  the  organism  is  con- 
verted into  heat,  and  it  is  not  possible  to  use  much  of  this  energy  as 
force.  These  and  other  peculiarities  of  living  bodies,  as  regards  the  pro- 
duction of  heat  and  force,  are  difficult  of  explanation.  In  the  essential 
fevers,  the  conditions  which  involve  the  abnormal  production  of  heat 
finally  consume  the  substance  of  the  tissues.  They  involve  especially 
an  increased  production  of  carbon  dioxide  and  urea  and  not  to  any  great 
extent  the  formation  of  water.  If  heat-producing  alimentary  substances 
and  alcohol  can  be  introduced  and  consumed,  the  tissues  are  thereby 
proportionally  saved  from  degeneration  and  destruction. 


PART  II 

MUSCULAR  MOVEMENTS— VOICE  AND  SPEECH 
—  NERVOUS  SYSTEM  — SPECIAL  SENSES  — 
EMBRYOLOGY 


CHAPTER   XVI 

MUSCULAR    MOVEMENTS 

Amorphous  contractile  substance  and  ameboid  movements  —  Ciliary  movements  —  Movements 
due  to  elasticity  —  Elastic  tissue  —  Muscular  movements  —  Contraction  of  involuntary  mus- 
cular tissue  —  Physiological  anatomy  of  the  voluntary  muscular  tissue  —  Connective  tissue 
—  Bloodvessels  and  lymphatics — Connection  of  the  muscles  with  the  tendons  —  Chemical 
composition  of  the  muscles — Physiological  properties  of  the  muscles  —  Elasticity  of  mus- 
cles—  Muscular  tonicity  —  Sensil:)ility  of  the  muscles — Muscular  contractility -and  excit- 
ability—  Muscular  contraction  —  Changes  in  the  form  of  fibres  during  contraction  —  Rigor 
mortis — Passive  organs  of  locomotion  —  Physiological  anatomy  of  the  bones  —  Lacunae  — 
Canaliculi  —  Bone-cells  or  corpuscles  —  Marrow  of  the  bones  —  Pericisteum  —  Physiologi- 
cal anatomy  of  cartilage  —  Cartilage-cavities  —  Cartilage-cells  —  Elastic  cartilage  and  fibro- 
cartilage. 

The  processes  connected  with  the  nutrition  of  animals  involve  cer- 
tain movements ;  and  almost  all  animals  possess  in  addition  the  power 
of  locomotion.  Many  of  these  movements  have  of  necessity  been  con- 
sidered in  connection  with  the  different  functions ;  as  the  action  of  the 
heart  and  vessels  in  the  circulation,  the  uses  of  the  muscles  in  respira- 
tion, the  muscular  acts  in  deglutition,  the  peristaltic  movements  and  the 
mechanism  of  defecation  and  urination.  There  remain,  however,  certain 
general  facts  in  regard  to  various  kinds  of  movement  and  the  mode  of 
action  of  the  different  kinds  of  muscular  tissue,  that  demand  more  or 
less  extended  consideration. 

Amorphous  Contractile  Substance  and  Ameboid  Movements.  —  In 
some  of  the  lowest  forms  of  beings,  in  which  hardly  anything  but 
amorphous  matter  and  a  few  granules  can  be  recognized  with  the 
microscope,  certain  movements  of  elongation  and  retraction  of  amor- 
phous substance  have  been  observed.  In  the  higher  animals,  similar 
movements  have  been  noted  in  certain  of  their  structures,  such  as  the 
leucocytes,  the  contents  of  the  ovum,  epithelial  cells  and  connective- 
tissue  cells.  These  movements  usually  are  simple  changes  in  the  form 
of  the  cell ;  and  they  depend  on  an  organic  substance  formerly  called 
sarcode  and  now  known  as  protoplasm,  which  has  already  been  described. 
In  the  anatomical  elements  of  adult  animals  of  the  higher  classes,  these 
movements  usually  appear  slow  and  gradual,  even  when  viewed  with 
high  magnifying  powers  ;  but  in  some  of  the  very  lowest  forms  of  life, 
the  movements  serve  as  a  means  of  progression  and  are  more  rapid, 

412 


CILIARY   MOVEMENTS 


413 


Such  movements  are  called  ameboid  ;  and  they  probably  are  analogous 
to  ciliary  movements,  the  cause  of  which,  however,  is  obscure. 

Ciliary  Movements.  —  The  epithelium  covering  certain  of  the  mucous 

membranes  is  provided  with  little  hair-like  processes  on  the  borders  of 

the  cells,  called  cilia.     These  are  in  constant  motion  from  the  beginning 

to  the  end  of  life ;  and  they  produce  currents  on  the  surfaces  of  the 

I 


Fig.  80. —  Ciliated  epitlielium  (Engelmann). 

A,  from  intestinal  epithelium  of  anodonta ;  B,  from  gill  of  anodonta ;    C,  D,  intestinal  epithelium  of 
cyclas. 

membranes  to  which  they  are  attached,  the  direction  being  usually 
from  within  outward.  In  man  and  in  the  warm-blooded  animals 
generally,  the  ciliated  or  vibratile  epithelium  is  of  the  variety  called 
columnar,  conoidal  or  prismoidal.  The  cilia  are  attached  to  the  thick 
ends  of  the  cells,  and  they  form  on  the  surface  of  the  membrane  a  con- 
tinuous sheet  of  moving  processes.  In  general  structure  the  ciliary 
processes  are  homogeneous,  and  they  gradually  taper  from  their  attach- 
ment to  the  cell  to  an  extremitv  of  excessive  tenuitv. 


414  MOVEMENTS 

The  presence  of  cilia  has  been  demonstrated  on  the  following  sur- 
faces :  The  respiratory  passages,  including  the  nasal  fossae,  the  pituitary 
membrane,  the  summit  of  the  larynx,  the  bronchial  tubes,  the  superior 
surface  of  the  velum  palati  and  the  Eustachian  tubes  ;  the  sinuses  about 
the  head ;  the  lachrymal  sac  and  the  internal  surface  of  the  eyelids  ; 
the  genital  passages  of  the  female,  from  the  middle  of  the  neck  of  the 
uterus  to  the  fimbriated  extremities  of  the  Fallopian  tubes ;  some  of  the 
seminal  passages;  the  ventricles  of  the  brain  and  some  unimportant  sit- 
uations. In  these  parts,  on  each  cell  of  conoidal  epithelium  are  six  to 
twelve  processes,  about  o  s^wT  o^  ^^  ^'^^^  (^  f^)  ^"  thickness  at  their  base, 
and  "5011-0  ^°  4oVo  ^^  ^^  ^'^^'^^  (5  to  6  /x)  in  length.  Between  the  cilia  and 
the  substance  of  the  cell,  there  usually  is  a  thin  transparent  disk.  The 
appearance  of  the  cilia  is  represented  in  Fig.  8o.  When  seen  in  situ, 
they  appear  regularly  disposed  over  the  surface,  are  of  nearly  equal 
length  and  are  slightly  inclined  in  the  direction  of  the  opening  of  the 
cavity  lined  by  the  membrane. 

When  the  ciliary  movements  are  seen  in  a  large  number  of  cells,  the 
appearance  is  well  illustrated  by  the  comparison  by  Henle  to  the  undula- 
tions of  a  field  of  wheat  agitated  by  the  wind.  In  watching  this  move- 
ment, it  usually  is  seen  to  gradually  diminish  in  rapidity,  until  what  at 
first  appeared  simply  as  currents,  produced  by  movements  too  rapid  to 
be  studied  in  detail,  are  revealed  as  distinct  undulations,  in  which  the 
action  of  individual  cilia  may  be  studied.  Several  kinds  of  movement 
have  been  described,  but  the  most  common  is  a  bending  of  the  cilia, 
simultaneously  or  in  regular  succession,  in  one  direction,  followed  by  an 
undulating  return  to  the  perpendicular.  The  other  movements,  such  as 
the  infundibuliform,  in  which  the  point  describes  a  circle  around  the 
base,  the  pendulum-movement  etc.,  are  not  common  and  are  unim- 
portant. 

The  combined  action  of  the  cilia  on  the  surface  of  a  mucous  mem- 
brane, moving  as  they  do  in  one  direction,  is  to  produce  currents  of 
considerable  power.  This  may  be  illustrated  under  the  microscope  by 
covering  the  surface  with  a  liquid  holding  little  solid  particles  in  suspen- 
sion, when  the  granules  are  tossed  from  one  portion  of  the  field  to 
another  with  considerable  force.  It  is  not  difficult,  indeed,  to  measure 
in  this  way  the  rapidity  of  the  ciliary  currents.  In  the  frog  it  has  been 
estimated  at  ^lo  to  yi-  of  an  inch  (loo  to  140  fx)  per  second,  the  num- 
ber of  vibratile  movements  being  seventy-five  to  one  hundred  and  fifty 
per  minute.  In  the  fresh-water  polyp  the  movements  are  more  rapid, 
being  two  hundred  and  fifty  or  three  hundred  per  minute.  There  is  no 
reliable  estimate  of  the  rapidity  of  the  ciliary  currents  in  man,  but  they 
probably  are  more  active  than  in  animals  low  in  the  scale. 


ELASTIC   TISSUE 


415 


The  movements  of  cilia,  like  those  observed  in  fully-developed 
spermatozoids,  seem  to  be  independent  of  nervous  influence,  and  they 
are  affected  only  by  local  conditions.  They  may  continue,  under  favor- 
able circumstances,  for  more  than  twenty-four  hours  after  death,  and 
they  can  be  seen  in  cells  detached  from  the  body,  when  moistened  with 
proper  solutions.  When  the  cells  are  moistened  with  water,  the  activ- 
ity of  their  movement  is  at  first  increased  ;  but  it  soon  disappears  as  the 
cells  become  swollen.  Acids  arrest  the  movements,  but  they  may  be 
excited  by  feebly  alkaline  solutions.  As  regards  the  uses  of  these  move- 
ments, it  is  sufficient  to  refer  to  the  physiology  of  the  parts  in  which 
cilia  are  found,  where  the  peculiarities  of  their  action  are  considered 
more  in  detail.  In  the  lungs  and  the  air-passages  generally  and  in  the 
genital  passages  of  the  female,  the  currents  are  of 
considerable  importance ;  but  it  is  difficult  to  imagine 
the  use  of  these  movements  in  certain  other  situa- 
tions, as  the  ventricles  of  the  brain. 

Movements  due  to  Elasticity.  —  There  are  certain 
important  movements  in  the  body  due  simply  to  the 
action  of  elastic  ligaments  or  membranes.  These  are 
distinct  from  muscular  movements  and  are  not  to  be 
classed  even  with  the  movements  produced  by  the 
resiliency  of  muscular  tissue,  in  which  muscular  to- 
nicity is  more  or  less  involved.  Movements  of  this 
kind  consist  simply  in  the  return  of  movable  parts  to 
a  certain  position  after  they  have  been  displaced  by 
muscular  action,  and  in  the  reaction  of  tubes  after 
forcible  distention,  as  in  the  walls  of  the  large  arteries. 

Elastic  Tissue.  —  Most  anatomists  adopt  the  divi- 
sion of  the  iibres  of  elastic  tissue  into  three  varieties. 
This  division  relates  to  the  size  of  the  fibres ;  and  all 
varieties  are  found  to  possess  essentially  the  same  chemical  composition 
and  general  properties.  On  account  of  the  yellow  color  of  this  tissue, 
presenting,  as  it  does,  a  decided  contrast  to  the  white  glistening  appear- 
ance of  the  inelastic  fibres,  it  frequently  is  called  the  yellow  elastic 
tissue. 

The  first  variety  of  elastic  tissue  is  composed  of  small  fibres,  usually 
intermingled  with  fibres  of  the  ordinary  inelastic  tissue.  They  possess 
all  the  chemical  and  physical  characters  of  the  larger  fibres  but  are 
very  fine,  measuring  2^|o¥  to  goVo  or  5A0  o^  ^n  inch  (i  to  4  or  5  /*)  in 
diameter.  If  acetic  acid  is  added  to  a  preparation  of  ordinary  connec- 
tive tissue,  the  inelastic  fibres  are  rendered  semitransparent,  but  the 
elastic  fibres  are  unaffected  and  become  quite  distinct.     They  are  then 


Fig.      81.  —  White 

fibrous  tissue  ;  one  end 
of  the  bundle  has  been 
teased  out  so  as  to  display 
the  component  fibriUcB 
(Piersol). 


4i6 


MOVEMENTS 


Fig.  82.  —  Elastic  fibres  iso- 
lated; from  the  adventitia  of  the 
aorta  (Piersol,  after  Schieffer- 
decker). 


seen  isolated  —  that  is,  never  arranged  in  bundles  —  usually  with  a  dark 
double  contour,  branching,  brittle,  and  when  broken,  their  extremities 
curled  and  presenting  a  sharp  fracture  like   a  piece  of  India  rubber. 

These  fibres  take  a  wavy  course  between  the 
bundles  of  inelastic  fibres  in  the  areolar  tissue 
and  in  most  of  the  ordinary  fibrous  mem- 
branes. They  are  found  in  greater  or  less 
abundance  in  the  situations  just  mentioned; 
in  the  ligaments,  but  not  the  tendons ;  in  the 
layers  of  non-striated  muscular  tissue  ;  the  true 
skin  ;  the  true  vocal  chords  ;  the  trachea, 
bronchial  tubes,  and  largely  in  the  parenchyma 
of  the  lungs  ;  the  external  layer  of  the  large 
arteries  ;  and,  in  brief,  in  nearly  all  situations 
in  which  ordinary  connective  tissue  exists. 

The  second  variety  of  elastic  tissue  is 
composed  of  fibres,  larger  than  the  first, 
ribbon-shaped,  with  well-defined  outlines,  anas- 
tomosing, undulating  or  curved  in  the  form  of 
the  letter  S,  presenting  curled  ends  and  sharp 
fracture,  like  the  smaller  fibres.  These  measure  -5  oVo  ^o  stVo  ^^  ^^  '\Viz\i 
(5  to  8  /u)  in  diameter.  Their  type  is  found  in  the  ligamenta  subflava 
and  the  ligamentum  nuchas.  They  are  also  found  in  some  of  the  liga- 
ments of  the  larvnx,  the  stylo-hyoid  ligament  and  the 
suspensory  ligament  of  the  penis. 

The  third  variety  of  elastic  tissue  is  found  forming 
the  middle  coat  of  the  large  arteries  and  has  already 
been  described  in  connection  with  the  vascular  sys- 
tem. The  fibres  are  large  and  flat,  inosculating  freely 
with  each  other  by  short  communicating  branches. 
These  anastomosing  fibres,  forming  the  so-called  fe- 
nestrated membranes,  are  arranged  in  layers,  and  the 
structure  is  sometimes  called  the  lamellar  elastic  tissue. 

The  physical  property  of  elasticity  plays  an  impor-    grouped  that  they  cm- 

.  .  _^  ,  stitiite  an  elastic  sheet 

tant  part  m  many  of  the  animal  functions.  Examples  _//^^  so-caiied  fenes- 
of  this  are  in  the  action  of  the  large  arteries  in  the    ^''^^"^   membrane   of 

"  Henle  (Piersol). 

circulation  and  in  the  resiliency  of  the  parenchyma  of 
the  lungs.  The  ligamenta  subflava  and  the  ligamentum  nuchae  are 
important  in  aiding  to  maintain  the  erect  posture  of  the  body  and  head 
and  to  restore  this  position  when  flexion  has  been  produced  by  muscular 
action.  Still,  the  contraction  of  muscles  also  is  necessary  to  keep  the 
body  in  a  vertical  position. 


Fig.  83.  —  Portion 
of  the  elastic  tissue  of 
the  Ultima  of  the  human 
aorta  ;  the  fibres  are  so 
broad    and    so    closely 


INVOLUNTARY   MUSCULAR    TISSUE 


417 


Muscular  Movements 

Muscular  movements  are  divided  into  voluntary  and  involuntary; 
and  usually  there  is  a  corresponding  division  of  the  muscles  as  regards 
their  minute  anatomy.  The  latter,  however,  is  not  absolute  ;  for  there 
are  certain  involuntary  actions,  like  the  contractions  of  the  heart  or  the 
movements  of  deglutition,  that  require  the  rapid  and  vigorous  contrac- 
tion characteristic  of  the  voluntary  muscular  tissue  ;  and  here  the  struc- 
ture resembles  that  of  the  voluntary  muscles. 

PJiysiological  Anatoviy  of  the  Involuntary  ]\hiscular  Tissue.  ■ — The 
involuntary  muscular  system  presents  a  striking  contrast  to  the  volun- 


Fig.  85.  —  Muscular 
fibres  from  the  aorta  of 
the  calf,  X  200  (Sappey). 

I,  I,  fibres  joined  with 
each  other ;  2,  2,  2,  isolated 
fibres. 


Fig.  86.  —  Muscular  fibres  from,  the 
uterus  of  a  woman  who  died  at  the  ninth 
month  of  utero-gestation,  x  350  (Sappey) . 

I,  I,  2,  short  wide  fibres;  3,  4,  5,  5, 
longer  and  narrower  fibres ;  6,  6,  two 
fibres  united  at  7;  8,  small  fibres  in 
process  of  development. 


Fig.  84.  —  Muscular 
fibres  from  the  urinary 
bladdS-  of  the  human  sub- 
ject, X  200  (Sappeyj . 

I,  I,  I,  nuclei;  2,  2,  2, 
borders  of  some  of  the 
■fibres  ;  3,  3,  isolated  fibres ; 
4,  4,  two  fibres  joined  to- 
gether at  5. 

tary  muscles,  not  only  in  its  minute  anatomy  and  mode  of  action,  but  in 
the  arrangement  of  its  fibres.  While  the  voluntary  muscles  are  almost 
invariably  attached  by  their  extremities  to  movable  parts,  the  involun- 
tary muscles  form  sheets  or  membranes  in  the  walls  of  hollow  organs, 
and  by  their  contraction  they  simply  modify  the  capacity  of  the  cavities 
which  they  surround.  On  account  of  the  peculiar  structure  of  the  fibres, 
they  have  been  called  muscular  fibre-cells,  smooth  muscular  fibres,  pale 
fibres,  non-striated  fibres,  fusiform  fibres  or  contractile  cells.  The  dis- 
tribution of  these  fibres  to  parts  concerned  in  the  organic  functions,  as 


41 8  MOVEMENTS 

the  alimentary  canal,  has  given  them  the  name  of  organic  muscular 
fibres,  or  fibres  of  organic  life.  In  their  natural  condition,  the  invol- 
untary muscular  fibres  are  pale,  finely  granular,  flattened,  and  of  an 
elongated  spindle-shape,  with  a  very  long,  narrow,  almost  linear  nucleus. 
The  nucleus  usually  has  no  distinct  nucleolus  and  sometimes  it  is  curved 
or  shaped  like  the  letter  S.  The  ordinary  length  of  these  fibres  is 
about  -g^Q  of  an  inch  (50  /i)  and  their  breadth  about  4:oVo  ^^  ^^  i"ch 
(6  /x).  In  the  gravid  uterus  they  undergo  remarkable  hypertrophy, 
measuring  here  g^j  to  -g^j-  of  an  inch  (300  to  500  /jl)  in  length,  and  j'St'o 
of  an  inch  (12  /x)  in  breadth. 

In  the  contractile  sheets  of  involuntary  muscular  tissue,  the  fibres 
are  arranged  side  by  side,  are  closely  adherent,  and  their  extremities 
are,  as  it  were,  dove-tailed  into  each  other.  Usually  the  borders  of  the 
fibres  are  regular  and  their  extremities  are  simple  ;  but  sometimes  the 
ends  are  forked  and  the  borders  present  one  or  more  little  projections. 
The  fibres  seldom  exist  in  a  single  layer  except  in  the  smallest  arterioles. 
Usually  the  layers  are  multiple,  being  superimposed  in  regular  order. 

Contraction  of  the  Invohintary  Muscular  Tissue.  —  The  mode  of  con- 
traction of  the  involuntary  muscles  is  peculiar.  It  does  not  take  place 
immediately  on  the  reception  of  a  stimulus,  applied  either  directly  or 
through  the  nerves,  but  it  is  gradual,  enduring  for  a  time  and  then 
followed  by  slow  and  gradual  relaxation.  A  description  of  the  peristaltic 
movements  of  the  intestines  gives  an  idea  of  the  mode  of  contraction 
of  these  fibres,  with  the  gradual  propagation  of  the  stimulus  along  the 
alimentary  canal  as  the  food  makes  its  impression  on  the  mucous  mem- 
brane. Another  illustration  is  afforded  by  labor-pains.  These  are  due 
to  the  muscular  contractions  of  the  uterus,  and  they  last  for  a  few  sec- 
onds or  one  or  two  minutes.  Their  gradual  access,  continuation  for  a 
certain  period,  and  gradual  disappearance  coincide  with  the  description 
of  contractions  of  the  involuntary  muscular  fibres. 

The  contraction  of  the  involuntary  muscular  tissue  is  relatively  slow, 
and  the  fibres  return  slowly  to  a  condition  of  repose.  The  movements 
are  always  involuntary.  Peristaltic  action  is  the  rule,  and  the  contrac- 
tion takes  place  progressively  and  without  oscillations.  Contractility 
persists  for  a  long  time  after  death.  Excitation  of  the  nerves  has  less 
influence  on  contraction  of  these  fibres  than  direct  excitation  of  the 
muscles.  The  involuntary  muscular  tissue  is  regenerated  rapidly,  while 
the  structure  of  the  voluntary  muscles  is  restored  with  difficulty  after 
destruction  or  division. 

Physiological  Atiatoiny  of  the  Voluntaiy  Muscular  Tissue.  —  A  vol- 
untary muscle  contains,  in  addition  to  its  contractile  substance,  fibres  of 
inelastic  and  elastic  tissue,  adipose  tissue,  abundant  bloodvessels,  nerves 


VOLUNTARY   MUSCULAR   TISSUE  419 

and  lymphatics,  with  certain  nuclear  and  cellular  anatomical  elements. 
The  muscular  system  in  a  well-proportioned  man  is  equal  to  about  two- 
fifths  of  the  weight  of  the  body.  Among  the  characteristic  properties 
of  the  muscles  are  elasticity,  a  constant  and  insensible  tendency  to 
contraction,  called  tonicity,  the  power  of  contracting  forcibly  on  the 
reception  of  a  proper  stimulus,  and  a  peculiar  kind  of  sensibility.  The 
muscular  tissue  is  made  up  of  a  great  number  of  microscopic  fibres, 
known  as  primitive  muscular  fasciculi.  These  are  called  red,  striated 
or  voluntary  fibres.  Their  structure  is  complex,  and  they  may  be  sub- 
divided longitudinally  into  fibrillas  and  transversely  into  disks.  In  very 
short  muscles,  some  of  the  primitive  fasciculi  may  run  the  entire  length 
of  the  muscle;  but  the  fasciculi  usually  are  1.2  to  1.6  inch  (30  to  40 
millimeters)  in  length.  The  fasciculi,  however,  do  not  inosculate  with 
each  other,  but  the  end  of  one  fasciculus  is  united  longitudinally  with 
the  end  of  another  by  a  strongly  adhesive  substance,  the  line  of  union 
being  oblique  ;  so  that  the  fibres  practically  run  the  entire  length  of  the 
muscle.  Exceptions  to  this  arrangement  are  the  branching  muscular 
fibres  of  the  heart  and  of  the  face  and  tongue.  Each  fasciculus  in 
ordinary  muscular  tissue  is  enclosed  in  its  own  sheath,  without  branching 
or  inosculation.  This  sheath  contains  the  true  muscular  substance  only, 
and  it  is  not  penetrated  by  bloodvessels,  nerves  or  lymphatics.  The 
color  of  the  muscular  fibres  by  transmitted  light  is  a  delicate  amber, 
resembling  the  color  of  the  blood-corpuscles. 

The  primitive  fasciculi  vary  in  size  in  different  individuals,  in  the 
same  individual  under  different  conditions  and  in  different  muscles.  As 
a  rule  they  are  smaller  in  young  persons  and  in  females  than  in  adult 
males.  They  are  comparatively  small  in  persons  of  slight  muscular 
development.  In  persons  of  great  muscular  vigor,  or  when  the  general 
muscular  system  or  particular  muscles  have  been  increased  in  size  and 
power  by  exercise,  the  fasciculi  are  relatively  larger.  It  is  probable 
that  physiological  increase  in  the  size  of  a  muscle  from  exercise  is  due 
to  an  increase  in  the  size  of  the  preexisting  fasciculi  and  not  to  the  forma- 
tion of  new  elements.  In  young  persons  the  fasciculi  are  yvW  ^°  T2V0" 
of  an  inch  (15  to  20  ^)  in  diameter.  In  the  adult  they  measure  ^j-I-q  to 
2^Q  of  an  inch  (55  to  lOO  ^t). 

The  appearance  of  the  primitive  muscular  fasciculi  under  the  micro- 
scope is  characteristic.  They  present  regular  transverse  striae,  formed 
of  alternating  dark  and  clear  bands  about  osoTo  *^^  ^^  inch  {i  f^)  wide. 
With  a  high  magnifying  power,  a  fine  transverse  line  is  obser\'ed  run- 
ning through  the  middle  of  each  one  of  the  clear  bands.  In  addition 
they  present  longitudinal  striae,  not  so  distinct,  and  difificult  to  follow  to 
any  extent  in  the  length  of  the  fasciculus,  but  tolerably  well  marked. 


420 


MOVEMENTS 


particularly  in  muscles  that  are  habitually  exercised  (see  Plate  IX, 
Fig.  6).  The  muscular  substance,  presenting  this  peculiar  striated 
appearance,  is  enclosed  in  a  thin  but  elastic  and  resisting  tubular 
membrane,  called  the  sarcolemma  or  myolemma.  This  envelope  can 
not  be  seen  in  ordinary  preparations  of  the  muscular  tissue ;  but  it 
frequently  happens  that  the  contractile  muscular  substance  is  broken, 
leaving  the  sarcolemma  intact,  which  gives  a  good  view  of  the  mem- 
brane and  conveys  an  idea  of  its  strength  and  elasticity.  Attached  to 
the  inner  surface  of  the  sarcolemma  are  small  elongated  nuclei  with 
their  long  diameter  in  the  direction  of  the  fascicuh. 

Connective  Tissue.  —  In  the  muscles  there  is  a  membrane  surround- 
ing a  number  of  the  primitive  fasciculi.  This  is  called  the  perimysium. 
The  fibrous  membranes  that  connect  together  the  secondary  bundles, 
with  their  contents,  are  enclosed  in  a  sheath  enveloping  the  entire 
muscle,  sometimes  called  the  external  perimysium.  The  peculiarity  of 
these  membranes  as  distinguished  from  the  sarcolemma  is  that  they 
have  a  fibrous  structure  and  are  connected  together  throughout  the 
muscle,  while  the  tubes  forming  the  sarcolemma  are  structureless  and 
each  one  is  distinct. 

The  name  usually  given  to  ordinary  fibrous  tissue  is  connective 
tissue.  It  has  been  called  cellular,  areolar  or  fibrous,  but  most  of  these 
names  were  given  without  a  clear  idea  of  its  structure.  Its  principal 
anatomical  element  is  a  fibre  of  excessive  tenuity,  wavy  and  with  a  sin- 
gle contour.  These  fibres  are  collected  into  bundles  of  variable  size 
and  are  held  together  by  an  adhesive  amorphous  substance.  The  wavy 
lines  that  mark  the  bundles  of  fibres  give  them  a  characteristic  appear- 
ance (see  Fig.  8i). 

The  direction  and  arrangement  of  the  fibres  in  the  various  tissues 
present  marked  differences.  In  the  loose  tissue  beneath  the  skin  and 
between  the  muscles  and  in  the  loose  structure  surrounding  some  of  the 
glands  and  connecting  the  sheaths  of  bloodvessels  and  nerves  to  the 
adjacent  parts,  the  bundles  of  fibres  form  a  large  network  and  are  wavy 
in  their  course.  In  the  strong  dense  membranes,  as  the  aponeuroses, 
the  proper  coats  of  many  glands,  the  periosteum  and  perichondrium  and 
the  serous  membranes,  the  waves  of  the  fibres  are  shorter  and  the  fibres 
themselves  interlace  much  more  closely.  In  the  ligaments  and  tendons 
the  fibres  are  more  nearly  straight  and  are  arranged  longitudinally. 

The  proportion  of  elastic  fibres  in  different  situations  is  variable ; 
but  they  are  all  of  the  smallest  variety  and  present  a  striking  contrast 
to  the  inelastic  fibres  in  form  and  size.  Although  they  are  very  small, 
the  elastic  fibres  always  present  a  double  contour. 

Certain  cellular  and  nuclear  elements  are  always  found  in  the  con- 


CHEMICAL   COMPOSITION    OF   THE    MUSCLES  42 1 

nective  tissue.  The  cells  are  known  as  connective-tissue  cells.  They 
are  irregular  in  size  and  form,  some  being  spindle-shaped  or  caudate, 
and  others,  star-shaped.  They  possess  one,  and  sometimes  two  or  three, 
clear  ovoid  nuclei  with  distinct  nucleoli.  On  the  addition  of  acetic  acid 
the  cells  disappear,  but  the  nuclei  are  unaffected.  It  is  impossible  to 
give  accurate  measurements  of  the  cells  on  account  of  their  great  varia- 
tions in  size.  Between  the  muscles,  and  in  the  substance  of  the  muscles 
between  the  bundles  of  fibres,  there  always  exists  a  greater  or  less  quan- 
tity of  adipose  tissue  in  the  meshes  of  the  fibrous  structure. 

Bloodvessels  and  Lymphatics.  —  The  muscles  are  abundantly  supplied 
with  bloodvessels,  usually  by  a  number  of  small  arteries  with  two  satel- 
lite veins.  The  capillary  arrangement  in  this  tissue  is  peculiar.  From 
the  smallest  arterioles,  capillary  vessels  are  given  off,  arranged  in  a  net- 
work with  tolerably  regular,  oblong,  rectangular  meshes,  their  long 
diameter  following  the  direction  of  the  fibres.  These  envelop  each 
primitive  fasciculus,  enclosing  it*  completely,  the  artery  and  vein  being 
on  the  same  side.  The  capillaries  are  smaller  than  in  any  other  part  of 
the  vascular  system  (see  Plate  X,  Fig.  i). 

The  arrangement  of  the  lymphatics  in  the  muscles  has  not  been 
definitely  ascertained.  There  are  lymphatics  surrounding  the  large 
vascular  trunks  of  the  extremities  and  of  the  abdominal  and  thoracic 
walls,  which,  it  would  appear,  must  come  from  the  substance  of  the 
muscles  ;    but  they  have  not  been  traced  to  their  origin. 

CoiiJiection  of  the  Muscles  with  the  Tetidons.  —  The  primitive  mus- 
cular fasciculi  terminate  in  little  conical  extremities  that  are  received 
into  corresponding  depressions  in  the  bundles  of  fibres  composing  the 
tendons ;  but  this  union  is  so  close  that  the  muscle  or  the  tendon  may 
be  ruptured  without  a  separation  at  the  point  of  union.  In  the  penni- 
form  muscles  this  arrangement  is  quite  uniform.  In  other  muscles 
it  is  essentially  the  same,  but  the  perimysium  seems  to  be  continuous 
with  the  loose  fibrous  tissue  enveloping  the  corresponding  tendinous 
bundles. 

Chemical  Composition  of  the  Muscles.  —  The  most  important  proteid 
constituent  of  the  muscles  is  myosin.  This  resembles  fibrin,  but  it 
presents  certain  points  of  difference  in  its  behavior  to  reagents,  by  which 
it  may  be  readily  distinguished.  One  of  its  peculiar  properties  is  that 
it  is  dissolved  at  an  ordinary  temperature  by  a  mixture  of  one  part  of 
hydrochloric  acid  and  ten  of  water.  Myosin  is  now  regarded  as  a  com- 
pound substance  containing  at  least  four  different  proteids  that  may 
be  separated  by  fractional  heat-coagulation  :  (i)  A  globulin  that  coagu- 
lates at  about  117°  Fahr.  (47°  C).  This  is  called  paramyosinogen.  (2)  A 
globulin  that  coagulates  at   133°  Fahr.  (56°  C).     (3)  A  globulin  that 


422  MOVEMENTS 

coagulates  at  146°  Fahr.  (63°  C).     This  is  called  myoglobulin.     (4)  An 
albumin,  analogous  to  serum-albumin,  called  myo-albumin. 

Combined  with  the  organic  constituents  of  the  muscular  substance 
are  mineral  salts  in  great  variety,  which  cannot  be  separated  without 
incineration.  Certain  excrementitious  matters  have  also  been  found  in 
the  muscles ;  and  probably  nearly  all  those  eliminated  by  the  kidneys 
exist  here,  although  they  are  taken  up  by  the  blood  as  fast  as  they  are 
produced  and  consequently  are  detected  with  difficulty.  The  muscles 
also  contain  inosite,  inosic  acid,  lactic  acid,  and  certain  volatile  acids  of 
fatty  origin.  During  life  the  muscular  liquid  is  slightly  alkaline,  but  it 
becomes  acid  soon  after  death.  The  muscle  itself,  during  contraction, 
has  an  acid  reaction.  The  muscular  juice  is  alkaline  or  neutral  after 
moderate  exercise  as  well  as  during  repose ;  but  when  a  muscle  is  made 
to  undergo  excessive  exercise,  the  lactic  and  other  acids  exist  in  greater 
quantity  and  the  reaction  becomes  acid. 

* 

Physiological  Properties  of  the  Muscles 

The  important  general  properties  of  the  striated  muscles  are  the 
following:  i.  elasticity;  2.  tonicity;  3.  sensibility  of  a  peculiar  kind ; 
4.  contractility  and  excitability.  These  are  all  necessary  to  the  physio- 
logical action  of  the  muscles.  Their  elasticity  is  brought  into  play  in 
opposing  muscles  or  sets  of  muscles ;  one  set  acting  to  move  a  part  and 
to  extend  the  antagonistic  muscles,  which,  by  virtue  of  their  elasticity, 
retract  when  the  extending  force  is  removed.  Their  tonicity  is  an  in- 
sensible and  a  more  or  less  constant  contraction,  by  which  the  action  of 
opposing  muscles  is  balanced  when  both  are  in  the  condition  of  what  is 
called  repose.  Their  sensibility  is  peculiar  and  is  expressed  chiefly  in 
the  sense  of  fatigue  and  in  the  appreciation  of  weight  and  of  resistance 
to  contraction.  Their  contractility  and  excitability  are  properties  that 
enable  them  to  contract  under  stimulation.  All  these  general  properties 
belong  strictly  to  physiology,  as  do  some  special  acts  that  are  not  neces- 
sarily involved  in  the  study  of  ordinary  descriptive  anatomy. 

Elasticity  of  Muscles.  —  The  true  muscular  substance  contained  in 
the  sarcolemma  is  eminently  contractile ;  and  although  it  may  possess  a 
certain  degree  of  elasticity,  this  property  is  most  strongly  marked  in  the 
accessory  anatomical  elements.  The  interstitial  fibrous  tissue  is  loose 
and  presents  a  certain  number  of  elastic  fibres ;  and  the  sarcolemma  is 
very  elastic.  It  is  probably  the  sarcolemma  that  gives  to  the  muscles 
their  retractile  power  after  simple  extension. 

Muscular  Tonicity.  —  The  muscles,  under  normal  conditions,  have  an 
insensible  and  a  constant  tendency  to  contract,  which  is  more  or  less 


MUSCULAR    CONTRACTILITY    AND    EXCITABILITY  423 

dependent  on  the  action  of  motor  nerves.  If,  for  example,  a  muscle 
is  cut  across  in  a  surgical  operation,  the  divided  extremities  become  per- 
manently retracted;  or  if  the  muscles  of  one  side  of  the  face  are  para- 
lyzed, the  muscles  on  the  opposite  side  insensibly  distort  the  features. 
It  is  difficult  to  explain  these  phenomena  by  assuming  that  tonicity  is 
due  to  reflex  action,  for  there  is  no  evidence  that  the  contraction  takes 
place  as  the  consequence  of  a  stimulus.  All  that  can  be  said  is  that  a 
muscle,  not  excessively  fatigued  and  with  its  nervous  connections  intact, 
is  constantly  in  a  state  of  insensible  contraction  more  or  less  marked. 

Sensibility  of  the  Muscles.  —  The  muscles  possess  that  kind  of  sensi- 
bility which  gives  an  appreciation  of  resistance,  immobility,  and  elasticity 
of  substances  that  are  grasped,  or  which,  by  their  weight,  are  opposed  to 
muscular  effort.  It  is  by  the  appreciation  of  weight  and  resistance  that 
the  force  required  to  accomplish  muscular  acts  is  regulated.  These 
properties  refer  chiefly  to  simple  muscular  efforts.  After  long-continued 
exertion,  there  is  a  sense  of  fatigue  that  is  peculiar  to  the  muscles.  It 
is  difficult  to  separate  this  entirely  from  the  sense  of  nervous  exhaustion, 
but  it  is  to  a  certain  extent  distinct;  for  when  suffering  from  the  fatigue 
that  follows  overexertion,  it  seems  as  though  a  nervous  stimulus  could 
be  sent  to  the  muscles,  to  which  they  are  for  the  time  unable  to  respond. 
When  muscles  are  thrown  into  tetanic  contraction,  a  peculiar  sensation 
is  produced,  which  is  entirely  different  from  painful  impressions  made 
on  ordinary  sensory  nerves.  In  the  cramps  of  cholera,  tetanus,  or 
the  convulsions  from  strychnin,  these  distressing  sensations  are  very 
marked.  The  general  sensibiHty  of  muscles  is  very  slight.  The  rather 
indefinite  property,  called  muscular  sense,  is  supposed  by  some  physiolo- 
gists to  be  connected  with  peculiar  structures  —  neuro-muscular  spindles 
—  that  will  be  described  in  connection  with  the  nervous  system. 

Mitsciilar  Contractility  and  Excitability.  —  During  life  and  under 
normal  conditions,  muscles  contract  in  obedience  to  a  proper  stimulus 
applied  either  directly  or  through  the  nerves.  In  the  natural  action 
of  the  organism,  this  contraction  is  induced  by  nervous  influence  either 
through  volition  or  reflex  action.  Still,  a  muscle  may  be  living  and 
yet  have  lost  its  contractility.  For  example,  after  a  muscle  has 
been  for  a  long  time  paralyzed  and  disused,  the  application  of  the 
most  powerful  stimulus  will  fail  to  induce  contraction  ;  but  when  exam- 
ined with  the  microscope,  it  is  found  that  the  nutrition  of  the  muscle 
has  become  profoundly  affected  and  that  the  contractile  substance  has 
disappeared.  Muscular  contractility  persists  for  a  certain  time  after 
death  and  in  muscles  separated  from  the  body ;  and  this  fact  has  been 
taken  advantage  of  by  physiologists  in  the  study  of  the  properties  of  the 
muscular  tissue. 


424  MOVEMENTS 

When  the  motor  nerves  are  divided,  the  nutrition  of  the  muscles  to 
which  they  are  distributed  is  disturbed  ;  and  although  muscular  con- 
tractility may  persist  for  some  time  after  nervous  excitability  has  disap- 
peared, it  is  much  diminished  at  the  end  of  six  weeks.  Some  varieties 
of  curare  paralyze  the  end-plates  of  the  motor  nerves,  leaving  the  sen- 
sory nerves  intact.  If  a  frog  is  poisoned  by  introducing  a  little  of  this 
agent  under  the  skin,  stimulation,  electric  or  mechanical,  applied  to  an 
exposed  nerve,  fails  to  produce  muscular  contraction ;  but  if  the  stimu- 
lus is  applied  directly  to  the  muscles,  they  will  contract  vigorously.^ 
If  a  frog  is  poisoned  with  potassium  sulphocyanate,  however,  the  con- 
trary effect  is  observed ;  that  is,  the  muscles  become  insensible  to  exci- 
tation, while  the  nervous  system  is  unaffected.  This  may  be  demonstrated 
by  applying  a  tight  ligature  around  the  body  in  the  lumbar  region, 
involving  all  the  parts  except  the  lumbar  nerves.  If  the  poison  is  now 
introduced  beneath  the  skin  above  the  ligature,  only  the  anterior  parts 
are  affected,  because  the  vascular  communication  with  the  posterior 
extremities  is  cut  off.  If  the  exposed  nerves  are  now  stimulated,  the 
muscles  of  the  legs  are  thrown  into  contraction,  showing  that  the  ner- 
vous conductivity  and  excitability  remain.  Reflex  movements  in  the 
posterior  extremities  also  may  be  produced  by  irritation  of  the  parts 
above  the  ligature.  These  experiments  leave  no  doubt  as  to  the  exist- 
ence of  an  independent  excitabihty  in  the  muscular  tissue.  Contractions 
of  muscles,  it  is  true,  are  excited  normally  through  the  nervous  system, 
and  artificial  stimulation  of  a  motor  nerve  is  the  most  efficient  method 
of  producing  the  simultaneous  action  of  all  the  fibres  of  a  muscle  or  of 
a  set  of  muscles ;  but  direct  electric,  mechanical  or  chemical  irritation 
of  the  muscles  themselves  will  produce  contraction  after  the  nervous 
connections  have  been  destroyed. 


Muscular  Contraction 

The  stimulus  of  the  will,  conveyed  through  the  conductors  of  motor 
impulses  from  the  brain  to  a  muscle  or  set  of  muscles,  excites  the  mus- 
cular fibres  and  causes  them  to  contract.  In  muscles  that  have  been 
exercised  and  educated,  this  action  is  regulated  with  great  nicety,  so 
that  the  most  delicate  and  rapid  as  well  as  powerful  contractions  may 
be  produced.  Certain  movements  not  under  the  control  of  the  will  are 
produced  as  the  result  of  unconscious  reflex  action  of  nervous  centres. 

1  It  has  been  shown,  by  a  very  simple  experiment,  that  curare  paralyzes  the  end-plates  only 
of  the  motor  nerves.  If  a  frog  is  poisoned  with  curare  and  one  leg  is  ligated  above  the  knee, 
leaving  the  nerve  out  of  the  ligature,  reflex  movements  may  be  excited  in  the  ligated  leg,  but 
not  in  other  parts.     This  shows  that  the  motor  nerves  still  retain  their  conductivity. 


MUSCULAR   CONTRACTION  425 

During  contraction  certain  important  changes  are  observed  in  the  mus- 
cles themselves  :  They  change  in  form,  consistence,  and  to  a  certain 
extent  in  their  constitution ;  the  different  periods  of  their  stimulation, 
contraction  and  relaxation  are  positive  and  well  marked ;  their  nutrition 
is  for  the  time  modified ;  they  develop  electric  currents ;  and  in  short, 
they  present  a  number  of  general  phenomena,  distinct  from  the  results 
of  their  action,  that  are  more  or  less  important. 

The  most  prominent  of  the  phenomena  accompanying  muscular 
action  are  shortening  and  hardening  of  the  fibres.  It  is  necessary  only 
to  observe  the  action  of  any  well-developed  muscle  to  appreciate  these 
changes.  The  active  shortening  is  shown  by  the  approximation  of  the 
points  of  attachment,  and  the  hardening  is  sufficiently  palpable.  The 
latter  phenomenon  is  marked  in  proportion  to  the  development  of 
the  true  muscular  tissue  and  its  freedom  from  inert  matter,  such  as  fat. 
Notwithstanding  the  marked  and  constant  changes  in  the  form  and 
consistence  of  the  muscles  during  contraction,  their  actual  volume  under- 
goes modifications  so  sHght  that  they  may  be  disregarded. 

Changes  in  the  Form  of  the  Muscular  Fibres  during  Contraction.  — 
An  essential  experimental  condition  in  the  study  of  the  mechanism  of 
muscular  action  is  to  imitate,  in  a  muscle  or  a  part  of  a  muscle  that  can 
be  subjected  to  direct  observation,  the  force  that  naturally  excites  it  to 
contraction.  The  application  of  electricity  to  the  nerve  is  the  most 
convenient  method  that  can  be  employed  for  this  purpose.  In  this 
way  a  single  contraction  may  be  produced,  or  by  employing  a  rapid 
succession  of  impulses,  so-called  tetanic  action  may  be  excited.  While 
the  electric  current  is  not  identical  with  nerve-impulses,  it  is  the  best 
substitute  that  can  be  used  in  experiments  on  muscular  contractility,  and 
it  has  the  advantage  of  affecting  but  little  the  physical  and  chemical 
integrity  of  the  nervous  and  muscular  tissues. 

A  description  of  the  electric  current  and  its  generation,  with  the 
different  forms  of  electric  apparatus,  belongs  properly  to  physics  and 
would  be  out  of  place  in  a  text-book  on  physiology.  It  is  sufficient  to 
say  that  apparatus  has  been  devised  for  the  study  of  muscular  contrac- 
tion that  enables  experimenters  to  stimulate  muscles  either  directly, 
or  indirectly  through  excitation  of  motor  nerves.  The  contractions  pro- 
duced by  exciting  a  muscle  through  stimulation  of  its  motor  nerve  most 
nearly  resemble  normal  muscular  action. 

In  the  study  of  the  phenomena  of  muscular  contraction,  a  so-called 
nerve-muscle  preparation  is  most  useful.     This  is  simply  the  leg  of  a. 
frog  detached  from  an  animal  just  killed,  the  skin  removed,  and  the 
sciatic  nerve  remaining  attached  to  the  muscles.     With  this  preparation, 
a  stimulus  may  be  applied  either  to  the  nerve  or  directly  to  the  muscle. 


426  MOVEMENTS 

When  the  nerve  is  stimulated  by  means  of  a  single  feeble  inductive 
shock,  the  muscle  contracts  almost  immediately  after  the  electric  dis- 
charge. There  is,  however,  a  short  interval  between  the  stimulation 
and  the  contraction.  This  is  called  the  latent  period,  and  it  occupies 
about  j^Q  of  a  second.  Then  follows  the  stage  of  muscular  contraction, 
which  rapidly  progresses  to  its  maximum.  The  period  of  contraction 
occupies  about  ^^  of  a  second.  The  muscle  then  rather  more  slowly 
returns  to  its  relaxed  condition.  This  period  occupies  a  little  less  than 
■^2  of  a-  second.  Not  counting  the  latent  period,  the  duration  of  a  mus- 
cular contraction  and  relaxation  is  about  jq  of  a  second.  A  part  of  the 
latent  period  is  occupied  in  the  conduction  of  the  stimulus  along  the 
nerve,  and  the  part  belonging  to  the  muscle  is  much  shorter.  Fol- 
lowing the  relaxation,  there  is  often  a  vibratory  wave  of  very  slight 
contractions,  due  to  the  elastic  reaction  of  the  muscular  fibres. 

A  stimulus  may  be  applied  to  a  nerve,  that  is  of  just  sufficient  strength 
to  produce  a  muscular  contraction.  This  is  called  the  minimal  strength 
of  stimulus.  By  gradually  increasing  the  strength  of  the  electric  cur- 
rent, a  maximal  stimulus  may  be  reached.  The  vigor  of  the  muscular 
contraction  is  proportional  to  the  strength  of  the  stimulus,  between  these 
two  extremes.  The  latent  period  is  shorter  with  a  strong  than  with  a 
weak  stimulation.  The  vigor  of  contraction  is  not  increased  by  increas- 
ing the  strength  of  the  stimulus  beyond  the  maximal  point. 

The  foot  in  a  muscle-nerve  preparation  may  be  loaded  with  a  weight. 
When  this  is  done,  provided  the  weight  be  not  too  great  to  be  lifted  by 
the  muscle,  the  extent  of  the  contraction  increases  with  the  weight  up 
to  what  may  be  called  the  maximum  of  contraction.  Beyond  this  point, 
however,  it  diminishes  until  the  weight  is  increased  beyond  the  power 
of  the  muscle.  Increasing  the  weight  increases  the  length  of  the  latent 
period. 

Repeated  stimulation,  especially  when  the  foot  is  weighted,  is 
followed  by  fatigue  of  the  muscle.  At  first  the  work  seems  gradually 
to  increase  the  power  of  the  contractions,  and  they  progress  to  a 
maximum  ;  but  then  fatigue  begins  and  the  power  gradually  diminishes 
until  the  muscle  becomes  exhausted. 

Within  certain  limits,  diminished  temperature  at  first  increases  the 
vigor  of  muscular  contractions,  which  afterward  are  gradually  dimin- 
ished. Moderate  increase  of  temperature  increases  the  vigor  of  the 
contractions  and  shortens  all  the  periods,  including  the  latent  period. 

In  an  entire  muscle,  the  contraction  is  in  the  form  of  a  wave.  With 
delicate  chronometric  apparatus,  the  rapidity  of  this  wave  between  two 
points  in  a  muscle  may  be  measured.  In  the  frog's  muscle,  the  wave 
moves  at  the  rate  of  about  120  inches  (3  meters)  in  a  second. 


MUSCULAR   CONTRACTION  427 

In  a  muscle-nerve  preparation,  the  effect  of  a  second  stimulus 
applied  to  the  nerve  before  the  first  contraction  is  concluded  is  to 
increase  the  extent  of  the  first  contraction.  Indicating  these  contrac- 
tions by  curves,  the  curve  of  the  second  contraction  is  superimposed  on 
the  first.  When  a  number  of  successive  stimuli  are  employed,  the 
curves  are  superimposed  until  a  maximum  is  reached.  Muscular  con- 
traction produced  in  this  way  is  called  incomplete  tetanus.  The  rate  of 
the  stimuli  required  to  produce  this  kind  of  tetanus  is  fifteen  to  twenty 
per  second.  Incomplete  tetanus  may  be  produced  by  voluntary  effort 
as  well  as  by  repeated  electric  shocks ;  and  this  explains  ordinary 
muscular  action.  In  voluntary  effort,  the  normal  stimulus  that  excites 
muscular  contraction  is  sent  from  the  nerve-centres  along  the  nerves 
in  the  form  of  what  are  called  impulses.  The  rate  at  which  these 
impulses  are  sent  out  by  the  nerve-cells  is  ten  to  twelve  in  a  second. 
By  the  superimposition  of  the  contractions,  the  force  exerted  by  a 
muscle  may  be  regulated  by  the  will.  Were  it  not  thus,  prolonged 
muscular  effort  would  be  impossible.  During  voluntary  contraction  a 
muscle  is  in  a  condition  of  incomplete  tetanus ;  but  this  must  not  be 
confounded  with  the  conditions  in  the  disease  known  as  tetanus  or  in 
poisoning  with  strychnin. 

A  muscle  possesses  extensibility  as  well  as  elasticity.  After  it  has 
been  stretched  to  its  limit,  when  the  force  is  removed  it  returns  to  its 
original  length.  When  any  elastic  body  that  is  stretched  afterward 
returns  to  exactly  its  original  dimensions,  it  is  said  to  be  endowed  with 
perfect  elasticity.  Elastic  tissue  is  an  example  of  this.  Muscles,  also, 
are  perfectly  elastic  structures. 

In  a  state  of  rest  there  is  a  feeble  electric  current  flowing  from  the 
general  surface  to  the  cut  surface.  This  is  called  the  current  of  rest 
(Du  Bois  Reymond).  When,  however,  the  muscle  contracts,  the  galva- 
nometer, which  has  been  deviated  by  the  current  of  rest,  shows  a  diminu- 
tion in  this  current,  and  it  may  return  to  zero  under  the  influence  of  a 
current  in  the  opposite  direction.  This  second  current  is  called  the 
current  of  action.  This  diminution  or  extinction  of  the  currents  of  rest 
is  known  as  negative  variation  of  muscle-current. 

Delicate  apparatus  for  measuring  changes  in  temperature  show  that 
muscular  action  is  attended  with  elevation  of  temperature  in  the  muscle 
itself.  In  large  animals  this  has  been  found  to  amount  to  several 
degrees ;  but  a  rise  in  temperature  may  be  noted  even  in  a  muscle-nerve 
preparation  from  a  frog.  By  the  thermopile,  variations  of  40^0"  ^^  ^ 
degree  C.  may  be  noted  (Helmholtz). 

Muscles  in  contraction  undergo  certain  important  chemical  changes. 
The  reaction  of  a  restina:  muscle  is  alkaline.     Muscular  action  results  in 


428  ■  MOVEMENTS 

the  production  of  sarcolactic  acid,  and  consequently  the  reaction  of  the 
muscles  becomes  acid.  During  contraction  a  muscle  consumes  oxygen 
and  gives  off  carbon  dioxide.  It  is  probable,  also,  that  other  katabolic 
products  are  formed  in  the  same  way. 

Rigor  Mortis.  —  At  a  certain  time  after  death,  the  entire  voluntary 
muscular  system  becomes  rigid,  and  the  muscles  will  not  contract  under 
stimulation.  This  is  due  to  a  gradual  coagulation  of  the  muscle-plasma. 
During  this  process  the  muscles  contract  and  give  off  heat  and  carbon 
dioxide  in  small  quantities.  The  muscles  first  affected  usually  are  those 
of  the  neck  and  lower  jaw  and  the  rigidity  gradually  extends  to  the  feet. 
Cadaveric  rigidity  begins  in  fifteen  minutes  to  seven  or  eight  hours  after 
death  and  lasts  until  putrefaction  sets  in.  It  disappears  in  the  same 
order,  as  regards  different   muscles,  in  which  it  began  and  extended. 

Passive  Organs  of    Locomotion 

The  study  of  locomotion  involves  a  knowledge  of  the  physiological 
anatomy  of  certain  passive  organs,  such  as  the  bones,  cartilages  and  liga- 
ments. Although  a  complete  history  of  the  structure  of  these  parts 
trenches  somewhat  on  the  domain  of  anatomy,  a  brief  description  of 
their  histology  will  practically  complete  the  account  of  the  tissues  of  the 
body,  with  the  exception  of  the  nervous  system  and  the  organs  of  re- 
production, which  will  be  taken  up  hereafter. 

Locomotion  is  effected  by  the  action  of  muscles  on  certain  passive 
movable  parts.  These  are  the  bones,  cartilages,  ligaments,  aponeuroses 
and  tendons.  The  fibrous  structures  have  already  been  described,  and 
it  remains  only  to  study  the  structure  of  bones  and  cartilages. 

Physiological  Anatomy  of  the  Bones.  —  The  bones  are  composed  of 
what  is  called  the  fundamental  substance,  with  cavities  and  canals  of 
peculiar  form.  The  cavities  contain  corpuscular  bodies  called  bone- 
corpuscles.  The  canals  of  larger  size  serve  for  the  passage  of  blood- 
vessels, while  the  smaller  canals  (canalicuH)  connect  the  cavities  with 
each  other  and  finally  with  the  vascular  tube  (see  Plate  X,  Fig.  2). 
Many  of  the  bones  present  a  medullary  cavity  filled  with  a  peculiar 
structure  called  marrow.  In  almost  all  bones  there  are  two  distinct  por- 
tions ;  one,  that  is  exceedingly  compact,  and  the  other,  more  or  less 
spongy,  or  cancellated.  The  bones  are  invested  with  a  membrane, 
containing  vessels  and  nerves,  called  periosteum. 

The  fundamental  substance  is  composed  of  an  organic  matter,  called 
ossein,  combined  with  various  inorganic  salts,  in  which  calcium  phos- 
phate largely  predominates.  In  addition  to  calcium  phosphate,  the 
bones  contain    calcium  carbonate,  calcium    fluoride,   magnesium    phos- 


PASSIVE    ORGANS    OF    LOCOMOTION 


429 


phate,  sodium  phosphate  and  sodium  chloride.  The  relative  propor- 
tions of  the  organic  and  inorganic  constituents  are- somewhat  variable; 
but  the  average  is  about  one-third  of  the  former  to  two-thirds  of  salts. 
This  proportion  is  necessary  to  the  proper  consistence  and  toughness  of 
the  bones. 

Anatomically,  the  fundamental  substance  of  the  bones  is  arranged 
in  the  form  of  regular  concentric  lamellae,  about  -g-^g^  of  an  inch  (8  fi  )  in 
thickness.  This  matter  is  of  an  indefinitely  and  faintly  striated  appear- 
ance, but  it  can  not  be  reduced  to  distinct  fibres.  In  the  long  bones  the 
arrangement  of  the  lamellae  is 
quite  regular,  surrounding  the 
Haversian  canals  and  forming 
what  are  sometimes  called  the 
Haversian  rods,  following  in  their 
direction  the  length  of  the  bone. 
In  the  short  thick  bones  the 
lamellae  are  more  irregular,  fre- 
quently radiating  from  the  central 
portion  toward  the  periphery. 

The  Haversian  canals  are  found 
in  the  compact  bony  structure. 
They  are  either  absent  or  very 
few  in  the  spongy  and  reticulated 
portions.  Their  form  is  rounded 
or  ovoid,  the  larger  canals  being 
sometimes  quite  irregular.  In 
the  long  bones  their  direction 
usually  is  longitudinal,  although 
they  often  anastomose  by  lateral 
branches.  Each  one  of  these 
canals  contains  a  bloodvessel,  and  their  disposition  constitutes  the 
vascular  arrangement  of  the  bones.  They  are  all  connected  with  open- 
ings on  the  surfaces  of  the  bones,  by  which  the  arteries  penetrate  and 
the  veins  emerge.  Their  size,  of  course,  is  variable.  The  largest  are 
about  Jq  of  an  inch  (400  /j.)  and  the  smallest  -^^-^  of  an  inch  (30  /j.) 
in  diameter.  Their  average  size  is  o-i-Q  to  w^  of  an  inch  (100  to  125  /x). 
In  a  transverse  section  of  a  long  bone  the  Haversian  canals  mav  be 
seen  cut  across  and  surrounded  by  twelve  to  fifteen  lamellae. 

LacnncB. — The  fundamental  substance  is  evervwhere  marked  by 
irregular  microscopic  excavations,  of  a  peculiar  form,  called  lacunas. 
They  are  connected  with  little  canals,  giving  them  a  stellate  appearance. 
These   canals   are  most  abundant    at  the   sides  of   the  lacunae.      The 


Fig.  87.  —  I'ascitlar  canals  and  lacuna  seen  in  a  lon- 
gitudinal section  of  the  humerus,  X  200  (Sappey). 

a,  a,  a,  vascular  canals;  b,  b,  b,  lacunae  and  can- 

aliculi  in  the  fundamental  substance. 


430 


MOVEMENTS 


lacunae  measure  12V0  ^°  ¥¥0  ^^  ^^  ^"^^  (-°  ^*^  3*^  ^)  ^"^  their  long 
diameter,  by  about  25V0  °f  ^^  ^"^^^  (10  yx)  in  width. 

Canaliculi.  —  These  are  little  wavy  canals,  connecting  the  lacunae 
with  each  other  and  presenting  communications  between  the  first  series 
of  lacunas  and  the  Haversian  canals.  Each  lacuna  presents  eighteen 
to  twenty  canaliculi  radiating  from  its  borders.  The  length  of  the  can- 
aliculi is  g^o  to  g^  of  an  inch  (30  to  40  fi),  and  their  diameter  is  about 
2  5W0  °^  ^^  ^^^'^  (^  ^)'  '^^^  arrangement  and  relations  of  the  Haversian 
canals,  lacunae  and  canaliculi  are  shown  in  Figure  88. 

Bone-cells,  or  Corpuscles.  —  These  structures  are  stellate,  granular, 
with  a  large  nucleus  and  several  nucleoli,  and  of  exactly  the  size  and 


Fig.  88.  —  Vascular  canals  and  lacunce  seen  in  a  transverse  section  of  the  humerus,  X  200  (Sappey) . 

I,  I,  I,  section  of  the  Haversian  canals;  2,  section  of  a  longitudinal  canal  divided  at  the  point  of 
its  anastomosis  with  a  transverse  canal.  Around  the  canals,  cut  across  perpendicularly,  are  seen  the 
lacunae  (with  their  canaliculi),  forming  concentric  rings. 


form  of  the  lacunae.  They  send  out  prolongations  into  the  canaliculi, 
but  it  has  been  impossible  to  ascertain  positively  whether  or  not  they 
form  membranes  lining  the  canaliculi  throughout  their  entire  length. 

Alaj-row  of  the  Bones.  —  The  marrow  is  found  in  the  medullary  cav- 
ities of  the  long  bones,  filling  them  completely  and  moulded  to  the  irreg- 
ularities of  their  walls.  It  is  also  found  filling  the  cells  of  the  spongy 
portion.  In  other  words,  with  the  exception  of  the  vascular  canals, 
lacunae  and  canaliculi,  the  marrow  fills  all  the  spaces  in  the  funda- 
mental substance.  The  cavities  of  the  bones  are  not  lined  with  a 
membrane  corresponding  to  the  periosteum,  and  the  marrow  is  applied 
directly  to  the  bony  substance.  In  the  foetus  and  in  young  children 
the  marrow  is  red  and  very  vascular.     In  the  adult  it  is  yellow  in  some 


PASSIVE    ORGANS    OF    LOCOMOTION  43 1 

bones  and  gray  or  gelatiniform  in  others.  It  contains  certain  pecul-ar 
cells  and  nuclei,  with  amorphous  matter,  adipose  vesicles,  connective  tis- 
sue, bloodvessels  and  nerves,  with  little  bodies,  called  myelocytes,  and 
free  nuclei.  These  are  found  in  greater  or  less  number  in  the  bones  at 
all  ages,  but  they  are  more  abundant  in  proportion  as  the  amorphous 
matter  and  fat-cells  are  deficient.  The  myelocytes  resemble  the 
leucocytes  of  the  blood  but  are  a  little  larger  and  each  has  a  vesicular 
nucleus.  They  are  capable  of  ameboid  movements.  In  addition,  the 
marrow  contains  erythroblasts,  acidophile  cells,  large  basophile  cells, 
leucocytes,  and  erythrocytes.  The  erythroblasts  multiply  by  karyoki- 
nesis,  lose  their  nuclei  and  become  red  blood-corpuscles.  The  uses 
and  destination  of  the  other  varieties  of  cells  have  not  been  definitely 
ascertained  (see  Plate  I).  Irregular  nucleated  patches,  described  under 
the  name  of  myeloplaxes,  or  giant-cells,  more  abundant  in  the  spongy 
portions  than  in  the  medullary  canals,  are  found  applied  to  the  internal 
surfaces  of  the  bones.  They  vary  in  size  and  form  (measuring  yo^QQ-  to 
gl-Q  of  an  inch,  or  20  to  1 00  fi  in  diameter),  are  finely  granular  and  pre- 
sent two  to  twenty  or  thirty  nuclei.  The  nuclei  are  clear  and  ovoid 
and  usually  contain  a  distinct  nucleolus.  The  myeloplaxes  are  ren- 
dered pale  by  acetic  acid  and  the  nuclei  are  then  brought  distinctly 
into  view.     They  are  especially  abundant  in  the  red  marrow. 

In  addition  to  the  anatomical  elements  just  described,  the  marrow 
contains  a  few  delicate  bundles  of  connective  tissue,  most  of  which 
accompany  the  bloodvessels.  In  the  foetus  the  adipose  vesicles  are  few 
or  may  be  absent ;  but  in  the  adult  they  are  quite  abundant,  and  in 
some  bones  they  seem  to  constitute  the  whole  mass  of  the  marrow. 
They  do  not  differ  materially  from  the  fat-cells  in  other  situations. 
Holding  these  different  structures  together,  is  a  variable  quantity  of 
semitransparent,  amorphous  or  slightly  granular  matter. 

The  nutrient  arteries  of  the  bones  send  branches  to  the  marrow, 
usually  two  in  number  for  the  long  bones,  which  are  distributed  betw-een 
the  various  anatomical  elements  and  finally  surround  the  fatty  lobules 
and  the  fat  vesicles  with  a  delicate  capillary  plexus.  The  veins  cor- 
respond to  the  arteries  in  their  distribution.  The  nerves  follow  the 
arteries  and  are  lost  when  these  vessels  no  longer  present  a  muscular 
coat.  Nothing  is  known  of  the  presence  of  lymphatics  in  any  part 
of  the  bones  or  in  the  periosteum. 

The  chief  physiological  interest  connected  with  the  marrow  of  the 
bones  is  in  its  relations  to  the  formation  of  blood-corpuscles.  This 
question  has  already  been  discussed  in  connection  with  the  development 
of  the  corpuscular  elements  of  the  blood. 

Periosteum.  —  In  most  of  the  bones  the  periosteum  presents  a  single 


432  MOVEMENTS 

layer  of  fibrous  tissue,  but  in  some  of  the  long  bones  two  or  three  layers 
may  be  demonstrated.  This  membrane  adheres  to  the  bone  but  can  be 
separated  without  much  difficulty.  It  covers  the  bones  completely, 
except  at  the  articular  surfaces,  where  its  place  is  supplied  by  carti- 
laginous incrustation.  It  is  composed  mainly  of  ordinary  fibrous  tissue 
with  small  elastic  fibres,  bloodvessels,  nerves  and  a  few  adipose 
vesicles. 

The  arterial  branches  ramifying  in  the  periosteum  are  quite  abun- 
dant, forming  a  close  anastomosing  plexus  which  sends  small  branches 
into  the  bony  substance.  There  is  nothing  peculiar  in  the  arrangement 
of  the  veins.  The  distribution  of  the  veins  in  the  bony  substance  itself 
has  been  very  little  studied. 

The  nerves  of  the  periosteum  are  abundant  and  form  in  its  sub- 
stance quite  a  close  plexus. 

The  adipose  tissue  is  variable  in  quantity.  In  some  parts  it  forms 
a  continuous  sheet,  and  in  others  the  vesicles  are  scattered  here  and 
there  in  the  substance  of  the  membrane. 

The  importance  of  the  periosteum  to  the  nutrition  and  regeneration 
of  the  bones  is  very  great.  Instances  are  on  record  where  bones  have 
been  removed,  leaving  the  periosteum,  and  in  which  the  entire  bone  has 
been  -reproduced.  The  importance  of  the  periosteum  has  been  still 
further  illustrated  by  the  experiments  of  OlHer  and  others,  on  trans- 
plantation of  this  membrane  in  the  different  tissues  of  living  animals, 
which  has  been  followed  by  the  formation  of  bone  in  these  situations. 

Physiological  Anatojny  of  Cartilage.  —  In  this  connection  the  struc- 
ture of  the  articular  cartilages  presents  the  chief  physiological  interest. 
The  articular  surfaces  of  all  the  bones  are  incrusted  with  a  layer  of 
cartilage,  varying  in  thickness  between  ^-^  and  ^^  of  an  inch  (0.5  and 
I  millimeter).  The  cartilaginous  substance  is  white,  opaline  and  semi- 
transparent  when  examined  in  thin  sections.  It  is  not  covered  with 
a  membrane,  but  in  the  non-articular  cartilages  it  has  an  investment 
analogous  to  the  periosteum,  called  perichondrium. 

Examined  in  thin  sections  cartilage  is  found  to  consist  of  a  homo- 
geneous fundamental  substance,  marked  with  excavations  called  carti- 
lage-cavities. The  intervening  substance  has  a  peculiar  organic  con- 
stituent called  chondrin.  The  organic  matter  is  united  with  a  certain 
proportion  of  inorganic  salts.  The  fundamental  substance  is  elastic 
and  resisting.  The  cartilages  are  closely  united  to  the  subjacent  bony 
tissue.  The  free  articular  surface  has  already  been  described  in  con- 
nection with  the  synovial  membranes. 

Cartilage-cavities.  — These  cavities  are  rounded  or  ovoid,  measuring 
i2TTr  ^°  Foo  °^  ^^  moh  (20  to  80  \i)  in  diameter.     They  are  smaller  in 


PASSIVE   ORGANS   OF   LOCOMOTION 


433 


r 


the  articular  cartilages  than  in  other  situations,  as  in  the  costal  carti- 
lages. They  are  simple  excavations  in  the  fundamental  substance, 
having  no  lining  membrane,  and  they  contain  a  small  quantity  of  a 
viscid  liquid  with  one  or  more  cells.  They  are  analogous  to  the  lacunae 
of  the  bones.  , 

Cartilage-cells.  —  Near  the    surface  of    the   articular    cartilages  the 
cavities  contain  each  a  single  cell ;  but  in  the  deeper  portions  the  cavi- 
ties are  long  and  contain  two  to       rrj^je;— -^s     ^  ^ 
twenty    cells    arranged    longitudi-     5^-^="=*    '^'^^  "" 
nally.      The    cells    are    about   the 

size  of  the  smallest  cavities.    They  ^ 

are  ovoid,  with  a  large  granular  ,,  _ 
nucleus.  They  often  contain  a  few 
small  globules  of  oil.  In  the  costal 
cartilages  the  cavities  are  not  abun- 
dant but  are  rounded  and  quite 
large.  The  cells  contain  usually 
a  certain  quantity  of  fatty  matter. 
The  appearance  of  the  ordinary 
articular  cartilage  is  represented 
in  Figure  89, 

The  ordinary  cartilages  have 
neither  bloodvessels,  lymphatics 
nor  nerves,  and  are  nourished  by 
imbibition  from  the  surrounding 
parts.  In  the  development  of  the 
body,  the  anatomy  of  the  cartilagi- 
nous tissue  possesses  peculiar  im- 
portance, from  the  fact  that  the 
deposition  of  cartilage,  with  a  few 
exceptions,  precedes  the  formation 
of  bone  (see  Plate  X,  Fig.  3). 

Elastic  Cartilage. — -This  variety 

of     cartilage     presents     certain     im-    tilage;  4,  4,  cavities  and  cells  of  the  middle  layer; 
.  5,  5,  cavities  and  cells  of  the  superficial  layer. 

portant  peculiarities  in  the  structure 

of  its  fundamental  substance.  It  exists  principally  in  the  cartilages  of 
the  ear  and  of  the  Eustachian  tubes,  the  cartilages  of  Santorini  and  of 
Wrisberg  and  the  epiglottis.  Elastic  cartilage  is  composed  of  fibrous 
tissue  with  a  great  predominance  of  elastic  fibres,  fusiform  nucleated 
fibres,  a  certain  number  of  adipose  vesicles,  cartilage-cells,  bloodvessels 
and  nerves.  The  fibrous  elements  above  mentioned  take  the  place  of  the 
homogeneous  fundamental  substance  of  ordinary  cartilage.     The  most 


Fig.  89. —  Vertical  section  of  diarthrodial  cartilage 
(Sappey). 

I,  I,  osseous  tissue ;  2,  2,  superficial  layer  of 
osseous  tissue  treated  with  hydrochloric  acid ; 
3,  3,  cavities  and  cells  of  the  deep  layer  of  car- 


434  MOV^EMENTS 

important  peculiarity  in  the  structure  of  this  tissue  is  that  it  is  abun- 
dantly supplied  with  bloodvessels  and  nerves  (see  Plate  X,  Fig.  4). 

Fibro-cartilage,  found  in  the  synchondroses,  the  interarticular  disks 
and  the  interv^ertebral  cartilages,  is  composed  of  interlacing  bundles  of 
fibrous  tissue  surrounding  individual  cartilage-cells  or  small  groups  of 
cells.  This  structure  more  nearly  resembles  tendon  than  it  does  true 
cartilage. 

The  reader  is  referred  to  works  on  anatomy  for  a  history  of  the 
action  of  the  muscles.  In  some  works  on  physiology  will  be  found 
descriptions  of  the  acts  of  walking,  running,  leaping,  swimming  etc.  ; 
but  it  has  been  thought  better  to  omit  these  subjects,  rather  than  to 
enter  so  minutely  as  would  be  necessary  into  purely  anatomical  details 
and  to  give  descriptions  of  movements  that  are  simple  and  famihar. 


CHAPTER   XVII 

VOICE   AND    SPEECH 

Physiological  anatomy  of  the   vocal   organs  —  Muscles   of  the   lan-nx  —  Crico-thvroid  muscles 

—  Arytenoid  muscle  —  Lateral  crico-arytenoid  muscles  —  Thyro-arytenoid  muscles  — 
Mechanism  of  the  production  of  the  voice  —  Movements  of  the  glottis  during  phonation 

—  Action  of  the  intrinsic  muscles  of  the  larynx  in  phonation  —  Action  of  accessory  vocal 
organs  —  Laryngeal  mechanism  of  the  vocal  registers  —  Vocal  registers  in  the  male  — 
Vocal  registers  in  the  female  —  Mechanism  of  speech  —  Vowels  —  Consonants  —  The 
phonograph  and  telephone. 

The  principal  organ  concerned  in  the  production  of  the  voice  is  the 
larynx.  The  accessory  organs  are  the  lungs,  trachea,  expiratory  mus- 
cles, the  mouth  and  the  resonant  cavities  about  the  face.  The  lungs 
furnish  the  air  by  which  the  vocal  chords  are  thrown  into  vibration,  and 
the  mechanism  of  this  action  involves  merely  modifications  of  expira- 
tion. By  the  action  of  the  expiratory  muscles  the  intensity  of  vocal 
sounds  is  regulated.  The  trachea  not  only  conducts  the  air  to  the 
larynx,  but  it  may  assist,  by  resonance,  in  modifying  the  quaHty  of  the 
voice.  Most  of  the  variations  in  tone  and  quality,  however,  are  effected 
by  the  action  of  the  larynx  itself  and  of  the  resonant  cavities  situated 
above. 

Physiological  Anatomy  of  the  Vocal  Organs. — The  vocal  chords  are 
stretched  across  the  superior  opening  of  the  larynx  from  before  back- 
ward. They  consist  of  two  pairs.  The  superior,  called  the  false  vocal 
chords,  or  the  ventricular  bands,  are  not  concerned  in  the  production  of 
the  voice.  They  are  less  prominent  than  the  inferior  chords,  although 
they  have  nearly  the  same  direction.  They  are  covered  with  a  thin 
mucous  membrane  that  is  closely  adherent  to  the  subjacent  tissue. 
The  chords  are  composed  of  ordinary  fibrous  tissue  with  a  few  elastic 
fibres. 

The  true  vocal  chords,  or  vocal  bands,  are  situated  just  below  the 
superior  chords.  Their  anterior  attachments  are  near  together,  at  the 
middle  of  the  thyroid  cartilage,  and  are  immovable.  Posteriorly  they 
are  attached  to  the  movable  arytenoid  cartilages  ;  and  by  the  action  of 
certain  muscles  their  tension  may  be  modified  and  the  chink  of  the 
glottis  may  be  opened  or  closed.  These  are  much  larger  than  the  false 
vocal  chords  and  they  contain  a  great  number    of   elastic  fibres.     Like 

435 


436 


VOICE    AND    SPEECH 


the  superior  vocal  chords  they  are  covered  with  a  very  thin  and  closely 
adherent  mucous  membrane.  The  mucous  membrane  over  the  borders 
of  the  chords  is  covered  with  flattened  epithelium  without  cilia.  There 
are  no  mucous  glands  in  the  membrane  covering  either  the  superior  or 

the  inferior  chords.  The  inferior  vocal 
chords  alone  are  directly  concerned  in  the 
production  of  the  voice. 

Muscles  of  the  Lajyux.  —  The  muscles 
of  the  larynx  are  classified  as  extrinsic  and 
intrinsic.  The  extrinsic  muscles  are  at- 
tached to  the  outer  surface  of  the  larynx 
and  to  adjacent  organs,  such  as  the  hyoid 
bone  and  the  sternum.  They  are  con- 
cerned chiefly  in  the  movements  of  eleva- 
tion and  depression  of  the  larynx.  The 
intrinsic  muscles  are  attached  to  the  differ- 
ent parts  of  the  larynx,  and  by  their  action 
on  the  articulating  cartilages  are  capable  of 
modifying  the  tension  of  the  vocal  chords. 
The  vocal  chords  can  be  rendered  tense 
or  lax  by  muscular  action.  Their  fixed 
point  is  in  front,  where  their  extremities, 
attached  to  the  thyroid  cartilage,  are  nearly 
or  quite  in  contact  with  each  other.  The 
arytenoid  cartilages,  to  which  they  are 
attached  posteriorly,  present  a  movable 
articulation  with  the  cricoid  cartilage ;  and 
the  cricoid,  which  is  narrow  in  front,  and 
is  wide  behind,  where  the  arytenoid  carti- 
lages are  attached,  presents  a  movable 
tion  of  the  posterior  portion  of  the    articulation  with  the  thyroid  cartilage.     It 

cricoid  cartilage ;    8,  section  ot  the  an-  -^  *^ 

is  evident,  therefore,  that  muscles  acting 
on   the  cricoid  can   cause  it  to   swing;  on 


Fig.  90. —  Vertical  section  of  the  hu- 
man larynx,  showing'  the  vocal  chords 
(Sappey). 

I,  ventricle  of  the  larynx  ;  2,  superior 
vocal  chord ;  3,  inferior  vocal  chord ; 
4,  arytenoid  cartilage;  5,  section  of 
the  arytenoid  muscle  ;  6,  6,  inferior  por- 
tion of  the  cavity  of  the  larynx;  7,  sec- 


terior  portion  of  the  cricoid  cartilage; 
9,  superior  border  of  the  cricoid  car- 
tilage ;  10,  section  of  the  thyroid  car- 
tilage; II,  II,  superior  portion  of  the    its  two  poiuts  of  articulation  with  the  in- 

cavity  of  the  larvnx;   12,  13,  arytenoid     r      •  r    ^^  .^  ■  ^  •    ■  .1 

gland;  14, 16, epiglottis;  15, 17,  adipose    lerior  cornua  of  the    thyroid,  raismg  the 
tissue;  18,  section  of  the  hyoid  bone;    anterior   portion   and   approximating   it  to 

19,  19,  20,  trachea. 

the  lower  edge  of  the  thyroid  ;  and  as  a 
consequence,  the  posterior  portion,  which  carries  the  arytenoid  carti- 
lages and  the  posterior  attachments  of  the  vocal  chords,  is  depressed. 
This  action  would,  of  course,  increase  the  distance  between  the  aryte- 
noid cartilages  and  the  anterior  portion  of  the  thyroid,  elongate  the  vocal 
chords,  and  subject  them  to  a  certain  degree  of  tension.     Experiments 


MUSCLES    OF    THE    LARYNX 


437 


have  shown  that  such  an  effect  is  produced  by  the  contraction  of  the 
crico-thyroid  muscles. 

The  articulations  of  the  different  parts  of  the  larynx  are  such  that 
the  arytenoid  cartilages  can  be  approximated  to  each  other  posteriorly, 
thus  diminishing  the  interval  between  the  posterior  attachments  of  the 
vocal  chords.  This  action  can  be  effected  by  contraction  of  the  single 
muscle  of  the  larynx  (the  arytenoid)  and  also  by  the  lateral  crico-aryte- 
noids.  The  thyro-arytenoid  muscles,  the  most  complex  of  all  the  in- 
trinsic muscles  in  their  attachments  and  the  direction  of  their  fibres,  are 
important  in  regulating  the  tension  and 
capacity  of  vibration  of  the  vocal  chords. 

The  posterior  crico-arytenoid  mus- 
cles, arising  from  each  lateral  half  of 
the  posterior  surface  of  the  cricoid 
cartilage  and  passing  upward  and  out- 
ward to  be  inserted  into  the  outer  angle 
of  the  inferior  portion  of  the  arytenoid 
cartilages,  rotate  these  cartilages  out- 
ward, separate  them  and  act  as  dilators 
of  the  chink  of  the  glottis.  These  mus- 
cles are  concerned  chiefly  in  the  respir- 
atory movements  of  the  glottis  during 
inspiration. 

The  muscles  mainly  concerned  in  the 
modifications  of  the  voice  by  their  action 
on  the  vocal  chords  are  the  crico- 
thyroids, the  arytenoid,  the  lateral  crico- 
arytenoids and  the  thyro-arytenoids. 
The  following  is  a  sketch  of  their  attach- 
ments and  mode  of  action  :  — 

Crico-thyroid  M?iscles.  —  These  muscles  are  situated  outside  of  the 
larynx,  at  the  anterior  and  lateral  portions  of  the  cricoid  cartilage. 
Each  muscle  is  of  a  triangular  form,  the  base  of  the  triangle  presenting 
posteriorly.  It  arises  from  the  anterior  and  lateral  portions  of  the 
cricoid  cartilage,  and  its  fibres  diverge  to  be  inserted  into  the  inferior 
border  of  the  thyroid  cartilage,  extending  from  the  middle  of  this  border 
posteriorly  as  far  back  as  the  inferior  cornua.  After  dividing  the  ner- 
vous filaments  distributed  to  these  muscles,  a  certain  degree  of  hoarse- 
ness of  the  voice  is  observed,  due  to  relaxation  of  the  vocal  chords ;  and 
by  imitating  their  action  mechanically  the  cricoid  and  thyroid  cartilages 
may  be  approximated  in  front,  carrying  back  the  arytenoid  cartilages  and 
rendering  the  chords  tense. 


Fig.  91.  — Posterior  view  of  the  muscles  of 
the  larynx  (Sappey). 

I,  posterior  crico-arytenoid  muscle  ;  2,  3, 

4,  different  fasciculi  of  the  arytenoid  muscle ; 

5,  aryteno-epiglottidean  muscle. 


438 


VOICE    AND    SPEECH 


Arytenoid  Muscle.  —  This  single  muscle  fills  the  space  between  the 
arytenoid  cartilages  and  is  attached  to  their  posterior  surfaces  and  bor- 
ders. Its  action  is  to  approximate  the  posterior  extremities  of  the  chords 
and  to  constrict  the  glottis,  so  far  as  the  articulations  of  the  arytenoid 
cartilage  with  the  cricoid  will  permit.  This  muscle  is  important  in 
phonation,  as  it  serves  to   fix   the  posterior  attachments  of   the  vocal 

chords  and  to    increase   the    efificiency  of 
certain  other  of  the  intrinsic  muscles. 

Lateral  Crico-aiytoioid  Muscles. — These 
muscles  are  in  the  interior  of  the  larynx. 
They  arise  from  the  sides  and  superior 
borders  of  the  cricoid  cartilage,  pass  up- 
ward and  backward  and  are  attached  to 
the  base  of  the  arytenoid  cartilages.  By 
dividing  all  the  filaments  of  the  recurrent 
laryngeal  nerves  except  those  distributed 
to  these  muscles  and  then  stimulating  the 
nerves,  it  is  shown  that  they  act  to  approxi- 
mate the  vocal  chords  and  constrict  the 
glottis,  particularly  in  its  interligamentous 
portion.  These  muscles,  with  the  aryte- 
noid, act  as  constrictors  of  the  larynx. 

TJiyro-arytenoid  Muscles.  —  These  mus- 
Fig.  ^1.- Lateral  view  of  the  muscles   clcs  are  situatcd  within  the  larynx.     They 
of  the  larynx  {-i^^^iiy) .  are  broad  and  flat  and  arise  in  front  from 

I,  body  of  the  hyoid  bone;  2,  vertical     t^g    upper    part    of    the    Crico-thvroid    mem- 
section  of  the  thvroid  cartilage;  3,  hori-  iirr^ 

zontai  section  of  the  thyroid  cartilage,    brauc  and  the  lower   half   of   the  thyroid 
turned  <ioNvnward  to  show  the  deep   cartilage.     From  this  line  of  origin,  each 

attachment  of  the  cnco-ihyroid  muscle;  *="  .  . 

4,  facet  of  articulation  of  the  small  cornu     muscle    paSSCS    backward    in    tWO    faSCiculi, 

I^SJSr^^Tt^S:.^.  both  being  attached  to  the  anterior  sur- 

tiiage;  6.  superior  attachment  of  the   facc  and  the  outer  borders  of  the  arytenoid 

crico-thyroid  muscle ;  7,  posterior  crico- 
arytenoid muscle  ;  8,  lateral  crico-aryte- 
noid  muscle  ;  9,  thyro-arytenoid  muscle  ; 


10,  arytenoid   muscle;    11,  aryteno-epi- 
glottidean    muscle ;    12,    middle    thyro- 


cartilages.  Stimulation  of  the  nervous 
filaments  distributed  to  these  muscles 
renders  the  vocal  chords  tense.    The  varia- 


hyoid  ligament;   13.  lateral  thyro-hyoid    ^jq^^    ^^^^    ^  ^g    produCcd    in    the    pitch 

ligament.  -^  ^  _  ^ 

and  quality  of  the  voice  by  the  action 
of  muscles  operating  directly  or  indirectly  on  the  vocal  chords  render 
the  problem  of  the  precise  mode  of  action  of  the  intrinsic  muscles 
of  the  larynx  complicated  and  difficult.  It  is  certain,  however,  that 
in  these  muscular  acts,  the  thyro-arytenoids  play  an  important  part. 
Their  contraction  regulates  the  thickness  of  the  chords,  while  at  the 
same  time  it  modifies  their  tension.     The  swelling  of  the  chords,  which 


MOVEMENTS    OF   THE    GLOTTIS    DURING    PRONATION  439 

may  be  rendered  regular  and  progressive  by  voluntary  action,  is  an 
important  element  in  determining  the  timbre  of  the  voice. 

Mechanism  of  the  Production  of  the  Voice.  —  If  the  glottis  is  exam- 
ined with  the  laryngoscope  during  ordinary  respiration,  the  wide  open- 
ing of  the  chink  during  forced  inspiration,  due  to  the  action  of  the 
posterior  crico-arytenoid  muscles,  can  be  observed  without  difficulty.  This 
action  is  effected  by  a  separation  of  the  posterior  points  of  attach- 
ment of  the  vocal  chords  to  the  arytenoid  cartilages.  During  ordinary 
expiration,  none  of  the  intrinsic  muscles  seem  to  act  and  the  larynx  is 
passive,  while  the  air  is  gently  forced  out  by  the  elasticity  of  the  lungs 
and  of  the  thoracic  walls ;  but  so  soon  as  a  vocal  effort  is  made,  the 
appearance  of  the  glottis  undergoes  a  change  and  it  becomes  modified 
in  the  most  varied  manner  with  the  different  modifications  in  pitch  and 
intensity  of  which  the  voice  is  capable.  Although  sounds  may  be  pro- 
duced, and  even  words  may  be  articulated,  with  the  act  of  inspiration, 
true  and  normal  phonation  takes  place  during  expiration  only.  It 
is  evident,  also,  that  the  inferior  vocal  chords  alone  are  concerned  in 
this  act. 

Moveme7tts  of  the  Glottis  during  Phonation.  —  It  is  somewhat  diffi- 
cult to  observe  with  the  laryngoscope  all  the  vocal  phenomena,  on 
account  of  the  epiglottis,  which  hides  a  considerable  portion  of  the 
vocal  chords  anteriorly,  especially  during  the  production  of  certain 
notes ;  but  the  patience  and  skill  of  Garcia  enabled  him  to  overcome 
most  of  these  difficulties,  and  to  settle,  by  autolaryngoscopy,  certain 
important  questions  in  regard  to  the  action  of  the  larynx  in  singing. 
It  is  fortunate  that  these  observations  were  made  by  one  versed  theo- 
retically and  practically  in  music  and  possessed  of  unusual  control  over 
the  vocal  organs.^ 

Garcia,  after  having  observed  the  respiratory  movements  of  the  larynx 
as  they  have  just  been  briefly  described,  noted  that  so  soon  as  any  vocal 
effort  was  made,  the  arytenoid  cartilages  were  approximated,  so  that  the 
glottis  appeared  as  a  narrow  slit  bounded  by  two  chords  of  equal  length, 
firmly  attached  posteriorly  as  well  as  anteriorly.  The  glottis  thus  under- 
goes a  marked  change.  A  nearly  passive  organ,  opening  for  the  pas- 
sage of  air  into  the  lungs  but  inactive  in  expiration,  has  now  become  a 
musical  instrument,  presenting  a  slit  with  borders  capable  of  accurate 
vibrations. 

1  Manoel  Garcia,  a  celebrated  teacher  of  singing  in  London,  is  regarded  as  the  inventor  of 
the  modern  laryngoscope.  He  used  this  instrument  for  the  study  of  the  voice  in  his  own  per- 
son and  presented  a  memoir  —  "Observations  on  the  Human  Voice" — to  the  Royal  Society,  in 
1855.  It  is  only  since  that  date  that  the  laryngoscope  has  been  used  for  medical  and  surgical 
purposes.  Garcia  is  now  living  and  celebrated  his  one-hundredth  birthday  in  London, 
March  17,  1905. 


440 


VOICE    AND    SPEECH 


The  approximation  of  the  posterior  extremities  of  the  vocal  chords 
and  their  tension  by  the  action  of  certain  of  the  intrinsic  muscles  are 
accomplished  just  before  the  vocal  effort  is  actually  made.  The  glottis 
being  thus  prepared  for  the  emission  of  a  particular  sound,  the  expira- 
tory muscles  force  air  through  the  larynx  with  the  required  power.  The 
power  of  the  voice  is  due  to  the  force  of  the  expiratory  act,  which  is 
regulated  chiefly  by  the  antagonistic  relations  of  the  diaphragm  and  the 
abdominal  muscles.  From  the  fact  that  the  diaphragm,  as  an  inspira- 
tory muscle,  is  directly  opposed  to  the  muscles  that  have  a  tendency  to 
push  the  abdominal  organs,  with  the  diaphragm  over  them,  into  the 
thoracic  cavity  and  thus  diminish  the  pulmonary  capacity,  the  expira- 
tory and  inspiratory  acts  may  be  balanced  so  nicely  that  the  most  deli- 
<j^  '  cate  vocal  vibrations  can  be  produced.     The 

glottis,  thus  closed  as  a  preparation  for  a  vocal 
act,  presents  a  certain  resistance  to  the  egress 
of  air.  This  is  overcome  by  the  action  of  the 
expiratory  muscles,  and  with  the  passage  of  air 
through  the  chink,  the  edges  of  the  true  vocal 
chords,  which  bound  the  opening,  are  thrown 
into  vibration.  Many  of  the  different  quali- 
ties that  are  recognized  in  the  human  voice 
are  due  to  differences  in  the  length,  breadth 
and  thickness  of  the  vibrating  bands ;  but 
aside  from  what  is  technically  known  as 
quality,  pitch  is  dependent  on  the  length  of 
the  opening  through  which  the  air  is  made  to 
pass  and  the  degree  of  tension  of  the  chords. 
The  mechanism  of  these  changes  in  the  pitch 
of  vocal  sounds  is  illustrated  by  Garcia  in  the 
following,  which  relates  to  what  is  known  as  the  chest-voice :  — 

"  If  we  emit  veiled  and  feeble  sounds,  the  larynx  opens  at  the  notes 
and  we  see  the  glottis  agitated  by  large  and  loose 
vibrations  throughout  its  entire  extent.     Its  lips  corn- 


Fig.  93.  —  Glottis  seen  with 
the  laryngoscope  during  the  e?nis- 
sion  of  high-pitched  sounds  (Le 
Bon).' 

I,  2,  base  of  the  tongue;  3,  4, 
epiglottis;  5,  6,  pharynx;  7,  aryte- 
noid cartilages;  8,  opening  be- 
tween the  true  vocal  chords ;  9, 
aryteno-epiglottidean  folds;  10, 
cartilage  of  Santorini;  11,  cunei- 
form cartilage  ;  12,  superior  vocal 
chords;   13,  inferior  vocal  chords. 


■JtzB- 


t— r: 


prehended  in  their  length  the  anterior  apophyses  of  the  arytenoid 
cartilages  and  the  vocal  chords ;  but,  I  repeat  it,  there  remains  no  tri- 
angular space. 

"As  the  sounds  ascend,  the  apophyses,  which  are  slightly  rounded 
on  their  internal  side,  by  a  gradual  apposition  commencing  at  the 
back,    encroach    on   the    length    of    the    glottis ;    and   as    soon   as   we 

reach   the  sounds    a they  finish    by   touching  each  other 

whole  extent ;   but  their  summits  are 
one   against  the    other  at  the  notes 


throughout    their 
only  solidly  fixed 


MOVEMENTS    OF   THE    GLOTTIS   DURING   PRONATION 


441 


In   some   organs   these   summits  are  a  little   vacillating 
^.  when  they  form  the  posterior  end  of  the  glottis,  and  two 
tT*"  or  three  half-tones  which  are  formed  show  a  certain  want 

of  purity  and  strength,  which  is  very  well  known  to  singers.     From 
the  vibrations,  having  become  rounder  and  purer,   are 
,  accomplished  by  the  vocal  hgaments  alone,  up  to  the  end 


tf  of  the  register. 

"  The  glottis  at  this  moment  presents  the  aspect  of  a  Hne  swelled 
toward  its  middle,  the  length  of  which  diminishes  still  more  as  the  voice 
ascends.  VVe  shall  also  see  that  the  cavity  of  the  larynx  has  become 
very  small,  and  that  the  superior  ligaments  have  contracted  the  extent 
of  the  ellipse  to  less  than  one-half." 

These  observ^ations  have  been  in  the  main  confirmed  by  Battaille, 
Emma  Seller  and  others  who  have  applied  the  laryngoscope  to  the 
study  of  the  voice  in  singing. 

In  childhood  the  general  characters  of  the  voice  are  essentially  the 
same  in  both  sexes.  The  larynx  is  smaller  than  in  the  adult  and  the 
vocal  muscles  are  more  feeble;  but  the  quality  of  the  vocal  sounds  at 
this  period  of  life  is  peculiarly  penetrating.  While  there  are  certain 
characters  that  distinguish  the  voices  of  boys  before  the  age  of  puberty, 
they  present,  as  in  the  female,  the  different  qualities  of  soprano  and 
contralto.  After  the  age  of  puberty,  the  female  voice  does  not  undergo 
any  very  marked  change,  except  in  the  development  of  additional 
strength  and  extended  compass,  the  quality  remaining  the  same ;  but 
in  the  male  there  is  a  rapid  change  at  this  time  in  the  development  of 
the  larynx,  and  the  voice  assumes  a  different  quality.  This  change 
usually  is  arrested  if  castration  is  performed  in  early  life ;  and  this 
operation  was  frequently  resorted  to  in  the  seventeenth  century  and 
earlier,  for  the  purpose  of  preserving  the  qualities  of  the  male  soprano 
and  contralto,  particularly  for  church-music.  It  is  only  of  late  years, 
indeed,  that  the  practice  of  castration  has  fallen  into  disuse  in  Italy, 

The  extreme  range  of  all  kinds  of  the  human  voice  taken  together 
is  equal  to  nearly  four  octaves  ;  but  it  is  rare  that  any  single  voice  has 
a  compass  of  more  than  two  and  a  half  octaves.  There  are  examples, 
however,  in  which  singers  have  acquired  a  compass  of  three  octaves. 
In  music  the  notes  are  written  the  same  for  the  male  as  for  the  female 
voice,  but  the  value  of  the  female  notes,  as  reckoned  by  the  number 
of  vibrations  in  a  second,  is  an' octave  higher  than  in  the  male. 

In  both  sexes  there  are  differences,  both  in  the  range  and  the  quality 
of  the  voice,  which  it  is  impossible  for  a  cultivated  musical  ear  to  mis- 
take. The  different  voices  in  the  male  are  the  bass,  the  tenor,  and  an 
intermediate  voice  called  the  barytone.     The  female  voices  are  the  con- 


442 


VOICE    AND    SPEECH 


tralto,  the  soprano,  and  the  intermediate,  or  mezzo-soprano.  In  the  bass 
and  barytone,  the  lower  and  middle  notes  are  the  most  natural ;  and 
while  the  higher  notes  may  be  acquired  by  cultivation,  they  do  not 
possess  the  same  quality  as  the  corresponding  notes  of  the  tenor.  The 
same  remarks  apply  to  the  contralto  and  soprano. 

The  following  scale  gives  the  ordinary  ranges  of  the  different  kinds 
of  voice ;  but  it  must  be  remembered  that  there  are  individual  instances 
in  which  these  limits  are  exceeded :  — 


256 


Soprano. 


1024 


171 


Contralto. 


684 


i 


E  r  G  A  B      c  d  e  f  c  a  b  c'  d'  e'  f  g'  a'  b' 


P^S=f 


^ 


80 


c"  d"  e"  f"  g"  a"  b"  c' 


Bass. 


342 


128 


Tenor. 


512 


The  accompanying  figures  indicate  the  number  of  vibrations  per  second  in  the  corresponding  tone. 
It  is  evident  that  from  c'  to  /'  is  common  to  all  voices;  nevertheless,  they  have  a  different  timbre. 
The  lowest  note  or  tone,  which,  however,  is  only  occasionally  sung  by  bass  singers,  is  the  contra-F, 
with  42  vibrations;  the  highest  note  of  the  soprano  voice  is  a'",  with  1708  vibrations  (Landois  and 
Stirling). 


There  is  really  no  great  difference  in  the  mechanism  of  the  different 
kinds  of  voice,  and  the  variations  in  pitch  are  due  chiefly  to  the  greater 
length  of  the  vocal  chords  in  the  low-pitched  voices  and  to  their  short- 
ness in  the  higher  voices.  The  differences  in  quahty  are  due  to  pecu- 
liarities in  the  conformation  of  the  larynx,  to  differences  in  its  size  and 
to  variations  in  the  size  and  form  of  the  auxiHary  resonant  cavities. 
Great  changes  in  the  quality  of  the  voice  may  be  effected  by  practice. 
A  cultivated  note,  for  example,  has  a  different  sound  from  a  harsh, 
irregular  vibration ;  and  by  practice,  a  tenor  may  imitate  the  quality  of 
the  base,  and  vice  versa,  although  the  effort  is  unnatural.  It  is  not 
unusual  to  hear  male  singers  imitate  closely  the  notes  of  the  female ; 
and  the  contralto  sometimes  can  imitate  the  voice  of  the  tenor  in  a 
surprisingly  natural  manner. 

The  wave-length  of  the  ordinary  speaking  voice  in  the  male  is  eight 
to  twelve  feet.  In  the  speaking  voice  of  the  female  and  in  children,  it 
is  two  to  four  feet. 

Action  of  tile  Intrinsic  Muscles  of  the  Larynx  in  PJionation.  —  In  the 
production  of  low  chest-notes,  in  which  the  vocal  chords  are  elongated 
and  are  at  the  minimum  of  tension  that  will  allow  of  regular  vibrations. 


ACTION    OF   ACCESSORY   VOCAL   ORGANS  443 

the  crico-thyroid  muscles  are  brought  into  action,  and  these  are  assisted 
by  the  arytenoid  and  the  lateral  crico-arytenoids,  which  combine  to  fix 
the  posterior  attachments  of  the  vibrating  ligaments.  It  will  be 
remembered  that  the  crico-thyroids,  by  approximating  the  cricoid  and 
thyroid  cartilages  in  front,  increase  the  distance  between  the  arytenoid 
cartilages  and  the  anterior  attachment  of  the  vocal  chords. 

As  the  notes  produced  by  the  larynx  become  higher  in  pitch,  the 
posterior  attachments  of  the  chords  are  approximated,  and  at  this  time 
the  lateral  crico-arytenoids  probably  are  brought  into  vigorous  action. 

The  uses  of  the  thyro-arytenoids  are  more  complex ;  and  it  is 
probably  in  great  part  by  the  action  of  these  muscles  that  the  varied 
and  delicate  modifications  in  the  rigidity  of  the  vocal  chords  are 
produced. 

The  differences  in  singers  as  regards  the  purity  of  their  notes  and 
intonation  are  due  in  part  to  the  accuracy  with  which  some  put  the 
vocal  chords  on  the  stretch ;  while  in  those  in  whom  the  voice  is  of 
inferior  quality,  the  action  of  the  muscles  is  more  or  less  vacillating  and 
the  tension  frequently  is  incorrect.  The  fact  that  some  singers  can 
make  the  voice  heard  above  the  combined  sounds  from  a  large  chorus 
and  orchestra  is  not  due  entirely  to  the  intensity  of  the  sound,  but  in 
great  measure  to  the  mathematical  equality  of  the  sonorous  vibrations 
and  the  comparative  absence  of  discordant  waves. ^ 

Actiojt  of  Accessoiy  Vocal  Organs.  —  A  correct  use  of  the  accessory 
organs  of  the  voice  is  of  great  importance  in  singing ;  but  the  action  of 
these  parts  is  simple  and  does  not  require  an  extended  description.  The 
human  vocal  organs,  indeed,  consist  of  a  vibrating  instrument,  the  larynx, 
and  of  certain  tubes  and  cavities  by  which  the  sound  is  reenforced  and 
modified. 

The  trachea  serves,  not  only  to  conduct  air  to  the  larynx,  but  to 
reenforce  the  sound  to  a  certain  extent  by  the  vibrations  of  the  column 
of  air  in  its  interior.  When  a  powerful  vocal  effort  is  made,  it  is  easy 
to  feel,  with  the  finger  on  the  trachea,  that  the  contained  air  is  thrown 
into  vibration. 

The  capacity  of  the  cavity  of  the  larynx  is  capable  of  certain  varia- 
tions. In  fact,  both  the  vertical  and  the  bilateral  diameters  are  dimin- 
ished in  high  notes  and  are  increased  in  low  notes.  The  vertical 
diameter  may  be  modified  slightly  by  ascent  and  descent  of  the  true 
vocal  chords,  and  the  lateral  diameter  may  be  reduced  by  the  action  of 
the  inferior  constrictors  of  the  pharynx  on  the  sides  of  the  thyroid 
cartilage. 

^  The  characters  of  musical  sounds,  both  vocal  and  instrumental,  will  be  considered  in  con- 
nection with  the  physiology  of  audition. 


444  VOICE    AND    SPEECH 

The  epiglottis,  the  superior  vocal  chords  and  the  ventricles  are  by 
no  means  indispensable  to, the  production  of  vocal  sounds.  In  the 
emission  of  high  notes  the  epiglottis  is  somewhat  depressed,  and  the  su- 
perior chords  are  brought  nearer  together;  but  this  affects  only  the 
form  of  the  resonant  cavity  above  the  glottis.  In  low  notes  the  superior 
chords  are  separated.  It  was  before  the  use  of  the  laryngoscope  in  the 
study  of  vocal  phenomena  that  the  epiglottis  and  the  ventricles  were 
thought  to  be  so  important  in  phonation.  Undoubtedly  the  epiglottis 
has  something  to  do  with  the  character  of  the  voice ;  but  its  action  is 
not  absolutely  necessary  or  even  important,  as  has  been  shown  in 
experiments  of  excising  the  part  in  living  animals. 

The  most  important  modifications  of  the  laryngeal  sounds  are  pro- 
duced by  the  resonance  of  air  in  the  pharynx,  mouth  and  nasal  fossae. 
This  resonance  is  indispensable  to  the  production  of  the  natural  voice. 
Under  ordinary  conditions,  in  the  production  of  low  notes  the  velum 
palati  is  fixed  by  the  action  of  its  muscular  fibres,  so  that  there  is  a 
reverberation  of  the  bucco-pharyngeal  and  naso-pharyngeal  cavities ; 
that  is,  the  velum  is  in  such  a  position  that  neither  the  opening  into 
the  nose  nor  the  opening  into  the  mouth  is  closed,  and  all  the  cavities 
resound.  As  the  notes  are  raised  in  pitch,  the  isthmus  contracts,  the 
part  immediately  above  the  glottis  also  is  constricted,  the  resonant 
cavity  of  the  pharynx  and  mouth  is  reduced  in  size,  until  finally,  in  the 
highest  notes  of  the  chest-register,  the  communication  between  the 
pharynx  and  the  nasal  fossae  is  closed  and  the  sound  is  reenforced 
entirely  by  the  pharynx  and  mouth.  At  the  same  time  the  tongue  —  a 
very  important  organ  to  singers,  particularly  in  the  production  of  high 
notes  —  is  drawn  backward.  The  point  being  curved  downward,  its 
base  projects  upward  posteriorly  and  assists  in  diminishing  the  capacity 
of  the  bucco-pharyngeal  cavity.  In  the  changes  which  the  pharynx 
thus  undergoes  in  the  production  of  different  notes,  the  uvula  acts  with 
the  velum  and  assists  in  the  closure  of  the  different  openings.  In  sing- 
ing up  the  scale,  this  is  the  mechanism,  as  far  as  the  chest-notes  extend. 
When,  however,  a  singer  changes  into  what  is  sometimes  called  the 
head-voice  (falsetto),  the  velum  palati  is  drawn  forward  instead  of  back- 
ward, and  the  resonance  takes  place  chiefly  in  the  naso-pharyngeal 
cavity. 

Laryngeal  MecJianism  of  the  Vocal  Registers.  —  One  difficulty,  at 
the  very  beginning  of  a  discussion  of  this  subject,  is  in  fixing  on  clear 
definitions  of  what  are  to  be  recognized  as  vocal  registers.  In  the  first 
place  it  must  be  understood  that  the  singing  voice  is  different  from  the 
speaking  voice.  Without  being  actually  so  far  discordant  as  to  offend 
a  musical  ear,  the   ordinary  voice  in  speaking  seldom  has  what  may 


VOCAL    REGISTERS  445 

be  called  strictly  a  musical  quality,  while  the  perfect  singing  voice  pro- 
duces true  musical  notes.  This  probably  is  due  to  the  fact  that  the 
inflections  of  the  voice  in  speaking  are  not  in  the  form  of  distinct  musi- 
cal intervals,  that  the  vibrations  follow  each  other  and  are  superimposed 
in  an  irregular  manner,  and  that  no  special  effort  is  made  to  put  the 
vocal  chords  on  any  definite  tension,  unless  to  meet  a  more  powerful 
expiratory  effort  when  the  voice  is  increased  in  force.  A  shout  or  a 
scream  is  not  a  singing  note.  This  difference  is  at  once  apparent  in  con- 
trasting recitative  with  ordinary  dialogue  in  operatic  performances. 

The  divisions  of  the  voice  into  registers,  made  by  physiologists,  are 
sometimes  based  on  theories  in  regard  to  the  manner  of  their  produc- 
tion ;  and  if  these  theories  are  not  correct,  the  division  into  registers 
must  be  equally  fault}'.  Again,  there  are  such  marked  differences 
betw^een  male  and  female  voices,  that  it  does  not  seem  possible  to  apply 
the  same  divisions  to  both  sexes.  There  is  no  difficulty,  however,  in 
recognizing  the  qualities  of  voices  called  bass,  barytone  and  tenor,  in  the 
male,  or  contralto,  mezzo  and  soprano,  in  the  female.  A  division  of  the 
voice  into  registers  should  be  one  easily  recognizable  by  singers  and  sing- 
ing teachers ;  and  this  must  be  different  for  male  and  for  female  voices. 
If  a  division  could  be  made  such  as  would  be  readily  recognized  by  the 
ear,  irrespective  of  theories,  it  would  remain  only  to  ascertain  as  nearly 
as  possible  the  exact  vocal  mechanism  of  each  register.  It  must  be 
remembered  that  the  voice  of  a  perfect  singer  shows  no  recognizable 
break,  or  line  of  division  between  the  vocal  registers,  except  when  a 
difference  is  made  apparent  in  order  to  produce  certain  legitimate 
musical  effects.  One  great  end  sought  to  be  attained  in  training  the 
voice  in  singing  is  to  make  the  voice  as  nearly  as  possible  uniform 
throughout  the  extent  of  its  range ;  and  this  has  been  measurably 
accomplished  in  certain  singers. 

Judging  of  different  registers  entirely  by  the  effect  produced  on  the 
ear,  both  by  cultivated  and  uncultivated  singers,  the  following  seem  to 
be  the  natural  divisions  of  the  male  voice  :  — 

1.  The  chest-register.  This  is  the  register  commonly  used  in 
speaking.  Though  usually  called  the  chest-voice,  it  has,  of  course,  no 
connection  with  any  special  action  of  the  chest,  except,  perhaps,  with 
reverberation  of  air  in  the  trachea  and  the  larger  bronchial  tubes. 
This  register  is  sensibly  the  same  in  the  male  and  in  the  female. 

2.  The  head-register.  In  cultivated  male  voices,  a  quality  is  often 
produced,  probably  by  diminished  power  of  the  voice,  with  some  modifi- 
cation in  the  form  and  capacity  of  the  resonant  cavities,  that  is  recog- 
nized as  a  "head-voice"  by  those  who  do  not  regard  the  head-register 
as  equivalent  to  the  falsetto. 


446  VOICE   AND    SPEECH 

3.  The  falsetto-register.  By  the  use  of  this  register  the  male  may 
imitate  the  voice  of  the  female.  Its  quality  is  different  from  that  of 
the  chest-voice,  and  the  transition  from  the  chest  to  falsetto  usually  is 
abrupt  and  quite  marked.  It  may  be  called  an  unnatural  voice  in  the 
male ;  still,  by  careful  cultivation,  the  transition  may  be  made  almost 
imperceptibly.  The  falsetto  never  has  the  power  and  resonance  of 
the  full  chest-voice.  It  resembles  the  head-voice,  but  every  good  singer 
can  recognize  the  fact  that  he  employs  a  different  mechanism  in  its 
production. 

Applying  an  analogous  method  of  analysis  to  the  female  voice,  the 
natural  registers  seem  to  be  the  following  :  — 

I.  The  chest-register.  This  register  is  the 
same  in  the  female  as  in  the  male. 

■2.  The  lower  medium  register,  usually  called 
the  medium.  This  is  the  register  commonly 
used  by  females  in  speaking. 

3.    The    upper    medium    register.      This    is 
sometimes    called     the     head-register     and    is 
V\^.<)i,.— Appearance  of  the  thought  by  somc  to  bc   produccd  by  precisely 
vocal  chords  in  the  production  of  |.j^g  g^^g  mcchauism  as  the  falsctto-rcgistcr  in 

the  chest-voice  (Mandl).  " 

the  male.     It  has,  however,  a  vibrant  quality,  is 
full  and  powerful  and  is  not  an  unnatural  voice  like  the  male  falsetto. 

4.  The  true  head-register.  This  is  the  pure  tone,  without  much 
vibrant  quality,  that   seems  analogous  to  the  male  falsetto. 

Vocal  Registers  in  the  Male.  —  According  to  the  division  and  defi- 
nitions just  given  of  the  vocal  registers,  in  the  male  voice  there  is  but 
one  natural  register,  extending  from  the  lowest  note  of  the  bass  to  the 
falsetto,  and  this  is  the  chest-register.  In  the  low  notes,  the  vocal 
chords  vibrate  and  the  arytenoid  cartilages  participate  in  this  vibration 
to  a  greater  or  less  extent.  In  the  low  notes,  also,  the  larynx  is  open ; 
that  is,  the  arytenoid  cartilages  do  not  touch  each  other.  As  the  notes 
are  raised  in  pitch,  the  arytenoid  cartilages  are  approximated  more  and 
more  closely,  and  they  touch  each  other  in  the  highest  notes,  the  vocal 
chords  alone  vibrating.  It  is  probable  that  the  degree  of  approximation 
of  the  arytenoid  cartilages  is  different  in  different  singers  and  that  the 
part  of  the  musical  scale  at  which  they  actually  touch  is  not  invariable. 

What  has  been  called,  in  this  classification,  the  head-register  of  the 
male,  is  not  a  full  round  voice,  but  the  notes  are  more  or  less  sotto  voce. 
This  peculiar  quality  of  voice  does  not  seem  to  have  been  made  the 
subject  of  laryngoscopic  investigation.  It  has  a  vibrant  character,  that 
is  modified  by  peculiar  action  of  the  resonant  cavities,  which  latter  has 
not  been  described.     It  is  not  probable  that  its  mechanism  differs  essen- 


VOCAL   REGISTERS 


447 


tially,  as  regards  th-e  action  of  the  glottis,  from  that  of  the  full  chest- 
register,  shown  in  Fig.  94. 

The  falsetto-register  in  the  male  undoubtedly  involves  such  a  division 
of  the  length  of  the  vocal  chords  that  only  a  portion  is  thrown  into 
vibration.  There  is  always  an  approximation  of  the  chords  in  their 
posterior  portion,  and  sometimes  also  in  their  anterior  portion.  This 
is  illustrated  in  Fig.  95. 

The  mechanism  by  which  the  vocal  chords  are  approximated  in  por- 
tions of  their  length  has  not  been  satisfactorily  explained ;  but  laryngo- 
scopic  examinations  leave  no  doubt  of  the  fact  of  such  action.  The 
extent  of  this  shortening  of  the  chords  must  vary  in  different  persons 
and  in  the  same  person,  probably,  in  the  production  of  falsetto-notes  of 
different  pitch.     According  to  Mrs.  Seller,  the  shortening  is  due  to  the 


Fig.  95.  —  Appearances  of  the  vocal  chords  in  the  production  of  the  falsetto-voice  (Mills). 

I,  the  larynx  during  falsetto-production;  after  Mandl.  II,  the  larynx  during  the  emission  of  falsetto- 
tones  ;  middle  range  ;  after  Holmes.  Ill,  the  larynx  of  the  female  during  the  production  of  head-tones, 
as  seen  by  the  author  (Mills). 


action  of  a  muscular  bundle,  called  the  internal  thyro-arytenoid,  on  little 
cartilages  extending  forward  from  the  arytenoid  cartilage  in  the  substance 
of  the  vocal  chords  as  far  as  the  middle  of  the  glottis ;  but  careful 
dissections  have  failed  to  confirm  this  view. 

Some  singers,  especially  tenors,  have  been  able  by  long  practice 
to  pass  from  the  chest  to  the  falsetto  so  skilfully  that  the  transition 
is  scarcely  apparent ;  but  the  falsetto  is  wanting  in  what  is  called  vibrant 
quality. 

Vocal  Registers  in  the  Female.  —  There  is  no  difference  between  the 
vocal  mechanism  of  the  chest-voice  in  the  sexes.  In  the  best  methods 
of  teaching  singing,  one  important  object  is  to  smooth  the  transition 
from  the  chest-voice  to  the  lower  medium.  The  full  chest-notes,  espe- 
cially in  contraltos,  closely  resemble  the  corresponding  notes  of  the 
tenor. 


448  VOICE    AND    SPEECH 

The  mechanism  of  the  lower  medium  and  upper  medium  in  females 
does  not  radically  differ  from  the  mechanism  of  the  chest-voice.  In 
these  registers  the  arytenoid  cartilages  become  more  and  more  closely 
approximated  to  each  other  as  the  voice  ascends  in  the  scale  until,  in 
the  higher  notes,  they  probably  are  firmly  in  apposition.  It  is  probable 
that  the  vocal  chords  alone  vibrate  in  the  lower  and  upper  medium, 
while  the  apophyses  of  the  arytenoid  cartilages  participate  in  the 
vibrations  in  the  female  chest-voice. 

The  vocal  chords  are  much  shorter  in  the  female  than  in  the  male. 
The  average  length  in  the  male  is  about  |  of  an  inch  (22  millimeters) 
and  in  the  female,  about  |  of  an  inch  (17  millimeters).  If  the  chords 
alone  vibrate,  without  the  apophyses  of  the  arytenoid  cartilages,  the 
difference  in  length  would  account  for  the  differences  in  pitch  of  the 
voice  in  the  sexes.  The  tenor  can  not  sing  above  the  chest-range  of 
the  female  voice  without  passing  into  the  falsetto,  to  produce  which 
he  must  actually  shorten  his  vocal  chords  so  that  they  are  as  short  or 
shorter  than  the  vocal  chords  of  the  female.  This  is  shown  by  the 
scale  of  range  of  the  different  voices  compared  with  the  length  of  the 
vocal  chords ;  and  this  idea  is  sustained  still  further  by  a  comparison 
of  "the  larynx  during  falsetto  production"  (Fig.  95).  In  the  male 
falsetto,  produced  by  this  shortening  of  the  vocal  chords,  the  more 
nearly  the  resonant  cavities  are  made  to  resemble,  in  form  and  capacity, 
the  corresponding  cavities  in  the  female,  the  more  closely  will  the  quality 
of  the  female  voice  be  imitated.  It  is  probable  that  the  vocal  bands  in 
the  female  present  a  thinner  and  narrower  vibrating  edge  than  the 
chords  in  the  male,  although  there  are  no  exact  anatomical  observations 
on  this  point.  This,  however,  would  account  for  the  clear  quality  of  the 
upper  registers  of  the  female  voice  as  compared  with  the  male  voice  or 
with  the  female  chest-register.  Analogous  differences  exist  in  reed- 
instruments,  such  as  the  clarinet  and  the  bassoon.  This  comparison 
of  the  female  upper  registers  with  the  male  falsetto  does  not  necessarily 
imply  a  similarity  in  the  mechanism  of  their  production,  as  is  assumed 
by  some  writers.  In  the  female  lower  and  upper  medium  registers, 
the  vocal  chords  vibrate  in  their  entire  length  ;  in  the  male  falsetto, 
the  chords  are  shortened  so  that  they  are  approximated  in  length  to  the 
length  of  the  chords  in  the  female. 

To  reduce  to  brief  statements  the  views  just  expressed,  based  partly 
on  laryngoscopic  examinations  —  that  are  far  from  complete  —  by  a 
number  of  competent  observers,  the  following  may  be  given  as  the 
mechanism  of  the  vocal  registers  in  the  female,  taking  no  account 
of  the  changes  in  form  and  capacity  of  the  resonant  cavities :  — 

I.    The    chest-voice    is    produced  by  "large  and  loose  vibrations" 


VOCAL    REGISTERS  449 

(Garcia)  of  the  entire  length  of  the  vocal  chords,  in  which  the  apophyses 
of  the  arytenoid  cartilages  participate  to  a  greater  or  less  extent,  these 
cartilages  not  being  in  close  apposition. 

2.  In  passing  to  the  lower  medium,  the  arytenoid  cartilages  probably 
are  not  closely  approximated,  but  they  do  not  vibrate,  the  vocal  chords 
alone  acting. 

3.  In  passing  to  the  upper  medium,  the  arytenoid  cartilages  probably 
are  closely  approximated,  and  the  vocal  chords  alone  vibrate,  but  they 
vibrate  in  their  entire  length. 

4.  The  head-register  —  which  may  be  called  the  female  falsetto  — 
bears  the  same  relation  to  the  lower  registers  in  both  sexes.  The  notes 
are  clear  but  deficient  in  vibrant  quality.  They  are  higher  in  the  female 
than  in  the  male  because  the  vocal  chords  are  shorter.  Laryngoscopic 
observations  demonstrating  this  fact  in  the  female  are  as  accurate  and 
definite  as  in  the  male  (see  Fig.  95). 

The  reasons  why  the  range  of  the  different  vocal  registers  is  limited 
are  the  following :  Within  the  limits  of  each  register,  the  tension  of  the 
vocal  chords  has  an  exact  relation  to  the  pitch  of  the  sound  produced. 
This  tension  is  of  course  restricted  by  the  limits  of  power  of  the  muscles 
acting  on  the  vocal  chords,  for  high  notes,  and  by  the  limit  of  possible 
regular  vibration  of  chords  of  a  certain  length,  for  low  notes.  The 
higher  the  tension  and  the  greater  the  rigidity  of  the  chords,  the  greater 
is  the  expiratory  force  required  to  throw  them  into  vibration;  and  this, 
also,  has  certain  limits.  It  is  not  desirable  to  push  the  lower  registers 
in  female  voices  to  their  utmost  limits.  All  competent  singing  teachers 
recognize  this  fact.  The  female  chest-register  may  be  made  to  meet  the 
upper  medium,  especially  in  contraltos ;  but  the  singer  then  has  practi- 
cally two  voices,  a  condition  often  existing  but  musically  intolerable.  In 
blending  the  different  registers  so  as  to  make  a  perfectly  uniform  single 
voice,  the  arytenoid  vibrations  should  be  rendered  progressively  and 
evenly  less  and  less  prominent,  until  they  imperceptibly  cease  when  the 
lower  medium  is  fully  reached;  the  arytenoid  cartilages  should  then  be 
progressively  and  evenly  approximated  to  each  other,  until  they  are  firmly 
in  contact  and  the  upper  medium  is  fully  reached.  The  female  vocal 
apparatus  is  then  perfect.  While  single  notes  of  the  chest-voice,  lower 
medium  and  upper  medium,  contrasted  with  each  other,  have  different 
qualities,  the  voice  is  even  throughout  its  entire  range  ;  and  the  proper 
shading  called  for  in  musical  compositions  can  be  made  in  any  part  of 
the  scale.  The  blending  of  the  male  chest-register  into  the  falsetto  and 
of  the  upper  medium  into  the  female  falsetto,  or  true  head-voice,  is  more 
difficult,  but  it  is  not  impossible.  Theoretically  this  must  be  done 
by  shortening  the   vocal   chords   gradually   and  progressively   and  not 


450  VOICE    AND    SPEECH 

abruptly,  unless  the  latter  method  be  required  to  produce  a  legitimate 
effect  of  contrast. 

Even  in  singing  identical  notes,  there  are  distinctly-recognizable  dif- 
ferences in  quality  between  the  bass,  barytone  and  tenor,  and  between 
the  contralto,  mezzo  and  soprano.  For  the  female  these  may  be  com- 
pared to  the  differences  in  identical  notes  played  on  different  strings  of 
the  violin.  For  the  male,  they  may  be  compared  to  the  qualities  of  the 
different  strings  of  the  cello.  Falsetto-notes  may  be  compared  to  har- 
monics produced  on  these  instruments. 

These  ideas  in  regard  to  the  mechanism  of  the  different  vocal  reg- 
isters have  resulted  from  a  study  of  these  registers,  first  from  an  aesthetic 
point  of  view ;  and  endeavoring  then  to  find  explanations  of  different 
qualities  of  sound  appreciated  by  the  ear,  in  laryngoscopic  and  other 
scientific  observations ;  not  by  reasoning  from  scientific  observations 
as  to  what  effects  on  the  ear  should  be  produced  by  certain  acts  per- 
formed by  the  vocal  organs.  It  may  be  stated,  in  this  connection,  that 
the  works  of  Bach,  Beethoven  and  other  old  masters  were  composed 
exactly  in  accordance  with  purely  physical  laws,  long  before  these  laws 
were  ascertained  and  defined,  as  has  been  done  by  Helmholtz  and 
others. 

Mechanism  of  Speech 

Articulate  language  consists  of  a  conventional  series  of  sounds  made 
for  the  purpose  of  conveying  certain  ideas.  There  being  no  universal 
language,  it  will  be  necessary  to  confine  the  description  of  speech  to  the 
language  in  which  this  work  is  written.  Language,  as  it  is  naturally 
acquired,  is  purely  imitative  and  does  not  involve  of  necessity  the  con- 
struction of  an  alphabet  with  its  combinations  into  syllables,  words  and 
sentences ;  but  as  civilization  has  advanced,  certain  differences  in  the 
accuracy  and  elegance  with  which  ideas  are  expressed  have  become 
associated  with  the  degree  of  development  and  cultivation  of  intellectual 
faculties.  Philologists  have  long  since  established  a  certain  standard  — 
varying,  to  some  extent,  with  usage  and  the  advance  of  knowledge,  but 
still  sufficiently  definite  —  by  which  the  correctness  of  modes  of  expres- 
sion is  measured.  It  is  not  proposed  to  discuss  the  science  of  language, 
or  to  consider,  in  this  connection  at  least,  the  peculiar  mental  operations 
concerned  in  the  expression  of  ideas,  but  to  take  the  language  as  it  exists 
and  to  describe  briefly  the  mechanism  of  the  production  of  the  most 
important  articulate  sounds. 

Almost  every  language  is  imperfect,  so  far  as  an  exact  correspond- 
ence between  its  sounds  and  written  characters  is  concerned.  The  Eng- 
lish language  is  full  of  incongruities  in  spelling,  such  as  silent  letters  and 


MECHANISM    OF    SPEECH  45 1 

arbitrary  and  unmeaning  variations  in  pronunciation ;  but  these  do  not 
belong  to  the  subject  of  physiology.  There  are,  however,  certain  natu- 
ral divisions  of  sounds  as  expressed  by  the  letters  of  the  alphabet. 

Vozvels.  —  Certain  articulate  sounds  are  called  vowel,  or  vocal,  from 
the  fact  that  they  are  produced  by  the  vocal  chords  and  are  but  slightly 
modified  as  they  pass  out  of  the  mouth.  The  true  vowels,  a,  e,  i,  o,  u, 
can  all  be  sounded  alone  and  may  be  prolonged  in  expiration.  These 
are  the  sounds  chiefly  employed  in  singing.  The  differences  in  their 
characters  are  produced  by  changes  in  the  position  of  the  tongue,  mouth 
and  lips.  The  vowel-sounds  are  necessary  to  the  formation  of  a  syllable  ; 
and  although  they  usually  are  modified  in  speech  by  consonants,  each 
one  may  of  itself  form  a  syllable  or  a  word.  In  the  construction  of 
syllables  and  words,  the  vowels  have  many  different  qualities,  the  chief 
differences  being  as  they  are  made  long  or  short.  In  addition  to  the 
modifications  in  vowel-sounds  by  consonants,  two  or  three  may  be  com- 
bined so  as  to  be  pronounced  in  a  single  vocal  effort,  when  they  are 
called  respectively,  diphthongs  and  triphthongs.  In  the  proper  diph- 
thongs, as  oi,  in  voice,  the  two  vowels  are  sounded.  In  the  improper 
diphthongs,  as  ea,  in  heat,  and  in  the  Latin  diphthongs,  as  ce,  in  Caesar, 
one  of  the  vowels  is  silent.  In  triphthongs,  as  eau,  in  beauty,  only  one 
vowel  is  sounded.  Y,  at  the  beginning  of  words,  usually  is  pronounced 
as  a  consonant;  but  in  other  positions  it  is  pronounced  as  e  or  i. 

An  important  question  relates  to  the  differences  in  the  quality  of  the 
different  vowel-sounds  when  pronounced  with  equal  pitch  and  intensity. 
The  cause  of  these  differences  was  studied  very  closely  in  the  latter  part 
of  the  last  century,  but  it  has  lately  been  rendered  clear  by  the  re- 
searches of  Helmholtz  and  of  Koenig.  In  this  connection  it  will  be 
sufficient  to  indicate  the  results  of  the  modern  investigations  very  briefly. 
It  will  be  seen  in  studying  the  physics  of  sound  in  connection  with  the 
sense  of  hearing,  that  nearly  all  sounds,  even  when  produced  by  a  single 
vibrating  body,  are  compound.  Helmholtz,  by  means  of  his  resonators, 
has  succeeded  in  analyzing  the  apparently  simple  sounds  into  different 
component  parts  and  has  shown  that  the  quality  of  such  sounds  may  be 
modified  by  reenforcing  certain  of  the  overtones,  as  they  are  called,  such 
as  the  third,  fifth  or  octave.  For  those  who  are  familiar  with  the  physics 
of  sound,  the  explanation  of  the  mechanism  of  the  production  of  vowel- 
sounds  is  readily  comprehensible.  The  reader  is  referred,  however,  to 
the  remarks  on  overtones  in  another  part  of  this  work,  under  the  head 
of  audition,  for  a  more  thorough  exposition  of  this  subject.  The  differ- 
ent vowel-sounds  may  be  emitted  with  the  same  pitch  and  intensity,  but 
the  sound  in  each  is  different  on  account  of  variations  in  the  resonant 
cavities  of  the  accessory  vocal  organs,  especially  the  mouth.     It  has 


452  VOICE   AND    SPEECH 

been  ascertained  experimentally  that  the  overtones  in  each  instance  are 
different  as  they  are  reenforced  by  the  vibrations  of  air  in  the  accessory 
vocal  organs,  in  some  instances  the  third,  in  others,  the  fifth  etc.,  being 
increased  in  intensity.  This  can  hardly  be  better  illustrated  than  by 
the  following  quotation  from  Tyndall,  in  which  modern  researches  have 
been  applied  to  the  vowel-sounds  of  the  English  language  :  — 

"  For  the  production  of  the  sound  U  {oo  in  hoop),  I  must  push  my 
lips  forward  so  as  to  make  the  cavity  of  the  mouth  as  deep  as  possible, 
at  the  same  time  making  the  orifice  of  the  mouth  small.  This  arrange- 
ment corresponds  to  the  deepest  resonance  of  which  the  mouth  is 
capable.  The  fundamental  tone  of  the  vocal  chords  is  here  reenforced, 
while  the  higher  tones  are  thrown  into  the  shade.  The  ^is  rendered  a 
little  more  perfect  when  a  feeble  third  tone  is  added  to  the  fundamental. 

"  The  vowel  O  is  pronounced  when  the  mouth  is  so  far  opened  that 
the  fundamental  tone  is  accompanied  by  its  strong  higher  octave.  A 
very  feeble  accompaniment  of  the  third  and  fourth  is  advantageous,  but 
not  necessary. 

"  The  vowel  A  derives  its  character  from  the  third  tone,  to  strengthen 
which  by  resonance  the  orifice  of  the  mouth  must  be  wider,  and  the  vol- 
ume of  air  within  it  smaller  than  in  the  last  instance.  The  second  tone 
ought  to  be  added  in  moderate  strength,  whilst  weak  fourth  and  fifth 
tones  may  also  be  included  with  advantage. 

"  To  produce  E  the  fundamental  tone  must  be  weak,  the  second  tone 
comparatively  strong,  the  third  very  feeble,  but  the  fourth,  which  is 
characteristic  of  this  vowel,  must  be  intense.  A  moderate  fifth  tone  may 
be  added.  No  essential  change,  however,  occurs  in  the  character  of  the 
sound  when  the  third  and  fifth  tones  are  omitted.  In  order  to  exalt 
the  higher  tones  which  characterize  the  vowel-sound  E,  the  resonant 
cavity  of  the  mouth  must  be  small. 

"  In  the  production  of  the  sound  a/i  !  the  higher  overtones  come 
principally  into  play ;  the  second  tone  may  be  entirely  neglected ;  the 
third  rendered  very  feebly ;  the  higher  tones,  particularly  the  fifth  and 
seventh,  being  added  strongly. 

"  These  examples  sufficiently  illustrate  the  subject  of  vowel-sounds. 
We  may  blend  in  various  ways  the  elementary  tints  of  the  solar  spec- 
trum, producing  innumerable  composite  colors  by  their  admixture.  Out 
of  violet  and  red  we  produce  purple,  and  out  of  yellow  and  blue  we 
produce  white.  Thus  also  may  elementary  sounds  be  blended  so  as  to 
produce  all  possible  varieties  of  clang-tint.  After  having  resolved  the 
human  voice  into  its  constituent  tones,  Helmholtz  was  able  to  imitate 
these  tones  by  tuning-forks,  and,  by  combining  them  appropriately 
together,   to  produce  the  clang-tints  of  all  the  vowels." 


MECHANISM    OF    SPEECH  453 

Consonants.  —  Some  of  the  consonants  have  no  sound  in  themselves 
and  serve  merely  to  modify  vowel-sounds.  These  are  called  mutes. 
They  are  b,  d,  k,  p,  t,  and  c  and  g  hard.  Their  office  in  the  formation 
of  syllables  is  sufficiently  apparent. 

The  consonants  known  as  semivowels  are  /,  /,  ni,  n,  r,  s,  and  c  and  g 
soft.  These  have  an  imperfect  sound  of  themselves,  approaching  in 
character  the  true  vowel-sounds.  Some  of  these,  /,  in,  n  and  r,  from 
the  facility  with  which  they  flow  into  other  sounds,  are  called  liquids. 
Orthoepists  have  further  divided  the  consonants  with  reference  to  the 
mechanism  of  their  pronunciation  :  d,  j,  s,  t,  z,  and  g  soft,  being  pro- 
nounced with  the  tongue  against  the  teeth,  are  called  dentals ;  d,  g,j,  k, 
/,  n  and  q  are  called  palatals;  b,p,  f,  v  and  nt  are  called  labials  ;  ni,  n 
and  ng  are  called  nasals  ;  and  k,  q,  and  c  and  g  hard  are  called  gutturals. 
After  the  description  already  given  of  the  voice,  it  is  not  necessary  to 
discuss  further  the  mechanism  of  these  simple  acts  of  articulation. 

For  the  easy  and  proper  production  of  articulate  sounds,  integ- 
rity of  the  mouth,  teeth,  lips,  tongue  and  palate  is  essential.  All  are 
acquainted  with  the  modifications  in  articulation  in  persons  in  whom  the 
nasal  cavities  resound  unnaturally  from  imperfection  of  the  palate  ;  and 
the  slight  peculiarities  observed  after  loss  of  the  teeth  and  in  harelip  are 
sufficiently  familiar.  The  tongue  usually  is  regarded,  also,  as  an  impor- 
tant organ  of  speech,  and  this  is  the  fact  in  the  great  majority  of  cases  ; 
but  instances  are  on  record  in  which  distinct  articulation  has  been  pre- 
served after  complete  destruction  of  this  organ.  These  cases,  however, 
are  unusual  and  they  do  not  invalidate  the  importance  of  the  tongue  in 
ordinary  speech. 

It  is  thus  seen  that  speech  consists  essentially  in  a  modification  of 
the  vocal  sounds  by  the  accessory  organs,  or  by  parts  situated  above 
the  larynx ;  the  latter  being  the  true  vocal  instrument.  While  the 
peculiarities  of  pronunciation  in  different  persons  and  the  difficulty  of 
acquiring  foreign  languages  after  the  habits  of  speech  have  been  formed 
show  that  the  organs  of  articulation  must  perform  their  office  with  gre^t 
accuracy,  their  movements  are  simple  and  vary  with  the  peculiarities 
of  different  languages. 

Whispering.  —  Articulate  sounds  may  be  produced  by  the  action  of 
the  resonant  cavities,  the  lips,  teeth  and  tongue,  in  which  the  larynx 
takes  no  part.  This  action  occurs  in  whispering  and  it  can  not  properly 
be  called  vocal.  It  is  difficult  to  make  any  considerable  variations  in 
the  pitch  of  a  whisper,  and  articulation  in  this  way  may  be  produced  in 
inspiration  as  well  as  in  expiration,  although  the  act  in  expiration  is 
more  natural  and  easy.  The  character  of  a  whisper  may  readily  be 
distinguished  from  that  of  the  faintest  audible  sound  involving-  vibration 


454  VOICE    AND    SPEECH 

of  the  vocal  chords.  In  aphonia  from  paralysis  of  the  vocal  muscles  of 
the  larynx,  patients  can  articulate  distinctly  in  whispering ;  but  in  cases 
of  chronic  bulbar  paralysis  (glosso-labio-laryngeal  paralysis)  speech  is 
entirely  lost. 

The  PhonograpJi  and  Telcp/ione. —  In  1877  a  remarkable  invention 
was  made  in  this  country,  by  Mr.  Thomas  A.  Edison,  which  possesses 
considerable  physiological  importance.  ]\Ir.  Edison  constructed  a  simple 
instrument,  called  the  phonograph,  which  will  repeat,  with  a  certain 
degree  of  accuracy,  the  peculiar  characters  of  the  human  voice  both  in 
speaking  and  singing  as  well  as  the  pitch  and  quality  of  musical  instru- 
ments. This  demonstrates  conclusively  the  fact  that  the  qualities  of 
vocal  sounds  depend  upon  the  form  of  the  sonorous  vibrations.  The 
following  are  the  main  features  in  the  construction  of  this  instrument  : 
It  consists  of  a  cylinder  of  iron  provided  with  very  fine  shallow  grooves 
in  the  form  of  a  close  spiral.  Upon  the  cylinder  a  sheet  of  tin-foil 
is  accurately  fitted.  Bearing  on  the  tin-foil  is  a  steel-point  connected 
with  a  vibrating  plate  of  mica  or  of  thin  iron.  The  vibrating  plate  is 
connected  with  a  mouth-piece  which  receives  the  vibrations  of  the  voice 
or  of  a  musical  instrument.  The  cylinder  is  turned  with  a  crank,  and 
at  the  same  time  the  plate  is  thrown  into  vibration  by  speaking  into 
the  mouth-piece.  As  the  disk  vibrates  in  consonance  with  the  voice, 
the  vibrations  are  marked  by  little  indentations  upon  the  tin-foil. 
When  this  has  been  done,  the  cylinder  is  moved  back  to  the  starting 
point  and  is  turned  again  at  the  same  rate  as  before.  As  the  steel-point 
passes  over  the  indentations  in  the  tin-foil,  the  plate  is  thrown  into 
vibration,  and  the  sound  of  the  voice  is  actually  repeated,  although 
diminished  in  intensity.  Many  improvements  have  lately  been  made  in 
the  phonograph,  which  have  added  much  to  its  character  illustrating  the 
various  qualities  of  the  human  voice.  The  telephone  illustrates  conduc- 
tion of  the  form  of  sound-waves.  As  is  well  known,  it  is  easy  to  recog- 
nize peculiarities  of  voice  in  using  this  instrument. 


CHAPTER    XVIII 

STRUCTURE  AND  PROPERTIES  OF  THE  NERVOUS  SYSTEM 

Divisions  and  structure  of  the  nervous  tissue  —  Medullated  ner^-e-fibres  —  Xon-meduUated 
nerve-fibres  —  Gelatinous  ner^"e-fibres  (fibres  of  Remakj  — Accessor*'  anatomical  elements 
of  the  nerves —  Branching  and  course  of  the  nerves  —  Termination  of  nerves  in  voluntary 
muscles — Termination  of  ner\-es  in  glands — Modes  of  termination  of  sensory  ner^-es  — 
Corpuscles  of  .Vater,  or  of  Pacini  —  Tactile  corpuscles  —  End-bulbs  —  General  mode  of 
termination  of  the  sensory  nerves — Structure  of  the  ner\'e-centres  —  Ner\'e-cells  —  Xissl's 
granules  —  The  neuron  —  Accessor}-  anatomical  elements  of  the  nerve-centres  —  Degen- 
eration and  regeneration  of  nerv'es  —  Motor  and  sensor}'  nerves — Mode  of  action  of  the 
motor  nerves  —  Associated  movements  —  Mode  of  action  of  the  sensor}'  nerves  —  Physi- 
ological differences  between  motor  and  sensorv'  nerves  — Nervous  excitability  and  conduc- 
tivity—  Rapidit}'  of  nervous  conduction  —  Personal  equation  —  Action  of  electricity  on 
the  nerves  —  Law  of  contraction  —  Electric  current  from  the  exterior  to  the  cut  surface 
of  a  nerve  —  Electrotonus,  anelectrotonus  and  catelectrotonus. 

The  nervous  system  is  anatomically  and  physiologically  distinct  from 
all  other  systems  and  organs.  It  receives  impressions  made  on  the  ter- 
minal branches  of  its  sensory  portion,  and  it  conveys  stimulus  to  parts, 
determining  and  regulating  their  actions  ;  but  it  gives  to  no  tissue  or 
organ  its  special  excitability  or  the  power  of  performing  its  particular 
office  in  the  economy.  The  nervous  system  connects  into  a  coordinated 
organism  all  parts  of  the  body.  It  is  the  medium  through  which  all 
impressions  are  received.  It  animates  or  regulates  all  movements,  vol- 
untary and  involuntary.  It  regulates,  also,  secretion,  nutrition,  calorifi- 
cation and  all  the  processes  of  organic  Ufe. 

In  addition  to  its  action  as  a  medium  of  conduction  and  communica- 
tion, the  nervous  system,  in  certain  of  its  parts,  is  capable  of  receiving 
impressions  and  of  generating  a  stimulating  influence,  or  force,  peculiar 
to  itself.  As  there  can  be  no  physiological  connection  or  coordination 
of  different  parts  of  the  organisms  without  nerves,  there  can  be  no 
unconscious  reception  of  impressions  giving  rise  to  involuntary  move- 
ments, no  appreciation  of  impressions,  general,  as  in  ordinary  sensation, 
or  special,  as  in  sight,  smell,  taste  or  hearing,  no  instinct,  volition,  thought 
or  even  knowledge  of  existence,  without  nerve-centres. 

Divisions  and  Structure  of  the  Nervous  Tissue 

The  nervous  tissue  presents  two  great  divisions,  each  with  distinct  ana- 
tomical as  well  as  physiological  differences.      One  of  these  divisions  is 

455 


456  NERVOUS    SYSTEM 

composed  of  fibres.  This  kind  of  nervous  matter  is  incapable  of  gen- 
erating a  force  or  impulse,  and  it  serves  only  as  a  conductor.  The 
other  division  is  composed  of  cells,  and  this  kind  of  nervous  matter, 
while  it  may  serve  as  a  conductor,  is  capable  of  generating  the  so-called 
nerve-force. 

The  nerve-fibres  and  cells  are  also  divided  into  two  great  systems, 
as  follows  :  — 

1.  The  cerebro-spinal  system,  composed  of  the  brain  and  spinal 
cord  with  the  nerves  directly  connected  with  these  centres.  This 
system  is  specially  connected  with  the  functions  of  relation,  or  of  ani- 
mal life.  The  centres  preside  over  general  sensation,  the  special  senses, 
voluntary  and  some  involuntary  movements,  intellection,  and,  in  short, 
all  functions  that  characterize  the  animal.  The  nerves  serve  as  the 
conductors  of  impressions  known  as  general  or  special  sensations  and 
of  the  stimulus  that  gives  rise  to  voluntary  and  certain  involuntary 
movements,  the  latter  being  the  automatic  movements  connected  with 
animal  life. 

2.  The  sympathetic,  or  organic  system.  This  system  is  specially 
connected  with  functions  relating  to  nutrition,  operations  that  have  their 
analogue  in  the  vegetable  kingdom  and  are  sometimes  called  the  func- 
tions of  vegetative  Ufe.  Although  this  system  presides  over  functions 
distinct  from  those  characteristic  of  and  peculiar  to  animals,  the  centres 
of  this  system  all  have  an  anatomical  and  physiological  connection  with 
the  cerebro-spinal  nerves. 

The  cerebro-spinal  system  is  subdivided  into  centres  presiding  over 
movements  and  ordinary  sensation  and  centres  capable  of  receiving 
impressions  connected  with  the  special  senses,  such  as  vision,  audition, 
olfaction  and  gustation.  The  nerves  receiving  these  special  impressions 
and  conveying  them  to  the  appropriate  centres  are  more  or  less  insensi- 
ble to  ordinary  impressions.  The  organs  to  which  these  special  nerves 
are  distributed  usually  are  of  a  complex  and  peculiar  structure ;  and 
they  present  accessory  parts  that  are  important  and  essential  in  the 
transmission  of  the  special  impressions  to  the  terminal  branches  of  the 
nerves. 

The  physiological  division  of  the  nervous  system  into  nerves  and 
nerve-centres  is  carried  out  as  regards  the  anatomical  structure  of  these 
parts,  although  they  are  connected  together  in  the  so-called  neuron. 
The  two  great  divisions  of  the  system,  anatomically  considered,  are 
nerve-cells  and  nerve-fibres. 

The  cells  of  the  nerve-centres,  while  they  may  transmit  impressions 
and  impulses,  are  the  only  parts  capable  of  generating  impulses;  and 
as  a  rule  they  do  not  receive  impressions  in  any  other  way  than  through 


MEDULLATED    NERVE-FIBRES  457 

nerve-fibres.  There  are,  however,  many  exceptions  to  this  rule,  as  in 
the  case  of  movements  following  direct  stimulation  of  the  sympathetic 
ganglia  and  certain  centres  in  the  brain  and  spinal  cord ;  but  the  cells 
of  many  of  the  gangha  belonging  to  the  cerebro-spinal  axis  are  insensi- 
ble to  direct  stimulation  and  can  receive  only  impressions  conducted  to 
them  by  the  nerves. 

The  nerve-fibres  act  as  conductors  and  are  incapable  of  gener- 
ating impulses.  There  is  no  exception  to  this  rule,  but  there  are  dif- 
ferences in  the  properties  of  certain  fibres.  The  nerves  generally,  for 
example,  receive  direct  impressions,  the  motor  filaments  conducting 
these  to  the  muscles  and  the  sensory  filaments  conveying  the  impres- 
sions to  the  centres.  These  fibres  also  conduct  impulses  generated  by 
the  nerve-centres ;  but  there  are  many  fibres,  such  as  those  composing 
the  white  matter  of  the  encephalon  and  the  spinal  cord,  that  are  insen- 
sible to  direct  stimulation,  while  they  convey  to  the  centres  impressions 
conveyed  to  them  by  sensory  nerves  and  conduct  to  the  motor  nerves 
impulses  generated  by  nerve-cells. 

In  the  natural  classification  of  nerve-fibres,  they  are  divided  into  two 
groups ;  one  embracing  fibres  that  have  the  conducting  element  alone, 
and  the  other  presenting  this  anatomical  element  surrounded  with  cer- 
tain accessory  structures.  In  the  course  of  the  nerves,  the  simple  fibres 
are  the  exception  and  the  other  variety  is  the  rule  ;  but  as  the  nerves  are 
followed  to  their  terminations  in  muscles  or  sensitive  parts  or  are  traced 
to  their  origin  in  the  nerve-centres,  they  lose  one  or  another  of  their 
coverings.  These  two  varieties  are  designated  as  medullated  and  non- 
medullated  fibres. 

Medullated  Nerve-fibres.  —  These  fibres  are  so  called  because,  in 
addition  to  the  axis-cylinder,  or  conducting  element,  they  contain, 
enclosed  in  a  tubular  sheath,  a  soft  substance  called  medulla.  This 
substance  is  strongly  refractive  and  gives  to  the  nerves  a  peculiar 
appearance  under  the  microscope,  from  which  they  are  sometimes  called 
dark-bordered  nerve-fibres.  As  the  whole  substance  of  the  fibre  is  en- 
closed in  a  tubular  membrane,  these  are  frequently  called  nerve-tubes. 

If  the  nerves  are  examined  while  fresh  and  unchanged,  their  ana- 
tomical elements  appear  in  the  form  of  simple  fibres  with  strongly 
accentuated  borders.  The  diameter  of  these  fibres  is  2  5V0  ^^  tyVo  °^ 
an  inch  (10  to  15  \x).  In  a  short  time  the  borders  become  darker  and 
the  fibres  assume  a  different  appearance.  By  the  use  of  certain 
reagents,  it  can  be  demonstrated  that  a  medullated  nerve-fibre  is  com- 
posed of  three  distinct  portions :  a  homogeneous  sheath,  a  semifluid 
matter  contained  in  the  sheath  and  a  delicate  central  band. 

The  tubular  sheath  of  the  nerve-fibres,  the  neurilemma,  is  a  some- 


458 


NERVOUS    SYSTEM 


what  elastic,  homogeneous  membrane,  presenting  oval  nuclei  with  their 
long  diameter  in  the  direction  of  the  tube.  This  is  sometimes  called  the 
sheath  of  Schwann.  It  exists  in  all  the  medullated  nerve-fibres,  large 
and  small,  except  those  in  the  white  portions  of  the  encephalon  and 
spinal  cord  and  the  trunk  of  the  auditory  nerve.  It  possibly  exists  in 
non-medullated  fibres,  although  its  presence  here  has  not  been  satisfac- 
torily demonstrated. 

The  medullary  substance  fills  the  tube  and  surrounds  the  central 
band.  This  is  called  by  various  names,  as  myelin,  white  substance  of 
Schwann,  medullary  sheath,  nervous    medulla  etc.      It  does  not  exist 

either  at  the  origin  of  the  nerves  in  the  gray 
substance  of  the  nerve-centres  or  at  the  periph- 
eral termination  of  the  nerves,  and  it  is  not 
a  conducting  element.  When  the  nerves  are 
perfectly  fresh,  this  substance  is  transparent, 
homogeneous,  and  strongly  refracting,  like  oil ; 
but  as  the  nerves  become  altered  by  desicca- 
tion, the  action  of  water,  acetic  acid  and  vari- 
ous other  reagents,  it  coagulates  into  an  opaque 
granular  mass.  In  the  white  substance  of  the 
encephalon  and  spinal  cord,  the  neurilemma  is 
wanting  and  the  fibres  present  only  the  axis- 
cylinder  surrounded  with  the  white  substance 
of  Schwann.  As  a  post-mortem  condition,  these 
fibres  present  under  the  microscope  varicosities 
at  irregular  intervals,  which  give  them  a  pe- 
culiar and  characteristic  appearance. 

The  medullated  nerve-fibres  do  not  have 
regular  outlines,  but  present  constrictions  at 
various  points  in  their  length,  called  the  con- 
strictions or  nodes  of  Ranvier.  At  these  nodes  the  medullary  substance 
is  wanting  and  the  neurilemma  is  in  contact  with  the  axis-cylinder. 

When  a  medullated  nerve-fibre  is  slightly  stretched,  a  number  of 
oblique  cuts  are  observed  running  across  the  fibre  and  extending  to  the 
axis-cylinder,  called  incisures.  These  involve  the  medullary  substance 
only  and  are  best  observed  when  this  substance  has  been  stained  with 
osmic  acid.  It  is  not  known  that  they  possess  any  physiological  impor- 
tance. 

The  axis-cylinder,  occupying  one-fifth  to  one-fourth  of  the  diameter 
of  the  nerve-tube,  is  the  conducting  portion  of  the  nerve.  In  the  ordi- 
nary medullated  fibres,  the  axis-cylinder  can  not  be  seen  in  the  natural 
condition,  because  it  refracts  in  the  same  manner  as  the  medullary  sub- 


Fig.  96. 


-Medullated  nerve-fibres 
(Piersol). 

A,  teased  in  salt  solution ;  x, 
shortly  after  death ;  y,  node  of 
Ranvier;  z,  post-mortem  distor- 
tions of  medullary  substance.  B, 
an  isolated  stained  fibre  ;  a,  axis- 
cylinder;  r,  node  of  Ranvier;  w, 
medullary  substance;  n,  neuri- 
lemma. 


NON-MEDULLATED    NERVE-FIBRES 


459 


stance;  and  it  can  not  easily  be  demonstrated  afterward,  on  account  of 
the  opacity  of  the  coagulated  matter.  If  a  fresh  nerve,  however,  is 
treated  with  strong  acetic  acid,  the  divided  ends  of  the  fibres  retract, 
leaving  the  axis-cylinder,  which  latter  is  but  slightly  affected  by  reagents. 
It  then  presents  itself  in  the  form  of  a  pale,  slightly-flattened  band,  with 
outlines  tolerably  regular,  though  slightly  varicose  at  intervals.  It  is 
somewhat  granular  and  finely  striated  in  a  longitudinal  direction.  This 
band  is  elastic  but  not  very  resisting.  What  serves  to  distinguish  it 
from  other  portions  of  the  nerve-fibre  is  its  insolubility  in  most  of  the 
reagents  employed  in  anatomical  investigations.  It  is  slightly  swollen 
by  acetic  acid  but  is  dissolved  after  prolonged  boiling.  If  nerve-tissue 
is  treated  with  a  solution  of  carmin,  the  axis-cylinder  only  is  colored. 
It  also  stains  with  gold  chloride.  It  has  been  observed  that  the  nerve- 
fibres  treated  with  silver  nitrate  present  in  the  axis- 
cylinder  well-marked  transverse  striations  (Fromann) ; 
and  some  anatomists  regard  both  the  nerve-cells  and 
the  axes  of  the  fibres  as  composed  of  two  substances, 
the  limits  of  which  are  marked  by  the  regular  striae 
thus  developed.  This,  however,  is  a  point  of  purely 
anatomical  interest.  The  presence  of  regular  and 
well-marked  striae  in  the  axis-cylinder  after  the  addi- 
tion of  a  solution  of  silver  nitrate  and  the  action  of 
light  can  not  be  doubted ;  but  it  has  not  yet  been 
determined  whether  these  markings  are  artificial  or 


Fig.    97. —  Gold-stained 
axis-cylinder  (Piersol). 

shows   component 


whether  the  axis-cylinder  is  really  composed  of  two  fibriiia;;  b,  shows  vari- 

1  .      ,         J.        ,  cose   nerve-fibrillae  near 

kmds  of  substance.  their   termination. 

For  some  time  it  has  been  known  that  the  axis- 
cyHnders  in  the  organs  of  special  sense,  in  the  final  distribution  of 
sensory  nerves  and  in  some  other  situations,  break  up  into  fibrillae.  A 
fibrillated  appearance,  indeed,  is  often  observed  in  nerves  in  their 
course,  and  it  is  now  the  common  opinion  that  the  axis-cylinders  are 
composed  of  fibrillae  held  closely  together  by  connective  substance. 
This  fibrillated  structure  of  the  nerves  is  quite  prominent  in  some  of  the 
lower  orders  of  animals. 

Non-7nediillated  Nerve-fib7'es.  — These  fibres,  which  are  largely  dis- 
tributed in  the  nervous  system,  appear  to  be  simple  prolongations,  with- 
out alteration,  of  the  axis-cylinders  of  the  medullated  fibres.  They  are 
found  chiefly  in  the  peripheral  terminations  of  the  nerves  and  in  the 
filaments  of  origin  of  the  fibres  from  the  nerve-cells.  Some  anatomists 
think  that  they  have  a  delicate  investing  membrane,  but  this  has  not 
been  satisfactorily  demonstrated. 

Gelatinous  Nerve-fibres  {^Fibres  of  Reinak).  —  There  has  been  some 


460 


NERVOUS    SYSTEM 


difference    of   opinion    in   regard    to    the    physiology  of   the    so-called 
gelatinous  nerve-fibres.     Some  anatomists  have  regarded  them  simply 

as  elements  of  connective  tissue,  and 
others  have  described  them  as  axis- 
cylinders  surrounded  with  a  nucleated 
sheath  ;  but  the  fibres  do  not  present 
the  lines  of  Fromann  when  treated 
with  silver  nitrate.  While  elements 
of  connective  tissue  may  have  been 
mistaken  for  true  nerve-fibres,  there 
are  in  the  nerves,  particularly  in  those 
belonging  to  the  sympathetic  system, 
fibres  resembling  the  nerve-fibres  of 
the  embryo.  These  are  the  gelati- 
nous nerve-fibres,  or  fibres  of  Remak. 
li'  ■    ■■     ifHi    "' -    li      All   the   nerves    have    this    structure 

Fig.  98.  —  Nodes  of  Ranvier  and  lines  of  Fro-      Until        about       the 

fifth  month  of  in- 

tra-uterine  life,  and 

in    the    regenera- 
tion of  nerves  after 

division  or  injury, 

the  new  elements 

ordinarily  assume 
this  form  before  they  arrive  at  their  full  development. 
The  gelatinous  nerve-fibres  present  the  following 
characters :  They  are  invested  with  a  delicate  neuri- 
lemma, are  flattened,  with  regular  and  sharp  borders, 
grayish,  pale  and  fibrillated,  with  very  fine  granules 
and  a  number  of  oval  longitudinal  nuclei,  a  charac- 
teristic which  has  given  them  the  name  of  nucleated 
nerve-fibres.  They  branch  frequently.  The  diameter 
of  the  fibres  is  about  g^^oo  of  an  inch  (3  /a).  The 
nuclei  have  nearly  the  same  diameter  as  the  fibres 
and  are  about  12V0  of  an  inch  (20  /x)  in  length. 
They  are  finely  granular  and  present  no  nucleoH. 
The  fibres  are  rendered  pale  by  the  action  of  acetic 
acid,  but  they  are  slightly  swollen  only,  and  present, 
in  this  regard,  a  marked  contrast  with  the  elements  of  connective  tissue. 
They  are  found  chiefly  in  the  sympathetic  system  and  in  that  particular 
portion  of  this  system  connected  with  involuntary  movements.  They 
usually  are  not  found  in  the  white  filaments  of  the  sympathetic. 


-  Nodes  of  Ranvier  and  lines  of  Fro- 
mann (Ranvier). 

A,  intercostal  nerve  of  the  mouse,  treated 
with  silver  nitrate,  X200.  B,  nerve-fibre  from 
the  sciatic  nerve  of  a  full-grown  rabbit,  X  600; 
A,  node  of  Ranvier;  M,  medullary  substance 
rendered  transparent  by  tlie  action  of  glycerin  ; 
CY,  axis-cylinder  presenting  the  lines  of  Fro- 
mann, which  are  very  distinct  near  the  node. 
The  lines  are  less  marked  at  a  distance  from 
the  node. 


Fig.  99.  —  Fibres  of  Re- 
mak, X  300  (Robin). 

With  the  gelatinous 
fibres  of  Remak,  are  seen 
two  of  the  ordinary  dark- 
bordered  nerve-fibres. 


ACCESSORY   AXATO.MICAL    ELEMENTS    OF   THE    NERVES       46 1 

Accessory  Anato^nical  Elements  of  the  Nerves.  —  The  nerves  present, 
in  addition  to  the  different  varieties  of  true  nerve-fibres  just  described, 
certain  accessory  anatomical  elements  common  to  nearly  all  the  tissues 
of  the  organism,  such  as  connective  tissue,  bloodvessels  and  lymphatics. 

Like  the  muscular  tissue,  the  nerves  are  made  up  of  their  true  ana- 
tomical elements —  the  nerve-fibres  —  held  together  into  primitive,  sec- 
ondary and  tertiary  bundles,  and  so  on,  in  proportion  to  the  size  of  the 
nerve.  The  primitive  fasciculi  are  surrounded  with  a  delicate  membrane 
called  the  sheath  of  Henle.  This  membrane  is  homogeneous  or  very 
finely  granular,  sometimes  marked  with  longitudinal  striae,  and  possess- 
ing elongated  granular  nuclei.  There  are  three  kinds  of  nuclei  either 
attached  to  or  situated  near  the  sheath.  These  are  ( i )  nuclei  attached 
to  the  inner  surface  of  the  sheath;  (2)  nuclei  belonging  to  the  nerve- 
fibres  within  the  sheath ;  and  (3)  nuclei  of  connective-tissue  elements 
near  the  sheath.  Silver  nitrate  discloses  the  borders  of  a  lining  endo- 
thelium. The  sheath  of  Henle  begins  at  the  point  where  the  nerve- 
fibres  emerge  from  the  white  portion  of  the  nervous  centres  and  it 
extends  to  their  terminal  extremities,  being  interrupted  by  the  ganglia 
in  the  course  of  the  nerves.  This  membrane  usually  envelops  a  primi- 
tive fasciculus  of  fibres,  branching  as  the  bundles  divide  and  pass  from 
one  trunk  to  another.  It  is  sometimes  found  surrounding  single  fibres. 
It  usually  is  not  penetrated  by  bloodvessels,  the  smallest  capillaries  of 
the  nerves  ramifying  in  its  substance  but  seldom  passing  through  to  the 
individual  nerve-fibres.  Within  the  sheath  of  Henle  are  sometimes 
found  elements  of  connective  tissue,  with  very  rarely  a  few  capillary 
bloodvessels  in  the  largest  fasciculi. 

The  quantity  of  fibrous  tissue  in  the  different  nerves  is  variable  and 
depends  on  the  conditions  to  which  they  are  subjected.  In  the  nerves 
within  the  bony  cavities,  where  they  are  entirely  protected,  the  fibrous 
tissue  is  very  scanty ;  but  in  the  nerves  between  muscles  there  is  a 
tolerably  strong  investing  membrane  or  sheath  surrounding  the  w^hole 
nerve  and  sending  into  its  interior  processes  which  envelop  smaller 
bundles  of  fibres.  This  sheath  is  formed  of  ordinary  fibrous  tissue,  with 
small  elastic  fibres  and  nucleated  connective-tissue  cells. 

The  greatest  part  of  the  fibrous  sheath  of  the  nerves  is  composed  of 
bundles  of  white  inelastic  tissue,  interlacing  in  every  direction  ;  but  it 
contains  also  many  elastic  fibres,  adipose  tissue,  a  network  of  arteries 
and  veins,  and  "nervi  nervorum,"  which  are  to  these  structures  what 
the  vasa  vasorum  are  to  bloodvessels.  The  adipose  tissue  is  constant, 
being  found  even  in  extremely  emaciated  persons. 

The  vascular  supply  to  most  of  the  ner\-es  is  rather  scanty.  The 
arteries  break  up   into  a  plexus  of  fine  capillaries,  arranged  in  oblong 


462 


NERVOUS    SYSTEM 


longitudinal  meshes  surrounding  the  fasciculi  of  fibres ;  but  they  rarely 
penetrate  the  sheath  of  Henle  and  usually  do  not  come  in  contact  with 
the  ultimate  nervous  elements.  The  veins  are  rather  more  voluminous 
and  follow  the  arrangement  of  the  arteries.  Lymph-spaces,  lined  with 
delicate  endothelium,  are  found  in  the  connective-tissue  sheaths  of  the 
bundles  of  fibres. 

Branching-  and   Course   of   the    Nerves. —  The    nerve-fibres   in    the 
course  of  the  nerves  have  no  connection  with  each  other  by  branching 

or  inosculation.  A  bundle  of 
--'■^  fibres  frequently  sends  branches 
to  other  nerves  and  receives 
branches  in  the  same  way  ;  but 
this  is  simply  the  passage  of 
fibres  from  one  sheath  to  an- 
other, the  fibres  themselves 
maintaining  throughout  their 
course  their  individual  physio- 
logical properties.  The  nerve- 
fibres  do  not  branch  or  inosculate 
except  near  their  terminations. 
When  there  is  branching  of 
meduUated  fibres,  it  is  always 
at-  the  site  of  one  of  the  nodes 
of  Ranvier. 

Tennination    of    Ne7'ves    in 


Fig.  100.  —  Branching'  of  a  nerve  in  an  abdojninal 
muscle  of  a  mouse,  X  120  (Sobotta). 

m,  muscular  fibres  ;  7ne,  motor  end-plates  ;  n,  nerve. 


Voluntary  Muscles. —  In  man  and  in  the  warm-blooded  animals  generally, 
the  medullated  nerve-fibres  divide  dichotomously  near  their  endings  in 
the  muscular  fibres,  the  divisions  taking  place  at  the  nodes  of  Ranvier. 
The  fibres  finally  resulting  from  these  divisions  pass  to  the  sarcolemma 
and  terminate  in  a  rather  prominent  mass  called  an  end-plate,  with  six 
to  twelve  or  sometimes  sixteen  nuclei  that  are  distinct  from  the  nuclei 
of  the  muscular  fibre.  The  tubular  membrane  of  the  nerve-fibre  here 
fuses  with  the  sarcolemma  and  the  medullary  substance  is  lost.  By 
the  action  of  gold  chloride,  it  has  been  shown  that  fibrils  arise  from 
the  under  surface  of  the  end-plates,  which  pass  into  the  substance  of  the 
muscular  fibres,  between  the  muscular  fibrillae.  These  fibrils  proba- 
bly are  connected  with  the  axis-cylinders,  but  their  exact  mode  of 
termination  in  the  muscular  substance  has  not  been  satisfactorily 
demonstrated. 

Although  the  sensibility  of  the  muscles  is  slight  as  compared  with 
that  of  the  skin  and  mucous  membranes,  they  are  not  insensible  and 
they  possess  nerve-fibres  other  than  those  exclusively  motor.     Through- 


TERMINATIONS    OF    THE    NERVES 


463 


ch 


out  the  substance  of  most  of  the  voluntary  muscles  are  so-called  neuro- 
muscular spindles,  made  up  of  small  bundles  of  fibres  surrounded  with 
a  rather  thick  covering  of  connective  tissue.  These  structures  are  one- 
eighth  to  one-third  of  an  inch  (3  to  8  millimeters)  long  and  about  -jj-g- 
inch  (0.2  millimeter)  in  diameter.  A  medulla  ted  nerve-fibre  passes  to  each 
spindle,  loses  its  medullary  sheath,  subdivides  and  the  non-medullated 
fibres  form  a  network  surrounding  the  sarcolemma.  It  is  not  certain 
that  they  then  penetrate  the  sarcolemma  and  terminate  in  the  muscular 
substance,  although  this  view  has  been  advanced.  These  spindles  are 
abundant  near  the  connections  of  the  muscles  with  the  tendons.  They 
do  not  exist  in  the  muscles  of  the 
eye  and  of  the  tongue.  The 
neuro-muscular  spindles  are  re- 
garded by  some  physiologists  as 
sensory  and  connected  with  the 
so-called  muscular  sense. 

Termination  of  Nerves  in  the 
Invohintary  Miiscnlar  Tissue.  — 
Nerve-fibres  form  a  plexus  in  the 
connective  tissue  surrounding 
the  involuntary  muscles  and 
then  send  small  fibres  into  the 
sheets  or  layers  of  muscular- 
fibre  cells,  which  branch  and 
probably  go  finally  to  the  nuclei 
of  these  structures.  In  many  Fig-  loi 
instances,  the  fine  terminal 
nerve-fibres  branch,  go  into  the 
nuclei  of  the  muscular  fibres  and  afterward  pass  out  to  join  with  other 
fibres  and  form  a  plexus. 

Termination  of  Nerves  in  Glands. —  Having  formed  a  more  or  less 
branching  plexus,  non-medullated  fibres  pass  directly  into  the  glandular 
cells  and  terminate  in  the  nucleoli.  Anatomists  have  also  described  and 
figured  multipolar  cells,  interspersed  with  the  glandular  cells,  in  which 
some  of  the  nerve-fibres  terminate.  These,  however,  are  not  found  in 
the  parotid.  These  nerve-fibres  are  regarded  as  glandular  nerves  and 
are  distinct  from  the  vasomotor  nerves. 

Modes  of  Terminatiojt  of  Sensory  Nerves. —  There  undoubtedly  are 
several  modes  of  termination  of  the  sensory  nerves  in  integument 
and  in  mucous  membranes,  some  of  which  have  been  quite  accurately 
described.  In  the  first  place,  anatomists  now  recognize  three  varieties 
of  corpuscular  terminations,  differing  in  their  structure,  probably,  accord- 


Two  motor  end-plates  from  a  muscle  of  a 
lizard,  X  250  (Sobotta). 

n,  entering  nerve-fibres ;  sch,  end-plate. 


464 


NERVOUS    SYSTEM 


ing  to  the  different  properties  connected  with  sensation  with  which 
the  parts  are  endowed.  In  addition  it  is  probable  that  sensory  nerves 
are  connected  with  the  hair-foUicles,  so  largely  distributed  throughout 
the  cutaneous  surface.  There  are,  also,  terminal  filaments  not  con- 
nected with  special  organs,  some  of  them,  perhaps,  ending  simply  in 
free  extremities  and  some  connected  with  epithelium. 

Corpuscles  of  Vater  or  of  Pacini. —  These  bodies  were  called  cor- 
puscles of  Pacini  until  it  was  shown  that  they  had  been  seen  about  a 
century  and  a  half  ago  by  Vater.  In  man  they  are  oval  or  egg-shaped 
and  measure  o\  to  \  of  an  inch  (i  to  4  millimeters)  in  length.  They 
are  found  in  the  subcutaneous  layer  on  the  palms  of  the  hands  and  the 

soles  of  the  feet,  and  are  most 
abundant  on  the  palmar  sur- 
faces   of   the   fingers    and   toes, 


.,<r-^- 


^^ 


^fr 


Fig.  102. 


particularly  the  third  phalanges. 
In   the    entire    hand    there    are 

,i.      about    six    hundred    and    about 

.'V     the  same   number  in   the  feet. 

.^^  They  are  sometimes,  but  not 
■^     constantly,  found  in  the  follow- 

y  ing  situations:  the  dorsal  sur- 
faces of  the  hands  and  feet, 
on  the  cutaneous  nerves  of  the 
arm,  the  forearm  and  the  neck, 
the  internal  pudic  nerve,  the 
intercostal  nerves,  the  articular 
nerves    of    the    extremities,   the 


Transverse  section  of  a  corpuscle  of  Vater 
X  30  (Author's  collection). 

Tiie  corpuscle  lies  in  the  pancreas,  portions  of    nerves    beneath    the    mammary 

which  are  shown  in  the  section,  which  is  deeply  stained      gl^nds,  the  nerveS  of  the  uippleS 
with  alum-carmin.  o  >  i  i 

and  in  the  substance  of  the 
muscles  of  the  hands  and  feet.  They  are  always  found  in  the  great 
sympathetic  plexuses,  in  front  of  and  by  the  sides  of  the  abdominal 
aorta,  and  behind  the  peritoneum,  in  the  vicinity  of  the  pancreas.  They 
have  been  observed  in  the  mesentery  and  near  the  coccygeal  gland. 

The  corpuscles  consist  of  several  layers  of  connective  tissue  enclos- 
ing one,  two  or  three  central  bulbs  in  which  are  found  the  ends  of  the 
nerve.  These  bulbs  are  finely  granular  and  nucleated  and  are  regarded 
by  most  anatomists  as  composed  of  connective  tissue.  At  the  base  of 
the  corpuscle  is  a  pedicle  formed  of  connective  tissue  surrounding  a 
medullated  nerve-fibre  which  penetrates  the  corpuscle.  Within  the 
corpuscle  the  medullary  substance  of  the  nerve-fibre  is  lost  and  only 
the  axis-cylinder  remains. 


TACTILE    CORPUSCLES 


465 


The  situation  of  these  corpuscles,  beneath  the  true  skin  instead  of 
in  its  substance,  shows  that  they  can  not  properly  be  considered  as 
tactile  corpuscles,  a  name  which  is  applied  to  other  structures  found  in 
the  papillae  of  the  corium  ;  and  it  is  impossible  to  assign  to  them  any 
special  use  connected  with  sensation,  such  as  the 
appreciation  of  temperature,  pressure  or  weight. 
All  that  can  be  said  in  regard  to  them  is  that  they 
constitute  one  of  the  several  modes  of  termination 
of  sensory  nerves. 

Tactile  Corpuscles .  — The  name  tactile  corpuscles 
implies  that  these  bodies  are  connected  with  the  sense 
of  touch  ;  and  this  view  is  sustained  by  the  fact  that 
they  are  found  almost  exclusively  in  parts  endowed 
in  a  marked  degree  with  tactile 
sensibility.  They  are  sometimes 
called  the  corpuscles  of  IMeissner 
and  Wagner,  after  the  anatomists 
by  whom  they  were  first  described. 
The  true  tactile  corpuscles  are 
Fig.  102,.  — Longif lid  I-  found  in  greatest  number  on  the 
maisectio7i  of  a  corpuscle  of  palmar  surfaccs  of  the  hands  and 

Vater  (Sappey).  j   ^1  1       ^  r  r 

nngers  and  the  plantar  surfaces  of 

I, baseof  tnecorpuscle ; 

2, apex;  3,  3,  substance  of  the   feet    and    toes.       They  exist, 

the   corpuscle,   in    layers;    ^^  -^    ^^^    gj,-^    ^^    ^j^^    ^^^^^    ^^ 

4,  4,  nerve  penetrating  the  ' 

corpuscle;  5,  cavity  of  the  the  hands  and  feet,  the  nipples  and 

corpuscle ;    6,     nerve ;     7,  r  .1  .       •  r  r  ^1 

nerve,  Nvhich  has  lost  its  ^  f cw  on  the  anterior  surface  of  the 
medullary  substance  and  forearm.     The   largest   papillae  of 

sheath ;  8,   termination   of      ,  ,  .  ,  ,  i         i  i 

the  nerve;  9,  granular  sub-  the  skm  are  fouud  ou  the  hands, 

stance  continuous  N.±h  the  feet  and  nipples,  where  the  tactile  ''^"''^' P'^"' ^'^f'^''- 

nerve  ma7i     cornini     ^Doam 

corpuscles     are     most     abundant,    and  DavidofF) . 
Corpuscles  do  not  exist  in  all  papillae,  and  thev   are       ^.  upper  portion,  in 

^  .  .  ^  which     onlv    the    epi- 

lound  chieny  m  those  called  compound,      in  an  area  a  theiiai  cells  are  repre- 
little  more  than  ^V  of  an  inch  square  (2.2  milHmeters   ^f'^'^l^f    ^-   ^^ows   a 

^  -  ^  ^  dendrite  coiled  around 

square),  on  the  third  phalanx  of  the  index-finger,  the  epithelial  cells;  c, 
Meissner  counted  four  hundred  papillae,  in  one  hundred  "'^":^-fi^''^- 
and  eight  of  which  he  found  tactile  corpuscles,  or  about  one  in  four. 
In  an  equal  area  on  the  second  phalanx,  he  found  forty  corpuscles  ;  on 
the  first  phalanx,  fifteen  ;  eight  on  the  skin  of  the  hypothenar  emi- 
nence ;  thirty-four  on  the  plantar  surface  of  the  ungual  phalanx  of  the 
great  toe ;  and  seven  or  eight  in  the  skin  on  the  middle  of  the  sole  of 
the  foot.  In  the  skin  of  the  forearm  the  corpuscles  are  very  rare. 
The   tactile  corpuscles    usually   occupy    special   papillae    that   are   not 


Fig.    104. —  Tactile 


466 


NERVOUS    SYSTEM 


provided  with  bloodvessels  ;   so  that  the  papillae  of  the  hand  may  be 
properly  divided  into  vascular  and  nervous. 

The  form  of  the  tactile  corpuscles  is  oblong,  with  the  long  diameter 
in  the  direction  of  the  papillae.  Their  length  is  -^^jj  to  050"  ^^  ^^  ^^^^ 
{66  to  100  ^l).  In  the  palm  of  the  hand  they  are  0-5-0  ^^  T4o  °^  ^^  ^'^'^^ 
(100  to  165  fi)  long,  and  --^\q  to  -g-^  of  an  inch  (45  to  50  /x)  in  thickness. 
They  usually  are  situated  at  the  summits  of  the  secondary  eminences  of 
the  compound  papillae.  They  consist  of  a  central  bulb  of  homogeneous 
or  slightly  granular  connective-tissue  substance,  harder  than  the  central 
bulb  of  the  corpuscles  of  Vater,  and  a  covering.  The  covering  is  comi- 
posed  of  connective  tissue  with  a  few  fine  elastic 
fibres.  One,  two,  and  sometimes  three  or  four 
dark-bordered  nerve-fibres  pass  from  the  subcu- 
taneous nervous  plexus  to  the  base  of  each  cor- 
puscle. These  surround  the  corpuscle  with  two 
or  three  spiral  turns,  and  they  terminate  in  pale 
extremities  on  the  surface  of  the  central  bulb. 

End-bulbs.  —  Under  this  name,  a  variety  of 
corpuscles  has  been  described  by  Krause  as  ex- 
isting in  the  conjunctiva  covering  the  eye  and  in 
the  semilunar  fold,  in  the  floor  of  the  buccal 
cavity,  the  tongue,  the  glans  penis  and  the  cli- 
toris. They  bear  some  analogy  to  the  tactile 
corpuscles,  but  they  are  smaller  and  more  simple 
in  their  structure.  They  form  rounded  or  oblong 
enlargements  at  the  ends  of  the  nerves,  which  are 
Fig.  ro$.— Corpuscle  of    composed  of  homogeneous  matter  with  a  delicate 


Krause  front  the  human  con- 
junctiva (Dogiel). 


a,  endothelial  envelope; 
b,  nucleus  of  a  connective- 
tissue  cell ;  c,  nerve-fibre. 


investment  of  connective  tissue,  lined  with  endo- 
thelial cells.  They  measure  yoVo  ^o  •257  °^  ^^ 
inch  (25  to  100  /i)  in  diameter.  In  the  parts 
provided  with  papillae,  they  are  situated  at  the 
summits  of  the  secondary  elevations.  The  arrangement  of  the  nerve- 
fibres  in  these  corpuscles  is  very  simple.  One,  two,  or  three  medullated 
fibres  pass  from  the  submucous  plexus  to  the  corpuscles.  The  investing 
sheath  of  the  fibres  is  here  continuous  with  the  connective  tissue  cover- 
ing of  the  corpuscle,  and  the  nerve-fibres  pass  into  the  corpuscle,  break 
up  into  two  or  three  divisions,  and  terminate  in  convoluted  or  knotted 
coils.  The  nerve-fibres  are  medullated  for  a  certain  distance,  but  their 
terminations  are  pale.  The  above  is  one  form  of  these  corpuscles. 
Sometimes,  however,  the  terminal  bulbs  are  oblong,  and  sometimes  but 
a  single  nerve-fibre  penetrates  the  bulb  and  terminates  in  a  simple  pale 
filament. 


MODE  OF  TERMINATION  OF  THE  SENSORY  NERVES 


467 


General  Mode  of  Termination  of  the  Sensory  Nerves.  —  The  actual 
termination  of  the  sensory  nerves  on  the  general  surface  and  in  mucous 
membranes  is  still  a  question  of  some  obscurity.  Although  anatomists 
have  arrived  at  a  pretty  definite  knowledge  of  the  sensory  corpuscles,  it 
must  be  remembered  that  there  is  an  immense  cutaneous  and  mucous 
surface  in  which  no  corpuscles  have  as  yet  been  demonstrated  ;  and  it 
is  in  these  parts,  endowed  with  what  may  be  called  general  sensibility, 
as  distinguished  from  the  sense  of  touch,  that  the  mode  of  termination 
of  the  nerves  demands  further  study. 

According  to  Kolliker,  in  the  great  majority  of  instances  the  sensory 
nerves  terminate  in  some  way  in  the  hair-follicles ;  and  this  would 
account  for  the  termination  of  the  nerves  in  by  far  the  greatest  portion 
of  the  skin,  as  there  are  few  parts  in  which  hair-follicles  do  not  exist ; 


Fig.  106.  —  Papillm  of  the  skin  of  the  palm  of  the  hand  (Sappey). 

I,  papilla  with  two  vascular  loops  ;  2,  papilla  with  a  tactile  corpuscle  ;  3,  papilla  with  three  vascular 
loops;  4,  5,  large  compound  papillse;  6,  6,  vascular  network  beneath  the  papillse ;  7,  7,  7,  7,  vascular 
loops  in  the  papillae;  8,  8,  8,  8,  nerves  beneath  the  papillae;  9,  9,  10,  11,  tactile  corpuscles. 

but  unfortunately  the  exact  mode  of  connection  of  the  nerves  with  these 
follicles  is  not  apparent.  The  following  seems  to  be  all  that  is  posi- 
tively known  of  the  terminations  of  the  nerves  on  the  general  surface : 

Medullated  nerve-fibres  form  a  plexus  in  the  corium,  which  gives 
off  filaments,  usually  non-medullated,  that  terminate  in  the  structures 
just  beneath  the  epidermis.  That  some  fibres  go  to  the  hair-follicles, 
there  can  be  no  doubt.  It  is  thought  by  some  histologists  that  pale 
fibres  form  a  network  around  and  between  the  cells  of  the  Malpighian 
layer  of  the  epidermis.  A  certain  number  of  fibres  pass  to  the  non- 
striated  muscular  fibres  of  the  skin.  A  certain  number  pass  to  papillae 
and  terminate  in  tactile  corpuscles,  and  others  pass  to  papillas  that  have 
no  tactile  corpuscles. 

In  the  mucous  membranes  the  mode  of  termination  is,  in  general 
terms,  by  a  delicate  plexus  just  beneath  the  epithelium,  coming  from  a 
submucous  plexus  analogous  to  the  deep  cutaneous  plexus.     In  certain 


468 


NERVOUS    SYSTEM 


membranes  the  nerves  terminate  in  end-bulbs,  or  corpuscles  of  Krause 
(see  Fig.  105,  p.  466).  In  the  cornea,  branching  nerve-fibres  pass  to 
the  nucleoli  of  the  corneal  corpuscles  and  to  the  nucleoli  of  the  cells 
of  the  posterior  layer  of  epithelium. 

Structure  of  the  Nen'e-ceutres.  — A  peculiar  pigmentary  matter  in  the 
nerve-cells  and  in  the  surrounding  granular  substance  gives  to  the  nerve- 
centres  a  grayish  color,  by  which  they  are  readily 
distinguished  from  the  white,  or  fibrous  division 
of  the  nervous  system.  Wherever  this  gray 
matter  is  found,  the  anatomical  elements  of  the 
tissue  are  cellular,  except  in  the  nerves  formed  of 
gray,  or  gelatinous  fibres.  Under  the  general 
division  of  nerve-centres  are  included,  anatomi- 
cally at  least,  the  gray  matter  of  the  cerebro- 
spinal centres,  the  ganglia  of  the  roots  of  the 
spinal  and  certain  of  the  cranial  nerves,  and  the 
ganglia  of  the  sympathetic  system.  In  these 
parts  are  found  cells,  which  constitute  the  essen- 
tial anatomical  element  of  the  tissue,  granular 
matter  resembling  the  contents  of  the  cells,  pale 
fibres  originating  in  prolongations  of  the  cells, 
elements  of  connective  tissue,  delicate  membranes 
enveloping  some  of  the  cells,  with  bloodvessels 
and  lymphatics. 

Nerve-cells.  —  The  following  varieties  of  cells 
exist  in  the  nerve-centres  and  constitute  their 
essential  anatomical  elements :  unipolar,  bipolar 
and  multipolar  cells.  These  cells  present  great 
differences  in  their  size  and  general  appearance, 
and  some  distinct  varieties  are  found  in  particular 
Fig.  107.  -  Unipolar  cell  portions  of  the  nervous  system.  Unipolar  and 
from  the  Gasserian  ganglion    bipolar   cclls    are   found   in   the   ganglia  of  the 

(Schwalbe).  ^    .    ,  ,   •        ,  ,•        r  .i  .      • 

,,,,,,        ,  ■     r    u     cranial  nerves  and  m  the  ganglia  of  the  posterior 

N,   N,   N,   nuclei    of    the  »       o  jr 

sheath;  z,  fibre  branching  at  roots  of  the  Spinal  ncrvcs.  Small  unipolar  cclls 
a  node  of  Ranvier.  ^^^  ^^^^^  .^^  ^^^  Sympathetic  ganglia.    Multipolar 

cells  present  three  or  more  prolongations.  Small  cells,  with  three  and 
rarely  four  prolongations,  are  found  in  the  posterior  cornua  of  the  gray 
matter  of  the  spinal  cord.  From  their  situation  they  have  been  called 
sensory  cells ;  and  they  are  found  in  greatest  number  in  parts  known  to  be 
endowed  exclusively  with  sensory  properties.  Large,  irregularly-shaped 
multipolar  cells,  with  a  number  of  poles,  or  prolongations,  are  found 
chiefly  in  the  anterior  cornua  of  the  gray  matter  of   the  spinal  cord, 


NERVE-CELLS 


469 


and  these  have  been  called  motor  cells.  They  sometimes  present  as 
many  as  ten  or  twelve  poles. 

Unipolar  cells,  such  as  exist  in  the  ganglia  of  the  nerves  as  dis- 
tinguished from  the  ganglia  of  the  cerebro-spinal  axis,  have  but  a  single 
prolongation,  which  is  continuous  with  a  ner\-e-fibre.  These  cells 
frequently  have  a  connective-tissue  envelope,  or  sheath,  which  is  pro- 
longed as  a  sheath  for  the  nerve.  Unipolar  cells,  with  a  connective- 
tissue  sheath,  the  pole  surrounded  with  a  spiral  fibre,  have  been  observed 
in  the  sympathetic  gangha  of  the  frog.  These  do  not  exist  in  the  human 
subject  or  in  the  mammalia,  and  nothing  is  known  of  the  uses  of  the 
spiral  fibres. 

Bipolar  cells  seem  to  be  nucleated  enlargements  in  the  course  of 
medullated  nerve-fibres.  Usually  the  medullary  substance  does  not 
extend  over  the  cell,  although  this  some- 
times occurs. 

Multipolar  cells  have  a  number  of 
poles,  but  there  is  always  one  pole  which 
does  not  branch  and  which  becomes  con- 
tinuous with  the  axis-cylinder  of  a  neri^e- 
fibre.  This  is  now  known  as  the  neurite, 
or  axis-cylinder  prolongation.  The  other 
poles,  called  dendrites,  or  protoplasmic 
prolongations,  branch  freely  and  are  lost 
in  the  intercellular  substance  (see  Plate 
XI,  Fig.  I). 

With  all  the  differences  in  the  size  and 
form  of  the  nerve-cells,  they  present  tol- 
erably uniform  general  characters  as  re- 
gards their  structure  and  contents.  With 
the  exception  of  the  unipolar  and  bipolar  cells,  they  are  irregular  in 
shape,  with  strongly-refracting  granular  contents,  frequently  a  consider- 
able number  of  pigmentary  granules,  and  always  a  distinct  nucleus  and 
nucleolus.  Many  cells  also  contain  little  angular  bodies  called  Xissl's 
granules  (see  Plate  XI,  Fig.  2;.  The  nucleus  in  the  adult  is  almost 
invariably  single,  although  in  rare  instances  two  have  been  noted.  Cells 
with  multiple  nuclei  are  often  observed  in  young  animals.  The  nucleoli 
usually  are  single,  but  there  may  be  as  many  as  four  or  five.  The 
diameter  of  the  cells  is  variable.  They  usually  measure  yoVr  ^*^  oTo 
of  an  inch  (20  to  50  ^);    but  there  are  many  of  larger  size  and  some 

are  smaller.  The  nuclei  measure  o  ch 0  ^*^  T2V0  °^  ^^  ^'^^^  ^^^  ^°  ^'^  l^)- 
The  nerve-cells  are  soft,  have  no  true  cell-membrane  and  are  fibrillated 
the  fibrillation  extending  into  the  poles. 


Fig.  108. — A,  unipolarnerve-ceU with 

a  spiral  fibre  ;  B,  bipolar  nerve-cell  (Lan- 
dois). 


470 


NERVOUS    SYSTEM 


Nerve-cells  present  many  peculiarities  as  they  are  found  in  different 
situations.  Some  of  these  will  be  described  here,  and  others  will  be 
considered  in  connection  with  the  study  of  special  nerve-centres  and 
the  structure  of  what  is  called  the  neuron. 

In  the  sympathetic  ganglia,  the  nerve-cells  usually  are  multipolar, 
and,  with  their  processes,  are  enclosed  in  a  sheath  lined  with  endothehum. 
Figure  109  represents  an  isolated  cell  from  a  sympathetic  ganglion  of  man. 
It  is  to  be  noted  that  this  cell,  hke  most  of  the  cells  of  the  central  ner- 
vous system,  is  multipolar.  Figure  1 10  represents  a  cell  from  the  electric 
organ  of  the  torpedo,  isolated  and  prepared  without  the  use  of  staining 
solutions.  This  cell  shows  the  characteristics  of  a  multipolar  nerve-cell : 
the   axis-cylinder   prolongation,  or  neurite,  the   so-called    protoplasmic 

prolongations,  or  dendrites, 
the  nucleus  and  nucleolus 
and  the  structure  of  the  cell- 
body. 

A^issfs  Grannies.  —  In  the 
cells  of  the  encephalon  and 
spinal  cord,  staining  deeply 
with  methylene  blue,  are 
found  small  angular  gran- 
ules, first  described  by  Nissl. 
These  extend  a  short  distance 
into  the  protoplasmic  pro- 
longations, and  the  stain  also 
is  taken  up  by  the  nucleus  and 
nucleolus  (see  Fig.  1 12,  page 
472,  and  Plate  XI,  Fig.  2). 
The  Nissl  granules  —  some- 
times called  tigroid  granules 
—  are  composed  of  chromo- 
plasm,  which  is  a  nucleo-pro- 
teid.  The  name  kinetoplasm 
has  been  given  to  this  sub- 
stance to  indicate  its  probable 
function.  It  is  thought  that  the  potential  activity  of  the  cell  is  stored 
up  in  the  chromoplasm,  which  is  used  in  the  discharge  of  nerve- 
impulses  during  the  activity  of  the  cell ;  and  that  during  periods  of  rest 
the  granules  are  formed  again.  It  has  been  noted,  indeed,  that  the 
discharge  of  nerve-impulses  brings  about  a  disintegration  of  Nissl's 
granules,  which  break  down  into  a  fine  granular  substance,  part  of 
which    temporarily    disappears.     This    result   of   cell-activity   is    called 


Fig.  109.  —  Sympathetic  ganglion-cell  from  man,  x  750 
(Key  and  Retzius) . 
A,  cell  with  nucleus  and  nucleolus;   B,  sheath  with 
nucleated-cell  lining ;   C,  branched  process ;  D,  axis-cyl- 
inder process. 


NERVE-CELLS  47 1 

chromatolysis.     When    cells    undergo    degeneration    and    atrophy,    the 
chromatoplasm  disappears.     This  process  is  called  disuse  atrophy. 


Fig.  no. —  Cell  from  the  electric  lobe  of  the  torpedo  (Schultze). 
a,  axis-cylinder;  b,  b,  b,  dendrites. 

The  Neuron.  —  The  prevailing  idea  now  is  that  the  nervous  system 
is  made  up  of  anatomically  and  physiologically  distinct  entities  called 


472 


NERVOUS    SYSTEM 


neurons.       The  neuron  is  composed  of  (i)  a  cell-body,  (2)  a  neurite, 

formerly  known  as  the  axis-cylinder  prolongation,  (3)  dendrites,  formerly 

called    protoplas-   --^;-,.. 

mic  prolongations 

and  (4)  collaterals, 

given  off  by  the  neurites.    The 

neurites     are    fibrillated,    and 

their  terminal  fibrils  are  called 

teloneurites.      In  their  course 

they  frequently  give  off  large 

numbers   of  collaterals.     The 

terminal  fibrils  of  the  dendrites 

are  called  telodendrites.     The 

cell-body  is  identical  with  what 

has  already  been  described  as 

the  nerve-cell.     The  unstained 

Fig.  no  shows  the  cell-body, 

the  neurite  and  the  protoplas- 
mic prolongations,  but  not  the 

collaterals,     teloneurites     and 

telodendrites.     It  is  supposed 

that  nerve-impulses    are    sent 

out  by  the  cell-body  through  the  neurites  and  that  impressions  are  received 

by  the  dendrites. 

Accessory  Anatomical  Elements  of 
the  Nerve-centres.  —  In  addition  to  the 
neurons,  which  probably  are  the  only 
structures  directly  concerned  in  in- 
nervation, are  the  following  accessory 
anatomical  elements :  i,  outer  cover- 
ings surrounding  some  of  the  cells ; 

2,  intercellular     granular      matter ; 

3,  peculiar  corpuscles  called  myelo- 
cytes (Robin);  4,  connective-tissue 
elements  ;  5,  neuroglia ;  6,  bloodves- 
sels and  lymphatics. 

Certain  of  the  cells  in  the  spinal 
ganglia   and   in  the    ganglia   of   the 
-SK^^.Yxi.  — Diagram  of  a  nerve-cell  to  show  the    Sympathetic   system    are  surrounded 
Nissi granules  (R.  y  Cajai).  ^^-^-i^  ^   covcring,  Tcmoved  a  Certain 

«   axis-cylinder  process;    3,  Nissl  granules ;     distance  from   the   Cell    itSClf    SO    aS   tO 
c,  achromatic  substance  between  them  ;  a,  nu- 
cleus;  ^,  dendrite  with  Nissl  granule  at  division,     be   nearly  twice   the   diameter   of   the 


Fig.  III.  —  Nerve-cells,  glia-cells  and  neuroglia, 
from  the  spinal  cord  of  the  ta//^(Lavdowsky). 
en,  neurites  ;  the  neurite  from  the  lower  cell  gives  off  a 
process.     The  arborescent  processes  are  dendrites  branch- 
ing among  the  fibres  of  neuroglia. 


COMPOSITION    OF    THE    NERVOUS    SUBSTANCE  473 

cell,  which  is  continuous  with  the  sheath  of  the  medullated  fibres.  This 
membrane  is  nucleated  and  is  composed  mainly  of  a  layer  of  very  deli- 
cate endothelium. 

In  the  gray  matter  of  the  nerve-centres,  there  is  a  finely  granular 
substance  between  the  cells,  which  closely  resembles  the  granular  con- 
tents of  the  cells  themselves.  In  addition  to  this  granular  matter  are 
peculiar  elements  called  by  Robin  myelocytes.  These  are  found  in  the 
cerebro-spinal  centres,  forming  a  layer  near  the  boundary  of  the  white 
substance,  particularly  in  the  cerebellum.  They  exist  in  the  form  of 
free  nuclei  and  nucleated  cells,  the  free  nuclei  being  by  far  the  more 
abundant.  The  nuclei  are  rounded  or  ovoid,  with  strongly  accentuated 
borders,  are  unaffected  by  acetic  acid,  are  finely  granular  and  usually 
are  without  nucleoH.  The  cells  are  rounded  or  slightly  polyhedric,  pale, 
clear  or  very  sHghtly  granular,  and  contain  bodies  similar  to  the  free 
nuclei.  The  free  nuclei  are  g^-g-  to  ^^q  of  an  inch  (5  to  6  /u,)  in  diam- 
eter, and  the  cells  measure  2-5V0  ^°  2  oVo'  ^^'^  sometimes  ^  5V0  of  an  inch 
(10,  12,  and  15  yu.).  These  elements  are  not  to  be  confounded  with 
the  so-called  myelocytes  found  in  bone-marrow. 

In  the  cerebro-spinal  centres  there  is  a  delicate  stroma  of  connective 
tissue,  chiefly  in  the  form  of  stellate  branching  cells,  which  serves  in 
a  measure  to  support  the  nervous  elements.  Neuroglia  closely  re- 
sembles connective  tissue,  but  the  cells  and  their  prolongations  are 
much  finer.  The  cells  are  sometimes  called  glia-cells,  or  spider-cells. 
Neuroglia,  however,  is  derived  from  the  epiblast  and  is  composed  of 
neurokeratin,  while  the  true  connective  tissues  are  derived  from  the 
mesoblast.  With  the  connective  tissue,  the  neuroglia  serves  to  support 
the  true  nervous  structures. 

The  bloodvessels  of  the  nerve-centres  form  a  capillary  network  with 
large  meshes.  The  gray  substance  is  richer  in  capillaries  than  the 
white.  A  peculiarity  of  the  vascular  arrangement  in  the  cerebro-spinal 
centres  has  already  been  described  in  connection  with  the  anatomy  of 
the  lymphatic  system.  The  bloodvessels  here  are  surrounded  by  what 
have  been  called  perivascular  canals.  These  are  radicles  of  the  lym- 
phatic system. 

Coviposition  of  the  Nervous  Stibstmice.  —  The  chemistry  of  the  ner- 
vous substance,  so  far  as  it  is  understood,  throws  little  light  on  its 
physiology.  Certain  proteids  have  been  extracted  which  possess  no 
more  than  a  purely  chemical  interest.  The  substance  called  cerebrin  is 
composed  of  carbon,  hydrogen,  oxygen  and  nitrogen,  without  either 
sulphur  or  phosphorus.  Protagon  is  a  nitrogenous  substance  containing 
phosphorus  (Liebreich,  1865),  and  probably  is  a  mixture  of  cerebrin 
and    lecithin.       Lecithin   is    regarded   as    a   nitrogenous    fat.       Other 


474  NERVOUS    SYSTEM 

substances  that  have  been  extracted  —  xanthin,  hypoxanthin,  inosite, 
creatin  and  various  volatile  fatty  acids  —  have  no  special  physiological 
interest  connected  with  the  nervous  system  and  are  found  in  many 
other  situations.  Cholesterin,  which  always  exists  in  considerable 
quantity  in  the  nervous  tissue,  has  been  considered  in  connection  with 
the  physiology  of  excretion.  The  ordinary  fats  are  in  combination  with 
other  fats  or  with  peculiar  acid  substances.  The  reaction  of  nerve- 
tissue  is  either  neutral  or  faintly  alkaline  under  normal  conditions, 
becoming  acid  soon  after  death. 

Degeneration  and  Regeneration  of  Nerves.  —  The  degenerations 
observed  in  nerves  separated  from  the  centres  to  which  they  normally 
are  attached,  first  studied  by  Waller,  in  1850,  are  now  used  in  following 
out  certain  nervous  connections  too  intricate  to  be  revealed  by  ordinary 
dissection.  This  is  known  as  the  Wallerian  method.  If  an  ordinary 
mixed  nerve  is  divided  in  its  course,  both  the  motor  and  sensory  fibres 
of  the  peripheral  portion  undergo  degeneration  and  lose  their  con- 
ductivity. As  regards  the  spinal  nerves,  degeneration  occurs  in  the 
motor  fibres  only,  when  the  anterior  spinal  root  has  been  divided,  and 
the  nerve  has  degenerated  fibres  (motor)  mixed  with  the  sensory  fibres, 
which  latter  retain  their  anatomical  and  physiological  integrity.  The 
motor  fibres  of  the  spinal  nerves  are  degenerated  when  separated  from 
their  connections  with  the  anterior  cornua  of  gray  matter  of  the  cord. 
If  the  posterior  roots  of  the  spinal  nerves  are  divided  beyond  the 
ganglia,  the  peripheral  sensory  fibres  degenerate ;  but  if  the  ganglia 
are  exsected,  the  central  as  well  as  the  peripheral  portions  degenerate. 
These  experiments  show  the  existence  of  centres  that  preside  over  the 
nutrition  of  the  nerves.  The  centres  for  the  motor  filaments  of  the 
spinal  nerves  are  in  the  anterior  cornua  of  gray  matter  of  the  cord. 
The  centres  for  the  sensory  fibres  are  the  ganglia  of  the  posterior  roots. 
The  centres  for  the  sensory  cranial  nerves  are  the  ganglia  on  their  roots  ; 
and  the  centres  for  the  motor  cranial  nerves  are  probably  the  gray  nuclei 
of  origin  of  these  nerves.  The  Wallerian  method  has  been  found  use- 
ful in  studying  the  paths  of  conduction  in  the  encephalon  and  spinal 
cord,  as  will  be  seen  in  connection  with  the  physiology  of  these  parts. 

The  excitability  of  the  motor  nerves  disappears  in  about  four  days 
after  their  section.  Of  course,  in  experiments  on  this  point,  it  is 
necessary  to  excise  a  portion  of  the  nerve  to  prevent  reunion  of  the 
divided  extremities ;  but  when  this  is  done,  after  about  the  fourth  day, 
stimulation  of  the  nerve  will  produce  no  contraction  of  muscles,  although 
the  latter  retain  their  contractility.  This  loss  of  excitability  is  gradual, 
and  it  continues,  whether  the  nerve  is  exposed  and  stimulated  from  time 
to  time  or  is  left  to  itself,  progressing  from  the  centres  to  the  periphery. 


MOTOR    AND    SENSORY   NERVES  475 

The  sensibility  of  the  sensory  nerves  disappears  from  the  periphery 
to  the  centres,  as  is  shown  in  dying  animals  and  in  experiments  with 
anesthetics.  The  sensibility  is  lost,  first  in  the  terminal  branches  of 
the  nerves,  next  in  the  trunks  and  in  the  posterior  roots  of  the  spinal 
nerves,  and  so  on  to  the  centres. 

Nerves  that  have  been  divided  may  be  regenerated  if  anatomical 
union  of  the  divided  ends  can  be  secured ;  and  this  sometimes  takes 
place  several  months  after  injury  to  the  nerves,  the  regeneration  occur- 
ring by  the  formation  of  new  fibres.  Mixed  nerves  are  regenerated  in 
this  way,  and  conduction  in  both  directions  finally  is  restored.  The 
sensory  conduction  appears  first,  and  next,  the  conduction  of  motor 
impulses.  The  restoration  of  the  physiological  properties  of  the  nerves 
occupies  several  weeks.  The  central  end  of  a  mixed  nerve  has  been 
made  to  unite  with  the  peripheral  end  of  another  mixed  nerve,  but  it  is 
doubtful  whether  a  divided  end  of  a  motor  nerve  can  be  united  to  the 
divided  end  of  a  sensory  nerve. 

Motor  and  Sensory  Nerves 

Aside  from  nerves  possessing  special  properties,  such  as  nerves  of 
sight,  hearing,  smell,  taste  and,  according  to  some  physiologists,  nerves 
of  touch,  temperature,  sense  of  weight  and  muscular  sense,  the  cerebro- 
spinal nerves  present  two  kinds  of  fibres.  These  are  (i)  centrifugal,  or 
motor  fibres,  and  (2)  centripetal,  or  sensory  fibres.  The  motor  fibres 
conduct  impulses  from  the  centres  to  the  muscles  and  excite  muscular 
contraction.  The  sensory  fibres  conduct  impressions  from  the  periphery 
to  the  centres,  which  are  appreciated  either  as  ordinary  sensation  or  as 
pain.  As  regards  the  nerves  arising  by  two  roots  from  the  spinal  cord, 
the  exact  anatomical  and  physiological  divisions  into  motor  and  sensory 
were  first  made  by  Magendie,  in  1822.  As  will  be  seen  farther  on,  this 
division  is  distinct  for  the  cranial  nerves,  so  that  it  is  universal  in  the 
cerebro-spinal  system.  The  importance  of  the  discovery  of  the  distinct 
properties  of  the  two  roots  of  the  spinal  nerves  is  such  that  it  merits  at 
least  a  brief  historical  account,  particularly  as  this  discovery  has  been 
quite  generally  attributed  to  Charles  Bell. 

The  first  definite  statement  in  regard  to  distinct  properties  of  the 
two  roots  of  the  spinal  nerves  was  made  by  Alexander  Walker,  in  1809, 
who  said  that  the  posterior  roots  were  for  motion  and  the  anterior  roots 
for  sensation,  —  the  exact  reverse  of  the  truth. 

In  a  pamphlet  privately  printed  by  Charles  Bell,  probably  in  181 1, 
and  "  submitted  for  the  observations  of  his  friends,"  the  view  was 
advanced  that  the  anterior  roots  are  both  motor  and  sensory  and  that 


476  NERVOUS    SYSTEM 

the  posterior  preside  over  "  the  secret  operations  of  the  bodily  frame,  or 
the  connections  which  unite  the  parts  of  the  body  into  a  system." 

In  1822,  Magendie,  as  the  result  of  experiments  on  the  exposed  roots 
in  living  dogs,  stated  that  "  he  was  able  at  that  time  to  advance  as 
positive,  that  the  anterior  and  the  posterior  roots  of  the  nerves  which 
arise  from  the  spinal  cord  have  different  functions,  that  the  posterior 
seem  more  particularly  destined  to  sensibility,  while  the  anterior  seem 
more  specially  connected  with  motion." 

All  observations  on  the  roots  of  the  spinal  nerves  show  that  the 
mixed  nerves  arising  from  the  cord  derive  their  motor  properties  from 
the  anterior  roots  and  their  sensory  properties  from  the  posterior  roots : 
and  since  the  publication  of  an  historical  review  of  the  question  of 
priority  between  Bell  and  Magendie  (Flint,  1868),  it  has  been  ad- 
mitted that  the  credit  of  this  discovery  belongs  to  Magendie. 

The  anterior  roots  possess  a  certain  degree  of  sensibility  in  addition 
to  their  motor  properties  (Magendie).  This  sensibility,  which  is  slight, 
is  derived  from  fibres  from  the  posterior  roots,  which  turn  back  to  go  to 
the  anterior  roots.  This  has  been  positively  demonstrated  by  the  Wal- 
lerian  method.  When  a  posterior  root  is  divided  beyond  the  ganglion, 
the  sensibility  of  the  corresponding  anterior  root  is  lost,  and  degenerated 
fibres  appear,  after  a  few  days,  in  the  anterior  roots.  This  sensibility 
of  the  anterior  roots  is  called  recurrent  sensibility.  Similar  relations 
exist  between  certain  of  the  motor  and  sensory  cranial  nerves. 

Mode  of  Action  of  the  Aloior  Nej'Z'cs.  —  As  regards  the  normal  action 
of  the  motor  nerves,  impulses,  the  nature  of  which  is  unknown,  gener- 
ated in  the  centres,  are  conducted  from  the  centres  to  the. peripheral 
distribution  of  the  nerves  in  the  muscles,  and  are  here  manifested  by 
contraction.  Their  mode  of  action,  therefore,  is  centrifugal.  When 
these  motor  filaments  are  divided,  the  connection  between  the  parts 
animated  by  them  and  the  centre  is  interrupted,  and  motion  in  these 
parts,  in  obedience  to  the  natural  stimulus,  becomes  impossible.  While, 
however,  it  is  not  always  possible  to  induce  generation  of  nerve-force  in 
the  centres  by  the  direct  apphcation  of  any  agent  to  them,  this  force 
may  be  imitated  by  stimulation  applied  to  the  nerve  itself.  A  nerve 
that  will  thus  respond  to  direct  stimulation  is  said  to  be  excitable. 

If  a  motor  nerve  is  divided,  electric,  mechanical  or  other  stimulus 
applied  to  the  extremity  connected  with  the  centres  produces  no  effect ; 
but  the  same  stimulus  applied  to  the  extremity  connected  with  the 
muscles  is  followed  by  contraction.  The  phenomena  indicating  that  a 
nerve  retains  its  physiological  properties  are  always  manifested  at  its 
peripheral  distribution,  and  these  do  not  vary  essentially  when  the  nerve 
is  stimulated  at  different  points  in  its  course.     For  example,  stimulation 


ACTION    OP^   MOTOR   AND    SENSORY   NERVES  477 

of  the  anterior  roots  near  the  cord  produces  contraction  in  the  muscles 
to  which  the  fibres  of  these  roots  are  distributed  ;  but  the  same  effect 
follows  stimulation  of  the  nerve  going  to  these  muscles,  in  any  parts  of 
its  course. 

So  far  as  their  physiological  action  is  concerned,  the  individual 
nerve-fibres  are  independent ;  and  the  relations  which  they  bear  to  each 
other  in  nervous  fasciculi  and  in  the  so-called  anastomoses  of  nerves 
involve  simple  contiguity.  Comparing  the  nerve-force  to  electricity, 
each  individual  fibre  seems  completely  insulated ;  and  a  stimulus  con- 
ducted by  it  to  muscles  does  not  extend  to  the  adjacent  fibres.  That  it 
is  the  axis-cylinder  which  conducts  and  the  medullary  tube  which  in- 
sulates, it  is  impossible  to  say  with  positiveness ;  but  it  is  more  than 
probable  that  the  axis-cylinder  is  the  only  conducting  element. 

Generation  of  motor  impulses  may  be  induced  by  an  impression 
made  on  sensory  nerves  and  conveyed  by  them  to  the  centres.  If,  for 
example,  a  certain  portion  of  the  central  nervous  system,  as  the  spinal 
cord,  is  isolated,  leaving  its  connections  with  the  motor  and  sensory 
nerves  intact,  these  phenomena  may  readily  be  observed.  An  impres- 
sion made  on  the  sensory  nerves  will  be  conveyed  to  the  gray  matter  of 
the  cord  and  will  induce  the  generation  of  a  motor  impulse  by  the  cells 
of  this  part,  which  will  be  conducted  to  the  muscles  and  give  rise  to 
contraction.  As  the  impulse,  in  such  observations,  seems  to  be  reflected 
from  the  cord  through  the  motor- nerves  to  the  muscles,  this  action  has 
been  called  reflex.  These  phenomena  constitute  an  important  division 
of  the  physiology  of  the  nervous  system  and  will  be  fully  considered  by 
themselves. 

Associated  Movements.  —  It  is  well  known  that  the  action  of  certain 
muscles  is  with  difficulty  isolated  by  an  effort  of  the  will.  This  applies 
to  sets  of  muscles  on  one  side  of  the  body  and  to  corresponding  muscles 
on  the  two  sides.  For  example,  it  is  almost  impossible,  without  great 
practice,  to  move  some  of  the  fingers,  at  the  same  time  restraining  the 
movements  of  the  others ;  and  the  action  of  certain  sets  of  muscles  of 
the  extremities  is  simultaneous.  The  toes,  which  are  but  little  used  as 
the  foot  is  confined  in  the  ordinary  dress,  are  capable  of  little  indepen- 
dent action.  It  is  difficult  to  move  one  eye  without  the  other,  or  to 
make  rapid  rotary  movements  of  one  hand  while  a  different  order  of 
movements  is  executed  with  the  other;  and  instances  of  this  kind  might 
be  multiplied. 

Many  associated  movements  may  be  influenced  in  a  remarkable 
degree  by  education,  of  which  no  better  examples  can  be  found  than 
in  skilful  performers  on  certain  musical  instruments,  such  as  the  piano, 
harp,  violin  and  other  stringed  instruments.     In  the  technical  study  of 


478  NERVOUS   SYSTEM 

such  instruments,  not  only  does  one  hand  become  almost  independent 
of  the  other,  but  very  complex  associated  movements  may  be  acquired. 
An  accomplished  pianist  or  violinist  executes  the  different  scales  auto- 
matically by  a  single  effort  of  the  will,  and  pianists  frequently  execute 
at  the  same  time  scales  with  both  hands,  the  action  being  opposed  to 
the  natural  association  of  movements. 

Looking  at  the  associated  movements  in  their  relations  to  the  mode 
of  action  of  the  motor  nerves,  it  seems  probable  that,  as  a  rule,  the 
anatomical  relations  of  the  nerves  are  such  that  a  motor  impulse  or  an 
effort  of  the  will  can  not  be  conducted  to  a  portion  only  of  a  muscle, 
but  must  act  on  the  whole  muscle,  and  the  same  is  true,  probably,  of 
certain  restricted  sets  of  muscles ;  but  the  association  of  movements  of 
corresponding  muscles  on  the  two  sides  of  the  body,  with  the  exception, 
perhaps,  of  the  muscles  of  the  eyes,  is  due  mainly  to  habit  and  may  be 
greatly  modified  by  education. 

Mode  of  Action  of  the  Sensory  Nerves.  —  The  sensory  nerve-fibres, 
like  the  fibres  of  the  motor  nerves,  are  independent  of  each  other  in 
their  action  ;  and  in  the  so-called  anastomoses  that  take  place  between 
sensory  nerves,  the  fibres  assume  no  new  relations,  except  as  regards 
contiguity. 

As  motor  fibres  convey  to  their  peripheral  distribution  impulses  pro- 
duced by  a  stimulus  applied  in  any  portion  of  their  course,  so  an  impres- 
sion made  on  a  sensory  nerve  is  always  referred  to  the  periphery.  A 
familiar  example  of  this  is  afforded  by  the  very  common  accident  of 
contusion  of  the  ulnar  nerve  as  it  passes  between  the  olecranon  and 
the  condyle  of  the  humerus.  This  is  attended  with  painful  tingling  of 
the  ring  and  little  finger  and  other  parts  to  which  the  filaments  of  this 
nerve  are  distributed,  without,  necessarily,  any  pain  at  the  point  of 
injury.  More  striking  examples  are  afforded  in  neuralgic  affections 
dependent  on  disease  of  or  pressure  on  the  trunk  of  a  sensory  nerve. 
In  such  cases,  excision  of  the  nerve  is  often  practised,  but  no  perma- 
nent reUef  follows  unless  the  section  be  made  between  the  affected  por- 
tion of  the  nerve  and  the  nerve-centres ;  and  the  pain  is  always  referred 
to  the  termination  of  the  nerve,  even  after  it  has  been  divided  between 
the  seat  of  the  disease  and  the  periphery,  leaving  the  parts  supplied  by 
the  nerve  insensible  to  direct  irritation.  In  cases  of  disease  it  is  not 
unusual  to  note  great  pain  in  parts  of  the  skin  that  are  insensible  to 
direct  impressions.  The  explanation  of  this  is  that  the  nerves  are 
paralyzed  near  their  terminal  distribution,  so  that  an  impression  made 
on  the  skin  can  not  be  conveyed  to  the  sensorium ;  but  the  trunks  of  the 
nerves  still  retain  their  conductivity  and  are  the  seat  of  diseased  action, 
producing  pain  referred  by  the  patient  to  the  periphery.     In  the  very 


NERVOUS    EXCITABILITY   AND    CONDUCTIVITY  479 

common  operation  of  restoring  the  nose  by  transplanting  skin  from  the 
forehead,  after  the  operation  has  been  completed,  the  skin  having  been 
entirely  separated,  and  united  in  its  new  relations,  the  patient  feels  that 
the  forehead  is  touched  when  the  finger  is  applied  to  the  artificial  nose. 
After  a  time,  however,  the  sensorium  becomes  accustomed  to  the  nev/ 
arrangement  of  the  parts  and  this  deceptive  feeling  disappears. 

There  are  certain  curious  nervous  phenomena,  that  are  not  without 
physiological  interest,  presented  in  persons  who  have  suffered  amputa- 
tions. It  has  long  been  observed  that  after  loss  of  a  limb,  the  sensa- 
tion of  the  part  remains ;  and  pain  is  frequently  experienced,  which  is 
referred  to  the  amputated  member.  Thus  a  patient  will  feel  distinctly 
the  fingers  or  toes  after  an  arm  or  a  leg  has  been  removed,  and  irrita- 
tion of  the  ends  of  the  nerves  at  the  stump  produces  sensations  referred 
to  the  missing  member.  After  a  time  the  sense  of  presence  of  the  lost 
limb  becomes  blunted,  and  it  may  in  some  cases  entirely  disappear. 
This  may  take  place  a  few  months  after  the  amputation,  or  the  sensa- 
tions may  remain  for  years.  Examples  have  been  reported  by  Miiller, 
in  which  the  sense  was  undiminished  thirteen,  and  in  one  case  twenty, 
years  after  amputation.  In  a  certain  number  of  cases,  however,  the  sense 
of  the  intermediate  part  is  lost,  the  feeling  in  the  hand  or  foot,  as  the 
case  may  be,  remaining  as  distinct  as  ever,  the  impression  being  that 
the  limb  is  gradually  becoming  shorter.  It  was  noted  by  Gueniot,  that 
the  sense  of  the  limb  becoming  shorter  exists  in  about  half  the  cases  of 
amputation  in  which  cioatrization  goes  on  regularly ;  and  in  these  cases, 
the  patient  finally  experiences  a  feeling  as  though  the  hand  or  foot  were 
in  direct  contact  with  the  stump. 

Physiological  Differences  between  Motor  and  Sensory  Nerve-fibres.  — 
It  has  not  been  shown  that  there  is  any  essential  anatomical  difference 
between  the  conducting  elements  of  motor  and  sensory  nerve-fibres ; 
but  the  physiological  differences  are  sufficiently  distinct,  as  has  already 
been  seen.  Under  normal  conditions,  motor  fibres  conduct  motor  im- 
pulses in  but  one  direction,  and  these  fibres  are  insensible.  Sensory 
fibres  conduct  impressions  always  in  the  opposite  direction,  and  they  do 
not  conduct  motor  impulses. 

Nervous  Excitability  and  Conductivity.  —  Immediately  or  soon  after 
death,  when  the  excitability  of  the  nerves  is  at  its  maximum,  they  may  be 
stimulated  by  mechanical,  chemical  or  electric  irritation,  all  these  agents 
producing  contraction  of  the  muscles  to  which  the  motor  filaments  are 
distributed.  Mechanical  irritation  —  simply  pinching  a  portion  of  the 
nerve,  for  example  —  produces  a  single  muscular  contraction;  but  if  the 
injury  to  the  nerve  is  such  as  to  disorganize  its  fibres,  that  portion  of 
the  nerve  will  no  longer  conduct  an  impulse.     Among  the  irritants  of 


48o  NERVOUS    SYSTEM 

this  kind,  are  extremes  of  heat  and  cold.  If  an  exposed  nerve  is  cauter- 
ized, a  vigorous  muscular  contraction  follows.  The  same  effect,  though 
less  marked,  may  be  produced  by  the  sudden  application  of  intense  cold. 
Among  chemical  reagents,  there  are  some  which  excite  the  nerves  and 
others  which  produce  no  effect;  but  these  are  not  important  from 
a  physiological  point  of  view,  except  common  salt,  which  is  sometimes 
used  when  it  is  desired  to  produce  tetanic  action.  Mechanical  stimula- 
tion and  the  action  of  certain  chemicals  are  capable  of  exciting  the 
nerves ;  but  when  their  action  goes  so  far  as  to  disorganize  the  fibres, 
the  conducting  power  of  these  fibres  is  lost.  While,  however,  stimula- 
tion of  the  nerve  above  the  point  of  such  injury  has  no  effect,  stimulation 
between  this  point  and  the  muscles  is  still  followed  by  contraction. 

The  excitability  of  a  nerve  is  not  to  be  confounded  with  its  conduc- 
tivity. A  nerve  is  excitable  when  its  stimulation  excites  muscular  action, 
the  impulse  being  conducted  to  the  muscle.  Acting  thus  as  a  conductor, 
the  nerve  is  said  to  possess  conductivity.  It  is  possible  to  destroy  for 
a  time  the  excitability  of  a  restricted  portion  of  a  nerve  without  affect- 
ing its  conductivity  ;  for  when  a  stimulus  is  applied  to  the  nerve  above 
this  portion,  it  is  followed  by  muscular  contraction,  the  impulse  being 
conducted  through  the  portion  that  has  been  rendered  inexcitable. 
Some  parts  of  the  nervous  system,  indeed,  normally  are  inexcitable 
under  direct  stimulation,  but  nevertheless  act  as  conductors. 

The  most  convenient  method  of  exciting  the  nerves  in  physiological 
experiments  is  by  means  of  electricity.  This  may  be  employed  without 
disorganizing  the  nerve-tissue,  and  it  consequently  admits  of  extended 
and  repeated  application.  The  action  of  electricity,  however,  with  the 
methods  of  preparing  the  nerves  and  muscles  for  experimentation,  will 
be  considered  under  a  separate  head. 

Rapidity  of  Ncrzwiis  Conduction. — The  first  accurate  estimates  of 
the  rapidity  of  nervous  conduction  were  made  by  Helmholtz,  in  1850, 
and  were  applied  to  the  motor  nerves  of  the  frog.  These  estimates 
were  arrived  at  by  an  application  of  the  graphic  method,  which  was 
afterward  considerably  extended  and  improved  by  Marey.  The  process 
employed  by  Marey,  which  is  essentially  the  same  as  that  used  in  more 
recent  investigations,  is  the  following :  — 

To  mark  small  fractions  of  a  second,  a  tuning-fork  vibrating  at  a 
known  rate  (five  hundred  times  in  a  second)  is  so  arranged  that  a  point 
connected  with  one  of  its  arms  is  made  to  play  against  a  strip  of  black- 
ened paper.  As  the  paper  remains  stationary,  the  point  makes  but  a 
single  mark  ;  but  when  the  paper  moves,  as  the  point  vibrates,  a  line  is 
produced  with  regular  curves,  each  curve  representing  -^\-^  of  a  second. 
If  a  lever  is  now  attached  to  a  muscle  and  so  arranged  as  to  indicate 


RAPIDITY   OF    NERVOUS    CONDUCTION  48 1 

on  the  paper,  moving  at  the  same  rate,  the  instant  when  contraction 
takes  place,  it  is  evident  that  the  interval  between  two  contractions 
produced  by  stimulating  the  nerve  at  different  points  in  its  course  may 
be  accurately  measured  ;  and  if  the  length  of  the  nerve  between  the  two 
points  of  stimulation  is  known,  the  difference  in  time  will  represent  the 
rate  of  nervous  conduction.  In  experiments  on  frogs  the  leg  is  prepared 
by  cutting  away  the  muscles  and  bone  of  the  thigh,  leaving  the  nerve 
attached.  The  lever  is  then  applied  to  the  muscles  of  the  leg,  and  the 
nerve  is  stimulated  successively  at  two  points,  the  distance  between 
them  being  measured. 

Employing  the  myograph  of  Marey,  Baxt,  in  the  laboratory  of  Helm- 
holtz,  succeeded  in  measuring  the  rate  of  nervous  conduction  in  the 
human  subject.  In  these  experiments,  the  swelling  of  the  muscle  dur- 
ing contraction  was  limited  by  enclosing  the  arm  in  a  plaster-mould,  and 
the  contraction  was  observed  through  a  small  opening.  By  then  excit- 
ing the  contraction  by  stimulating  the  radial  nerve  successively  at  dif- 
ferent distances  from  the  muscle,  the  estimate  was  made.  The  rate  in 
the  human  subject  was  thus  estimated  at  one  hundred  and  eleven  feet 
(33.9  meters)  per  second. 

The  method  used  in  determining  the  rate  of  conduction  in  motor 
nerves  —  an  estimation  of  the  difference  in  time  of  the  passage  of  a 
stimulus  applied  to  a  nerve  at  two  points  situated  at  a  known  distance 
from  each  other — has  been  applied  to  the  conduction  of  sensations. 
Hirsch  made  the  first  attempt  to  solve  this  question,  in  1861.  He 
employed  the  delicate  chronometric  instruments  used  in  astronomy  and 
noted  the  difference  in  time  between  the  appreciation  of  an  impression 
made  on  a  part  of  the  body  far  removed  from  the  brain,  as  the  toe, 
and  an  impression  made  on  the  cheek.  This  process  admitted  of  a 
rough  estimate  of  about  one  hundred  and  eleven  feet  (33.9  meters)  per 
second  as  the  rate  of  sensory  conduction. 

It  is  not  necessary  to  describe  fully  the  apparatus  by  means  of 
which  the  most  recent  estimates  of  the  rate  of  nervous  conduction  have 
been  made.  The  general  results  of  the  observations  of  Helmholtz,  Marey, 
Baxt,  Schleske  and  of  many  others  nearly  correspond  with  the  estimates 
just  given,  and  they  show  that  the  rate  is  about  the  same  for  motor  and 
sensory  nerves.  This  rate  is  modified  by  various  conditions.  It  is 
diminished  in  the  anelectrotonic  and  increased  in  the  catelectrotonic 
condition  of  nerves.  In  the  frog  Helmholtz  observed  that  the  rate  was 
much  reduced  by  cold;  at  32°  Fahr.  (0°  C.)  being  not  more  than  one- 
tenth  as  rapid  as  at  60°  or  70°  Fahr.  (15.5°  or  21.11°  C). 

The  rate  of  transmission  of  impulses  and  impressions  through  the 
spinal  cord  has  been  investigated  by  calculating  the  distances  between 


482  NERVOUS    SYSTEM 

nerves  as  they  are  given  off  at  different  points  and  measuring  the  time 
required  for  the  appreciation  of  certain  impressions  and  the  beginning 
of  certain  movements.  While  these  observations  are  not  absolutely- 
exact,  their  general  results  are  of  considerable  physiological  interest. 
According  to  Burkhardt,  the  rate  of  motor  conduction  in  the  cord  is 
about  one-third  of  the  normal  rate  in  the  motor  nerves  As  compared 
with  the  sensory  nerves,  the  cord  conducts  tactile  impressions  a  little 
faster  and  painful  impressions  less  than  one-half  as  fast. 

Attempts  have  been  made  to  estimate  the  duration  of  acts  involving 
the  central  nervous  system,  such  as  the  reflex  phenomena  of  the  spinal 
cord  or  the  operations  of  the  cerebral  hemispheres  These  have  been 
partially  successful,  or,  at  least,  they  have  shown  that  the  reflex  and  the 
cerebral  acts  require  a  distinctly  appreciable  period  of  time.  This  in 
itself  is  an  important  fact ;  although  the  duration  of  these  acts  has  not 
been  measured  with  absolute  accuracy.  As  the  general  result  of 
experiments  on  these  points,  it  has  been  found  that  the  reflex  action  of 
the  spinal  cord  occupies  more  than  twelve  times  the  period  required  for 
the  transmission  of  stimulus  or  impressions  through  the  ner\'es.  Bon- 
ders found,  in  experiments  on  his  own  person,  that  an  act  of  volition 
required  o\  of  a  second,  and  one  of  simple  distinction  or  recognition  of 
an  impression,  ^V  of  a  second.  These  estimates,  however,  are  merely 
approximate;  and,  until  they  attain  greater  accuracy,  it  is  unnecessary 
to  describe  in  detail  the  apparatus  employed. 

Aside  from  what  have  been  described  as  reflex  acts,  it  is  found  that 
when  impulses  or  impressions  pass  through  cells,  there  is  a  distinct 
retardation  or  delay  in  conduction,  amounting  to  about  0.006  of  a 
second  for  afferent  conduction  in  the  spinal  cord  and  about  0.05  for 
efferent  conduction.  These  figures,  however,  are  approximations  and 
are  interesting  chiefly  as  indicating  an  action  of  nerve-cells  different 
from  ordinary  conduction  by  nerve-fibres,  that  has  not  been  satisfac- 
torily explained.  It  is  probable  that  the  delay  is  due  to  a  redistribution 
of  the  impulses  by  the  cells  to  the  synapses  through  which  the  conduc- 
tion is  continued  in  one  direction  or  the  other. 

Personal  Equation. —  In  recording  astronomical  observations,  it 
has  been  found  that  a  certain  time  elapsed  between  the  actual  observa- 
tion of  a  phenomenon  and  the  moment  of  its  record.  This  error,  which 
is  equal  to  the  interval  of  time  between  the  impression  made  on  the 
retina  and  the  muscular  act  by  which  a  record  is  made,  is  not  the  same 
in  different  persons  or  even  in  the  same  person  at  all  times.  It  may 
amount  to  ^  of  a  second  or  even  more,  and  it  may  be  as  low  as  -^^  of  a 
second.  If  this  difference  is  due  to  different  rates  of  nervous  conduc- 
tion, and  not  entirely  to  variations  in  the  rapidity  of  mental  operations, 


ACTION    OF   ELECTRICITY   ON   THE    NERVES  483 

it  is  evident  that  the  velocity  of  the  nerve-current  must  vary  very  con- 
siderably in  different  individuals. 

Action  of  Electricity  on  the  Nerves. —  So  long  as  the  nerves  retain 
their  excitability  and  anatomical  integrity,  they  will  respond  to  properly 
applied  electric  stimulus.  Experiments  may  be  made  on  the  exposed 
nerves  in  living  animals  or  in  animals  just  killed ;  and  of  all  classes,  the 
cold-blooded  animals  present  the  most  favorable  conditions,  on  account 
of  the  persistence  of  nervous  and  muscular  excitability  for  a  consider- 
able time  after  death.  Experimenters  commonly  use  frogs,  on  account 
of  the  long  persistence  of  the  physiological  properties  of  their  tissues 
and  the  facility  with  which  certain  parts  of  the  nervous  system  can  be 
exposed.  For  ordinary  experiments  on  nervous  conduction,  the  parts 
are  prepared  by  detaching  the  posterior  extremities,  removing  the  skin, 
and  cutting  away  the  bone  and  muscles  of  the  thigh  so  as  to  leave  the 
leg  with  the  sciatic  nerve  attached.  A  frog's  leg  thus  isolated  presents 
a  nervous  trunk  one  or  two  inches  (25  or  50  millimeters)  in  length, 
attached  to  the  muscles,  which  will  respond  to  a  feeble  electric  stimulus. 
It  is  by  experiments  made  on  frogs  prepared  in  this  way,  that  most  of 
the  important  facts  in  regard  to  the  action  of  electricity  on  the  nervous 
system  have  been  developed. 

In  physiological  experiments  it  is  sometimes  necessary  to  use  differ- 
ent forms  of  electrical  apparatus  in  order  to  study  different  properties 
and  phenomena  of  nerve  and  muscle.  A  description  of  the  apparatus 
thus  used  would  be  out  of  place  in  this  work,  and  it  will  be  necessary 
only  to  enumerate  and  describe  the  different  currents  used  and  the 
manner  of  their  application.  Many  of  the  phenomena,  also,  described 
by  electro-physiologists,  although  curious  and  interesting,  have  little 
apparent  application  to  human  physiology  or  to  the  practice  of  medi- 
cine. A  description  of  such  phenomena  may  well  be  brief  in  a  work 
for  the  use  of  students  and  practitioners  of  medicine. 

In  studying  the  action  of  nerve  and  muscle,  experimenters  often  use 
what  is  called  a  single  faradic,  or  induction  shock,  with  a  duration  of 
about  YoVo"  (0.0008)  of  a  second.  The  excitation,  therefore,  is  practically 
instantaneous.  These  single  shocks  are  produced  by  Du  Bois-Reymond's 
apparatus,  which  is  a  modification  of  the  faradic,  or  induction  battery. 
It  will  be  seen  farther  on  that  somewhat  different  effects  are  produced 
by  the  stimulus,  due  to  closing  and  opening  the  circuit,  and  that  with  a 
feeble  current,  no  contractions  occur  at  any  other  time.  The  contrac- 
tions thus  produced  are  known  respectively  as  opening  and  closing.  By 
the  use  of  Du  Bois-Reymond's  keys,  either  the  closing  or  the  opening 
excitation  may  be  diverted  from  the  nerve,  and  a  single  closing  or  open- 
ing shock  may  be  applied  at  will. 


484  NERVOUS    SYSTEM 

What  is  commonly  known  as  an  interrupted  current  is  a  faradic 
or  induced  current,  in  which  the  closing  and  opening  excitations  follow 
each  other  with  greater  or  less  rapidity,  and  the  intervals  may  be  regu- 
lated so  that  they  occur  at  a  regular  rate.  A  rapid  succession  of  induc- 
tion-shocks produces  a  more  or  less  prolonged  muscular  action,  called 
tetanic  contraction.  The  number  of  successive  shocks  in  a  second 
required  to  produce  a  tetanic  condition  of  a  muscle  varies  in  different 
animals  and  in  different  muscles  in  the  same  animal.  The  minimum 
seems  to  be  about  sixteen  per  second,  with  a  considerable  range  of  vari- 
ation. Very  rapid  stimuli,  even  more  than  3000  per  second,  will  pro- 
duce tetanic  contraction. 

The  faradic,  or  induced  current  is  different  in  its  effects,  under 
certain  conditions  of  the  nerves  and  muscles,  from  an  interrupted  gal- 
vanic, or  primary  current.  This  question  is  important  in  practical  medi- 
cine in  determining  the  so-called  "reaction  of  degeneration"  of  nerve 
and  muscle. 

The  constant  current,  under  certain  conditions,  has  no  effect  that 
is  indicated  by  muscular  phenomena,  contraction  occurring  only  on  clos- 
ing or  opening  the  circuit.  This  is  known  as  the  galvanic,  or  primary 
current.  It  produces,  however,  a  peculiar  condition  of  nerves  and 
muscles,  which  will  be  described  under  the  head  of  electrotonus.  The 
primary  current  is  derived  directly  from  the  cells  of  a  galvanic  battery, 
and  this  is  to  be  distinguished  from  the  faradic,  or  induced  current. 
The  faradic  current  is  induced  in  a  coil  of  small  insulated  wire,  brought 
near  and  parallel  to  and  partly  or  entirely  surrounding  a  coil  of  larger 
wire  carrying  the  primary  current.  When  the  circuit  of  the  primary 
current  is  closed,  the  direction  of  the  induced  current  is  the  reverse  of 
that  of  the  primary  current.  When  the  primary  circuit  is  opened,  the 
induced  current  has  the  same  direction  as  the  primary  current.  The 
direction  of  the  primary  current  is  uniform,  but  the  direction  of 
the  induced  current  alternates  with  each  interruption  of  the  primary 
current.  These  induced  currents  are  of  momentary  duration,  being 
produced  only  when  the  primary  current  is  closed  and  opened.  A  rapid 
interruption  of  the  primary  current  is  produced  by  what  is  called  a 
rheotome,  or  current-interrupter,  which  is  attached  to  all  induction- 
batteries. 

The  points  or  surfaces  used  in  closing  a  circuit  within  which  a 
portion  of  nerve  or  muscle  is  included  are  called  electi"odes.  They 
usually  are  designated  as  the  copper,  or  positive  electrode  or  pole,  and 
the  zinc,  or  negative  electrode  or  pole.  The  positive  pole  is  also  called 
the  anode,  and  the  negative  pole,  the  cathode.  The  direction  of  the 
current,  when  the  circuit  is  closed,  is  from  the  anode  to  the  cathode. 


ACTION    OF    ELECTRICITY   ON    THE    NERVES  485 

When  a  galvanic  current  is  passed  through  a  liquid  or  a  moist 
animal  tissue,  decomposition  occurs,  by  what  is  known  as  electrolysis, 
or  internal  polarization.  The  products  of  this  decomposition,  called 
ions,  are  of  course  different  in  different  Hquids  or  moist  tissues.  These 
accumulate  at  the  poles  and  after  a  time  disturb  the  currents  and  the 
phenomena  produced,  the  electrolytic  process  acting  in  the  same  way 
as  an  exciting  electric  current.  In.  animal  tissues,  acids  accumulate  at 
the  anode,  and  alkalies,  at  the  cathode.  The  ions  which  pass  to  the 
anode  are  called  anions,  and  those  which  accumulate  at  the  cathode  are 
called  cations.  In  physiological  experiments,  it  often  is  desirable  to 
eliminate  electrolysis,  or  internal  polarization,  and  this  is  done  by  using 
the  non-polarizable  electrodes  devised  by  Du  Bois-Reymond.  These 
may  be  described  as  follows :  "  The  researches  of  Regnault,  Matteucci 
and  Du  Bois-Reymond  have  proved  that  such  electrodes  can  be  made  by 
taking  two  pieces  of  carefully  amalgamated  pure  zinc  wire,  and  dipping 
these  in  a  saturated  solution  of  zinc  sulphate  contained  in  tubes,  their 
lower  ends  being  closed  by  means  of  modeller's  clay  moistened  with  a 
0.6  per  cent  normal  saline  solution.^  The  contact  of  these  electrodes 
with  the  tissues  does  not  give  rise  to  polarity  "  (Landois  and  Stirling). 

It  is  evident  that  the  galvanic  current  may  be  applied  to  a  nerve 
so  that  the  direction  may  in  the  one  case  follow  the  course  of  the  nerve, 
that  is,  from  the  centre  to  the  periphery,  and  in  the  other,  be  opposite 
to  the  course  of  the  nerve.  These  are  called  respectively  descending 
and  ascending  currents.  When  the  positive  pole  (copper)  is  placed 
nearer  the  origin  of  the  nerve,  and  the  negative  pole  (zinc)  below  this 
point  in  the  course  of  the  nerve,  the  galvanic  current  follows  the  nor- 
mal direction  of  the  motor  conduction,  and  this  is  called  the  descending 
current.  When  the  poles  are  reversed  and  the  direction  is  from  the 
periphery  toward  the  centre,  it  is  called  the  ascending  current.  It  will 
be  convenient  to  speak  of  these  two  currents  respectively  as  descend- 
ing and  ascending,  in  detailing  experiments  on  the  action  of  electricity 
on  the  nerves. 

The  main  points  to  be  noted  in  regard  to  the  effects  of  the  appli- 
cation of  electricity  to  an  exposed  nerve  are  the  action  of  constant  cur- 
rents, the  phenomena  observed  on  closing  and  on  opening  the  circuit 
and  the  effects  of  an  interrupted  current. 

During  the  passage  of  a  feeble  constant  current  through  a  nerve, 
whatever  be  its  direction,  there  are  no  convulsive  movements  and  no 
evidences  of  pain.     This  fact  has  long  been  recognized  by  physiologists, 

^  Using  ordinary  electrodes,  when  brought  in  contact  with  an  animal  tissue,  they  become 
surrounded  with  positive  and  negative  ions,  which  form  miniature  batteries  giving  off  an  electric 
stimulus  when  the  circuit  is  closed  or  opened. 


486  NERVOUS    SYSTEM 

who  at  first  limited  the  effects  of  electricity  on  the  nerves  to  two  periods, 
one  at  the  closing  of  the  circuit  and  the  other  at  its  opening.  It  will  be 
seen,  however,  that  the  passage  of  electricity  through  a  portion  of  a 
nervous  trunk  produces  a  peculiar  condition  in  the  nerve,  described 
under  the  name  of  electrotonus ;  but  the  fact  remains  that  neither  mo- 
tion nor  sensation  is  excited  in  a  mixed  nerve  during  the  actual  passage 
of  a  feeble  constant  current. 

Laiv  of  Contraction.  —  All  who  have  experimented  on  the  action  of 
galvanism  on  the  nerves  have  noted  the  fact  alluded  to  above,  that  con- 
traction occurs  only  on  closing  or  on  opening  the  circuit.  Take,  for 
example,  a  frog's  leg  prepared  with  the  nerve  attached :  Place  one  pole 
of  a  galvanic  apparatus  on  the  nerve  and  then  make  the  connection,  in- 
cluding a  portion  of  the  nerve  in  the  circuit.  With  the  feeblest  current, 
contraction  occurs  only  on  closing  the  circuit.  With  what  is  called  the 
"  weak  "  current  (Pfluger),  contraction  occurs  only  on  closing  the  circuit, 
for  currents  in  either  direction.  With  the  "  moderate  "  current,  contrac- 
tion occurs  both  on  closing  and  on  opening  the  circuit,  for  currents  in 
either  direction.  With  the  "  strong"  current,  contraction  occurs  only  on 
closing  the  circuit,  with  the  descending  current,  and  only  on  opening  the 
circuit,  with  the  ascending  current.  The  above  phenomena  constitute 
what  is  called  Pfliiger's  "  law  of  contraction."  The  explanations  of  this 
law  are  the  following  :  — 

The  stimulus  that  gives  rise  to  a  closing  contraction  occurs  at  the 
cathode,  when  the  electrotonus  produced  by  the  passage  of  the  current 
begins.  The  stimulus  which  produces  an  opening  contraction  occurs  at 
the  anode,  when  the  electrotonus  ceases.  The  impulse  is  always  stronger 
when  the  electrotonus  begins  than  when  it  ceases.  Therefore,  when  the 
current  is  so  feeble  that  but  one  contraction  is  produced,  this  contraction 
occurs  only  on  closing  the  circuit,  for  both  ascending  and  descending 
currents. 

With  the  "  moderate  "  current,  the  strength  of  the  opening  as  well 
as  of  the  closing  impulse  is  sufficient  to  produce  a  contraction  ;  and  con- 
tractions therefore  occur  both  on  opening  and  closing  the  circuit,  for 
both  ascending  and  descending  currents. 

"  Strong  "  currents  produce  closing  contraction  with  the  descending 
current,  for  the  reason  that  the  current  destroys  the  conductivity  of  that 
portion  of  the  nerve  included  between  the  poles  of  the  battery,  and,  the 
stimulus  occurring  only  at  the  cathode  (see  above),  and  the  cathode 
being  applied  to  that  portion  of  the  nerve  nearer  the  muscle,  the  closing 
impulse  only  is  conveyed  to  the  muscle.  The  opening  impulse  (at  the 
anode)  is  cut  off  from  the  muscle  by  the  loss  of  conductivity  in  the  in- 
trapolar  portion  of  the  nerve.     With  the  ascending  current,  the  opening 


LAW    OF    CONTRACTION  487 

impulse,  occurring  at  the  anode,  which  is  nearer  the  muscle,  produces 
an  opening  contraction,  and  the  closing  impulse,  which  is  at  the  cathode, 
is  not  conducted  to  the  muscle. 

While  the  constant  current  usually  does  not  excite  contractions  dur- 
ing the  actual  time  of  its  passage  through  a  nerve,  with  a  certain  strength 
of  current  the  muscle  is  thrown  into  a  tetanic  condition.  This  is  called 
"closing  tetanus."  When  a  constant  current,  not  of  sufficient  strength 
to  produce  closing  tetanus,  is  passed  for  several  minutes  through  a  long 
extent  of  nerve,  a  vigorous  contraction  occurs  on  opening  the  circuit, 
which  is  followed  by  tetanus  lasting  for  several  seconds.  This  is  called 
"  opening  tetanus."  After  a  time  —  this  varying  with  the  excitability  of 
the  nerve  and  the  strength  of  the  current — the  descending  current  will 
destroy  the  nervous  excitability ;  but  it  may  be  restored  by  repose,  or 
more  quickly,  by  the  passage  of  an  ascending  current.  If  the  ascend- 
ing current  is  passed  first  for  a  few  seconds,  a  contraction  follows  the 
opening  of  the  circuit ;  and  this  contraction,  within  certain  limits,  is 
more  vigorous  the  longer  the  current  is  passed.  At  the  same  time,  the 
prolonged  passage  of  the  ascending  current  increases  the  excitability  of 
the  nerve  for  any  kind  of  stimulus. 

After  a  certain  time  —  which  varies  in  different  animals  —  the  ner- 
vous excitability  becomes  somewhat  enfeebled  by  exposure  of  the  parts. 
The  phenomena  then  observed  belong  to  the  conditions  involved  in  the 
process  of  "  dying  "  of  the  nerve.  In  the  later  stages  of  this  condition, 
the  phenomena  may  be  formulated  as  follows  :  — 

If  the  sciatic  nerve  attached  to  the  leg  of  a  frog,  prepared  in  the 
usual  way  for  such  experiments,  is  subjected  to  a  feeble  galvanic  cur- 
rent, there  is  a  time  when  muscular  contraction  takes  place  only  at  the 
instant  when  the  circuit  is  closed,  no  contraction  occurring  when  the 
circuit  is  opened ;  and  this  occurs  only  with  the  descending  current. 
With  the  ascending  current,  contraction  of  the  muscles  occurs  only 
when  the  circuit  is  opened,  and  none  takes  place  when  the  circuit  is 
closed.  These  phenomena  are  distinct  after  the  excitability  of  the  parts 
has  become  somewhat  diminished  by  exposure  or  by  electric  stimulation 
of  the  nerve. 

If  a  sufficiently  powerful  constant  current  is  passed  through  a  nerve, 
disorganization  of  its  tissue  takes  place,  and  the  nerve  finally  loses  its 
excitabihty,  as  it  does  when  bruised,  ligatured,  or  when  its  structure  is 
destroyed  in  any  other  way.  It  was  thought  by  Galvani  that  a  current 
directed  exactly  across  a  nerve,  so  as  to  pass  at  right  angles  to  its  fibres, 
does  not  give  rise  to  muscular  contraction.  This  view  is  commonly 
accepted  by  physiologists. 

The  muscular  contraction  produced  by  electric  stimulation  of  a  nerve 


NERVOUS    SYSTEM 

is  more  vigorous  the  greater  the  extent  of  the  nerve  included  between 
the  poles  of  the  battery.  This  fact  has  long  been  observed,  and  its  ac- 
curacy may  easily  be  verified.  It  would  naturally  be  expected  that  the 
greater  the  amount  of  stimulation,  the  more  marked  would  be  the  mus- 
cular action ;  and  the  stimulation  seems  to  be  increased  in  proportion  to 
the  extent  of  nerve  through  which  the  current  is  made  to  pass. 

The  excitability  of  a  nerve,  it  is  well  known,  may  be  exhausted  by 
repeated  applications  of  electricity,  whatever  be  the  direction  of  the 
current ;  and  it  is  more  or  less  completely  restored  by  repose.  When  it 
has  been  exhausted  for  the  descending  current,  it  will  respond  to  the 
ascending  current,  and  vice  versa  ;  and  after  it  has  been  exhausted  by 
the  descending  current,  it  is  restored  more  promptly  by  stimulation  with 
the  ascending  current  than  by  repose,  and  vice  versa.  This  phenom- 
enon, observed  by  Volta,  is  known  as  "voltaic  alternation." 

Many  of  the  phenomena  illustrating  the  law  of  contraction  may  be 
observed  without  the  use  of  complicated  apparatus.  A  simple  form  of 
battery,  very  convenient  for  some  of  these  experiments,  consists  of  alter- 
nate copper  and  zinc  wires  wound  around  a  piece  of  wood  bent  in  the 
form  of  a  horseshoe  and  terminating  in  two  platinum  points  representing 
the  positive  and  negative  poles.  This  forms  a  sort  of  electric  forceps, 
about  eight  inches  (20  centimeters)  long,  which,  when  moistened  with 
water  slightly  acidulated,  will  give  a  current  of  about  the  proper  strength 
for  many  simple  experiments. 

The  law  of  contraction  is  applicable  to  inhibitory  nerves,  as  the  in- 
hibitory nerve  of  the  heart,  the  difference  being  that  stimulation  pro- 
duces inhibition  instead  of  contraction.  It  also  holds  good  for  sensory 
nerves,  the  effects  being  observed  by  noting  the  reflex  contractions 
produced  (Pfliiger). 

A  peculiar  phenomenon,  described  by  Matteucci,  has  been  called 
"  induced  muscular  contraction."  If  the  nerve  of  a  galvanoscopic  frog's 
leg  is  placed  in  contact  with  the  muscles  of  another  leg  prepared  in  the 
same  way,  stimulation  of  the  nerve,  giving  rise  to  contraction  of  the 
muscles  with  which  the  nerve  of  the  first  leg  is  in  contact,  will  induce 
contraction  in  the  muscles  of  both.  This  experiment  may  be  extended, 
and  contractions  may  thus  be  induced  in  a  series  of  legs,  the  nerve  of 
one  being  in  contact  with  the  muscles  of  another.  It  is  shown  that 
"  induced  contraction  "  is  not  due  to  an  actual  propagation  of  the  elec- 
tric current,  but  to  a  stimulus  attending  the  muscular  contraction  itself, 
by  the  fact  that  the  same  phenomena  occur  when  the  first  contraction  is 
produced  by  mechanical  or  chemical  excitation  of  the  nerve.  It  prob- 
ably is  due  to  the  negative  variation  of  the  muscle-current  during  con- 
traction (see  page  427). 


ELECTROTOx\US  489 

Electric  Current  from  the  Exterior  to  the  Cut  Surface  of  a  Nerve.  — 
Before  studying  certain  phenomena  presented  in  nerves  of  which  a  por- 
tion is  subjected  to  the  action  of  a  constant  galvanic  current,  it  is  impor- 
tant to  note  the  fact  that  there  exists  in  the  nerves,  as  in  the  muscles,  a 
current  with  a  direction  from  the  exterior  to  the  cut  surface.  It  has 
been  roughly  estimated  that  the  nerve-current  has  one-eighth  to  one- 
tenth  the  intensity  of  the  muscle-current.  The  existence  of  the  nerve- 
current  has,  so  far  as  known,  no  more  physiological  significance  than 
the  analogous  fact  observed  in  the  muscular  tissue.  Currents  exist  also 
in  the  skin  and  in  mucous  membranes,  the  direction  being  from  the 
outer  surface,  which  is  positive,  to  the  inner  surface,  which  is  negative.^ 

Electrotonus,  Anelectrotonus  and  Catelcctrotonns.  —  When  a  constant 
galvanic  current  is  passed  through  a  portion  of  a  freshly-prepared 
nerve,  a  large  part  of  the  entire  nerve  is  brought  into  a  peculiar  electric 
condition.  While  in  this  state,  the  nerve  will  deflect  the  needle  of  a 
galvanometer  and  its  excitability  is  modified.  This  is  due  to  an  electric 
tension  of  the  entire  nerve,  induced  by  the  passage  of  a  current  through 
a  portion  of  its  extent.  This  condition  is  called  electrotonus.  There 
is  also  a  peculiar  condition  of  that  portion  of  the  nerve  near  the  anode, 
differing  from  the  condition  of  the  nerve  near  the  cathode.  Near  the 
anode  the  excitability  of  the  nerve  is  diminished,  and  this  condition  is 
called  anelectrotonus.  Near  the  cathode  the  excitability  is  increased, 
and  this  condition  is  called  catelectrotonus.  These  phenomena  have 
been  the  subject  of  extended  investigation  by  electro-physiologists ;  and 
although  the  conditions  are  not  to  be  included  in  the  physiological  prop- 
erties of  the  nerves,  they  have  considerable  pathological  and  therapeutic 
importance.  It  is  well  known,  for  example,  that  electricity  often  is  one 
of  the  most  efficient  agents  at  command  for  the  restoration  of  the 
properties  of  nerves  affected  with  disease ;  and  the  constant  current 
has  been  extensively  and  successfully  used  as  a  therapeutic  agent.  The 
constant  current,  in  restoring  the  normal  condition  of  nerves,  must  influ- 
ence, not  only  that  portion  included  between  the  poles  of  the  battery, 
but  the  entire  nerve  ;  and  the  electrotonic  condition,  with  its  modifica- 
tions, in  a  measure  explains  how  this  result  may  be  obtained. 

The  electrotonic  condition  is  marked  in  proportion  to  the  excitability 
of  the  nerve,  and  it  is  either  absent  or  very  feeble  in  nerves  that  are 
dead  or  have  lost  their  excitability.  If  a  strong  ligature  is  applied  to 
the  extrapolar  portion  of  a  nerve,  or  if  the  nerve  is  divided  and  the  cut 
ends  are  brought  in  contact  with  each  other,  the  electrotonic  condition  is 

^  The  current  described  above  was  called  by  Du  Bois-Reymond  the  "current  of  rest." 
Some  writers  now  adopt  the  view  of  Hermann  that  this  current  does  not  exist  in  normal  muscle 
or  nerve  but  is  due  to  injury  of  the  tissue. 


490 


NERVOUS    SYSTEM 


either  not  observed  or  is  feeble.  These  facts  show  that  the  phenomena 
of  electrotonus  depend  on  the  physiological  integrity  of  nerves.  A  dead 
nerve  or  one  that  has  been  divided  or  ligated  may  present  these  phe- 
nomena under  the  stimulation  of  a  powerful  current  —  and  then  only  to 
a  slight  degree — when  the  condition  depends  on  the  purely  physical 
properties  of  the  nerve  as  a  conductor;  but  these  phenomena  are  not 
to  be  compared  with  those  observed  in  nerves  that  retain  their  physio- 
logical properties. 

As  stated  above,  the  electrotonic  condition  is  not  restricted  to  that 
portion  of  the  nerve  included  between  the  poles  of  the  battery.  The 
condition  of  the  portion  between  the  poles  is  called  intrapolar  electroto- 
nus, and  the  condition  of  the  nerve  outside  of  the 
poles  is  called  extrapolar  electrotonus. 

When  a  portion  of  a  nerve  is  subjected  to  a 
moderately  strong  constant  current,  the  condi- 
tions of  the  extrapolar  portions  corresponding  to 
the  two  poles  of  the  battery  are  different.  Near 
the  anode  the  excitability  of  the  nerve  and  the 
rate  of  nervous  conduction  are  diminished.  If, 
however,  a  galvanometer  is  applied  to  this  portion 
of  the  nerve,  its  electromotive  power,  measured 
by  the  deflection  of  the  galvanometric  needle,  is 
increased.  On  the  other  hand,  near  the  cathode 
the  excitability  of  the  nerve  is  increased,  as  well 
as  the  rate  of  nervous  conduction,  but  the  electro- 
motive power  is  diminished. 

The  anelectrotonic  condition,  on  the  one 
hand,  and  the  catelectrotonic  condition,  at  the 
other  pole  of  the  battery,  are  marked  in  extra- 
polar  portions  of  the  nerve  and  are  to  be  recognized,  as  well,  in  that 
portion  through  which  the  current  is  passing ;  but  between  the  poles, 
there  is  a  point  where  these  conditions  meet,  as  it  were,  and  where 
the  excitability  is  unchanged.  This  is  called  the  neutral  point.  When 
the  galvanic  current  is  of  moderate  strength,  the  neutral  point  is 
about  midway  between  the  poles.  "  When  a  weak  current  is  used,  the 
neutral  point  approaches  the  positive  pole,  while  in  a  strong  current, 
it  approaches  the  negative  pole.  In  other  words,  in  a  weak  current 
the  negative  pole  rules  over  a  wider  territory  than  the  positive  pole, 
whereas  in  a  strong  current  the  positive  pole  prevails"  (Rutherford). 
The  conditions  of  extrapolar  excitability  vary  with  the  direction  of 
the  current  applied  to  the  nerve.  A  convenient  stimulus  with  which  to 
measure  this  excitability  is  a  solution  of   common  salt,  which  excites 


-  Method  of  test- 
ing excitability  in  electrotonus 
(Landois). 

The  positive  poles  are  + 
and  the  negative  poles  are  —  ; 
R,  R\,  R,  A*!,  points  excited  by 
the  saline  solution. 


NEGATIVE    VARIATION 


491 


more  or  less  powerful  tetanic  contractions  of  the  muscles.  These  varia- 
tions are  illustrated  in  Fig.  113. 

In  Fig.  112),  A,  a.  descending  constant  current  is  applied  to  the  nerve. 
When  the  circuit  is  open,  the  salt  applied  to  the  nerve  at  R  produces 
contractions  of  the  muscle.  If  the  circuit  is  closed,  the  contractions 
either  become  much  less  vigorous  or  cease,  on  account  of  the  dimin- 
ished excitability  near  the  anode.  This  is  called  descending  extrapolar 
anelectrotonus.  If  the  salt  is  applied  at  R-^,  the  contractions  are  in- 
creased in  vigor  by  closing  the  circuit,  on  account  of  the  increased 
excitabiUty  of  the  nen,'e  near  the  cathode.  This  is  called  descending 
extrapolar  catelectrotonus. 

In  Fig.  113,  B,  the  conditions  are  reversed.  The  polarizing  current 
here  must  be  very  weak,  as  a  strong  current  may  destrov  the  conduc- 
tivity of  the  intrapolar  portion  of  the  nerve  and  thus  prevent  the  con- 
duction of  the  stimulus  to  the  muscle  when  the  salt  is  applied  at  R.  On 
closing  the  circuit,  there  is  ascending  extrapolar  catelectrotonus  at  R, 
and  ascending  extrapolar  anelectrotonus  at  R-^. 

Within  certain  limits,  the  greater  the  strength  of  the  constant  cur- 
rent applied  to  the  nerve  and  the  greater  the  length  of  nerve  included 
between  the  poles  of  the  battery,  the  greater  is  the  deflection  of  the 
galvanoscopic  needle,  by  which  the  electrotonic  condition  is  measured. 

Electrotonic  conditions  in  sensory  nerves  are  measured  bv  reflex 
movements  produced  by  the  action  of  a  stimulus  applied  to  these 
nerves.  The  variations  in  excitabiHty  of  inhibitory  nerves  are  indicated 
by  increase  or  diminution  in  the  inhibitory  action.  These  phenomena 
are  analogous  to  those  obserA-ed  in  motor  nerves.  The  influence  of  a 
constant  current  on  the  muscle-current  is  distinct  though  feeble,  produc- 
ing a  kind  of  electrotonic  condition  of  muscle. 

Negative  Variation.  —  When  a  rapidly-interrupted  current  is  applied 
to  a  nerve  so  as  to  produce  a  tetanic  condition  of  the  muscles  to  which 
it  is  distributed,  the  normal  or  tranquil  nerv^e-current  (current  of  rest)  is 
overcome,  and  a  galvanoscopic  needle  applied  to  the  nerve,  which  was 
first  deviated  by  the  nerve-current,  will  be  observed  to  retrograde  and 
may  return  to  zero  (Du  Bois-Reymond;.  This  may  also  be  observed  to 
a  slight  degree  under  the  influence  of  mechanical  or  chemical  stimulation 
of  the  nerve,  the  natural  nerve-current  being  diminished,  but  usually  not 
abohshed.  The  variation  of  the  needle  under  the  influence  of  these  con- 
ditions has  been  called  negative  variation.  It  is  observed  in  greater  or 
less  degree  when  impulses  of  any  kind  are  passing  through  a  nerve,  this 
conduction  constituting  what  is  known  as  the  current  of  action.  These 
phenomena  are  analogous  to  the  negative  variation  of  muscle-currents, 
which  has  already  been  described. 


CHAPTER   XIX 

SPINAL    NERVES  — MOTOR    CRANIAL   NERVES 

Spinal  nerves  —  Cranial  nerves  —  Motor  oculi  comn^unis  (third  nerve) — Physiological  anat- 
omy —  Properties  and  uses  of  the  motor  oculi  communis  —  Patheticus,  or  trochlearis 
(fourth  nerve)  —  Physiological  anatomy  —  Properties  and  uses  of  the  patheticus —  Motor 
oculi  externus,  or  abducens  (sixth  nerve)  —  Physiological  anatomy  —  Properties  and  uses 
of  the  motor  oculi  communis  —  Nerve  of  mastication  (the  small,  or  motor  root  of  the  fifth 
nerve)  —  Physiological  anatomy  —  Properties  and  uses  of  the  nerve  of  mastication  — 
Facial,  or  nerve  of  expression  (seventh  nerve)  — -Physiological  anatomy  —  General  properties 
of  the  facial  —  Uses  of  branches  of  the  facial  given  off  within  the  aqueduct  of  Fallopius  — 
Uses  of  the  chorda  tympani  —  Influence  of  certain  branches  of  the  facial  on  the  movements 
of  the  palate  and  uvula  —  Uses  of  the  external  branches  of  the  facial  —  Spinal  accessory 
(eleventh  nerve) —  Physiological  anatomy — -Properties  and  uses  of  the  spinal  accessory  — 
Uses  of  the  internal  branch  from  the  spinal  accessory  to  the  pneumogastric  —  Influence  of 
the  internal  branch  of  the  spinal  accessory  on  deglutition  —  Influence  of  the  spinal  acces- 
sory on  the  heart — Uses  of  the  external,  or  muscular  branches  of  the  spinal  accessory  — 
Sublingual  (twelfth  nerve) — Physiological  anatomy  —  Properties  and  uses  of  the  sub- 
lingual. 

With  a  knowledge  of  the  general  properties  of  the  nerves  belonging 
to  the  cerebro-spinal  system,  it  is  easy  to  understand  the  uses  of  most 
of  the  special  nerves,  simply  from  their  anatomical  relations.  This  is 
especially  true  of  the  spinal  nerves.  These,  in  general  terms,  are  dis- 
tributed to  the  muscles  of  the  trunk  and  extremities,  to  the  sphincters 
and  the  integument  covering  these  parts,  the  posterior  segment  of  the 
head,  and  to  certain  mucous  membranes.  It  is  evident,  therefore,  that 
an  account  of  the  exact  office  of  each  nervous  branch  would  necessitate 
a  full  description,  not  only  of  the  nerves,  but  of  the  muscles  of  the  body, 
which  is  manifestly  within  the  scope  only  of  treatises  on  descriptive 
anatomy. 

Spinal  Nerves 

There  are  thirty-one  pairs  of  spinal  nerves  ;  eight  cervical,  twelve 
dorsal,  five  lumbar,  five  sacral  and  one  coccygeal.  Each  nerve  arises 
from  the  spinal  cord  by  an  anterior  (motor)  and  a  posterior  (sensory) 
root,  the  posterior  root  being  the  larger  and  having  a  ganglion.  Imme- 
diately beyond  the  ganglion,  the  two  roots  unite  into  a  single  mixed 
nerve,  which  passes  out  of  the  spinal  canal  by  an  intervertebral  fora- 
men. The  nerve  thus  constituted  is  possessed  of  motor  and  sensory 
properties.     It  divides  outside  of  the  spinal  canal  into  two  branches, 

492 


SPINAL    NERVES 


493 


anterior  and  posterior,  both  containing  motor  and  sensory  filaments, 
which  are  distributed  respectively  to  the  anterior  and  the  posterior  parts 
of  the  body.  The  anterior  branches  are  the  larger,  and  they  supply  the 
limbs  and  all  parts  in  front  of  the  spinal  column. 

The  anterior  branches  of  the  upper  four  cervical  nerves  form  the 
cervical  plexus  ;  and  the  four  inferior  cervical    ner\'es,  with    the    first 


Fig.  114.  —  Cervical  porfiofi  of 
the  spinal  cord  (Hirschfeld). 


Fig.  115. — Dorsal  portion  of  Fig.  116.  —  Inferior  por- 

the  spinal  cord  (Hirschfeld).  tion  of  the  spinal  cord,  and 

Cauda  equina  (Hirschfeld) . 

I,  antero-inferior  wall  of  the  fourth  ventricle ;  2,  superior  peduncle  of  the  cerebellum ;  3,  middle 
peduncle  of  the  cerebellum ;  4,  inferior  peduncle  of  the  cerebellum  ;  5,  inferior  portion  of  the  posterior 
median  columns  of  the  cord  ;  6,  glosso-pharyngeal  nerve  ;  7,  pneumogastric  ;  8,  spinal  accessory  nerve  ; 
9,  9,  9,  9,  dentated  ligament ;  10,  10,  10,  10,  posterior  roots  of  the  spinal  nerves  ;  11,  11,  11,  w,  posterior 
lateral  grooz'e  ;  12,  12,  12,  12,  ganglia  of  the  posterior  roots  of  the  nerves  ;  13,  13,  anterior  roots  of  the 
nerves  ;  14,  division  of  the  nerves  into  two  branches  ;  15.  lower  extremity  of  the  cord;  16,  16,  coccygeal 
ligament;  17,  17,  cauda  equina;  I-VHI,  cervical  nerves ;  I,  H,  HI,  IV-XII,  dorsal  ?ie?-ves ;  I,  H-V, 
lumbar  nerves  ;  I-V,  sacral  nerves. 


dorsal,  form  the  brachial  plexus.  The  anterior  branches  of  the  dorsal 
nerves,  with  the  exception  of  the  first,  supply  the  walls  of  the  chest  and 
abdomen.  These  nerves  go  directly  to  their  distribution  without  form- 
ing a  plexus.  The  anterior  branches  of  the  upper  four  lumbar  nerves 
form  the  lumbar  plexus.  The  anterior  branch  of  the  fifth  lumbar  nerve 
and  a  branch  from  the  fourth  unite  with  the  anterior  branch  of  the  first 


494  NERVOUS    SYSTEM 

sacral,  forming  the  lumbo-sacral  nerve,  and  enter  into  the  sacral  plexus. 
The  upper  three  anterior  sacral  nerves,  with  a  branch  from  the  fourth, 
form  the  sacral  plexus.  The  greatest  portion  of  the  fourth  anterior 
sacral  is  distributed  to  the  pelvic  viscera  and  the  muscles  of  the  anus. 
The  fifth  anterior  sacral  and  the  coccygeal  are  distributed  to  parts 
about  the  coccyx. 

The  posterior  branches  of  the  spinal  nerves  are  quite  simple  in  their 
distribution.  With  one  or  two  exceptions,  of  no  great  physiological 
importance,  these  nerves  pass  backward  from  the  main  trunk,  divide 
into  two  branches,  external  and  internal,  and  their  filaments  of  distri- 
bution go  to  the  muscles  and  to  integument  behind  the  spinal  column. 

It  is  further  important  to  note  that  all  the  cerebro-spinal  nerves 
anastomose  with  the  sympathetic. 


Cranial  Nerves 

Many  of  the  cranial  nerves  are  peculiar,  either  as  regards  their 
general  properties  or  in  their  distribution  to  parts  concerned  in  special 
functions.  In  some  of  these  nerves,  the  most  important  facts  con- 
cerning their  distribution  have  been  ascertained  only  by  physiological 
experimentation,  and  their  anatomy  is  inseparably  connected  with  their 
physiology.  It  would  be  desirable,  if  it  were  possible,  to  classify  these 
nerves  with  reference  strictly  to  their  properties  and  uses  ;  but  this  can 
be  done  only  to  a  certain  extent.  The  common  classification  of  the 
cranial  nerves  is  the  arrangement  of  Sommerring,  in  which  the  nerves 
are  numbered  from  before  backward  in  the  order  in  which  they  pass 
out  of  the  skull,  making  twelve  pairs. 


Classification  of  the  Cranial  Nerves 
Nerves  of  Special  Sense 

Olfactory.     (First  pair.) 

Optic.     (Second  pair.) 

Auditory.     (Eighth  pair.) 

Gustatory,  comprising  a  part  of  the  glosso-pharyngeal  (ninth  pair) 
and  a  small  filament  from  the  facial  (seventh  pair)  to  the  lingual  branch 
of  the  fifth  pair. 

Nerves  of  Motion 

Nerves  of  motion  of  the  eyeball,  comprising  the  motor  oculi  com- 
munis (third  pair),  the  patheticus  (fourth  pair),  and  the  motor  oculi 
externus  (sixth  pair). 


CLASSIFICATION    OF   THE    CRANIAL   NERVES 


495 


Nerve  of  mastication,  or  motor  root  of  the  fifth  pair. 

Facial,  sometimes  called  the  nerve  of  expression.     (Seventh  pair.) 

Spinal  accessory.     (Eleventh  pair.) 

Sublingual.     (Twelfth  pair.) 

Nerves  of  General  Sensibility 

Trifacial,  or  large  root  of  the  fifth  pair. 

A  portion  of  the  glosso-pharyngeal.     (Ninth  pair.) 

Pneumogastric.     (Tenth  pair.) 

In  the  above  arrangement  the  nerves  are  classified  according  to  their 
properties  at  their  roots.  In  their 
course,  some  of  these  nerves  be- 
come mixed  and  their  branches 
are  both  motor  and  sensory,  such 
as  the  pneumogastric  and  the 
inferior  maxillary  division  of 
the   trifacial. 

The  nerves  of  special  sense 
have  little  or  no  general  sensi- 
bility ;  and  with  the  exception 
of  the  gustatory  nerves,  they  do 
not  present  ganglia  on  their 
roots,  in  this,  also,  differing  from 
the  ordinary  sensory  nerves. 
They  are  capable  of  conveying 
to  the  nerve-centres  only  certain 
peculiar  impressions,  such  as 
odors,  for  the  olfactory  nerves, 
light,  for  the  optic  nerves,  and 
sound,  for  the  auditory  nerves. 
The  proper  transmission  of 
these  impressions,  however,  in- 
volves the  action    of   accessory 


Fig.  117. — Roots  of  the  cranial  nerves  (Hirschfeld). 


I,  olfactory;  II,  optic;  III,  motor  octili  communis; 
IV,  patheticus;   V,  nerve  of  mastication  and  trifacial; 
VI,  motor  oculi  externus ;  VII,  facial;  VIII,  auditory; 
IX,  glosso-pharyngeal ;  X,  pneumogastric;  XI,  spinal 
parts,     more     or     less     complex;     accessory;    XII,  sublingual.     The   numbers    i   to   15 
.  refer  to  branches  that  will  be  described  hereafter. 

and    the    properties    of     these 

nerves  will  be  considered  in  connection  with  the  physiology  of  the  spe- 
cial senses. 

Motor  Oculi  Communis  (Third  Nerve) 

The  third  cranial  nerve  is  the  most  important  of  the  motor  nerves 
distributed  to  the  muscles  of  the  eyeball.  Its  physiology  is  readily 
understood  in  connection  with  its  distribution,  the  only  point  at  all  obscure 


496 


NERVOUS    SYSTEM 


being  its  relations  to  the  movements  of  the  iris,  concerning  which  the 
results  of  experiments  are  somewhat  contradictory. 

Physiological  Ajiatoiny. — The  apparent  origin  of  the  third  nerve  is 
from  the  inner  edge  of  the  crus  cerebri,  directly  in  front  of  the  pons 
Varolii  and  midway  between  the  pons  and  the  corpora  albicantia.  It 
presents  here  eight  or  ten  filaments,  of  nearly  equal  size,  which  soon 
unite  into  a  single  rounded  trunk. 

The  deep  origin  of  the  nerve  has  been  studied  by  means  of  dissec- 
tions of  the  encephalon  fresh  and  hardened  by  different  liquids.     From 

the  groove  by  which  they  emerge  from 
the  encephalon,  the  fibres  spread  out 
in  a  fan-shape,  the  middle  filaments 
passing  inward,  the  anterior,  inward 
and  forward,  and  the  posterior,  in- 
ward and  backward.  It  is  probable 
that  the  middle  filaments  pass  to  the 
median  line  and  decussate  with  corre- 
sponding fibres  from  the  opposite 
side.  The  anterior  filaments  pass 
forward  and  are  lost  in  the  optic 
thalamus.  The  posterior  filaments  on 
either  side  pass  backward  to  a  gray 
nucleus  beneath  the  aqueduct  of  Syl- 
vius and  here  decussate  with  fibres 
from  the  opposite  side.  This  decus- 
sation of  the  fibres  of  origin  of  the 
third  nerves  is  important  in  connec- 
tion with  the  harmony  of  action  of 
the  iris  and  the  muscles  of  the  eyes 
on  the  two  sides. 

The  third  nerve,  as  it  passes  into 
the  orbit  by  the  sphenoidal  fissure, 
divides  into  two  branches.  The  superior,  which  is  the  smaller,  passes 
to  the  superior  rectus  muscle  of  the  eye  and  certain  of  its  filaments  are 
continued  to  the  levator  palpebrae  superioris.  The  inferior  division 
breaks  up  into  three  branches.  The  internal  branch  passes  to  the 
internal  rectus  muscle  ;  the  inferior  branch,  to  the  inferior  rectus ;  the 
external  branch,  the  largest  of  the  three,  is  distributed  to  the  inferior 
oblique  muscle,  and  in  its  course  it  sends  a  short  and  thick  filament  to 
the  lenticular,  or  ophthalmic  ganglion  of  the  sympathetic.  It  is  this 
branch  which  is  supposed,  through  the  short  ciliary  nerves  passing  from 
the  lenticular  ganglion,  to  furnish  motor  filaments  to  the  ciliary  muscle  and 


Fig.    Ii8.  —  Distribution   of  the   motor  oculi 
cominunis  (Hirschteld). 

I,  trunk  of  the  motor  oculi  communis  ;  2,  su- 
perior bra7ich  ;  ■^,  filaments  which  this  branch 
sends  to  the  superior  rectus  and  the  levator 
palpebri  superioris ;  4,  branch  to  the  internal 
rectus;    5,    branch    to    the    inferior    rectus; 

6,  branch    to    the    inferior    oblique    muscle; 

7,  branch  to  the  lenticular  ganglion  ;  8,  motor 
oculi  externus  ;  9,  filaments  of  the  motor  oculi 
externus  anastomosing  with  the  sympathetic; 
10,  ciliary  nerves. 


MOTOR  OCULI   COMMUNIS  497 

the  iris.  In  its  course  this  nerve  receives  a  few  deHcate  filaments  from  the 
cavernous  plexus  of  the  sympathetic  and  a  branch  from  the  ophthalmic 
division  of  the  trifacial. 

Properties  and  Uses  of  the  Motor  Ocidi  Cominunis.  —  Stimulation  of 
the  root  of  the  third  nerve  in  a  living  animal  produces  contraction  of  the 
muscles  to  which  it  is  distributed,  but  no  pain.  If  the  stimulus,  however, 
is  applied  a  little  farther  on  in  the  course  of  the  nerve,  there  are  evi- 
dences of  sensibility ;  and  this  is  readily  explained  by  its  communica- 
tions with  the  ophthalmic  branch  of  the  trifacial.  At  its  root,  therefore, 
this  nerve  is  exclusively  motor  and  its  office  is  connected  with  the  action 
of  muscles. 

The  phenomena  observed  after  section  of  the  motor  oculi  communis 
in  living  animals  are  the  following: — ■ 

1.  Falling  of  the  upper  eyelid,  or  blepharoptosis. 

2.  External  strabismus,  immobility  of  the  eye  except  in  an  outward 
direction,  inability  to  rotate  the  eye  on  its  antero-posterior  axis  in  certain 
directions  and  slight  protrusion  of  the  eyeball. 

3.  .  Dilatation  of  the  pupil,  with  a  certain  degree  of  interference  with 
the  movements  of  the  iris. 

The  falling  of  the  upper  eyelid  is  constantly  observed  after  division 
of  the  third  nerve  in  living  animals  and  always  follows  its  complete  paral- 
ysis in  the  human  subject.  An  animal  in  which  the  nerve  has  been 
divided  can  not  raise  the  lid  but  can  press  the  lids  together  by  a  volun- 
tary effort.  In  the  human  subject  the  falling  of  the  lid  gives  to  the  face 
a  peculiar  and  characteristic  expression.  The  complete  loss  of  power 
shows  that  the  levator  palpebras  superioris  muscle  depends  on  the  third 
nerve  entirely  for  its  motor  filaments. 

The  external  strabismus  and  the  immobility  of  the  eyeball  except  in 
an  outward  direction  are  due  to  paralysis  of  the  internal,  superior  and 
inferior  recti  muscles,  the  external  rectus  acting  without  its  antagonist. 
This  condition  requires  no  further  explanation.  These  points  are 
illustrated  by  the  experiment  of  dividing  the  nerve  in  rabbits.  If  the 
head  of  the  animal  is  turned  inward,  on  exposing  the  eye  to  a  bright 
light,  the  globe  will  turn  outward  by  the  action  of  the  external  rectus ; 
but  if  the  head  is  turned  outward,  the  globe  remains  motionless. 

It  is  somewhat  difficult  to  note  the  effects  of  paralysis  of  the  inferior 
oblique  muscle,  which  also  is  supplied  by  the  third  nerve.  This  muscle, 
acting  from  its  origin  at  the  inferior  and  internal  part  of  the  circum- 
ference of  the  base  of  the  orbit  to  its  attachment  at  the  inferior  and 
external  part  of  the  posterior  hemisphere  of  the  eyeball,  gives  to  the 
globe  a  movement  of  rotation  on  an  oblique  horizontal  axis,  downward 
and   backward,  directing  the  pupil  upward  and  outward.     When  this 


498  NERVOUS    SYSTEM 

muscle  is  paralyzed,  the  superior  oblique,  having  no  antagonist,  rotates 
the  globe  upward  and  inward,  directing  the  pupil  downward  and  out- 
ward. The  action  of  the  oblique  muscles  is  observed  when  the  head  is 
moved  alternately  toward  one  shoulder  and  the  other.  In  the  human 
subject,  when  the  inferior  oblique  muscle  on  one  side  is  paralyzed,  the 
eye  can  not  move  in  a  direction  opposite  to  the  movements  of  the  head, 
as  it  does  upon  the  sound  side,  so  as  to  keep  the  pupil  fixed,  and  there  is 
double  vision. 

When  all  the  muscles  of  the  eyeball  except  the  external  rectus  and 
superior  oblique  are  paralyzed,  as  they  are  by  section  of  the  third  nerve, 
the  globe  is  slightly  protruded,  simply  by  the  relaxation  of  most  of  its 
muscles.  An  opposite  action  is  easily  observed  in  a  cat  with  the  facial 
nerve  divided  so  that  it  can  not  close  the  lids.  When  the  cornea  is  touched, 
all  the  muscles,  particularly  the  four  recti,  act  to  draw  the  globe  into  the 
orbit,  which  allows  the  lid  to  fall  slightly  and  projects  the  little  membrane 
which  serves  as  a  third  eyelid  in  these  animals. 

The  third  nerve  sends  a  filament  to  the  ophthalmic  ganglion  of  the 
sympathetic,  and  from  this  ganglion  the  short  ciliary  nerves  take  their 
origin  and  pass  to  the  iris.  While  it  is  true  that  division  of  the  third 
nerve  affects  the  movements  of  the  iris,  it  becomes  a  question  whether 
this  be  a  direct  influence  or  an  influence  exerted  primarily  on  the  ganglion, 
not,  perhaps,  differing  from  the  general  effects  on  the  sympathetic  gan- 
glia that  follow  destruction  of  their  branches  of  communication  with  the 
motor  nerves. 

The  third  nerve  animates  the  muscular  fibres  that  contract  the  pupil, 
the  contraction  produced  by  stimulation  of  the  optic  nerves  being  reflex 
in  its  character.  The  reflex  action  by  which  the  iris  is  contracted  is  not 
instantaneous,  like  most  of  the  analogous  phenomena  observed  in  the 
cerebro-spinal  system,  and  its  operations  are  rather  characteristic  of  the 
action  of  the  sympathetic  system  and  non-striated  muscular  tissue.  It 
has  been  found,  also,  that  the  pupil  is  not  immediately  dilated  after 
division  of  the  third  nerve.  Several  hours  after  the  operation,  however, 
the  pupil  usually  is  found  dilated,  and  it  may  slowly  contract  when  the 
eye  is  exposed  to  the  light. 

Experiments  have  shown,  also,  that  although  the  pupil  contracts 
feebly  and  slowly  under  the  stimulus  of  light  after  division  of  the  motor 
oculi,  it  will  dilate  under  the  influence  of  belladonna  and  can  be  made 
to  contract  by  operating  on  other  nerves.  It  is  well  known,  for  example, 
that  division  or  stimulation  of  the  fifth  nerve  produces  contraction  of 
the  pupil.  This  takes  place  after  as  well  as  before  division  of  the  third 
nerve.  Section  of  the  sympathetic  in  the  cervical  region  also  contracts 
the  pupil,  and  this  occurs  after  paralysis  of  the  motor  oculi.     These 


PATHETICUS,    OR    TROCHLEARIS  499 

facts  show  that  the  third  is  not  the  only  nerve  capable  of  acting  on  the 
iris  and  that  it  is  not  the  sole  avenue  for  the  transmission  of  reflex  in- 
fluences. 

When  the  eye  is  turned  inward  by  a  voluntary  effort,  the  pupil  is 
contracted ;  and  when  the  axes  of  the  two  eyes  are  made  to  converge 
strongly,  as  in  looking  at  near  objects,  the  contraction  is  very  con- 
siderable. 

The  third  nerve  contains  filaments  that  preside  over  voluntary 
movements  of  the  ciliary  muscle  in  the  accommodation  of  the  eye  to 
vision  at  different  distances. 

The  following  case  illustrates,  in  the  human  subject,  nearly  all  the 
phenomena  following  paralysis  of  the  motor  oculi  communis  in  experi- 
ments on  the  lower  animals  :  — 

The  patient  was  a  girl,  nineteen  years  of  age,  with  complete  paraly- 
sis of  the  nerve  on  the  left  side.  There  was  slight  protrusion  of  the 
eyeball,  complete  ptosis,  with  the  pupil  moderately  dilated  and  insen- 
sible to  ordinary  impressions  of  light.  The  sight  was  not  affected,  but 
there  was  double  vision,  except  when  objects  were  placed  before  the 
eyes  so  that  the  axes  were  parallel,  or  when  an  object  was  seen  with 
but  one  eye.  The  axis  of  the  left  eye  was  turned  outward,  but  it  was 
not  possible  to  detect  de\dation  upward  or  downward.  On  causing 
the  patient  to  incline  the  head  alternately  to  one  shoulder  and  the  other, 
it  was  evident  that  the  affected  eye  did  not  rotate  in  the  orbit  but 
moved  with  the  head.  This  seemed  to  be  a  case  of  complete  and  un- 
complicated paralysis  of  the  third  nerve. 

Patheticus,  or  Trochlearis  (Fourth  Nerve) 

The  physiology  of  the  patheticus  resolves  itself  into  the  action  of 
a  single  muscle,  the  superior  oblique. 

Physiological  Anatomy.  —  The  apparent  origin  of  the  patheticus  is 
from  the  superior  peduncles  of  the  cerebellum ;  but  it  may  easily  be 
followed  to  the  valve  of  Vieussens.  The  deep  roots  can  be  traced,  pass- 
ing from  without  inward,  to  the  following  parts :  One  filament  is  lost  in 
the  substance  of  the  peduncles ;  other  filaments  pass  from  before  back- 
ward into  the  valve  of  Vieussens  and  are  lost,  and  a  few  pass  into  the 
frenulum  ;  a  few  filaments  pass  backward  and  are  lost  in  the  corpora 
quadrigemina ;  but  the  greatest  number  pass  to  the  median  line  and 
decussate  with  corresponding  filaments  from  the  opposite  side.  The 
fibres  can  be  traced  to  a  nucleus  in  the  floor  of  the  aqueduct  of  Sylvius, 
beneath  the  nucleus  of  the  third  nerve.  The  decussation  of  the  fibres 
of  origin  of  the  fourth  nerve  has  the  same  physiological  significance  as 


500 


NERVOUS    SYSTEM 


the  decussation  of  the  roots  of  the  third.  From  this  origin,  the  patheti- 
cus  passes  into  the  orbit  by  the  sphenoidal  fissure  and  is  distributed  to 
the  superior  obhque  muscle  of  the  eyeball.  In  the  cavernous  sinus  it 
receives  branches  of  communication  from  the  ophthalmic  branch  of  the 
fifth,  but  these  are  not  closely  united  with  the  nerve.  A  small  branch 
passes  into  the  tentorium,  and  one  joins  the  lachrymal  nerve,  these, 
however,  being  exclusively  sensory  and  coming  from  the  ophthalmic 

branch  of  the  fifth.     It  also  receives  a 
few  filaments  from  the  sympathetic. 

Properties  and  Uses  of  the  PatJieti- 
cus.  —  Direct  observations  on  the  pa- 
theticus  in  living  animals  have  shown 
that  it  is  motor  and  its  stimulation 
excites  contraction  of  the  superior 
oblique  muscle  only.  This  muscle 
arises  just  above  the  inner  margin  of 
the  optic  foramen,  passes  forward 
along  the  upper  wall  of  the  orbit  at 
its  inner  angle  to  a  little  cartilaginous 
ring  which  serves  as  a  pulley.  From 
its  origin  to  this  point  it  is  muscular. 
Its  tendon  becomes  rounded  just 
before  it  passes  over  the  pulley, 
where  it  makes  a  sharp  curve,  passes 
outward  and  slightly  backward  and 
becomes  spread  out  to  be  attached  to 
the  globe  at  the  superior  and  external 
part  of  its  posterior  hemisphere.  It 
acts  on  the  eyeball  from  the  pulley  at  the  upper  and  inner  portion  of  the 
orbit  as  the  fixed  point  and  rotates  the  eye  on  an  oblique  horizontal  axis, 
from  below  upward,  from  without  inward  and  from  behind  forward. 
By  its  action  the  pupil  is  directed  downward  and  outward.  It  is  the 
antagonist  of  the  inferior  oblique,  the  action  of  which  has  been  de- 
scribed in  connection  with  the  motor  oculi  communis.  When  the 
patheticus  is  paralyzed,  the  eyeball  is  immovable  so  far  as  rotation  is 
concerned.  When  the  head  is  moved  toward  the  shoulder,  the  eye  does 
not  rotate  to  maintain  the' globe  in  the  same  relative  position  and  there 
is  double  vision. 

Paralysis  confined  to  the  fourth  nerve  in  the  human  subject  is  rather 
unusual.  "  In  seventy-seven  cases  of  paralysis  of  a  single  oculomotor 
nerve  I  found  the  third  nerve  affected  in  thirty-one  cases,  the  fourth  in 
nine,  and  the  sixth  in  thirty-seven."  — (Nettleship.) 


Fig. 


119.  —  Distribution     of  the    patheticus 
(Hirschfeld). 

I,  olfactory  nerve;  II,  optic  nerves;  III, 
motor  oculi  communis;  W ,  patheticus,  by  the 
side  of  the  ophthalmic  branch  of  the  fifth,  and 
passing  to  the  superior  oblique  muscle;  IV, 
motor  oculi  externus  ;  i,  ganglion  of  Gasser  ; 
2,  3,  4,  5,  6,  7,  8,  9,  10,  ophthalmic  division  of 
the  fifth  nerve,  with  its  branches. 


MOTOR    OCULI    EXTERNUS,    OR   ABDUCENS 


5or 


Motor  Oculi  Externus,  or  Abducens  (Sixth  Nerve) 

Like  the  patheticus,  the  motor  oculi  externus  is  distributed  to  but 
a  single  muscle.  Its  uses,  therefore,  are  apparent  from  a  study  of  its 
distribution  and  properties. 

Physiological  Anatomy.  —  The  apparent  origin  of  the  sixth  nerve 
is  from  the  groove  separating  the  anterior  corpus  pyramidale  of  the 
medulla  oblongata  from  the  pons  Varolii,  from  the  upper  portion  of  the 
medulla  and  from  the  lower  portion  of  the  pons  next  the  groove.  Its 
origin  at  this  point  is  by  two  roots  : 
an  inferior  root,  which  is  the  larger 
and  comes  from  the  corpus  pyrami- 
dale ;  and  a  superior  root,  sometimes 
wanting,  which  seems  to  come  from 
the  lower  portion  of  the  pons.  All 
anatomists  are  agreed  that  the  deep 
iibres  of  origin  of  this  nerve  pass  to 
the  gray  matter  in  the  floor  of  the 
fourth  ventricle.  It  is  not  known  that 
the  fibres  of  the  two  sides  decussate. 
From  this  origin  the  nerve  passes  into 
the  orbit  by  the  sphenoidal  fissure 
and  is  distributed  exclusively  to  the 
external  rectus  muscle  of  the  eyeball. 
In  the  cavernous  sinus  it  anastomoses 
with  the  sympathetic  through  the 
carotid  plexus  and  receives  a  filament 
from  Meckel's  ganglion.  It  also  re- 
ceives sensory  filaments  from  the 
ophthalmic  branch  of  the  fifth.  It  is  thought  by  some  anatomists  that 
this  nerve  occasionally  sends  a  small  filament  to  the  ophthalmic  gan- 
glion ;  and  this  branch,  which  is  exceptional,  exists  in  those  cases  in 
which  paralysis  of  the  motor  oculi  communis,  which  usually  furnishes 
all  the  motor  filaments  to  this  ganglion,  is  not  attended  with  immobility 
of  the  iris. 

Properties  aizd  Uses  of  the  Motor  Oc?di  Externics.  —  Direct  experi- 
ments have  shown  that  the  motor  oculi  externus  is  insensible  at  its 
origin,  its  stimulation  producing  contraction  of  the  external  rectus 
muscle  and  no  pain.  The  same  experiments  illustrate  the  action  of  the 
nerve,  inasmuch  as  its  stimulation  is  followed  by  contraction  of  the 
muscle  and  deviation  of  the  eye  outward.  Division  of  the  nerve  in 
the  lower  animals  or  its  paralysis  in  the  human  subject  is  attended  with 


Fig.  120.  —  Distribution  of  the  motor  oculi  ex- 
terttus  (Hirschfeld). 

I,  trunk  of  the  motor  oculi  communis,  with 
its  branches  (2,  3,  4,  5,  6,  7)  ;  8,  motor  oculi 
externus,  passing  to  the  external  rectus  mus- 
cle ;  9,  filaments  of  the  ??iotor  oculi  externus, 
anastomosing  with  the  sympathetic  ;  10,  ciliary 
nerves. 


502  NERVOUS   SYSTEM 

internal,  or  converging  strabismus,  due  to  the  unopposed  action  of  the 
internal  rectus  muscle. 

In  regard  to  the  associated  movements  of  the  eyeball,  it  is  important 
to  note  that  all  the  muscles  of  the  eye  that  have  a  tendency  to  direct 
the  pupil  inward  or  produce  the  simple  movements  upward  and 
downward  (the  internal,  inferior,  and  superior  recti)  are  animated  by  a 
single  nerve,  the  motor  oculi  communis,  this  nerve  also  supplying,  how- 
ever, the  inferior  oblique  ;  and  that  each  of  two  muscles  that  move  the 
globe  so  as  to  direct  the  pupil  outward  (the  superior  oblique  and  the 
external  rectus)  is  supplied  by  a  special  nerve.  The  movements  of 
the  eyeball  will  be  described  more  in  detail  in  connection  with  the 
physiology  of  vision. 

Nerve  of  Mastication  (the  Small,  or  Motor  Root  of  the 

Fifth  Nerve) 

The  motor  root  of  the  fifth  nerve  is  distinct  from  its  sensory  portion 
until  it  emerges  from  the  cranial  cavity  by  the  foramen  ovale.  It  is  then 
closely  united  with  the  inferior  ma.xillary  division  of  the  large  root ;  but 
at  its  origin  it  has  been  shown  to  be  motor,  and  its  section  in  the  cranial 
cavity  has  demonstrated  its  distribution  to  a  particular  set  of  muscles. 

Physiological  Anatomy.  —  The  apparent  origin  of  the  fifth  nerve  is 
from  the  lateral  portion  of  the  pons  Varolii.  The  small,  or  motor  root 
arises  from  a  point  a  little  higher  and  nearer  the  median  line  than  the 
large  root,  from  which  it  is  separated  by  a  few  fibres  of  the  white  sub- 
stance of  the  pons.  At  the  point  of  apparent  origin,  the  small  root 
presents  six  to  eight  rounded  filaments.  If  a  thin  layer  of  the  pons 
covering  these  filaments  is  removed,  the  roots  will  be  found  penetrating 
its  substance,  becoming  flattened,  passing  under  the  superior  peduncles 
of  the  cerebellum  and  going  to  a  gray  nucleus,  with  large  multipolar 
cells,  in  the  anterior  wall  of  the  fourth  ventricle  near  the  median  line. 
At  this  point  the  fibres  change  their  direction,  passing  from  without 
inward  and  from  behind  forward  toward  the  median  line,  the  fibres 
diverging  widely.  The  posterior  fibres  pass  to  the  median  line  and 
certain  of  them  decussate  with  fibres  from  the  opposite  side.  The 
anterior  fibres  pass  toward  the  aqueduct  of  Sylvius  and  are  lost. 
The  fibres  become  changed  in  their  character  when  they  are  followed 
inward  beyond  the  anterior  wall  of  the  fourth  ventricle.  Here  they  lose 
their  white  color,  become  gray  and  present  a  number  of  globules  of 
gray  substance  between  their  filaments. 

From  the  origin  above  described,  the  small  root  passes  beneath  the 
ganglion  of  Gasser,  —  from  which  it  sometimes,  though  not  constantly, 


NERVE    OF   MASTICATION 


503 


receives  a  filament  of  communication,  —  lies  behind  the  inferior  maxil- 
lary division  of  the  large  root  and  passes  out  of  the  cranial  cavity  by 
the  foramen  ovale.  Within  the  cranium  the  two  roots  are  distinct ;  but 
after  the  small  root  passes  through  the  foramen,  it  is  united  by  a  mutual 
interlacement  of  fibres  with  the  sensory  branch. 

The  inferior  maxillary  nerve,  made  up  of  the  motor  root  and  the 
inferior  maxillary  division  of  the  sensory  root,  just  after  it  passes  out 


Fig.  121.  — Distribution  of  the  small  root  of  the  fifth  nerve  (Hirschfeld) . 

I,  branch  to  the  masseter  muscle  ;  2,  filament  of  this  branch  to  the  temporal  muscle  ;  3,  buccal  branch  ; 
4,  branches  anastomosing  with  the  facial  nerve  ;  5,  fila?nent  from  the  buccal  branch  to  the  temporal 
muscle  ;  6,  branches  to  the  external  pterygoid  muscle  ;  7,  middle  deep  temporal  branch  ;  8,  auriculo-tem- 
poral  nerve;  9,  temporal  branches;  10,  auricular  branches;  11,  anastomosis  with  the  facial  nerve; 
12,  lingual  branch  ;  13,  branch  of  the  small  root  to  the  mylo-hyoid  muscle  ;  14,  inferior  dental  nerve,  with 
its  branches  (15,  15)  ;   16,  mental  branch  ;   17,  anastomosis  of  this  branch  with  the  facial  nerve. 

by  the  foramen  ovale,  divides  into  two  branches,  anterior  and  posterior. 
The  anterior  branch,  which  is  the  smaller,  is  composed  almost  entirely 
of  motor  filaments  and  is  distributed  to  the  muscles  of  mastication.  It 
gives  off  five  branches.  The  first  passes  to  be  distributed  to  the  mas- 
seter muscle,  in  its  course  occasionally  giving  off  a  small  branch  to 
the  temporal  muscle  and  a  filament  to  the  articulation  of  the  inferior 
maxilla  with  the  temporal  bone.     The  two  deep  temporal  branches  are 


504  NERVOUS    SYSTEM 

distributed  to  the  temporal  muscle.  The  buccal  branch  sends  filaments 
to  the  external  pterygoid  and  the  temporal  muscles,  and  a  small  branch 
is  distributed  to  the  internal  pterygoid  muscle.  From  the  posterior 
branch,  which  is  chiefly  sensory  but  contains  some  motor  filaments, 
branches  are  sent  to  the  mylo-hyoid  muscle  and  to  the  anterior  belly 
of  the  digastric.  In  addition  the  motor  branch  of  the  fifth  sends  fila- 
ments to  the  tensor  muscles  of  the  velum  palati. 

Experiments  have  shown  that  the  buccinator  muscle  receives  no 
motor  filaments  from  the  fifth  but  is  supplied  entirely  by  the  facial. 
The  buccal  branch  of  the  fifth  sends  motor  filaments  to  the  external 
pterygoid  and  the  temporal,  its  final  branches  of  distribution  being 
sensory  and  going  to  integument  and  mucous  membrane. 

In  treating  of  the  physiology  of  digestion,  a  table  has  been  given 
of  the  muscles  of  mastication  with  a  description  of  their  action.  It  will 
be  seen  by  reference  to  this  table  that  the  following  muscles  depress  the 
lower  jaw  :  the  anterior  belly  of  the  digastric,  the  mylo-hyoid,  the  genio- 
hyoid and  the  platysma  myoides.  Of  these  the  digastric  and  the  mylo- 
hyoid are  animated  by  the  motor  root  of  the  fifth  ;  the  genio-hyoid  is 
supplied  by  filaments  from  the  sublingual ;  and  the  platysma  myoides, 
by  branches  from  the  facial  and  from  the  cervical  plexus.  All  the 
muscles  that  elevate  the  lower  jaw  and  move  it  laterally  and  antero- 
posteriorly,  namely,  the  temporal,  masseter,  and  the  internal  and 
external  pyterygoids,  —  the  muscles  most  actively  concerned  in  mas- 
tication, —  are  animated  by  the  motor  root  of  the  fifth. 

Properties  and  Uses  of  the  Nerve  of  Mastication.  —  The  anatomical 
distribution  of  the  small  root  of  the  fifth  nerve  points  at  once  to  its  uses. 
Charles  Bell  called  it  the  nerve  of  mastication,  in  182 1,  although  he  did 
not  relate  any  experiments  in  regard  to  its  action.  Anatomical  and 
physiological  writers  since  that  time  have  adopted  this  view.  It  would 
be  difficult  if  not  impossible  to  stimulate  the  root  in  the  cranial  cavity  in 
a  living  animal ;  but  its  faradization  in  animals  just  killed  determines 
movements  of  the  lower  jaw.  Experiments  have  demonstrated  the 
physiological  properties  of  the  small  root,  which  is  without  doubt  a 
nerve  of  motion  only. 

There  is  little  left  to  say  in  regard  to  the  uses  of  the  motor  root  of  the 
fifth  nerve,  in  addition  to  the  description  of  the  action  of  the  muscles  of 
mastication,  contained  in  the  chapters  on  digestion,  except  as  regards 
the  action  of  the  filaments  sent  to  the  muscles  of  the  velum  palati.  In 
deglutition  the  muscles  of  mastication  are  indirectly  involved.  This  act 
can  not  be  well  performed  unless  the  mouth  is  closed  by  these  muscles. 
When  the  food  comes  in  contact  with  the  velum  palati,  muscles  are 
brought    into  action  which    render    this  membrane   tense,  so  that    the 


FACIAL,   OR   NERVE    OF    EXPRESSION  505 

opening  is  adapted  to  the  size  of  the  alimentary  bolus.  These  muscles 
are  animated  by  the  motor  root  of  the  fifth.  This  nerve,  then,  is  not 
only  the  nerve  of  mastication,  animating  all  the  muscles  concerned  in 
this  act  except  two  of  the  most  unimportant  depressors  of  the  lower  jaw 
(the  genio-hyoid  and  the  platysma  myoides),  but  it  is  concerned  indi- 
rectly in  deglutition. 

Facial,  or  Nerve  of  Expression  (Seventh  Nerve) 

The  anatomical  relations  of  the  facial  nerve  are  quite  intricate  and  it 
communicates  freely  with  other  nerves.  So  far  as  can  be  determined 
by  experiments  on  living  animals,  this  nerve  is  exclusively  motor  at 
its  origin  ;  but  in  its  course  it  presents  anastomoses  with  the  sympathetic, 
and  with  branches  of  the  fifth  and  the  cervical  nerves,  receiving  sensory 
filaments. 

Physiological  Anatomy. — The  facial  nerve  has  its  apparent  origin 
from  the  lateral  portion  of  the  medulla  oblongata,  or  bulb,  in  the  groove 
between  the  olivary  and  restiform  bodies  just  below  the  border  of  the  pons 
Varolii,  its  trunk  being  internal  to  the  trunk  of  the  auditory  nerve.  It 
is  separated  from  the  auditory  by  two  filaments  constituting  what  is 
known  as  the  intermediary  nerve  of  Wrisberg,  or  the  portio  inter  duram 
et  mollem.  As  this  little  nerve  joins  the  facial  it  usually  is  included  in 
its  root. 

Anatomists  have  endeavored  to  trace  the  fibres  of  the  facial  from 
their  point  of  emergence  from  the  encephalon  to  their  true  origin,  but 
with  results  not  entirely  satisfactory.  Its  fibres  pass  inward,  with  one 
or  two  deviations  from  a  straight  course,  to  the  floor  of  the  fourth 
ventricle,  where  they  spread  out  and  become  fan-shaped.  In  the 
floor  of  the  fourth  ventricle  certain  of  the  fibres  have  been  thought  to 
terminate  in  the  cells  of  the  gray  substance,  and  others  have  been  traced 
to  the  median  line,  where  they  decussate ;  but  the  course  of  many  of  the 
fibres  has  not  been  satisfactorily  established.  The  fibres  of  origin  of 
the  intermediary  nerve  of  Wrisberg  have  been  traced  to  the  nucleus 
of  the  glosso-pharyngeal. 

It  is  evident  from  physiological  experiments  that  the  decussation  of 
the  fibres  in  the  floor  of  the  fourth  ventricle  itself  is  not  very  important. 
Vulpian  made,  in  dogs  and  rabbits,  a  longitudinal  section  in  the  middle 
line  of  the  ventricle,  which  would  necessarily  have  divided  the  fibres 
passing  from  one  side  to  the  other,  without  producing  notable  paraly- 
sis of  the  facial  nerves  on  either  side.  This  observation  shows  that  the 
main  decussation  of  the  fibres  animating  the  muscles  of  the  face  takes 
place  in  some  other  situation. 


5o6 


NERVOUS    SYSTEM 


Certain  pathological  facts  bearing  on  the  question  of  decussation  of 
the  filaments  of  origin  of  the  facial  have  long  been  recognized.  They 
are  in  brief  as  follows  :  When  there  is  lesion  of  the  brain-substance 
anterior  to  the  pons  Varolii,  the  phenomena  due  to  paralysis  of  the 
facial  are  observed  on  the  same  side  as  the  hemiplegia,  opposite  the  side 
of  injury  to  the  brain.     When  the  lesion  is  either  in  or  below  the  pons, 


Fig.  122.  —  Superficial  branches  of  the  facial  and  the  fifth  (Hirschfeld)  . 

I,  trunk  of  the  facial ;  2,  posterior  auricular  nerve;  3,  branch  which  it  receives  from  the  cervical 
plexus  ;  4,  occipital  branch;  5,  6,  branches  to  the  muscles  of  the  ear  ;  7,  digastric  branches  ;  8,  branch 
to  the  stylo-hyoid  muscle;  g,  superior  tenninal  branch;  10,  temporal  branches;  xi,  frontal  branches; 
12,  branches  to  the  orbicularis  palpebrarum  ;  i-^,  nasal,  or  suborbital  branches;  1^,  buccal  branches; 
15,  inferior  terminal  branch;  16,  mental  branches;  17,  cervical  branches;  18,  superficial  temporal 
nerve  (branch  of  the  fifth)  ;  19,  20,  frontal  nerves  (branches  of  the  fifth)  ;  21,  22,  23,  24,  25,  26,  27, 
(branches  of  the  fifth)  ;  28,  29,  30,  31,  32   (branches  of  the  cervical  nerves). 

the  face  is  affected  on  the  same  side,  and  not  on  the  side  of  the  hemi- 
plegia. This  is  called  alternate  paralysis.  In  view  of  these  facts,  the 
phenomenon  of  hemiplegia  of  one  side  and  facial  paralysis  on  the  other 
is  regarded  as  indicating,  with  tolerable  certainty,  that  injury  to  the 
brain  has  occurred  on  the  same  side  as  the  facial  paralysis,  either 
within  or  posterior  to  the  pons  Varolii. 


FACIAL,    OR    NERVE    OF   EXPRESSION  507 

As  already  stated,  the  fibres  of  origin  of  the  facial  have  been  traced 
to  the  floor  of  the  fourth  ventricle,  where  a  few  decussate  but  most  of 
them  are  lost.  The  question  now  is,  whether  or  not  the  fibres  pass  up 
through  the  pons  and  decussate  above,  as  the  pathological  facts  just 
noted  would  seem  to  indicate.  Anatomical  researches  on  this  point 
are  not  satisfactory;  and  the  existence  of  such  a  decussation  has  not 
been  clearly  demonstrated.  The  pathological  observations  neverthe- 
less remain ;  and  however  indefinite  anatomical  researches  may  have 
been,  there  can  be  no  doubt  that  lesions  in  one  lateral  half  of  the  pons 
affect  the  facial  on  the  same  side,  while  lesions  above  the  pons  have  a 
crossed  action.  The  most  that  can  be  said  on  this  point  is  that  it  is  a 
reasonable  inference  from  pathological  facts  that  the  nerves  decussate 
anterior  to  the  pons. 

The  main  root  of  the  facial,  the  auditory  nerve  and  the  intermediary 
nerve  of  Wrisberg  pass  together  into  the  internal  auditory  meatus.  At 
the  bottom  of  the  meatus,  the  facial  and  the  nerve  of  Wrisberg  enter  the 
aquasductus  Fallopii,  following  its  course  through  the  petrous  portion  of 
the  temporal  bone.  In  the  aqueduct  the  nerve  of  Wrisberg  presents  a 
little  ganglioform  enlargement  (geniculate  ganglion)  of  a  reddish  color, 
which  has  been  shown  to  contain  nerve-cells.  The  main  root  and  the 
intermediary  nerve  then  unite  and  form  the  common  trunk  of  the  facial, 
which  emerges  from  the  cranial  cavity  by  the  stylo-mastoid  foramen. 
It  is  thought  by  some  anatomists  that  the  intermediary  nerve  of  Wrisberg 
arises  from  the  glosso-pharyngeal,  which  communicates  with  the  facial 
in  the  tympanum.  A  branch  has  been  described  going  from  the  glosso- 
pharyngeal to  the  geniculate  ganglion.  It  has  been  seen  that  the 
fibres  of  origin  of  this  nerve  come  from  the  nucleus  of  the  glosso- 
pharyngeal. 

In  the  aquaeductus  Fallopii  the  facial  gives  off  the  following 
branches : — 

1.  The  large  petrosal  branch  is  given  off  at  the  ganglioform  enlarge- 
ment and  goes  to  Meckel's  ganglion. 

2.  The  small  petrosal  branch  is  given  off  at  the  ganglioform  en- 
largement or  a  very  short  distance  beyond  it  and  passes  to  the  otic 
ganglion. 

3.  A  small  branch,  the  tympanic,  is  distributed  to  the  stapedius 
muscle. 

4.  The  chorda  tympani  passes  through  the  cavity  of  the  tympanum 
and  joins  the  lingual  branch  of  the  inferior  maxillary  division  of  the  fifth 
as  it  passes  between  the  two  pterygoid  muscles,  with  which  nerve  it  be- 
comes closely  united. 

5.  Opposite  the  point  of  origin  of  the  chorda  tympani,  a  communi- 


5o8  NERVOUS    SYSTEM 

eating  branch  passes  between  the  facial  and  the  pneumogastric,  connect- 
ing these  nerves  by  a  double  inosculation. 

The  five  branches  above  described  are  given  off  in  the  aquaeductus 
Fallopii.  The  following  branches  are  given  off  after  the  nerve  has 
emerged  from  the  cranial  cavity :  — 

1.  Just  after  the  facial  has  passed  out  at  the  stylo-mastoid  foramen, 
it  sends  a  small  communicating  branch  to  the  glosso-pharyngeal  nerve. 
This  branch  is  sometimes  wanting. 

2.  The  posterior  auricular  nerve  is  given  off  by  the  facial  a  little 
below  the  stylo-mastoid  foramen.  Its  superior  branch  is  distributed  to  the 
retrahens  aurem  and  the  attollens  aurem.  In  its  course  this  nerve  re- 
ceives a  communicating  branch  of  considerable  size  from  the  cervical 
plexus  by  the  auricularis  magnus.  It  sends  some  filaments  to  the  integu- 
ment. The  inferior,  or  occipital  branch,  the  larger  of  the  two,  is  dis- 
tributed to  the  occipital  portion  of  the  occipito-frontalis  muscle  and  to 
integument. 

3.  The  digastric  branch  is  given  off  near  the  root  of  the  posterior 
auricular.  It  is  distributed  to  the  posterior  belly  of  the  digastric  muscle. 
In  its  course  it  anastomoses  with  filaments  from  the  glosso-pharyngeal. 
From  the  plexus  formed  by  this  anastomosis,  filaments  are  given  off  to 
the  digastric  and  to  the  stylo-hyoid  muscles. 

4.  Near  the  stylo-mastoid  foramen  a  small  branch  is  given  off  which 
is  distributed  exclusively  to  the  stylo-hyoid  muscle. 

5.  Near  thfe  stylo-mastoid  foramen,  or  sometimes  a  little  above  it,  a 
long  delicate  branch  is  given  off,  which  is  not  noticed  in  many  works  on 
anatomy.  It  is  described,  however,  by  Hirschfeld,  under  the  name  of 
the  lingual  branch.  It  passes  behind  the  stylo-pharyngeal  muscle  and 
then  by  the  sides  of  the  pharynx  to  the  base  of  the  tongue.  In  its  course 
it  receives  one  or  two  branches  from  the  glosso-pharyngeal  nerve,  which 
are  nearly  as  large  as  the  original  branch  from  the  facial.  As  it  passes 
to  the  base  of  the  tongue  it  anastomoses  again  by  a  number  of  filaments 
with  the  glosso-pharyngeal.  It  then  sends  filaments  of  distribution  to 
the  mucous  membrane  and  finally  passes  to  the  stylo-glossus  and  palato- 
glossus muscles. 

Having  given  off  these  branches,  the  trunk  of  the  facial  passes 
through  the  parotid  gland,  dividing  into  its  two  great  terminal 
branches  :  — 

I.  The  temporo-facial  branch,  the  larger,  passes  upward  and  forward 
to  be  distributed  to  the  superficial  muscles  of  the  upper  part  of  the 
face  ;  namely,  the  attrahens  aurem,  the  frontal  portion  of  the  occipito- 
frontalis,  the  orbicularis  palpebrarum,  corrugator  supercilii,  pyramidalis 
nasi,  levator  labii    superioris,  levator  labii    superioris  alaeque  nasi,  the 


FACIAL,    OR    NERVE    OF   EXPRESSION  509 

dilators  and  compressors  of  the  nose,  part  of  the  buccinator,  the  levator 
anguli  oris  and  the  zygomatic  muscles.  In  its  course  it  receives 
branches  of  communication  from  the  auriculo-temporal  branch  of  the 
inferior  maxillary  nerve.  It  joins  also  with  the  temporal  branch  of  the 
superior  maxillary  and  with  branches  of  the  ophthalmic.  It  thus 
becomes  a  mixed  nerve  and  is  distributed  in  part  to  integument. 

2.  The  cervico-facial  nerve  passes  downward  and  forward  to  supply 
the  buccinator,  orbicularis  oris,  risorius,  levator  labii  inferioris,  depressor 
labii  inferioris,  depressor  anguli  oris  and  platysma. 

General  Properties  of  the  Facial  Nerve.  —  It  has  long  been  recog- 
nized that  the  facial  is  the  motor  nerve  of  the  superficial  muscles  of  the 
face  and  that  its  division  produces  paralysis  of  motion  and  no  marked 
effects  on  sensation.  It  is  evident,  also,  from  the  communications 
between  the  facial  with  the  fifth,  that  it  contains  in  its  course  sensory 
fibres.  Indeed,  all  who  have  operated  on  this  nerve  have  found  that  it 
is  slightly  sensory  after  it  has  emerged  from  the  cranial  cavity.  It  is 
a  question,  however,  of  great  importance  to  determine  whether  or  not 
the  facial  be  endowed  with  sensibility  by  virtue  of  its  own  fibres  of 
origin.  The  main  root  evidently  is  from  the  motor  tract,  resembles  the 
anterior  roots  of  the  spinal  nerves  and  is  distributed  to  muscles ;  but 
this  root  is  joined  by  the  intermediary  nerve  of  Wrisberg,  which  pre- 
sents a  small  ganglionic  enlargement  that  is  analogous  to  the  gangha 
on  the  posterior  roots  of  the  spinal  nerves.  The  testimony  of  direct 
experimentation  is  in  favor  of  the  insensibility  of  the  facial  at  its  origin. 
It  is  true  that  the  intermediary  nerve  of  Wrisberg  has  a  certain  ana- 
tomical resemblance  to  the  sensory  nerves,  chiefly  by  reason  of  its 
ganglioform  enlargement ;  but  direct  experiments  are  wanting,  to  show 
that  it  is  a  nerve  of  general  sensibility. 

Uses  of  the  Brandies  of  the  Facial  given  off  witJiin  the  Aqnediict  of 
Fallopins.  —  The  first  branch,  the  large  petrosal,  is  the  motor  root  of 
Meckel's  ganglion.  This  will  be  referred  to  again,  in  connection  with 
the  sympathetic  system.  The  second  branch,  the  small  petrosal,  is  one 
of  the  motor  roots  of  the  otic  ganglion.  The  third  branch,  the  tym- 
panic, is  distributed  exclusively  to  the  stapedius  muscle.  The  second 
and  third  branches  will  be  considered  again,  in  connection  with  the 
physiology  of  the  internal  ear.  The  fourth  branch,  the  chorda  tympani, 
is  so  important  that  it  demands  special  consideration.  The  fifth  branch 
is  given  off  opposite  the  origin  of  the  chorda  tympani  and  passes  to  the 
pneumogastric,  to  which  nerve  it  probably  supplies  motor  filaments. 
In  this  branch,  sensory  filaments  pass  from  the  pneumogastric  and 
constitute  a  part  of  the  sensory  connections  of  the  facial. 

Uses    of  the    Chorda    Tympani.  —  This  nerve  passes  between  the 


5IO 


NERVOUS    SYSTEM 


bones  of  the  ear  and  through  the  tympanic  cavity  to  the  lingual  branch 
of  the  inferior  maxillary  division  of  the  fifth,  which  it  joins  at  an  acute 
angle,  between  the  pterygoid  muscles.  As  regards  the  portion  of  the 
facial  that  furnishes  the  filaments  of  the  chorda  tympani,  it  is  nearly 
certain   that  these  come  from  the  intermediary  nerve  of  Wrisberg. 

There  can  be  no  doubt  in  regard  to  the  influence  of  the  chorda 
tympani  on  the  sense  of  taste  in  the  anterior  two-thirds  of  the  tongue. 
In  cases  of  disease  or  injury  in  which  the  root  of  the  facial  is  involved 
so  that  the  chorda  tympani  is  paralyzed,  in  addition  to  the  ordinary 
phenomena  of  paralysis  of  the  superficial  muscles  of  the  face,  there  is 

loss  of  taste  in  the  anterior  two- 
thirds  of  the  tongue  on  the  side 
corresponding  to  the  lesion.  The 
action  of  the  chorda  tympani  will 
be  considered  again,  in  connec- 
tion with  the  physiology  of  gus- 
tation. 

Influence  of  Certain  Branches 
of  tile  Facial  on  the  Mo-oements 
of  the  Palate  and  Uvula.  — 
There  can  be  little  doubt  that 
filaments  from  the  facial  animate 
certain  of  the  movements  of  the 
velum  palati  and  the  uvula.  It 
has  been  observed  that  in  cer- 
tain cases  of  facial  paralysis  the 
palate  on  one  side  is  flaccid  and 
the  uvula  is  drawn  to  the  opposite 
side ;  but  these  phenomena  do  not  occur  unless  the  nerve  is  affected 
at  its  root  or  within  the  aquaeductus  Fallopii.  It  is  true  that  the 
uvula  frequently  is  drawn  to  one  side  or  the  other  in  persons  unaffected 
with  facial  paralysis,  but  it  is  none  the  less  certain  that  it  is  deviated 
as  a  consequence  of  paralysis  of  the  facial  in  some  instances.  The 
filaments  of  the  facial  which  influence  the  levator  palati  and  azygos 
uvulae  muscles  are  derived  from  the  large  petrosal  branch  of  the  nerve, 
passing  to  the  muscles  through  Meckel's  ganglion,  the  filaments  to  the 
palato-glossus  and  the  palato-pharyngeus  being  given  off  from  the 
glosso-pharyngeal,  but  originally  coming  from  an  anastomosing  branch 
of  the  facial. 

In  view  of  examples  of  paralysis  of  the  palate  and  uvula  in  certain 
cases  of  facial  palsy,  the  frequent  occurrence  of  contractions  of  the 
muscles  of  these  parts  following  stimulation  of  the  facial  and  the  reflex 


Fig.  123. —  Chorda-tympani  nerve  (Hirschfeld). 

I,  2,  3,  4,  facial  nerve  passing  through  the 
aquaeductus  Fallopii;  5,  ganglioform  enlargement 
(geniculate  ganglion);  6,  great  petrosal  nerve; 
7,  spheno-palatine  ganglion  ;  8,  small  petrosal  nerve  ; 
9,  chorda  tympani;  10,  ii,  12,  13,  various  branches 
of  the  facial ;   14,  14,  15,  glosso-pharyngeal  nerve. 


FACIAL,    OR   NERVE    OF    EXPRESSION  511 

action  through  the  glosso-pharyngeal  and  the  facial,  there  can  be  little 
doubt  that  the  muscles  of  the  palate  and  uvula  receive  filaments 
of  distribution  from  the  seventh  nerve.  The  effects  of  paralysis  of 
these  muscles  are  manifested  by  more  or  less  trouble  in  deglutition  and 
in  the  pronunciation  of  certain  words,  with  difficulty  in  the  expulsion 
of  mucus  collected  in  the  back  part  of  the  mouth  and    the  pharynx. 

Uses  of  the  External  BrancJies  of  the  Facial.  —  The  general  action  of 
the  branches  of  the  facial  going  to  the  superficial  muscles  of  the  face  is 
sufficiently  evident,  in  view  of  what  is  known  of  the  distribution  of 
these  branches  and  the  general  properties  of  the  nerve.  It  is  now 
recognized  as  the  nerve  that  presides  over  the  movements  of  the  super- 
ficial muscles  of  the  face,  not  including  those  directly  concerned  in  the 
act  of  mastication.  This  being  its  general  action,  it  is  easy  to  assign  to 
each  of  the  external  branches  its  particular  office. 

Just  after  the  facial  has  passed  out  at  the  stylo-mastoid  foramen,  it 
sends  to  the  glosso-pharyngeal  the  communicating  branch,  the  action  of 
which  has  just  been  mentioned  in  connection  with  the  movements  of  the 
palate. 

The  posterior  auricular  branch,  becoming  partly  sensory  by  the 
accession  of  filaments  from  the  cervical  plexus,  gives  sensibility  to  the 
integument  on  the  back  part  of  the  ear  and  over  the  occipital  portion 
of  the  occipito-frontalis  muscle.  It  animates  the  retrahens  and  the 
attollens  aurem,  muscles  that  are  little  developed  in  man  but  are  im- 
portant in  certain  of  the  inferior  animals.  It  also  animates  the  posterior 
portion  of  the  occipito-frontalis. 

The  branches  distributed  to  the  posterior  belly  of  the  digastric  and 
to  the  stylo-hyoid  muscle  simply  animate  these  muscles,  one  of  the 
uses  of  which  is  to  assist  in  deglutition.  The  same  may  be  said  of 
filaments  that  go  the  stylo-glossus. 

The  two  great  branches  distributed  upon  the  face,  after  the  trunk  of 
the  nerve  has  passed  through  the  parotid  gland,  have  the  most  prominent 
action.  Both  these  branches  are  slightly  sensory,  from  their  connections 
with  other  nerves,  and  are  distributed  in  small  part  to  integument. 

The  temporo-facial  branch  animates  all  the  muscles  of  the  upper 
part  of  the  face.  In  complete  paralysis  of  this  branch,  the  eye  is  con- 
stantly open,  even  during  sleep,  on  account  of  paralysis  of  the  orbicu- 
laris muscle.  In  cases  of  long  standing,  the  globe  of  the  eye  may 
become  inflamed  from  constant  exposure,  from  abolition  of  the  move- 
ments of  winking  by  which  the  tears  are  distributed  over  its  surface 
and  little  foreign  particles  are  removed,  and,  in  short,  from  absence  of 
the  protective  action  of  the  hds.  In  these  cases  the  lower  lid  may 
become  slightly  everted.     The  frontal  portion  of  the  occipito-frontalis, 


512 


NERVOUS    SYSTEM 


the  attrahens  aurem  and  the  corrugator  supercihi  muscles,  are  also 
paralyzed.  The  most  prominent  symptom  of  paralysis  of  these  muscles 
is  inability  to  corrugate  the  brow  on  one  side. 

Paralysis  of  the  muscles  that  dilate  the  nostrils  has  been  shown  to 
have  an  important  influence  on  respiration  through  the  nose.  In  in- 
stances of  complete  paralysis  of  the  nostril  of  one  side,  there  frequently 
is  some  difficulty  in  inspiration,  even  in  the  human  subject. 

Physiologists  have  noted  an  interference  with  olfaction,  due  to  the 
inability  to  inhale  with  one  nostril,  in  cases  of  facial  paralysis.  The 
influence  of  the  nerve  in  the  act  of  conveying  odorous  emanations  to 
the  olfactory  membrane  is  sufficiently  evident  after  what  has  been  said 
concerning  the  action  of  the  facial  in  respiration. 

The  effects  of  paralysis  of  the  other  superficial  muscles  of  the  face 
are  manifested  in  the  distortion  of  the  features,  on  account  of  the  unop- 
posed action  of  the  muscles  of  the  sound  side,  a  phenomenon  that  is 
sufficiently  familiar.  When  facial  palsy  affects  one  side  and  is  complete, 
the  angle  of  the  mouth  is  drawn  to  the  opposite  side,  the  eye  on  the 
affected  side  is  widely  and  permanently  opened,  even  during  sleep,  and 
the  face  has  on  that  side  a  peculiarly  expressionless  appearance.  When 
a  patient  affected  in  this  way  smiles  or  attempts  to  grimace,  the  dis- 
tortion is  much  increased.  The  lips  are  paralyzed  on  one  side,  which 
sometimes  causes  a  flow  of  saliva  from  the  corner  of  the  mouth.  In  the 
lower  animals  that  use  the  lips  in  prehension,  paralysis  of  these  parts 
interferes  considerably  with  the  taking  of  food.  The  flaccidity  of  the 
paralyzed  lips  and  cheek  in  the  human  subject  sometimes  causes  a  puff- 
ing movement  with  each  act  of  expiration,  as  if  the  patient  were  smoking 
a  pipe. 

The  buccinator  is  not  supplied  by  filaments  from  the  nerve  of  masti- 
cation but  is  animated  solely  by  the  facial.  Paralysis  of  this  muscle 
interferes  materially  with  mastication,  from  a  tendency  to  accumulation 
of  the  food  between  the  teeth  and  the  cheek.  Patients  complain  of  this 
difficulty,  and  they  sometimes  keep  the  food  between  the  teeth  by  press- 
ure with  the  hand.  In  the  rare  instances  in  which  both  facial  nerves 
are  paralyzed,  there  is  very  great  difficulty  in  mastication,  from  the 
cause  just  mentioned. 

The  action  of  the  external  branches  of  the  facial  is  thus  sufficiently 
simple ;  and  it  is  only  as  its  deep  branches  affect  the  sense  of  taste,  the 
movements  of  deglutition,  etc.,  that  it  is  difficult  to  ascertain  their  exact 
office.  As  this  is  the  nerve  of  expression  of  the  face,  it  is  in  the  human 
subject  that  the  phenomena  attending  its  paralysis  are  most  prominent. 
When  both  sides  are  affected,  the  aspect  is  remarkable,  the  face  being 
absolutely  expressionless  and  looking  as  if  it  were  covered  with  a  mask. 


SPINAL   ACCESSORY    NERVE 


513 


Spinal  Accessory  (Eleventh  Nerve) 

The  spinal  accessory  nerve,  from  the  great  extent  of  its  origin,  its 
important  anastomoses  with  other  nerves  and  its  pecuHar  course  and  dis- 
tribution, has  long  engaged  the  atten- 
tion of  anatomists  and  physiologists, 
who  have  advanced  many  theories  in 
regard  to  its  office.  Its  physiological 
history,  however,  may  properly  be 
said  to  begin  with  the  experiments  of 
Claude  Bernard. 

Physiological  Anatomy.  —  The  ori- 
gin of  this  nerve  is  very  extensive. 
A  certain  portion  arises  from  the 
lower  half  of  the  bulb,  and  the  rest 
takes  its  origin  below,  from  the  upper 
two-thirds  of  the  cervical  portion  of 
the  spinal  cord.  That  portion  of  the 
root  which  arises  from  the  medulla 
oblongata  is  called  the  bulbar  portion, 
the  roots  from  the  cord  constituting 
the  spinal  portion.  Inasmuch  as 
there  is  a  marked  difference  between 
the  uses  of  these  two  portions,  the 
anatomical  distinction  just  mentioned 
is  important. 

The  superior  roots  arise  by  four 
or  five  filaments  from  the  lower  half 
of  the  medulla  oblongata,  below  the 
origin  of  the  pneumogastrics.  These 
filaments  of  origin  pass  to  a  gray  nu- 
cleus in  the  medulla. 

The  spinal  portion  of  the  nerve 
arises  from  the  upper  part  of  the 
spinal  cord,  between  the  anterior  and 
posterior  roots  of  the  upper  four  or 
five  cervical  nerves.  The  filaments 
of  origin  are  six  to  eight  in  number. 
The  most  inferior  of  these  usually  is 
single,  the  other  filaments  frequently  being  arranged  in  pairs.  These 
take  their  origin  from  the  lateral  portion  of  the  cord  and  are  con- 
nected with  the  anterior  cornua  of  gray  matter. 


Fig.  124. 


—  Spitial  accessory  nerve 
(Hirschfeld) . 


I,  trunk  of  the  facial  nerve ;  2,  2,  glosso- 
pharyngeal nerve;  3,3,  pneumogastric ;  4,4, 
4,  trunk  of  the  spinal  accessory  ;  5,  sublingual 
nerve ;  6,  superior  cervical  ganglion ;  7,  7, 
anastomosis  of  the  first  two  cervical  nerves; 
8,  carotid  branch  of  the  sympathetic ;  9,  10, 
II,  12,  13,  branches  of  the  glosso-pharyngeal ; 
14,  15,  branches  of  the  facial ;  16,  otic  gan- 
glion ;  17,  auricular  branch  of  tlie  pneumo- 
gastric; 18,  anastomosing  branch  from  the 
spinal  accessory  to  the  pneumogastric ;  19, 
anastomosis  of  the  first  pair  of  cervical  nerves 
vk'ith  the  sublingual;  20,  anastomosis  of  the 
spinal  accessory  with  the  second  pair  of  cer- 
vical nerves  ;  21,  pha7y7igeal  plexus;  22,  su- 
perior laryngeal  nerve;  23,  external  laryngeal 
nerve;  24,  middle  cervical  ganglion. 


514  NERVOUS    SYSTEM 

Following  the  nerve  from  its  most  inferior  filament  of  origin  upward, 
it  gradually  increases  in  size  by  union  with  its  other  roots,  enters  the 
cranial  cavity  by  the  foramen  magnum,  and  passes  to  the  jugular  foramen, 
by  which  it  emerges,  with  the  glosso-pharyngeal,  the  pneumogastric  and 
the  internal  jugular  vein. 

In  its  course  the  spinal  accessory  anastomoses  with  several  nerves. 
Just  as  it  enters  the  cranial  cavity,  it  receives  filaments  of  communica- 
tion from  the  posterior  roots  of  the  upper  two  cervical  nerves.  These 
filaments,  however,  are  not  constant.  It  frequently,  though  not  con- 
stantly, sends  a  few  filaments  to  the  superior  ganglion,  or  the  ganglion 
of  the  root  of  the  pneumogastric.  After  it  has  emerged  by  the  jugular 
foramen  it  sends  a  branch  of  considerable  size  to  the  pneumogastric, 
from  which  nerve  it  receives  a  few  filaments  of  communication.  In  its 
course  it  also  receives  filaments  of  communication  from  the  anterior 
branches  of  the  second,  third  and  fourth  cervical  nerves. 

In  its  distribution  the  spinal  accessory  presents  two  branches.  The 
internal,  or  anastomotic  branch  passes  to  the  pneumogastric  just  below 
the  plexiform  enlargement,  which  is  sometimes  called  the  ganglion  of 
the  trunk  of  the  pneumogastric.  This  branch  is  composed  principally 
if  not  entirely  of  the  filaments  that  take  their  origin  from  the  bulb.  As 
it  joins  the  pneumogastric  it  subdivides  into  two  smaller  branches.  The 
first  of  these  forms  a  portion  of  the  pharyngeal  branch  of  the  pneumo- 
gastric. The  second  becomes  intimately  united  with  the  pneumogastric, 
lying  at  its  posterior  portion,  and  furnishes  filaments  to  the  inferior,  or 
recurrent  laryngeal  branch,  which  is  distributed  to  all  the  muscles  of  the 
larynx  except  the  crico-thyroid.  The  passage  of  the  filaments  from  the 
spinal  accessory  to  the  pharyngeal  branch  of  the  pneumogastric  is 
readily  observed ;  but  the  fact  that  filaments  from  this  nerve  pass  to  the 
larynx  by  the  recurrent  laryngeal  has  been  ascertained  only  by  physio- 
logical experiments.  In  the  chimpanzee,  however,  the  internal  branch 
does  not  go  to  the  pneumogastric  but  passes  directly  to  the  muscles  of 
the  larynx  (Vrolik). 

The  external,  or  large  branch  of  the  spinal  accessory,  called  the  mus- 
cular branch,  penetrates  and  passes  through  the  posterior  portion  of  the 
upper  third  of  the  sterno-cleido-mastoid  muscle.  It  then  goes  to  the 
anterior  surface  of  the  trapezius,  which  muscle  receives  its  ultimate 
branches  of  distribution.  In  its  passage  through  the  sterno-cleido-mas- 
toid, it  joins  with  branches  from  the  second  and  third  cervical  nerves  and 
sends  filaments  of  distribution  to  the  muscle.  Although  the  two  muscles 
just  mentioned  receive  motor  filaments  from  the  spinal  accessory,  they 
are  also  supplied  from  the  cervical  nerves ;  and  consequently  they  are 
not  entirely  paralyzed  when  the  spinal  accessory  is  divided. 


SPINAL   ACCESSORY    NERVE  515 

Properties  and  Uses  of  the  Spinal  Accessory.  —  Notwithstanding  the 
difficulty  in  exposing  and  operating  on  the  roots  of  the  spinal  accessory, 
it  has  been  demonstrated  that  their  stimulation  produces  convulsive 
movements  in  certain  muscles.  By  stimulating  the  filaments  that  arise 
from  the  bulb,  contractions  of  the  muscles  of  the  pharynx  and  larynx 
are  produced,  but  no  movements  of  the  sterno-mastoid  and  trapezius. 
Stimulation  of  the  roots  arising  from  the  spinal  cord  produces  move- 
ments of  the  two  muscles  just  mentioned  and  no  movements  in  the 
larynx.  In  view  of  these  experiments,  it  is  evident  that  the  true  fila- 
ments of  origin  of  the  spinal  accessory  are  motor ;  and  it  is  further  evi- 
dent that  the  filaments  from  the  bulb  are  distributed  to  the  muscles  of 
the  pharynx  and  larynx,  while  the  filaments  from  the  spinal  cord  go  to 
the  sterno-cleido-mastoid  and  trapezius. 

The  trunk  of  the  spinal  accessory,  after  the  nerve  has  passed  out  of 
the  cranial  cavity,  has  a  certain  degree  of  sensibility.  If  the  nerve  is 
divided,  the  peripheral  extremity  manifests  recurrent  sensibility,  but  the 
central  end  also  is  sensible,  probably  from  direct  filaments  of  communi- 
cation from  the  cervical  nerves  and  the  pneumogastric. 

Uses  of  the  Inter jial  BrancJi  from  the  Spinal  Accessory  to  the  Pneitnio- 
gastric.  —  Bischoff  (1832)  attempted  to  ascertain  the  uses  of  this  branch 
by  dividing  the  roots  of  the  spinal  accessory  on  both  sides  in  a  living 
animal.  The  results  of  his  experiments  may  be  stated  in  a  very  few 
words :  He  attempted  to  divide  all  the  roots  of  the  nerves  on  both 
sides  by  dissecting  down  to  the  occipito-atloid  space  and  penetrating 
into  the  cavity  of  the  spinal  canal.  In  the  first  three  experiments  on 
dogs,  the  animals  died  so  soon  after  section  of  the  nerves  that  no  satis- 
factory results  were  obtained.  In  two  succeeding  experiments  on  dogs, 
the  animals  recovered.  After  division  of  the  nerves  the  voice  became 
hoarse,  but  a  few  weeks  later  it  became  normal.  On  killing  the  ani- 
mals, an  examination  of  the  parts  showed  that  some  of  the  filaments  of 
origin  had  not  been  divided.  An  experiment  was  then  made  on  a  goat, 
but  this  was  unsatisfactory,  as  the  roots  were  not  completely  divided. 
Finally  another  experiment  was  made  on  a  goat.  In  this  the  results 
were  more  satisfactory.  After  division  of  the  nerve  on  one  side,  the 
voice  became  hoarse.  As  the  filaments  were  divided  on  the  opposite 
side,  the  voice  was  enfeebled,  until  finally  it  became  extinct.  The  sound 
emitted  afterward  was  one  that  could  in  no  wise  be  called  voice  {"'qui 
neutiquam  vox  appellari pottiit''). 

Bernard,  who  determined  exactly  the  influence  of  the  spinal  acces- 
sory over  the  vocal  movements  of  the  larynx,  first  repeated  the  experi- 
ments of  Bischoff ;  but  the  animals  operated  on  died  so  soon  from 
hemorrhage  or  other  causes  that  his  observations  were  not  satisfactory. 


5i6  NERVOUS    SYSTEM 

After  many  unsuccessful  trials,  he  succeeded  in  overcoming  all  difficul- 
ties by  following  the  trunk  of  the  nerve  back  to  the  jugular  foramen, 
seizing  it  here  with  a  strong  forceps  and  drawing  it  out  by  the  roots. 
The  operation  usually  is  most  successful  in  cats,  although  Bernard  fre- 
quently succeeded  in  other  animals. 

When  one  spinal  accessory  is  extirpated,  the  vocal  sounds  are  hoarse 
and  unnatural.  When  both  nerves  are  torn  out,  in  addition  to  the  dis- 
turbance of  deglutition  and  the  partial  paralysis  of  the  sterno-mastoid 
and  trapezius  muscles,  the  voice  becomes  extinct.  Animals  operated  on 
in  this  way  move  the  jaws  and  make  evident  efforts  to  cry,  but  no  vocal 
sound  is  emitted.  Bernard  kept  animals,  with  both  nerves  extirpated, 
for  several  months  and  did  not  observe  any  return  of  the  voice.  His 
observations,  which  have  been  fully  confirmed  (Flint),  show  that  the  in- 
ternal branch  of  the  spinal  accessory  is  the  nerve  of  phonation.  The 
filaments  that  preside  over  the  vocal  movements  of  the  larynx  pass  in 
greatest  part  through  the  recurrent  laryngeal  branches  of  the  pneumo- 
gastrics ;  but  the  recurrent  laryngeals  also  contain  filaments  from  other 
motor  nerves,  which  latter  are  concerned  in  the  respiratory  movements 
of  the  glottis. 

Influence  of  the  Internal  BrancJi  of  the  Spinal  Accessory  on  Degluti- 
tio7t.  —  There  are  two  ways  in  which  deglutition  is  affected  through  this 
nerve  :  i.  When  the  larynx  is  paralyzed  as  a  consequence  of  extirpation 
of  both  nerves,  the  glottis  can  not  be  completely  closed  to  prevent  the 
entrance  of  foreign  bodies  into  the  air-passages.  In  rabbits  particularly, 
it  has  been  noted  that  particles  of  food  penetrate  the  trachea  and  find 
their  way  into  the  lungs.  2.  The  spinal  accessory  furnishes  filaments 
to  the  pharyngeal  branch  of  the  pneumogastric,  and  through  this  nerve 
it  directly  affects  the  muscles  of  deglutition  ;  but  the  muscles  animated 
in  this  way  by  the  spinal  accessory  have  a  tendency  to  draw  the  lips  of 
the  glottis  together,  while  they  assist  in  passing  the  alimentary  bolus  into 
the  oesophagus.  When  these  important  acts  are  wanting,  there  is  some 
difficulty  in  the  process  of  deglutition  itself,  as  well  as  danger  of  passage 
of  foreign  particles  into  the  larynx. 

Influence  of  the  Spinal  Accessory  on  the  Heart.  —  The  spinal  accessory 
furnishes  to  the  pneumogastric  the  inhibitory  fibres  that  influence  the 
action  of  the  heart.  A  sufficiently  powerful  faradic  current  passed 
through  one  pneumogastric  will  in  some  animals  arrest  the  cardiac 
movements ;  and  it  has  been  noted  that  the  influence  of  the  right  nerve 
on  the  heart  is  greater  than  that  of  the  left.  Waller  found  that  if  he 
extirpated  the  spinal  accessory  on  one  side,  after  four  or  five  days  the 
action  of  the  heart  could  not  be  arrested  by  stimulating  the  pneumogas- 
tric of  the  same  side ;  but  inhibition  followed  stimulation  of  the  pneumo- 


SPINAL   ACCESSORY    NERVE 


517 


gastric  of  the  opposite  side,  where  the  connections  with  the  spinal 
accessory  were  intact.  In  these  observations  it  seemed  necessary  that 
a  sufficient  time  should  elapse  after  extirpation  of  the  spinal  accessory 
for  the  excitability  of  the  filaments  that  join  the  pneumogastric  to 
become  extinct ;  but  the  experiments  are  sufficient  to  show  the  direct 
inhibitory  influence  of  the  spinal  accessory  on  the  heart.  After  ex- 
tirpation of  the  spinal  accessory,  degenerated  fibres  are  found  in  the 
trunk  of  the  pneumogastric.  The  mechanism  of  inhibition  of  the  heart 
has  already  been  considered  in  connection  with  the  physiology  of  the 
circulation. 

Uses  of  the  External,  or  Muscular  Branch  of  the  Spinal  Accessory.  — 
Observations  have  shown  that  the  internal  branch  of  the  spinal  acces- 
sory, and  the  internal  branch  only,  is  directly  concerned  in  the  vocal 
movements  of  the  larynx,  and  to  a  great  extent  in  the  closure  of  the 
glottis  during  deglutition.  It  has  been  noted  in  addition  that  animals 
in  which  both  branches  have  been  extirpated  present  irregularity  of  the 
movements  of  the  anterior  extremities  and  suffer  from  shortness  of  breath 
after  violent  muscular  exertion.  The  use  of  the  corresponding  extremi- 
ties in  the  human  subject  is  so  different  that  it  is  not  easy  to  make  a 
direct  application  of  these  experiments ;  still,  certain  inferences  may  be 
drawn  from  them  in  regard  to  the  action  of  the  external  branch  in 
man. 

In  prolonged  vocal  efforts  the  vocal  chords  are  put  on  the  stretch, 
and  the  act  of  expiration  is  different  from  that  in  tranquil  breathing. 
In  singing,  for  example,  the  shoulders  frequently  are  fixed ;  and  this  is 
done  to  some  extent  by  the  action  of  the  sterno-cleido-mastoid  and  the 
trapezius.  It  is  probable,  then,  that  the  action  of  the  branch  of  the 
spinal  accessory  which  goes  to  these  muscles  has  a  certain  synchronism 
with  the  action  of  the  branch  going  to  the  larynx  and  the  pharynx ;  the 
one  fixing  the  upper  part  of  the  chest  so  that  the  expulsion  of  the  air 
through  the  glottis  may  be  more  nicely  regulated  by  the  expiratory 
muscles,  and  the  other  acting  on  the  vocal  chords. 

In  violent  muscular  effort,  the  glottis  is  closed,  the  thorax  is 
fixed  after  a  full  inspiration  and  respiration  is  arrested  so  long  as  the 
effort,  if  it  be  not  too  prolonged,  is  continued.  The  same  synchronism, 
therefore,  obtains  in  this  as  in  prolonged  vocal  efforts.  In  experiments 
in  which  the  muscular  branch  only  has  been  divided,  shortness  of  breath, 
after  violent  muscular  effort,  is  observed ;  and  this  probably  is  due  to 
lack  of  synchronous  action  of  the  sterno-cleido-mastoid  and  trapezius. 
The  irregularity  in  the  movements  of  progression  in  animals  in  which 
either  both  branches  or  the  muscular  branches  alone  have  been  divided 
is  due  to  anatomical  peculiarities. 


5i8  NERVOUS    SYSTEM 


Sublingual  (Twelfth  Nerve) 

The  last  of  the  motor  cranial  nerves  is  the  sublingual ;  and  its  action 
is  intimately  connected  with  the  physiology  of  the  tongue  in  deglutition 
and  articulation,  although  the  sublingual  is  also  distributed  to  certain  of 
the  muscles  of  the  neck. 

Physiological  Anatomy.  —  The  apparent  origin  of  the  subungual  is 
from  the  bulb,  in  the  groove  between  the  olivary  body  and  the  anterior 
pyramid,  on  the  line  of  the  anterior  roots  of  the  spinal  nerves.  At  this 
point  its  root  is  formed  of  ten  to  twelve  filaments,  which  extend  from 
the  inferior  portion  of  the  olivary  body  to  about  the  junction  of  the 
upper  with  the  middle  third  of  the  bulb.  These  filaments  of  origin  are 
separated  into  two  groups,  superior  and  inferior.  From  this  apparent 
origin,  the  filaments  have  been  traced  into  the  gray  matter  of  the  floor 
of  the  fourth  ventricle,  between  the  deep  origin  of  the  pneumogastric 
and  the  glosso-pharyngeal.  It  is  probable  that  some  of  the  filaments  of 
origin  of  these  nerves  decussate  in  the  floor  of  the  fourth  ventricle. 
The  superior  and  inferior  filaments  of  origin  of  the  nerve  unite  to  form 
two  bundles,  which  pass  through  distinct  perforations  in  the  dura  mater. 
These  two  bundles  then  pass  into  the  anterior  condyloid  foramen  and 
unite  into  a  single  trunk  as  they  emerge  from  the  cranial  cavity. 

After  the  sublingual  has  passed  out  of  the  cranial  cavity  it  anasto- 
moses with  several  nerves.  It  sends  a  filament  of  communication  to 
the  sympathetic  as  it  branches  from  the  superior  cervical  ganglion. 
Soon  after  it  has  passed  through  the  foramen  it  sends  a  branch  to  the 
pneumogastric.  It  anastomoses  by  two  or  three  branches  with  the 
upper  two  cervical  nerves,  the  filaments  passing  in  both  directions 
between  the  nerves.  It  anastomoses  with  the  lingual  branch  of  the 
fifth  by  two  or  three  filaments  passing  in  both  directions. 

In  its  distribution  the  sublingual  presents  several  peculiarities :  — 

Its  first  branch,  the  decendens  noni,  passes  down  the  neck  to  the 
sterno-hyoid,  sterno-thyroid  and  omo-hyoid  muscles. 

The  thyro-hyoid  branch  is  distributed  to  the  thyro-hyoid  muscle. 

The  other  branches  are  distributed  to  the  stylo-glossus,  hyo-glossus, 
genio-hyoid  and  genio-hyo-glossus  muscles,  their  terminal  filaments  going 
to  the  intrinsic  muscles  of  the  tongue. 

It  is  thus  seen  that  the  sublingual  nerve  is  distributed  to  all  the 
muscles  in  the  infra-hyoid  region,  the  action  of  which  is  to  depress  the 
larynx  and  the  hyoid  bone  after  the  passage  of  the  alimentary  bolus 
through  the  pharynx ;  to  one  of  the  muscles  in  the  supra-hyoid  region, 
the  genio-hyoid ;  to  most  of  the  muscles  that  move  the  tongue  ;  and  to 


SUBLINGUAL    NERVE 


519 


the  muscular  fibres  of  the  tongue  itself.  The  action  of  these  muscles 
and  of  the  tongue  itself  in  deglutition  has  already  been  fully  discussed. 
Properties  and  Uses  of  the  Sublingual.  —  The  fact  that  the  sublin- 
gual nerve  arises  from  a  continuation  of  the  motor  tract  of  the  spinal 
cord  and  has  no  ganglion  on  its  main  root  would  lead  to  the  suppo- 
sition that  it  is  an  exclusively  motor  nerve.     Experiments  on  the  inferior 


Fig.  125.  —  Distribution  of  the  subli?igual  nerve  (Sappey)  . 

I,  root  of  the  fifth  nerve;  2,  ganglion  of  Gasser;  3,  4,  5,  6,  7,  9,  10,  12,  branches  and  anastomoses 
of  the  fiith  nerve  ;  11,  submaxillary  ganglion  ;  13,  anterior  belly  of  the  digastric  muscle ;  14,  section  of 
the  mylo-hyoid  muscle;  15,  glosso-pharyngeal  nerv^e;  16,  ganglion  of  Andersch;  17,  18,  branches  of 
the  glosso-pharyngeal  nerve ;  19,  19,  pneumogastric ;  20,  21,  ganglia  of  the  pneumogastric ;  22,  22, 
superior  laiyngeal  branch  of  the  pneumogastric;  23,  spinal  accessor}'  nerve;  24,  sublingual  nerve; 
25,  descendens  nnni  ;  26,  thyro-hyoid  branch  ;  27,  terminal  branches  ;  28,  two  branches,  one  to  the  genio- 
hyo-glossus  and  the  other  to  the  genio-hyoid  muscle  ;  8,  chorda  t\'mpani. 


animals,  taken  in  connection  with  the  anatomical  characters  of  the  nerve, 
render  it  almost  certain  that  its  root  is  devoid  of  sensibility  at  its  origin. 
All  modern  experimenters  have  confirmed  the  observations  of  Mayo  and 
of  Magendie,  in  regard  to  the  sensibility  of  the  sublingual  after  it  has 
passed  out  of  the  cranial  cavity.  The  anastomoses  of  this  ner\-e  with 
the  upper  two  cervical  nerves,  with  the  pneumogastric,  and  with  the 
lingual  branch  of  the  fifth,  afford  a  ready  explanation  of  this. 


520  NERVOUS    SYSTEM 

The  sublingual  may  easily  be  exposed  in  the  dog  by  making  an 
incision  just  below  the  border  of  the  lower  jaw,  dissecting  down  to  the 
carotid  artery  and  following  the  vessel  upward  until  the  nerve  is  seen 
as  it  crosses  its  course.  On  applying  a  feeble  faradic  current  at  this 
point,  there  are  evidences  of  sensibility  and  the  tongue  is  moved  at 
each  stimulation. 

The  phenomena  following  section  of  both  sublingual  nerves  point 
directly  to  their  uses.  The  most  notable  fact  observed  after  this 
operation  is  that  the  movements  of  the  tongue  are  lost,  while  general 
sensibility  and  the  sense  of  taste  are  not  affected.  The  phenomena 
following  division  of  these  nerves  consist  simply  in  loss  of  power  over 
the  tongue,  with  considerable  difficulty  in  deglutition. 

In  the  human  subject  the  sublingual  usually  is  more  or  less  affected 
in  hemiplegia.  In  these  cases,  as  the  patient  protrudes  the  tongue 
the  point  is  deviated.  This  is  due  to  the  unopposed  action  of  the  genio- 
hyo-glossus  on  the  sound  side,  which,  as  it  protrudes  the  tongue,  directs 
the  point  toward  the  side  affected  with  paralysis. 


CHAPTER   XX 

TRIFACIAL    NERVE  — PNEUMOGASTRIC    NERVE 

Trifacial  (large  root  of  the  fifth  nerve) — -Physiological  anatomy — Properties  and  uses  of  the 
trifacial  —  Immediate  effects  of  division  of  the  trifacial  —  Remote  effects  of  division  of  the 
trifacial  —  Pneumogastric  (tenth  nerve)  —  Physiological  anatomy — Properties  and  uses 
of  the  auricular  nerves  —  Properties  and  uses  of  the  pharyngeal  nerves  —  Properties  and 
uses  of  the  superior  laryngeal  nerves  —  Properties  and  uses  of  the  inferior,  or  recurrent 
larjmgeal  nerves  —  Properties  and  uses  of  the  cardiac  nerves  —  Depressor  nerve  —  Proper- 
ties and  uses  of  the  pulmonary  nerves  —  Effects  of  division  of  the  pneumogastrics  on  respira- 
tion—  Effects  of  faradization  of  the  pneumogastrics  on  respiration  —  Properties  and  uses 
of  the  oesophageal  nerves  —  Properties  and  uses  of  the  abdominal  nerves  —  Influence  of  the 
pneumogastrics  on  the  liver — Influence  of  the  pneumogastrics  on  the  stomach  and  intes- 
tines—  Effects  of  faradization  —  Influence  of  section  of  the  pneumogastrics  on  the  move- 
ments of  the  stomach  —  Influence  of  the  pneumogastrics  on  the  small  intestine. 

Trifacial  (Large  Root  of   the  Fifth  Nerve) 

A  SINGLE  nerve,  the  large  root  of  the  fifth  pair,  called  the  trifacial  or 
the  trigeminal,  gives  general  sensibility  to  the  face  and  to  the  head  as 
far  back  as  the  vertex.  This  nerve  is  important,  not  only  as  the  great 
sensitive  nerve  of  the  face,  but  on  account  of  its  connections  with  other 
nerves  and  its  relations  to  the  organs  of  special  sense. 

Physiological  Anatomy.  — The  apparent  origin  of  the  large  root  of 
the  fifth  is  from  the  lateral  portion  of  the  pons  Varolii,  at  a  point  pos- 
terior and  inferior  to  the  origin  of  the  small  root,  from  which  it  is  sepa- 
rated by  a  few  transverse  fibres  of  white  substance.  The  deep  origin 
is  far  removed  from  its  point  of  emergence  from  the  encephalon.  The 
roots  pass  entirely  through  the  substance  of  the  pons,  from  without 
inward  and  from  before  backward,  without  any  connection  with  the 
fibres  of  the  pons  itself.  By  this  course  the  fibres  reach  the  bulb,  where 
the  roots  divide  into  three  bundles.  The  anterior  bundle  passes  from 
behind  forward,  between  the  anterior  fibres  of  the  pons  and  the  cere- 
bellar portion  of  the  restiform  bodies,  to  anastomose  with  the  fibres  of 
the  auditory  nerve.  The  other  bundles,  which  are  posterior,  pass,  one 
in  the  anterior  wall  of  the  fourth  ventricle  to  the  lateral  tract  of  the 
bulb  and  the  other,  becoming  grayish  in  color,  to  the  restiform  bodies, 
from  which  they  may  be  followed  as  far  as  the  point  of  the  calamus 
scriptorius.     A  few  fibres  from  the  two  sides  decussate  at  the  median 

521 


522 


NERVOUS    SYSTEM 


line  in  the  anterior  wall  of  the  fourth  ventricle.  From  this  origin  the 
large  root  of  the  fifth  passes  obliquely  upward  and  forward  to  the  gan- 
glion of  Gasser,  which  is  situated  in  a  depression  in  the  petrous  portion 
of  the  temporal  bone,  on  the  internal  portion  of  its  anterior  face. 

The  Gasserian  ganglion  is  semilunar  in  form,  with  its  concavity  look- 
ing upward  and  inward.    At  the  ganglion  the  nerve  receives  filaments  of 

communication  from  the  carotid 
plexus  of  the  sympathetic.  This 
is  important  in  view  of  certain 
remote  effects  that  follow  division 
of  the  fifth  nerve  through  the 
ganglion  in  living  animals. 

At  the  ganglion  of  Gasser, 
from  its  anterior  and  external 
portion,  are  given  off  a  few  small 
and  unimportant  branches  to  the 
dura  mater  and  the  tentorium. 

From  the  convex  border  of 
the  ganglion  the  three  great  di- 
visions arise,  which  have  given  to 
the  nerve  the  name  of  trifacial 
or  trigeminal.  These  are  :  i,  the 
ophthalmic  ;   2,  the  superior  max- 


Fig.  126. 


•  Principal  branches  of  the  large  root  of 
the  fifth  nerve  (Robin). 

a, ganglion  of  Gasser;  a-w,  ophthalmic  division 
of  the  fifth  ;  b,  ophthalmic  ganglion  ;  c,  branch  from 
the  ophthalmic  division  of  the  fifth  to  the  ophthalmic 

^crtj//^^//(7«,- a',  motor  ocuii  communis;  ^,  carotid;  /     illary  ;    3,  the  mfcrior  maxillary. 

ciliary   nerves  ;  g,    cornea   and   ins ;   ci-h,   superior      ^j^^  ophthalmic  and  SUpCHOr  maX- 

jnaxillary  division  of  the  fifth  ;  t,  fivo  branches  from  ^  ^ 

the  superior  maxillary  division  of  the  fifth  to  the    illary   divisions    are    derived   cn- 

spheno-palatine  ganglion;;,   deep   petrosal   nerve;  .      ,      .               ,        sensorv  rOOt      The 

k,  filaments  from  the  motor  root  of  the  fifth  to  the  tirciy  irom  ine  SCnSOry  rOOt.      1  nc 

internal   muscle   of  the   malleus;    /,   naso-palatine  inferior     maxiUary    divisioU     joinS 
ganglion ;    m,   otic   ganglion ;    n,   small    superficial 


petrosal  nerve ;  o,  branches  of  the  fifth  to  the  sub- 
7naxillary  ganglion  ;  p,  branches  to  the  sublingual 
gland;  q,  facial  nerve;  r,  sympathetic  ganglion; 
s,  nerve  of  masticaiion ;  /,  chorda  tympani,  joining 
the  lingual  branch  of  the  fiftli ;  u.  Vidian  nerve ; 
V,  branch  from  the  motor  root  to  the  internal  ptery- 
goid muscle;  w,  branch  of  the  fifth  to  the  lachrymal 
gland ;  x,  bend  of  the  facial  nerve;  y,  middle  me- 
ningeal artery;  2,  filament  from  the  carotid  plexus 
to  the  ophthalmic  ganglion;  (i  and  2  are  not  in 
the  figure)  3,  external  spheno-palatine  filaments; 
4,  spheno-palatine  ganglion  ;  5,  naso-palatine  nerve ; 
6,  anterior  palatine  nerve;  7,  inferior  maxillary 
division  of  the  fifth  ;  8,  nerve  of  Jacobson. 


the  motor  root  and  with  it  forms 
a  mixed  nerve. 

The  ophthalmic,  the  first  di- 
vision of  the  fifth,  is  the  smallest 
of  the  three.  Before  it  enters 
the  orbit  it  receives  filaments  of 
communication  from  the  sympa- 
thetic, sends  small  branches  to 
all  the  motor  nerves  of  the  eye- 


ball and  gives  off  a  small  recur- 
rent branch  which  passes  between  the  layers  of  the  tentorium. 

Just  before  the  ophthalmic  enters  the  orbit  by  the  sphenoidal  fissure 
it  divides  into  three  branches,  the  lachrymal,  frontal  and  nasal. 

The  lachrymal,  the  smallest  of  the  three,  sends  a  branch  to  the  orbi- 


TRIFACIAL   NERVE 


523 


tal  branch  of  the  superior  maxillary  nerve,  passes  through  the  lachrymal 
gland,  to  which  certain  of  its  filaments  are  distributed,  and  its  terminal 
filaments  go  to  the  conjunctiva  and  to  the  integument  of  the  upper 
eyelid. 

The  frontal  branch,  the  largest  of  the  three,  divides  into  the  supra- 
trochlear and  supraorbital  nerves.  The  supratrochlear  passes  out  of  the 
orbit  between  the  supraorbital 
foramen  and  the  pulley  of  the 
superior  oblique  muscle.  It 
sends  in  its  course  a  long  fila- 
ment to  the  nasal  branch  and  is 
finally  lost  in  the  integument  of 
the  forehead.  The  supraorbital 
passes  through  the  supraorbital 
foramen,  sends  a  few  filaments 
to  the  upper  eyelid  and  sup- 
plies the  forehead,  the  anterior 
and  the  median  portions  of  the 
scalp,  the  mucous  membrane  of 
the  frontal  sinus  and  the  peri- 
cranium covering  the  frontal 
and  parietal  bones. 

The  nasal  branch,  before  it 
penetrates  the  orbit,  gives  off  a 
long  filament  to  the  ophthalmic 
ganglion.  It  then  gives  off  the 
long  ciliary  nerves,  which  pass 
to  the  ciliary  muscle  and  iris. 
Its  trunk  finally  divides  into  the 
external  nasal,  or  infratrochle- 
aris,  and  the  internal  nasal,  or 
ethmoidal.  The  infratrochlearis 
is  distributed  to  the  integument 
of  the  forehead  and  nose,  to  the  internal  surface  of  the  lower  eyelid,  the 
lachrymal  sac  and  the  caruncula.  The  internal  nasal  is  distributed  to 
the  mucous  membrane  and  also  in  part  to  the  integument  of  the 
nose. 

The  superior  maxillary  division  of  the  fifth  passes  out  of  the  cranial 
cavity  by  the  foramen  rotundum,  traverses  the  infraorbital  canal  and 
emerges  on  the  face  by  the  infraorbital  foramen.  Branches  from  this 
nerve  are  given  off  in  the  spheno-maxillary  fossa  and  the  infraorbital 
canal  before  it  emerges  upon  the  face.     In  the  spheno-maxillary  fossa, 


Fig.   127.  —  Ophthalmic  division  of  the  fifth 
(Hirschfeld). 

1,  ganglion  of  Gasser  ;  2,  ophthahnic  division  of  the 
fifth  ;  3,  lachrymal  branch  ;  4,  frontal  branch  ;  5,  ex- 
ternal frontal ;  6,  ititernal  frontal ;  7,  supratrochlear  ; 
^,  nasal  branch  ;  9,  external  nasal ;  10,  internal  nasal ; 
II,  anterior  deep  temporal  nerve;  12,  middle  deep 
temporal  nerve ;  13,  posterior  deep  temporal  nerve ; 
14,  origin  of  the  superficial  temporal  nerve ;  15,  great 
superficial  petrous  nerve.  I  to  XII,  roots  of  the 
cranial   nerves. 


524 


NERVOUS    SYSTEM 


the  first  branch  is  the  orbital,  which  passes  into  the  orbit,  giving  off 
one  branch,  the  temporal,  which  passes  through  the  temporal  fossa 
by  a  foramen  in  the  malar  bone  and  is  distributed  to  the  integument  on 
the  temple  and  the  side  of  the  forehead.  Another  branch,  the  malar, 
which  likewise  emerges  by  a  foramen  in  the  malar  bone,  is  distributed 
to  the  integument  over  this  bone.  In  the  spheno-maxillary  fossa,  are 
also  given  off  two  branches,  which  pass  to  the  spheno-palatine,  or 
Meckel's  ganglion.  From  this  portion  of  the  nerve,  branches  are 
given  off,  the  two  posterior  dental  nerves,  which  are  distributed  to  the 
molar  and  bicuspid  teeth,  the  mucous  membrane  of  the  corresponding 

alveolar    processes    and 
to  the  antrum. 

In  the  infraorbital 
canal,  a  large  branch, 
the  anterior  dental,  is 
given  off  to  the  teeth 
and  mucous  membrane 
of  the  alveolar  processes 
not  supplied  by  the  pos- 
terior dental  branches. 
This  branch  anasto- 
moses with  the  posterior 
dental. 

The  terminal  branches 
upon  the  face  are  dis- 
tributed to  the  lower 
eyelid  (the  palpebral 
branches),  to  the  side 
of  the  nose  (the  nasal 
branches),  anastomosing 
with  the  nasal  branch  of 
the  ophthalmic,  and  to  the  integument  and  mucous  membrane  of  the 
upper  lip  (the  labial  branches). 

The  inferior  maxillary  is  a  mixed  nerve,  composed  of  the  inferior 
division  of  the  large  root  and  the  entire  small  root.  The  distribution 
of  the  motor  filaments  has  already  been  described.  This  nerve  passes 
out  of  the  cranial  cavity  by  the  foramen  ovale,  and  then  separates  into 
the  anterior  division,  containing  nearly  all  the  motor  filaments,  and  the 
posterior  division,  which  is  chiefly  sensory.  The  sensory  portion  breaks 
up  into  the  following  branches  :  — 

I.  The  auriculo-temporal  nerve  supplies  the  integument  in  the  tem- 
poral region,  the  external  auditory  meatus,  the  integument  of  the  ear,  the 


Fig.  128.  —  Superior  maxillary  division  of  the  fifth  (Hirschfeld) . 

I,  ganglion  of  Gasser  ;  2,  lachrymal  branch  of  the  ophthalmic 
division ;  3,  superior  maxillary  division  of  the  fifth  ;  4,  orbital 
branch;  5,  lachrymo-palpcbral  filament ;  6,  malar  branch;  7, 
temporal  branch  ;  8,  sphefio-palatine  gan^^lion  ;  9,  Vidian  nerve  ; 
10,  great  superficial  petrosal  nerve ;  11,  facial  nerve;  12,  branch 
of  the  Vidian  nerve ;  13,  anterior  and  tzvo  posterior  dental 
branches  ;  14,  branch  to  the  mucous  membratie  of  the' alveolar  pro- 
cesses ;  15,  terminal  branches  of  the  superior  maxillary  division  ; 
16,  branch  of  the  facial. 


TRIFACIAL   NERVE 


525 
It   also    sends 


temporo-maxillary  articulation  and    the  parotid  gland 
branches  of  communication  to  the  facial. 

2.  The  lingual  branch  is  distributed  to  the  mucous  membrane  of  the 
tongue  as  far  as  the  point,  the  mucous  membrane  of  the  mouth,  the 
gums  and  the  sublingual  gland.  This  nerve  receives  a  branch  from 
the  facial  (the  chorda  tympani)  which  has  already  been  described.    From 


Fig.  129.  —  Inferior  maxillary  division  of  the  fifth  (Hirschfeld). 

I,  branch  from  the  motor  root  to  the  masseter  muscle;  2,  filaments  from  this  branch  to  the  tem- 
poral muscle  ;  3,  buccal  branch  ;  5,  6,  7,  branches  to  the  muscles  ;  8,  ajiriculo-temporal  nerve ; 
9,  temporal  branches ;  10,  auricular  branches ;  11,  anastomosis  with  the  facial  nerve ;  12,  lingual 
branch  ;  13,  branch  of  the  motor  root  to  the  mylo-hyoid  muscle;  14,  15,  15,  inferior  dental  nerve,  with 
its  branches  ;  i5,  mental  branch  ;  17,  anastot?iosis  of  this  branch  with  the  facial  nerve . 

this  nerve,  also,  are  given  off  two  or  three  branches  that  pass  to  the 
submaxillary  ganglion. 

3.  The  inferior  dental  nerve,  the  largest  of  the  three,  passes  in  the 
substance  of  the  inferior  maxillary  bone,  beneath  the  teeth,  to  the  men- 
tal foramen,  where  it  emerges  upon  the  face.  The  most  important  sen- 
sory branches  are  those  which  supply  the  pulps  of  the  teeth  and  the 
branches  upon  the  face.  The  nerve  emerging  on  the  face  by  the  men- 
tal foramen,  called  the  mental  nerve,  supplies  the  integument  of  the  chin, 


526  NERVOUS    SYSTEM 

the  lower  part  of  the  face  and  the  lower  lip.  It  also  sends  certain  fila- 
ments to  the  mucous  membrane  of  the  mouth. 

Properties  and  Uses  of  the  Trifacial.  —  The  trifacial  is  the  great  sen- 
sory nerve  of  the  face  and  of  the  mucous  membranes  Hning  the  cavities 
about  the  head.  It  is  impossible  to  stimulate  this  nerve  at  its  origin 
without  seriously  involving  other  parts ;  but  observations  in  regard  to 
the  properties  of  the  large  root  go  to  show  that  it  is  an  exclusively  sen- 
sory nerve,  and  that  its  sensibility  is  very  acute  as  compared  with  other 
nerves.  It  was  divided  in  the  cranial  cavity  by  Mayo  (i 822-1 823), 
Fodera  (1823)  and  Magendie  (1824).  Magendie  divided  the  nerve  at 
its  root  by  introducing  a  small  cutting  stylet  through  the  skull.  He 
succeeded  in  keeping  the  animals  alive  for  several  days  or  weeks  and 
noted  in  his  experiments  immediate  loss  of  sensibility  in  the  face  on 
the  side  on  which  the  nerve  had  been  divided.  When  this  operation 
is  performed  without  accident,  the  cornea  and  the  integument  and 
mucous  membrane  on  that  side  of  the  head  are  deprived  of  sensibility 
and  may  be  pricked,  lacerated  or  burned  without  any  evidence  of  pain. 
Almost  always  the  small  root  of  the  fifth  is  divided  as  well  as  the  large 
root,  and  the  muscles  of  mastication  are  paralyzed  on  one  side ;  but 
with  this  exception,  there  is  no  paralysis  of  motion,  sensation  alone  being 
destroyed. 

Immediate  Effects  of  Division  of  the  Trifacial.  — This  nerve  has  not 
been  exposed  in  the  cranial  cavity  in  Hving  animals  ;  but  its  branches  on 
the  face  and  the  lingual  branch  of  the  inferior  maxillary  division  have 
been  operated  on  and  found  to  be  exquisitely  sensitive.  Physiologists 
have  exposed  the  roots  in  animals  immediately  after  death  and  have 
found  that  stimulation  of  the  large  root  carefully  insulated  produces  no 
muscular  contraction.  All  who  have  divided  this  root  in  living  animals 
have  recognized,  not  only  that  it  is  sensitive,  but  that  its  sensibility  is 
far  more  acute  than  that  of  any  other  nervous  trunk  in  the  body. 

So  far  as  audition  and  olfaction  are  concerned,  there  are  no  special 
effects  immediately  following  section  of  the  trifacial ;  but  there  are  cer- 
tain important  phenomena  observed  in  connection  with  the  eye  and  the 
organs  of  taste. 

At  the  instant  of  division  of  the  fifth,  the  eyeball  is  protruded  and 
the  pupil  becomes  strongly  contracted.  The  pupil,  however,  usually  is 
restored  to  the  normal  condition  in  a  few  hours.  After  division  of  the 
nerve,  the  lachrymal  secretion  is  diminished,  but  this  is  not  the  cause  of 
the  subsequent  inflammation,  for  the  eyes  are  not  inflamed,  even  after 
extirpation  of  both  lachrymal  glands. 

Another  of  the  immediate  effects  of  complete  division  of  the  fifth 
nerve  is  loss  of  general  sensibility  in  the  tongue.     Most  experiments 


REMOTE    EFFECTS    OF    DIVISION    OF   THE    TRIFACIAL  527 

on  the  influence  of  this  nerve  on  the  general  sensibility  and  the  sense 
of  taste  in  the  tongue  have  been  made  by  dividing  the  lingual  branch  of 
the  inferior  maxillary  division.  When  this  branch  is  irritated,  there  are 
evidences  of  intense  pain.  When  it  is  divided,  the  general  sensibility 
and  the  sense  of  taste  are  destroyed  in  the  anterior  portion  of  the 
tongue.  It  will  be  remembered,  however,  that  the  chorda  tympani 
joins  the  lingual  branch  of  the  fifth  as  it  passes  between  the  pterygoid 
muscles,  and  that  section  of  this  branch  of  the  facial  abolishes  the  sense 
of  taste  in  the  anterior  two-thirds  of  the  tongue.  If  the  gustatory  prop- 
erties of  the  lingual  branch  of  the  fifth  be  derived  from  the  chorda 
tympani,  lesions  of  the  fifth  not  involving  this  nerve  would  be  followed 
by  loss  of  general  sensibility,  but  the  taste  would  be  unaffected.  This 
has  been  shown  to  be  the  fact,  by  cases  of  paralysis  of  general  sensibilitv 
of  the  tongue  without  loss  of  taste  in  the  human  subject,  which  will  be 
discussed  more  fully  in  connection  with  the  physiology  of  gustation. 

Among  the  immediate  effects  of  section  of  the  fifth,  is  interference 
with  the  reflex  acts  of  deglutition.  After  section  of  the  superior  laryn- 
geal branches  of  the  pneumogastrics,  no  movements  of  deglutition 
follow  stimulation  of  the  mucous  membrane  of  the  top  of  the  larynx. 
When  the  fifth  is  divided  on  one  side,  stimulation  of  the  velum  on  the 
corresponding  side  has  no  effect,  while  movements  of  deglutition  are 
produced  by  irritating  the  velum  on  the  sound  side.  These  experiments 
show  that  the  fifth  nerve  is  important  in  the  reflex  phenomena  of 
deglutition  as  a  sensory  nerve,  conveying  the  impression  from  the 
velum  palati  to  the  nerve-centres.  This  action  probably  takes  place 
through  filaments  that  pass  from  the  fifth  to  the  mucous  membrane 
through  Meckel's  ganglion. 

Remote  Ejfects  of  Division  of  the  Trifacial.  —  After  section  of  the 
fifth  nerve  in  the  cranial  cavity,  the  immediate  loss  of  sensibility  of  the 
integument  and  mucous  membranes  of  the  face  and  head  usuallv  is 
supplemented  with  serious  disturbances  in  the  nutrition  of  the  eye,  the 
ear  and  the  mucous  membranes  of  the  nose  and  mouth.  After  a  period 
varying  between  a  few  hours  and  one  or  two  days  following  the  operation, 
the  eye  on  the  affected  side  becomes  the  seat  of  purulent  inflammation, 
the  cornea  becomes  opaque  and  ulcerates,  the  humors  are  discharged 
and  the  organ  is  destroyed.  Congestion  of  the  parts  usually  is  very 
prominent  a  few  hours  after  division  of  the  nerve.  At  the  same  time 
there  is  an  increased  discharge  from  the  mucous  membranes  of  the  nose 
and  mouth  on  the  affected  side,  and  ulcers  appear  on  the  tongue  and 
lips.  It  is  probable,  also,  that  disorders  in  the  nutrition  of  the  auditory 
apparatus  follow  the  operation,  although  these  are  not  so  prominent. 
Animals  affected  in  this  way  usually  die  in  fifteen  to  twenty  days. 


528  NERVOUS    SYSTEM 

In  the  early  experiments  of  Magendie,  it  was  noted  that  "  the  altera- 
tions in  nutrition  are  much  less  marked  "  when  the  division  is  effected 
behind  the  ganglion  of  Gasser  than  when  it  is  done  in  the  ordinary  way 
through  the  ganghon.  It  is  difficult  enough  to  divide  the  nerve  com- 
pletely, within  the  cranium,  and  is  almost  impossible  to  make  the 
operation  at  will  through  or  behind  the  ganghon ;  and  the  phenomena 
of  inflammation  are  absent  only  in  exceptional  and  accidental  instances. 
Magendie  offered  no  satisfactory  explanation  of  these  differences  in  the 
consecutive  phenomena,  but  the  facts  have  been  repeatedly  verified. 
In  a  number  of  experiments  in  which  the  nerve  was  divided  in  the 
cranial  cavity  (Flint),  the  consecutive  inflammatory  effects  were  nearly 
always  observed;  but  in  an  experiment  made  in  1868,  the  nerve  was 
completely  divided  on  the  left  side,  as  was  shown  by  total  loss  of  sensi- 
bility of  the  parts  to  which  it  is  distributed,  and  the  animal  (a  rabbit) 
lived  nearly  four  months.  Four  days  after  the  operation  the  loss  of 
sensibihty  was  still  complete.  There  was  very  little  redness  of  the 
conjunctiva  of  the  left  eye,  and  a  slight  streak  of  opacity,  so  slight  that 
it  was  distinguished  with  some  difficulty.  Twelve  days  after  the  opera- 
tion, the  sensibility  of  the  left  eye  was  distinct  but  slight.  There  was 
no  redness  of  the  conjunctiva,  and  the  opacity  of  the  cornea  had 
disappeared.  The  animal  was  in  good  condition,  and  the  line  of  con- 
tact of  the  upper  with  the  lower  incisors,  when  the  jaws  were  closed, 
was  very  oblique.  The  animal  was  kept  alive  by  careful  feeding  with 
bread  and  milk  for  one  hundred  and  seven  days  after  the  operation,  and 
there  was  no  inflammation  of  the  organs  of  special  sense.  It  died  at  that 
time  of  inanition,  having  become  extremely  emaciated.  The  animal 
never  recovered  power  over  the  muscles  of  the  left  side,  and  the  incisors 
grew  to  a  great  length,  seriously  interfering  with  mastication. 

The  explanation  of  the  phenomena  of  disordered  nutrition  in  the 
organs  of  special  sense,  particularly  the  eye,  following  division  of  the 
fifth,  is  not  afforded  by  the  section  of  this  nerve  alone ;  for  when 
the  loss  of  sensibility  is  complete  after  division  of  the  nerve  behind 
the  Gasserian  ganglion,  these  results  may  not  follow.  They  are  not 
explained  by  deficiency  in  the  lachrymal  secretion ;  for  they  are  not 
observed  when  both  lachrymal  glands  have  been  extirpated.  They  are 
not  due  simply  to  an  enfeebled  general  condition  ;  for  in  the  experiment 
just  detailed,  the  animal  died  of  inanition,  after  section  of  the  nerve, 
without  any  evidences  of  inflammation.  In  view  of  the  fact  that  section 
of  the  sympathetic  filaments  is  well  known  to  modify  the  nutrition  of 
parts  to  which  they  are  distributed,  producing  congestion  and  increase 
in  temperature,  it  is  rational  to  infer  that  the  modifications  in  nutrition 
which   follow  section  of  the  fifth  after  it  receives  filaments  from  the 


REMOTE    EFFECTS    OF    DIVISION    OF    THE   TRIFACIAL 


529 


sympathetic  system,  not  occurring  when  these  sympathetic  filaments 
escape  division,  are  to  be  attributed  to  lesion  of  the  sympathetic  and  not 
to  the  division  of  the  sensory  nerve  itself. 

The  following  explains,  in  a  measure  at  least,  the  consecutive  inflam- 
matory effects  of.  section  of  the  fifth  with  its  communicating  sympathetic 
filaments  :  By  dividing  the  sympathetic,  the  eye  and  the  mucous  mem- 
branes of  the  nose,  mouth  and  ear  are  rendered  hyperemic,  the  tempera- 
ture is  raised  and  the  processes  of  nutrition  are  exaggerated.  This 
condition  of  the  parts  would  seem  to  require  a  full  supply  of  nutritive 
material  from  the  blood  in  order  to  maintain  the  condition  of  exagger- 
ated nutrition  ;  but  when  the  blood  is  impoverished — probably  as  the 
result  of  deficiency  in  the  introduction  of  nutritive  matter,  from  paralysis 
of  the  muscles  of  mastication  on  one  side — -the  nutritive  processes  in 
these  delicate  parts. are  seriously  modified,  so  as  to  constitute  inflam- 
mation. It  has  been  observed,  however,  that  inflammation  of  the  eye 
does  not  follow  section  of  the  fifth  when  the  part  is  protected  from 
external  irritation,  as  by  sewing  together  the  eyelids.  It  must  be,  as  it 
seems,  that  the  delicate  structures  of  the  organs  of  special  sense, 
especially  vision,  are  rendered  vulnerable  by  the  loss  of  sensibility  and 
the  hyperemia,  the  congestion  following  this  operation  readily  passing 
into  inflammation.  Under  these  conditions,  when  the  eye  is  completely 
protected  from  irritation,  inflammation  may  not  occur. 

Pathological  facts  in  confirmation  of  experiments  on  the  fifth  pair 
in  the  lower  animals  are  not  wanting ;  but  it  must  be  remembered 
that  in  cases  of  paralysis  of  the  nerve  in  the  human  subject,  it  is  not 
always  possible  to  locate  exactly  the  seat  of  the  lesion  and  to  appreciate 
fully  its  extent,  as  can  be  done  when  the  nerve  is  divided  by  an  opera- 
tion. In  these  cases  it  sometimes  occurs  that  the  phenomena,  particu- 
larly those  of  modified  nutrition,  are  more  or  less  contradictory. 

Cases  of  paralysis  of  the  fifth  in  the  human  subject  in  the  main 
confirm  the  results  of  experiments  on  the  inferior  animals.  In  cases  in 
which  the  fifth  nerve  alone  is  involved  in  the  disease,  without  the  facial, 
there  is  simply  loss  of  sensibility  on  one  side,  the  movements  of  the 
superficial  muscles  of  the  face  being  unaffected.  When  the  small  root 
is  involved,  the  muscles  of  mastication  on  one  side  are  paralyzed ;  but 
in  certain  reported  cases  in  which  this  root  escaped,  there  was  no 
muscular  paralysis.  The  senses  of  sight,  hearing  and  smell,  except  as 
they  are  affected  by  consecutive  inflammation,  are  little  if  at  all  dis- 
turbed in  uncomplicated  cases.  The  sense  of  taste  in  the  anterior  por- 
tion of  the  tongue  is  perfect,  except  in  those  cases  in  which  the  facial, 
the  chorda  tympani  or  the  lingual  branch  of  the  fifth  after  it  had  been 
joined  by  the  chorda  tympani  is  involved  in  the  disease.     In  some  cases 


■530  NERVOUS    SYSTEM 

there  is  no  alteration  in  the  nutrition  of  the  organs  of  special  sense  ;  but 
in  this  respect  the  facts  in  regard  to  the  seat  of  the  lesion  are  not  so 
satisfactory  as  in  experiments  on  the  lower  animals,  it  being  difficult  to 
limit  exactly  the  boundaries  of  the  lesion. 


Pneumogastric  (Tenth  Nerve) 

Of  all  the  cranial  nerves,  the  pneumogastric  presents  the  greatest 
number  of  anastomoses,  the  most  remarkable  course  and  the  most  varied 
uses.  Arising  from  the  bulb  by  a  purely  sensory  root,  it  communicates 
with  at  least  five  motor  nerves  and  is  distributed  largely  to  muscular 
tissue,  both  of  the  voluntary  and  the  involuntary  variety.  On  account 
of  its  wide  distribution  and  wandering  course,  it  is  often  called  the  vagus 
or  par  vagum. 

Physiological  Anatomy.  —  The  apparent  origin  of  the  pneumogastric 
is  from  the  lateral  portion  of  the  bulb,  just  behind  the  olivary  body, 
between  the  roots  of  the  glosso-pharyngeal  and  the  spinal  accessory. 
The  deep  origin  is  mainly  from  what  is  called  the  nucleus  of  the  pneu- 
mogastric, at  the  inferior  portion  of  the  gray  substance  in  the  floor  of 
the  fourth  ventricle.  The  course  of  the  fibres,  traced  from  without 
inward,  is  somewhat  intricate. 

The  deep  origins  of  the  pneumogastric  and  glosso-pharyngeal  nerves 
appear  to  be  in  the  main  identical.  Tracing  the  filaments  from  without 
inward,  they  may  be  followed  in  four  directions :  ( i )  The  anterior 
filaments  pass  from  without  inward,  first  very  superficially,  in  the  direc- 
tion of  the  olivary  body  ;  but  they  then  turn  and  pass  deeply  into  the 
substance  of  the  restiform  body,  in  which  they  are  lost.  (2)  The  pos- 
terior filaments  are  superficial,  and  they  pass,  with  the  fibres  of  the  resti- 
form body,  toward  the  cerebellum.  (3)  Of  the  intermediate  filaments, 
the  anterior  pass  through  the  restiform  body,  the  greatest  number  extend- 
ing to  the  median  line,  in  the  floor  of  the  fourth  ventricle.  A  few  fibres 
are  lost  in  the  middle  fasciculi  of  the  bulb  and  a  few  pass  toward  the  brain. 
(4)  The  posterior  intermediate  filaments  traverse  the  restiform  body  to 
the  floor  of  the  fourth  ventricle,  where  some  pass  to  the  median  line  and 
others  descend  in  the  substance  of  the  bulb.  It  is  difficult  to  follow  the 
fibres  of  origin  of  the  pneumogastrics  beyond  the  median  line  ;  but 
recent  observations  leave  no  doubt  of  the  fact  that  many  of  these  fibres 
decussate  in  the  floor  of  the  fourth  ventricle. 

There  are  two  ganglionic  enlargements  belonging  to  the  pneumo- 
gastric. In  the  jugular  foramen,  is  a  well-marked,  grayish,  ovoid  en- 
largement, one-sixth  to  one-fourth  of  an  inch  (4.2  to  6.4  millimeters)  in 
length,  called  the  jugular  ganglion,  or  the  ganglion  of  the  root.     This 


PNEUiMOGASTRIC   NERVE 


531 


is  united  by  two  or  three  filaments  with  the  ganglion  of  the  glosso- 
pharyngeal. It  is  a  true  gangUon,  containing  nerve-cells.  After  the 
nerve  has  emerged  from  the  cranial 
cavity,  it  presents  on  its  trunk  an- 
other grayish  enlargement,  half  an 
inch  to  an  inch  (12  to  25  millimeters) 
in  length,  called  the  ganglion  of  the 
trunk.  This  has  a  plexiform  struc- 
ture, the  white  fibres  being  mixed 
with  grayish  fibres  and  nerve-cells. 
The  exit  of  the  nerve  from  the  cranial 
cavity  is  by  the  jugular  foramen,  or 
posterior  foramen  lacerum,  in  com- 
pany with  the  spinal  accessory,  the 
glosso-pharyngeal  nerve  and  the  in- 
ternal jugular  vein. 

Anastomoses.  —  There  are  occa- 
sional filaments  of  communication 
that  pass  from  the  spinal  accessory  to 
the  ganghon  of  the  root  of  the  pneu- 
mogastric,  but  these  are  not  constant. 
After  both  nerves  have  emerged 
from  the  cranial  cavity,  an  important 
branch  of  considerable  size  passes 
from  the  spinal  accessory  to  the 
pneumogastric,  with  which  it  be- 
comes closely  united.  Experiments 
have  shown  that  these  filaments  from 
the  spinal  accessory  pass  in  great  part 
to  the  larynx  by  the  inferior  laryn- 
geal nerves. 

In  the  aquaeductus  Fallopii,  the 
facial  nerve  gives  off  a  filament  of 
communication  to  the  pneumogastric, 
at  the  ganglion  of  the  root.  This 
filament,  joined  at  the  ganglion  by 
sensory  filaments  from  the  pneumo- 
gastric and  some  filaments  from  the 
glosso-pharyngeal,  is  called  the  au- 
ricular branch  of  Arnold.  By  some 
anatomists  it  is  regarded  as  a  branch  of  the  facial  and  by  others  it  is 
described  with  the  pneumogastric. 


Fig.  130. 


Anastomoses  of  the  pneumogastric 
(Hirschfeld). 

I,  facial  nerve  ;  '2,  glosso-pharyngeal  nerve  ; 
2',  anastomoses  of  the  glosso-pharyngeal  with 
the  facial ;  3,  3,  pneumogastric,  with  its  two 
ganglia  ;  4,  4,  spitial  accessory  ;  5,  sublingual 
nerve;  6,  superior  cervical  ganglion  of  the 
sympathetic  ;  7,  anastomotic  arcade  of  the  first 
two  cervical  nerves  ;  8,  carotid  branch  of  the 
superior  cervical  ganglion  of  the  sympathetic  ; 
9,  nerve  of  Jacobson  ;  10,  branches  of  this 
nerve  to  the  sympathetic;  11,  branch  to  the 
Eustachian  tube;  12,  branch  to  the  fenestra 
ovalis;  13,  branch  to  the  fenestra  rotunda; 
14,  external  deep  petrous  nerve ;  15,  internal 
deep  petrous  nerve  ;  16,  otic  ganglion  ;  17,  au- 
ricular branch  of  the  pneumogastric  ;  18,  anas- 
tomosis of  the  p7ieumogastric  2vith  the  spinal 
accessory  ;  ig,  anastomosis  of  the  pneumogastric 
with  the  sublingual ;  20,  anastomosis  of  the 
spinal  accessory  with  the  second  pair  of  cervi- 
cal nerves;  21,  pharyngeal  plexus;  22,  supe- 
rior laryngeal  nerve ;  23,  external  laryngeal 
nerve;  24,  middle  cervical  ganglion. 


532 


NERVOUS    SYSTEP/I 


Two  or  three  small  filaments  of  communication  pass  from  the  sub- 
lingual to  the  ganglion  of  the  trunk  of  the  pneumogastric. 

At  the  ganghon  of  the  trunk,  the  pneumogastric  usually  receives 
filaments  of  communication  from  the  arcade  formed  by  the  anterior 
branches  of  the  first  two  cervical  nerves.  These,  however,  are  not 
constant. 

The  pneumogastric  is  connected  with  the  sympathetic  system  by  a 
number  of  filaments  of  communication  from  the  superior  cervical  gan- 
glion, passing  in  part  upward  toward  the  ganglion  of  the  root  of  the 
pneumogastric,  and  in  part  transversely  and  downward.  These  fila- 
ments frequently  are  short,  and  they  bind  the  sympathetic  ganghon 
to  the  trunk  of  the  nerve.  The  main  trunk  of  the  pneumogastric 
and  its  branches  receive  a  few  filaments  of  communication  from  the 
middle  and  inferior  cervical  and  the  upper  dorsal  gangUa  of  the  sym- 
pathetic. 

The  pneumogastric  frequently  sends  a  slender  filament  to  the 
glosso-pharyngeal  nerve,  at  or  near  the  ganglion  of  Andersch, 
Branches  from  the  pneumogastric  join  branches  from  the  glosso- 
pharyngeal, the  spinal  accessory  and  the  sympathetic,  to  form  the 
pharyngeal  plexus. 

Distribution.  —  Although  the  pneumogastric  nerves  on  the  two  sides 
do  not  present  any  important  differences  in  the  destination  of  their 
filaments  as  far  down  as  the  diaphragm,  the  distribution  of  the 
abdominal  branches  is  not  the  same.  The  most  important  branches 
are  the  following  :  — 

1.  Auricular.  5.  Cardiac  (cervical  and  thoracic). 

2.  Pharyngeal.  6.  Pulmonary  (anterior  and  posterior). 

3.  Superior  laryngeal.  7.  CEsophageal. 

4.  Inferior,  or  recurrent  laryngeal.  8.  Abdominal. 

The  auricular  nerves  are  sometimes  described  in  connection  with  the 
facial.  They  are  given  off  from  the  ganglion  of  the  trunk  of  the  pneu- 
mogastric and  are  composed  of  filaments  of  communication  fromi  the 
facial  and  from  the  glosso-pharyngeal  as  well  as  of  filaments  from  the 
pneumogastric  itself.  The  nerves  thus  constituted  are  distributed  to 
the  integument  of  the  upper  portion  of  the  external  auditory  meatus 
and  a  small  filament  is  sent  to  the  membrana  tympani. 

The  pharyngeal  nerves  are  given  off  from  the  superior  portion  of 
the  ganglion  of  the  trunk,  and  they  contain  a  large  number  of  the  fila- 
ments of  communication  which  the  pneumogastric  receives  from  the 
spinal  accessory.  In  their  course  by  the  sides  of  the  superior  constrictor 
muscles  of  the  pharynx,  these  nerves  anastomose  with  filaments  from 


DISTRIBUTION    OF    THE    PXEUMOGASTRICS 


533 


the  glosso-pharyngeal  and  the  superior  cervical  ganglion  of  the  sympa- 
thetic, to  form  what  is  known  as  the  pharyngeal  plexus.  The  ultimate 
filaments  of  distribution  pass  to  the  muscles  and  the  mucous  membrane 


Fig.  131.  —  Distribution  of  the  pneumogastric  (Hirschfeld) . 

I,  trunk  of  the  left  pneumogastric  ;  2,  ganglion  of  the  trtiiik  ;  3,  anastomosis  zvith  the  spinal  acces- 
sory ;  4,  anastomosis  -with  the  sublingual ;  5,  pharyngeal  branch  {the  auricular  branch  is  not  shown  in 
the  figure)  ;  6,  superior  lary?2geal  branch  ;  ■],  external  laryngeal  nerve  ;  %,  laryngeal  plexus  ;  g,  g,  in- 
ferior laryngeal  branch  ;  10,  cervical  cardiac  branch  ;  11,  thoracic  cardiac  branch  ;  12,  I'l,,  pulmonary 
branches ;  14,  lingual  branch  of  the  fifth  ;  15,  lower  portion  of  the  sublingual ;  16,  glosso-pharyngeal; 
17,  spinal  accessory ;  18,  19,  20,  spinal  nerves ;  21,  phrenic  nerve ;  22,  23,  spinal  nerves  ;  24,  25,  26,  27, 
28,  29,  30,  sympathetic  ganglia. 


of  the  pharynx.  Physiological  experiments  have  shown  that  the  motor 
influence  transmitted  to  the  pharyngeal  muscles  through  the  pharyngeal 
branches  of  the  pneumogastric  is  derived  from  the  spinal  accessory. 

The  superior  laryngeal  nerves  are  given  off  from  the  lower  part  of 


534  NERVOUS    SYSTEM 

the  ganglion  of  the  trunk.  Their  filaments  come  from  the  side  opposite 
the  point  of  junction  of  the  pneumogastric  with  the  communicating 
branch  from  the  spinal  accessory,  so  that  probably  the  superior  laryn- 
geal contain  few  if  any  motor  fibres  from  the  eleventh  nerve.  The 
superior  laryngeal  gives  off  the  external  laryngeal,  a  long,  delicate  branch 
which  sends  a  few  filaments  to  the  inferior  constrictor  of  the  pharynx 
and  is  distributed  to  the  crico-thyroid  muscle  and  the  mucous  membrane 
of  the  ventricle  of  the  larynx.  The  external  laryngeal  anastomoses  with 
the  inferior  laryngeal  nerve  and  with  the  sympathetic.  The  internal 
branch  is  distributed  to  the  mucous  membrane  of  the  epiglottis,  the 
base  of  the  tongue,  the  aryteno-epiglottidean  fold  and  the  mucous  mem- 
brane of  the  larynx  as  far  down  as  the  true  vocal  chords.  A  branch 
from  this  nerve,  in  its  course  to  the  larynx,  penetrates  the  arytenoid 
muscle,  to  which  it  sends  a  few  filaments,  but  these  are  sensory.  This 
branch  also  supplies  the  crico-thyroid  muscle.  It  anastomoses  with  the 
inferior  laryngeal  nerve.  An  important  branch,  described  by  Cyon  and 
Ludwig,  in  the  rabbit,  under  the  name  of  the  depressor  nerve,  arises  by 
two  roots,  one  from  the  superior  laryngeal  and  the  other  from  the  trunk 
of  the  pneumogastric.  It  passes  down  the  neck  by  the  side  of  the  sym- 
pathetic, and  in  the  chest  it  joins  filaments  from  the  thoracic  sympathetic, 
to  pass  to  the  heart,  between  the  aorta  and  the  pulmonary  artery.  This 
nerve  is  not  isolated  in  the  human  subject,  but  it  is  probable  that  analo- 
gous fibres  exist  in  man  in  the  trunk  of  the  pneumogastric. 

It  is  important  from  a  physiological  point  of  view  to  note  that  the 
superior  laryngeal  nerve  is  the  nerve  of  sensibility  of  the  upper  part  of 
the  larynx  as  well  as  of  the  supralaryngeal  mucous  membranes,  and 
that  it  animates  a  single  muscle  of  the  larynx  (the  crico-thyroid)  and  the 
inferior  constrictor  of  the  pharynx. 

The  inferior,  or  recurrent  laryngeal  nerves  present  some  slight  dif- 
ferences in  their  anatomy  on  the  two  sides.  On  the  left  side  the  nerve 
is  the  larger  and  is  given  off  at  the  arch  of  the  aorta.  Passing  beneath 
this  vessel,  it  ascends  in  the  groove  between  the  trachea  and  the  oesoph- 
agus. In  its  upward  course  it  gives  off  filaments  that  join  the  cardiac 
branches,  filaments  to  the  muscular  tissue  and  mucous  membrane  of  the 
upper  part  of  the  oesophagus,  filaments  to  the  mucous  membrane  and 
the  intercartilaginous  muscular  tissue  of  the  trachea,  one  or  two  fila- 
ments to  the  inferior  constrictor  of  the  pharynx  and  a  branch  that  joins 
the  superior  laryngeal.  Its  terminal  branches  penetrate  the  larynx 
behind  the  posterior  articulation  of  the  thyroid  with  the  cricoid  cartilage 
and  are  distributed  to  all  the  intrinsic  muscles  of  the  larynx,  except  the 
crico-thyroids,  which  latter  are  supplied  by  the  superior  laryngeal.  On 
the  right  side  the  nerve  winds  from  before  backward  around  the  sub- 


DISTRIBUTION    OF   THE    PNEUMOGASTRICS  535 

clavian  artery  and  has  essentially  the  same  course  and  distribution  as 
on  the  left  side,  except  that  it  is  smaller  and  has  fewer  filaments  of 
distribution. 

The  important  physiological  point  connected  with  the  anatomy  of 
the  recurrent  laryngeals  is  that  they  animate  all  the  intrinsic  muscles 
of  the  larynx  except  the  crico-thyroid.  Experiments  have  shown  that 
these  nerves  contain  a  large  number  of  motor  filaments  derived  from  the 
spinal  accessory. 

The  cervical  cardiac  branches,  two  or  three  in  number,  arise  from 
the  pneumogastrics  at  different  points  in  the  cervical  portion  and  pass  to 
the  cardiac  plexus,  which  is  formed  in  great  part  of  filaments  from  the 
sympathetic.  The  thoracic  cardiac  branches  are  given  off  from  the 
pneumogastrics  below  the  origin  of  the  inferior  laryngeals  and  join 
the  cardiac  plexus. 

The  anterior  pulmonary  branches  are  few  and  delicate  as  compared 
with  the  posterior  branches.  They  are  given  off  below  the  origin  of 
the  thoracic  cardiac  branches,  send  a  few  filaments  to  the  trachea  and 
then  form  a  plexus  that  surrounds  the  bronchial  tubes  and  follows  the 
bronchial  tree  to  its  terminations  in  the  air-cells.  The  posterior  pulmo- 
nary branches  are  larger  and  greater  in  number  than  the  anterior.  They 
communicate  freely  with  sympathetic  filaments  from  the  upper  three 
or  four  thoracic  ganglia  and  then  form  the  great  posterior  pulmonary 
plexus.  From  this  plexus  a  few  filaments  go  to  the  inferior  and  pos- 
terior portion  of  the  trachea,  a  few  pass  to  the  muscular  tissue  and 
mucous  membrane  of  the  middle  portion  of  the  oesophagus  and  a  few 
are  sent  to  the  posterior  and  superior  portion  of  the  pericardium.  The 
plexus  then  surrounds  the  bronchial  tree  and  passes  with  its  ramifica- 
tions to  the  pulmonary  tissue,  like  the  corresponding  filaments  of  the 
anterior  branches.  The  pulmonary  branches  are  distributed  to  the 
mucous  membrane  and  not  to  the  walls  of  the  bloodvessels. 

The  oesophageal  branches  take  their  origin  from  the  pneumogastrics 
above  and  below  the  pulmonary  branches.  These  branches  from  the  two 
sides  join  to  form  the  oesophageal  plexus,  their  filaments  of  distribution 
going  to  the  muscular  tissue  and  the  mucous  membrane  of  the  lower 
third  of  the  oesophagus. 

The  abdominal  branches  are  quite  different  in  their  distribution  on 
the  two  sides. 

On  the  left  side  the  nerve,  which  is  here  anterior  to  the  cardiac 
opening  of  the  stomach,  immediately  after  its  passage  by  the  side  of  the 
oesophagus  into  the  abdomen,  divides  into  a  number  of  branches,  which 
are  distributed  to  the  muscular  walls  and  the  mucous  membrane  of  the 
stomach.     As  the  branches  pass  from  the  lesser  curvature,  they  take 


536  NERVOUS    SYSTEM 

a  downward  direction  and  go  to  the  liver,  and  with  another  branch  run- 
ning between  the  folds  of  the  gastro-hepatic  omentum,  they  follow  the 
course  of  the  portal  vein  in  the  hepatic  substance.  The  branches 
of  this  nerve  anastomose  with  the  nerve  of  the  right  side  and  with  the 
sympathetic. 

The  right  pneumogastric,  situated  posteriorly,  at  the  oesophageal 
opening  of  the  diaphragm  sends  a  few  filaments  to  the  muscular  coat 
and  the  mucous  membrane  of  the  stomach,  passes  backward  and  is  dis- 
tributed to  the  liver,  spleen,  kidneys,  suprarenal  capsules  and  finally  to 
the  entire  small  intestine.  From  the  splenic  plexus,  filaments  derived 
from  the  pneumogastric  go  to  the  pancreas.  Before  the  nerves  pass  to 
the  intestines,  there  is  a  free  anastomosis  and  interchange  of  filaments 
between  the  right  and  the  left  abdominal  branches. 

General  Propcftics  of  the  Roots  of  Origin  of  the  Pnenmogastrics.  — 
The  sensibility  of  the  pneumogastrics  in  the  neck,  while  it  is  dull  as 
compared  with  the  properties  of  other  sensory  nerves,  is  nevertheless 
distinct.  It  is  impossible,  however,  to  expose  the  roots  of  the  nerves  in 
living  animals  before  they  have  received  communicating  motor  filaments, 
without  such  mutilation  as  would  interfere  with  accurate  observations  ; 
but  in  animals  just  killed,  if  the  roots  are  exposed  and  divided  so  as  to 
avoid  reflex  movements,  and  if  care  is  taken  to  avoid  stimulation  of 
motor  filaments  from  adjacent  nerves,  it  is  found  that  the  application 
of  electricity  to  the  peripheral  end  of  the  root  from  its  origin  to  the 
ganghon  gives  rise  to  no  movements.  It  may  therefore  be  assumed 
that  the  true  filaments  of  origin  of  the  pneumogastrics  are  exclusively 
sensory,  or  at  least  that  they  have  no  motor  properties. 

Properties  and  Uses  of  the  Auricular  Nerves.  —  The  auricular  nerves 
are  sometimes  described  with  the  facial  and  sometimes  with  the  pneu- 
mogastric. They  contain  filaments  from  the  facial,  the  pneumogastric 
and  the  glosso-pharyngeal.  The  sensory  filaments  of  these  nerves  give 
sensibility  to  the  upper  part  of  the  external  auditory  meatus  and  to  the 
membrana  tympani.  The  meatus  also  receives  filaments  from  the 
trifacial. 

Properties  and  Uses  of  the  PJiaryngeal  Nerves.  —  The  pharyngeal 
branches  of  the  pneumogastric  are  mixed  nerves,  their  motor  filaments 
being  derived  from  the  spinal  accessory  ;  and  their  direct  action  on  the 
muscles  of  deglutition  belongs  to  the  physiological  history  of  the  last- 
named  nerve.  As  already  stated  in  treating  of  the  spinal  accessory, 
the  filaments  of  communication  that  go  to  the  pharyngeal  branches  of 
the  pneumogastric  are  distributed  to  the  pharyngeal  muscles. 

It  is  impossible  to  divide  all  the  pharyngeal  filaments  in  living  ani- 
mals and  observe  directly  how  far  the  general  sensibility  of  the  pharynx 


LARYNGEAL    NERVES  537 

and  the  reflex  phenomena  of  deglutition  are  influenced  by  this  section. 
So  far  as  one  can  judge  from  the  distribution  of  the  filaments  to  the 
mucous  membrane,  it  would  seem  that  they  combine  with  the  pharyngeal 
filaments  of  the  fifth,  and  possibly  with  sensory  filaments  from  the 
glosso-pharyngeal,  in  giving  general  sensibility  to  these  parts. 

In  experiments  on  the  reflex  phenomena  of  deglutition,  it  has  been 
shown  that  the  action  of  the  pharyngeal  muscles  can  not  be  excited  by 
stimulation  of  the  mucous  membrane  of  the  supralaryngeal  region  and 
the  pharynx  after  section  of  the  fifth  and  of  the  superior  laryngeal 
branches  of  the  pneumogastrics.  This  would  seem  to  indicate  that  the 
pharyngeal  branches  of  the  pneumogastrics  are  of  little  importance  in 
these  reflex  phenomena. 

Properties  and  Uses  of  the  Superior  Laryngeal  Nerves.  —  The  stimu- 
lation of  these  nerves  produces  intense  pain  and  contraction  of  the 
crico-thyroids ;  but  it  has  been  shown  by  experiment  that  the  arytenoid 
muscles,  through  which  the  nerves  pass,  receive  no  motor  filaments. 
The  influence,  of  the  nerves  on  the  muscles  resolves  itself  into  the  action 
of  the  crico-thyroids,  which  has  been  treated  of  fully  under  the  head 
of  phonation.  When  these  muscles  are  paralyzed  the  voice  becomes 
hoarse.  The  filaments  to  the  inferior  muscles  of  the  pharynx  are  few 
and  comparatively  unimportant.  The  superior  laryngeals  do  not  receive 
their  motor  supply  from  the  spinal  accessory. 

The  sensory  filaments  of  the  superior  laryngeals  have  important 
uses  connected  with  the  protection  of  the  air-passages  from  the  entrance 
of  foreign  matters,  particularly  in  deglutition  ;  and  they  also  are  con- 
cerned in  the  reflex  action  of  the  constrictors  of  the  pharynx.  When 
both  superior  laryngeals  have  been  divided  in  living  animals,  liquids 
often  pass  in  small  quantity  into  the  larynx,  owing  to  the  absence  of  the 
reflex  closure  of  the  glottis  when  foreign  matters  are  brought  in  con- 
tact with  its  superior  surface,  and  the  occasional  occurrence  of  inspira- 
tion during  deglutition. 

Aside  from  the  protection  of  the  air-passages,  the  superior  laryngeal 
is  one  of  the  sensory  nerves  through  which  the  reflex  acts  in  deglutition 
operate.  There  are  certain  parts  that  depend  for  their  sensibility  entirely 
on  this  nerve ;  namely,  the  mucous  membrane  of  the  epiglottis,  of  the 
aryteno-epiglottidean  fold  and  of  the  larynx  as  far  down  as  the  true 
vocal  chords.  When  an  impression  is  made  on  these  parts,  as  when 
they  are  touched  with  a  piece  of  meat,  regular  and  natural  movements 
of  deglutition  ensue. 

If  the  superior  laryngeal  nerves  are  divided  and  a  stimulus  is  applied 
to  their  central  ends,  movements  of  deglutition  are  observed,  and  there 
also  is  arrest  of  the  action  of  the  diaphragm.     From  these  experiments, 


538  NERVOUS    SYSTEM 

it  would  seem  that  the  impression  which  gives  rise  to  the  movements  of 
deglutition  aids  in  protecting  the  air-passages  from  the  entrance  of  for- 
eign matters  by  temporarily  arresting  the  inspiratory  act. 

Properties  and  Uses  of  tJie  Inferior,  or  Recurrent  Laryngeal  Nerves.  — 
The  anatomical  distribution  of  these  nerves  shows  that  their  most  impor- 
tant action  is  connected  with  the  muscles  of  the  larynx.  The  few  fila- 
ments given  off  in  the  neck  to  join  the  cardiac  branches  are  probably  not 
very  important.  It  is  proper  to  note,  however,  that  the  inferior  laryn- 
geal nerves  supply  the  muscular  tissue  and  mucous  membrane  of  the 
upper  part  of  the  oesophagus  and  trachea,  and  one  or  two  branches  are 
sent  to  the  inferior  constrictor  of  the  pharynx.  The  action  of  these 
filaments  is  sufficiently  evident. 

The  inferior  laryngeals  contain  chiefly  motor  filaments,  as  is  evident 
from  their  distribution  as  well  as  from  the  effects  of  direct  stimulation. 
All  who  have  experimented  on  these  nerves  have  noted  little  or  no  evi- 
dence of  pain  when  they  are  irritated  or  divided. 

One  of  the  most  important  uses  of  the  recurrents  relates  to  the  pro- 
duction of  vocal  sounds.  In  connection  with  the  physiology  of  the 
internal,  or  communicating  branch  from  the  spinal  accessory  to  the 
pneumogastric,  it  has  been  shown  that  this  branch  is  the  true  nerve  of 
phonation.  Before  the  uses  of  the  spinal  accessory  were  fully  under- 
stood, experiments  on  the  inferior  laryngeals  led  to  the  opinion  that 
these  were  the  nerves  of  phonation,  as  loss  of  voice  follows  their  divi- 
sion in  living  animals.  It  is  true  that  these  nerves  contain  the  filaments 
which  preside  over  the  vocal  movements  of  the  larynx  ;  but  it  is  also  the 
fact  that  these  vocal  filaments  are  derived  from  the  spinal  accessory,  and 
that  the  recurrents  contain  as  well  motor  filaments  which  preside  over 
movements  of  the  larynx  not  concerned  in  the  production  of  vocal  sounds. 

The  muscles  of  the  larynx  concerned  in  phonation  are  the  crico-thy- 
roids,  animated  by  the  superior  laryngeals,  and  the  arytenoid,  the  lateral 
crico-arytenoids  and  the  thyro-arytenoids,  animated  by  the  inferior  laryn- 
geals. The  posterior  crico-arytenoids  are  respiratory  muscles,  and  these 
are  not  affected  by  extirpation  of  the  spinal  accessories,  but  the  glottis  is 
still  capable  of  dilatation,  so  that  inspiration  is  not  impeded.  If,  however, 
the  spinal  accessories  are  extirpated  and  the  larynx  is  then  exposed  in  a  liv- 
ing animal,  the  glottis  remains  dilated,  but  will  not  close  when  irritated.  If 
the  inferior  laryngeals  are  then  divided,  the  glottis  is  mechanically  closed 
with  the  inspiratory  act,  and  the  animals  often  die  of  suffocation.  In 
view  of  the  varied  sources  from  which  the  pneumogastrics  receive  their 
motor  filaments,  it  is  easy  to  understand  how  certain  of  these  may  pre- 
side over  the  vocal  movements,  and  others,  from  a  different  source,  may 
animate  the  respiratory  movements  of  the  glottis. 


CARDIAC   AND    PULMONARY    NERVES  539 

The  obstruction  to  the  entrance  of  air  into  the  lungs  is  a  sufficient 
explanation  of  the  increase  in  the  number  of  the  respiratory  acts 
after  division  of  both  recurrents.  The  acceleration  of  respiration  is 
much  greater  in  young  than  in  adult  animals.  This  does  not  apply  to 
very  young  animals,  in  which  section  of  the  recurrents  produces  almost 
instant  death. 

Feeble  stimulation  of  the  central  ends  of  the  inferior  laryngeals, 
after  their  division,  produces  rhythmical  movements  of  deglutition,  coin- 
cident usually  with  arrest  of  the  action  of  the  diaphragm.  These  phe- 
nomena are  commonly  observed  in  rabbits,  but  they  are  not  constant. 
The  reflex  action  of  these  nerves  in  deglutition  probably  is  dependent 
on  the  communicating  filaments  which  they  send  to  the  superior  laryn- 
geal nerves. 

Properties  and  Uses  of  tJie  Cardiac  Xerirs.  —  The  chief  uses  of  the 
cardiac  branches  relate  to  the  influence  of  the  pneumogastrics  on  the 
action  of  the  heart.  This  has  already  been  considered  in  connection 
with  the  physiology  of  the  circulation.  The  effect  of  dividing  the  pneu- 
mogastrics in  the  neck  is  to  remove  the  heart  from  the  influence  of  its 
inhibitory  nerves  ;  but  at  the  same  time  the  operation  profoundly  affects 
the  respiratory  movements,  and  this  latter  effect  must  be  eliminated 
so  far  as  possible  in  studying  the  influence  of  the  pneumogastrics  on 
the  circulation.  The  same  remark  applies  to  the  experiment  of  faradiz- 
ation of  the  pneumogastrics  in  the  neck.  The  cardiac  branches  are 
operated  on  with  difficulty,  and  most  experiments  have  been  made  on 
the  cervical  portion  of  the  pneumogastric  itself. 

Faradization  of  the  pneumogastrics  in  the  neck  arrests  the  action  of 
the  heart  in  diastole.  This  is  a  direct  action  and  is  due  to  the  excita- 
tion of  the  inhibitory  fibres,  which  are  derived  from  the  spinal  accessory 
nerves.  The  phenomena  following  stimulation  of  these  nerves  have 
already  been  described  in  connection  with  the  physiology  of  the  circu- 
lation and  the  properties  and  uses  of  the  spinal  accessories. 

Depressor  Nerve.  —  While  this  nerve  is  not  isolated  in  the  human 
subject,  it  is  probable  that  fibTres,  the  action  of  which  is  analogous  to 
that  observed  in  animals  in  which  the  nerve  is  anatomically  distinct, 
exist  in  the  trunk  of  the  pneumogastric.  The  action  of  the  depressor 
nerves,  which  is  reflex,  has  already  been  described  in  connection  with 
the  physiology  of  the  circulation. 

Properties  and  Uses  of  the  Pulmonary  Xerves.  —  The  trachea, 
bronchia  and  the  pulmonary  structure  are  supplied  with  motor  and 
sensory  filaments  by  branches  of  the  pneumogastrics.  The  recurrent 
laryngeals  supply  the  upper  part,  and  the  pulmonary  branches,  the  lower 
part  of  the  trachea,  the  lungs  themselves  being  supplied  by  the  pulmo- 


540  NERVOUS   SYSTEM 

nary  branches  alone.  The  sensibiHty  of  the  mucous  membrane  of  the 
trachea  and  bronchia  is  due  to  the  pneumogastrics ;  and  these  parts  are 
insensible  to  irritation  when  the  nerves  have  been  divided  in  the  neck. 

Effects  of  Division  of  the  Pneumogastrics  on  Respiration.  —  Section  of 
both  pneumogastrics  in  the  neck  usually  is  followed  by  death  in  two  to 
five  days.  In  very  young  animals,  death  may  occur  almost  instantly 
from  paralysis  of  the  respiratory  movements  of  the  glottis.  It  has  been 
found  by  all  experimenters  that  animals  survived  and  presented  no  very 
distinct  abnormal  phenomena  after  section  of  one  nerve.  Animals 
operated  on  in  this  way  present  hoarseness  of  the  voice  and  a  slight 
increase  in  the  number  of  respiratory  acts.  Some  observers  have  found 
the  corresponding  lung  partly  emphysematous  and  partly  engorged 
with  blood,  and  others  have  not  noted  any  change  in  the  pulmonary 
structure. 

When  both  nerves  are  divided  in  full-grown  dogs,  the  effect  on 
the  respiratory  movements  is  very  marked.  For  a  few  seconds  the 
number  of  respiratory  acts  may  be  increased ;  but  so  soon  as  the  ani- 
mal becomes  tranquil,  the  number  is  very  much  diminished  and  the 
movements  change  their  character.  The  inspiratory  acts  become  unusu- 
ally profound  and  are  attended  with  excessive  dilatation  of  the  thorax. 
The  animal  usually  is  quiet  and  indisposed  to  move.  Under  these  con- 
ditions the  number  of  respirations  may  fall  from  sixteen  or  eighteen  to 
four  per  minute. 

In  most  animals  that  die  from  section  of  both  pneumogastrics,  the 
lungs  are  found  engorged  with  blood,  and,  as  it  were,  carnified,  so  that 
they  sink  in  water.  This  condition  probably  is  not  the  result  of  inflam- 
mation of  the  pulmonary  parenchyma,  although  this  was  the  view  for- 
merly entertained,  and  it  is  now  held  by  some  physiologists.  Bernard 
found  that  the  pulmonary  lesion  did  not  exist  in  birds,  although  section 
of  both  nerves  was  fatal.  It  had  previously  been  ascertained  that  in 
some  animals  death  takes  place  with  no  alteration  of  the  lungs.  When 
the  entrance  of  the  secretions  into  the  air-passages  is  prevented  by  the 
introduction  of  a  canula  into  the  trachea,  solidification  of  the  lungs  is 
nevertheless  observed.  Those  who  regard  the  condition  as  inflamma- 
tory call  it  a  "vagus  pneumonia,"  due  to  division  of  "trophic"  fibres 
of  the  pneumogastrics ;  but  the  mechanism  and  immediate  causes  of 
the  pulmonary  changes  are  obscure  and  have  not  been  satisfactorily 
explained. 

The  pneumogastrics  sometimes  reunite  after  division.  The  following 
observation  (Flint,  1874)  illustrates  this  fact,  which  has  frequently  been 
noted  :  Both  pneumogastrics  were  divided  in  the  neck  in  a  medium- 
sized  dog.     The  pulse  was  immediately  increased  from  one  hundred  and 


CESOPHAGEAL   NERVES  541 

twenty  to  two  hundred  and  forty  in  the  minute,  and  the  number  of 
respirations  fell  from  twenty-four  to  four  or  six.  In  ten  days  the  pulse 
and  respirations  had  become  normal.  The  dog  was  then  killed  by 
section  of  the  medulla  oblongata  and  reunion  of  the  divided  ends  of  the 
nerves  was  found  to  be  nearly  complete. 

Effects  of  Faradization  of  the  Pnenviogastrics  on  Respiration.  —  Fara- 
dization of  the  pneumogastrics  in  the  neck,  if  the  current  is  sufficiently 
powerful,  arrests  respiration.  This  arrest  may  be  produced  at  any  time 
with  reference  to  the  respiratory  act,  either  in  expiration  or  inspiration, 
although  it  is  more  readily  effected  in  expiration.  During  the  passage 
of  the  current,  the  general  movements  of  the  animal  also  are  arrested. 
Although  respiration  may  always  be  arrested  in  this  way,  quite  a  power- 
ful current  is  required.  During  the  passage  of  a  very  feeble  current, 
the  respirations  are  accelerated.  They  are  then  retarded  as  the  current 
is  made  stronger,  until  they  finally  cease. 

The  following  are  the  phenomena,  observed  by  Bert,  during  the 
passage  of  a  powerful  faradic  current  :  — 

"  If  an  excitation  is  employed  sufficiently  powerful  to  arrest  respira- 
tion in  inspiration,  all  respiratory  movements  may  be  made  to  cease  at 
the  very  moment  when  the  excitation  is  applied  (inspiration,  half- 
inspiration,  expiration),  either  by  operating  on  the  pneumogastric,  or 
operating  on  the  laryngeal.  .  .  . 

"Any  feeble  excitation  of  centripetal  nerves  increases  the  number 
of  the  respiratory  movements ;  any  powerful  excitation  diminishes 
them.  A  powerful  excitation  of  the  pneumogastrics,  of  the  superior 
laryngeal,  of  the  nasal  branch  of  the  infraorbital,  may  arrest  them  com- 
pletely ;  if  the  excitation  is  sufficiently  energetic,  the  arrest  takes  place 
at  the  very  moment  it  is  applied.  Finally,  sudden  death  of  the  animal 
may  follow  a  too  powerful  impression  thus  transmitted  to  the  respira- 
tory centre  :  all  this  being  true  for  certain  mammalia,  birds  and  reptiles." 

The  above  expresses  the  most  important  experimental  facts  at 
present  known  in  regard  to  the  influence  of  stimulation  of  the  pneumo- 
gastrics on  respiration.  The  pulmonary  branches  themselves  are  so 
deeply  situated  that  they  have  not  as  yet  been  made  the  subject  of 
direct  experiment,  with  any  positive  and  satisfactory  results.  The 
pneumogastrics  undoubtedly  are  the  nerves  concerned  in  the  reflex 
acts  of  normal  respiration.  Their  relations  to  these  movements,  how- 
ever, will  be  considered  in  connection  with  the  action  of  the  respiratory 
nerve-centres. 

Properties  and  Uses  of  the  (Esophageal  Nei'ves.  — The  muscular  walls 
and  the  mucous  membrane  of  the  oesophagus  are  supphed  entirely  by 
branches   from    the   pneumogastrics.      The   upper  portion  is   supplied 


542 


NERVOUS    SYSTEM 


by  filaments  from  the  inferior  laryngeal  branches,  the  middle  portion,  by 
filaments  from  the  posterior  pulmonary  branches,  and  the  inferior  por- 
tion receives  the  oesophageal  branches.  These  branches  are  both  sen- 
sory and  motor ;  but  probably  the  motor  filaments  largely  predominate, 
for  the  mucous  membrane,  although  it  is  sensible  to  the  extremes  of 
heat  and  cold,  the  feeling  of  distention,  and  a  burning  sensation  on  the 
application  of  strong  irritants,  is  not  acutely  sensitive. 

That  the  movements  of  the  oesophagus  are  animated  by  branches 
from  the  pneumogastrics,  has  been  clearly  shown  by  experiments.  In 
the  first  place,  except  in  animals  in  which  the  anatomical  distribution  of 
the  nerves  is  different  from  the  arrangement  in  the  human  subject,  the 
entire  oesophagus  is  paralyzed  by  division  of  the  nerves  in  the  neck. 
When  the  pneumogastrics  are  divided  in  the  cervical  region  in  dogs,  if 
the  animals  attempt  to  swallow  a  considerable  quantity  of  food,  the 
upper  part  of  the  oesophagus  is  found  enormously  distended.  Bernard 
noted  in  a  dog  in  which  a  gastric  fistula  had  been  established,  that  arti- 
cles of  food  given  to  the  animal  did  not  pass  into  the  stomach,  although 
he  made  efforts  to  swallow.  An  instant  after  the  attempt,  the  matters 
were  regurgitated,  mixed  with  mucus,  but  of  course  did  not  come  from 
the  stomach. 

Direct  experiments  on  the  roots  of  the  pneumogastrics  have  shown 
that  these  nerves  influence  the  movements  of  the  oesophagus,  and  that 
the  motor  filaments  involved  do  not  come  from  the  spinal  accessories ; 
but  it  is  not  known  from  what  nerves  these  motor  filaments  are  derived. 

Properties  and  Uses  of  the  Ahdommal  Nerves.  —  In  view  of  the 
extensive  distribution  of  the  terminal  branches  of  the  pneumogastrics 
to  the  abdominal  organs,  it  is  evident  that  the  action  of  these  nerves 
must  be  important,  particularly  since  it  has  been  shown  that  the  right 
nerve  is  distributed  to  the  entire  small  intestine. 

Injiuejice  of  tJie  Pnciimogastiics  on  the  Liver.  —  There  is  very  little 
known  in  regard  to  the  influence  of  the  pneumogastrics  on  the  secretion 
of  bile ;  and  the  most  important  experiments  on  the  innervation  of  the 
liver  relate  to  the  production  of  glycogen.  If  both  pneumogastrics  are 
divided  in  the  neck,  and  if  the  animal  is  killed  at  a  time  varying  between 
a  few  hours  and  one  or  two  days  after,  the  liver  contains  no  sugar, 
under  the  conditions  in  which  it  usually  is  found.  From  experiments 
of  this  kind,  Bernard  concluded  that  the  glycogenic  processes  are  sus- 
pended when  the  nerves  are  divided.  The  experiments,  however,  made 
by  irritating  the  pneumogastrics,  were  more  satisfactory,  as  in  these  he 
looked  for  sugar  in  the  blood  and  in  the  urine  and  did  not  confine  his 
examinations  for  sugar  to  the  substance  of  the  liver. 

After  division  of  pneumogastrics  in  the  neck,  if  the  peripheral  ends 


ABDOMINAL   NERVES  543 

are  stimulated  there  is  no  effect  on  the  liver  ;  but  when  the  stimulus  is 
applied  to  the  central  ends,  the  glycogenic  processes  become  exagger- 
ated and  sugar  makes  its  appearance  in  the  blood  and  in  the  urine. 
Bernard  made  a  number  of  experiments  illustrating  this  point,  on  dogs 
and  rabbits.  The  current  employed  usually  was  feeble,  and  it  was 
continued  for  five  or  ten  minutes  two  or  three  times  in  an  hour.  In 
some  instances  the  stimulation  was  continued  for  thirty  minutes.  From 
these  experiments,  it  is  assumed  that  the  physiological  production  of 
glycogen  by  the  liver  is  reflex  and  is  due  to  an  impression  conveyed  to 
the  nerve-centres  through  the  pneumogastrics.  The  inhalation  of  irri- 
tating vapors  and  of  anesthetics  produces  an  increased  glycogenic 
action  in  the  liver.  The  effects  of  irritating  the  floor  of  the  fourth 
ventricle,  by  which  temporary  diabetes  is  produced,  have  been  con- 
sidered in  connection  with  the  glycogenic  action  of  the  liver. 

htjiuence  of  the  Pneumogastrics  on  the  Stomach  and  Intestines.  — 
Little  or  nothing  is  known  in  regard  to  the  action  of  the  pneumo- 
gastrics on  the  spleen,  kidneys  and  suprarenal  capsules.  The  influence 
of  these  nerves  on  the  stomach  and  intestine  will  be  considered  under 
the  following  heads  :  — ■ 

1.  The  effects  of  faradization  of  the  nerves. 

2.  The  effects  of  section  of  the  nerves  on  the  movements  of  the 
stomach  in  digestion. 

3.  The  influence  of  the  nerves  on  the  small  intestine. 

Effects  of  Faradization.  —  The  stomach  contracts  under  stimulation 
of  the  pneumogastrics  in  the  neck,  not  instantly,  but  after  five  or  six 
seconds.  Stimulation  of  the  splanchnic  nerves,  however,  while  it  pro- 
duces movements  of  the  intestines,  does  not  affect  the  stomach.  Judg- 
ing from  the  tardy  contraction  of  the  stomach  and  the  analogy  between 
the  action  of  the  pneumogastrics  on  this  organ  and  the  action  of  the 
sympathetic  nerves  on  the  non-striated  muscular  tissue,  it  has  been 
assumed  that  the  motor  action  of  the  pneumogastrics  is  due,  not  to  the 
proper  filaments  of  these  nerves,  but  to  filaments  derived  from  the 
sympathetic.  This,  however,  is  not  exactly  in  accord  with  experimental 
facts ;  for  it  has  lately  been  known  that  the  pneumogastrics  are  the 
excito-secretory  nerves  of  the  stomach  and  pancreas  (Pawlow). 

Effects  of  Section  of  tJie  Pnenniogastrics  on  the  Movements  of  the 
Stomach.  —  If  the  pneumogastrics  are  divided  in  the  neck  in  a  dog  in 
full  digestion,  in  which  a  gastric  fistula  has  been  established  so  that  the 
interior  of  the  organ  can  be  explored,  the  following  phenomena  are 
observed :  — 

In  the  first  place,  before  division  of  the  nerves,  the  mucous  mem- 
brane of  the  stomach  is  turgid,  its  reaction  is  intensely  acid   and  the 


544  NERVOUS    SYSTEM 

finger  introduced  through  the  fistula  is  firmly  grasped  by  the  contrac- 
tions of  the  muscular  walls.  When  the  pneumogastrics  are  divided,  the 
contractions  of  the  muscular  walls  cease,  the  mucous  membrane  becomes 
pale,  the  secretion  of  gastric  juice  apparently  is  arrested  and  the  sensi- 
bility of  the  organ  is  abolished. 

Notwithstanding  the  apparent  arrest  of  the  movements  of  the  stom- 
ach in  digestion  by  section  of  the  pneumogastrics,  it  has  been  shown 
that  substances  may  be  slowly  passed  to  the  pylorus,  and  that  the 
movements,  although  they  are  greatly  diminished  in  activity,  are  not 
entirely  abolished.  The  movements  occurring  after  section  of  the 
nerves  have  been  attributed  to  local  irritation  of  the  intramuscular  ter- 
minal nervous  filaments. 

The  influence  of  the  pneumogastrics  on  the  general  processes  of 
digestion,  the  sensations  of  hunger  and  thirst  and  on  absorption  from 
the  alimentary  canal  have  already  been  considered  in  connection  with 
the  physiology  of  digestion  and  absorption. 

Injlitcnce  of  the  Pneumogastrics  on  the  Small  Intesti}ie.  —  The  pneu- 
mogastrics influence  intestinal  as  well  as  gastric  secretion.  After 
section  of  the  nerves  in  the  cervical  region,  powerful  cathartics  (croton- 
oil,  calomel,  podophyllin,  jalap,  arsenic  etc.)  fail  to  produce  purgation, 
even  in  doses  sufficient  to  cause  death.  The  articles  used  may  be  given 
by  the  mouth  just  before  dividing  the  nerves  or  may  be  injected  under  the 
skin. 

Stimulation  of  the  pneumogastrics  excites  peristaltic  movements  of 
the  small  intestine.  Experiments  on  the  lower  animals  have  shown, 
however,  that  if  the  nerve  is  stimulated  during  peristalsis,  the  move- 
ments are  inhibited  for  a  few  moments,  but  afterward  are  increased  in 
activity. 

The  cranial  nerves  that  have  been  considered  are  the  third,  fourth, 
fifth,  sixth,  seventh,  tenth,  eleventh  and  twelfth.  The  anatomical  and 
physiological  history  of  the  olfactory  (first),  optic  (second),  auditory 
(eighth),  gustatory  (branch  of  the  seventh  and  a  part  of  the  ninth)  and 
of  the  general  sensory  nerves  so  far  as  they  are  concerned  in  the  sense 
of  touch,  belongs  properly  to  the  chapters  on  the  special  senses. 


CHAPTER   XXI 

THE    SPINAL   CORD 

Membranes  of  the  encephalon  and  spinal  cord  —  Cephalo-rachidian  liquid  —  Physiological 
anatomy  of  the  spinal  cord — Columns  of  Tiirck  —  Crossed  pyramidal  tracts  —  Anterior 
ground  columns  —  Lateral  bundles  —  Ascending  and  descending  cerebellar  fasciculi  — 
Direct  cerebellar  fasciculi  —  Columns  of  Burdach  —  Columns  of  GoU  —  Directions  of  nerve- 
fibres  in  the  cord  —  General  properties  of  the  spinal  cord  —  Relations  of  the  posterior  white 
columns  of  the  cord  to  muscular  coordination  —  Nerve-centres  in  the  spinal  cord — Reflex 
action  of  the  spinal  cord — Reflexes  in  man. 

The  nervous  structures  contained  in  the  cavity  of  the  cranium  and 
in  the  spinal  canal,  exclusive  of  the  roots  of  the  cranial  and  spinal  nerves, 
constitute  the  cerebro-spinal  axis.  This  portion  of  the  nervous  system 
is  composed  of  white  and  gray  matter.  The  fibres  of  the  white  matter 
act  solely  as  conductors.  The  gray  matter  constitutes  a  chain  of 
ganglia,  which  act  as  nerve-centres,  receiving  impressions  and  gen- 
erating impulses.  Certain  parts  of  the  gray  matter  also  serve  as 
conductors. 

The  cerebro-spinal  axis  is  enveloped  in  membranes  for  its  protec- 
tion and  for  the  support  of  its  nutrient  vessels.  It  is  surrounded  to  a 
certain  extent  with  liquid,  and  it  presents  cavities,  as  the  ventricles  of 
the  brain  and  the  central  canal  of  the  cord,  that  contain  liquid.  The 
gray  matter  is  distinct  from  the  white,  even  to  the  naked  eye.  In  the 
spinal  cord  the  white  substance  is  external  and  the  gray  is  internal. 
The  surface  of  the  brain  presents  an  external  layer  of  gray  matter,  the 
white  substance  being  internal.  In  the  white  substance  of  the  brain, 
also,  are  collections  of  gray  matter.  The  white  matter  of  the  cerebro- 
spinal axis  is  composed  largely  of  fibres.  The  gray  substance  is 
composed  largely  of  cells. 

The  encephalon  is  contained  in  the  cranial  cavity  and  consists  of  the 
cerebrum,  cerebellum,  pons  Varolii  and  the  bulb,  or  medulla  oblongata. 
In  the  human  subject  and  in  many  of  the  higher  animals,  its  surface  is 
marked  with  convolutions  by  which  the  extent  of  its  gray  substance  is 
much  increased.  The  cerebrum,  the  cerebellum  and  most  of  the  enceph- 
alic ganglia  are  connected  with  the  white  substance  of  the  encephalon 
and  with  the  spinal  cord.  All  the  cerebro-spinal  nerves  are  connected 
with  the  encephalon  and  the  spinal  cord. 
2N  545 


546  NERVOUS    SYSTEM 

Membranes  of  the  Ejicephalon  and  Spinal  Cord.  —  The  membranes  of 
the  brain  and  spinal  cord  are  the  dura  mater,  the  arachnoid  and  the  pia 
mater. 

The  dura  mater  of  the  encephalon  is  a  dense  membrane  in  a  single 
layer  and  is  composed  chiefly  of  ordinary  fibrous  tissue.  That  portion 
which  lines  the  cranial  cavity  is  adherent  to  the  bones.  In  certain  situ- 
ations it  is  separated  into  two  layers  and  bounds  what  are  known  as 
the  venous  sinuses.  The  dura  mater  also  sends  off  certain  folds  or 
processes.  One  of  these  passes  into  the  longitudinal  fissure  and  is 
called  the  falx  cerebri ;  another  lies  between  the  cerebrum  and  the  cere- 
bellum and  is  called  the  tentorium ;  another  is  situated  between  the 
lateral  halves  of  the  cerebellum  and  is  called  the  falx  cerebelli.  The 
dura  mater  is  closely  attached  to  the  bone  at  the  border  of  the  foramen 
magnum.  From  this  point  it  passes  into  the  spinal  canal  and  forms  a 
loose  covering  for  the  cord.  In  the  spinal  canal,  the  membrane  is  not 
adherent  to  the  bones,  which  have,  like  most  other  bones  in  the  body,  a 
special  periosteum.  At  the  foramina  of  exit  of  the  cranial  and  the 
spinal  nerves,  the  dura  mater  sends  out  processes  which  envelop  the 
nerves,  with  the  fibrous  sheaths  of  which  they  soon  become  continuous. 
The  subdural  space  contains  a  small  quantity  of  liquid. 

The  arachnoid  is  a  delicate  membrane,  resembling  the  serous  mem- 
branes, except  that  it  presents  but  one  layer.  Its  inner  surface  is  cov- 
ered with  a  layer  of  endothelium.  There  is  a  considerable  quantity  of 
liquid  between  the  arachnoid  and  the  pia  mater  surrounding  the  cerebro- 
spinal axis,  in  what  is  called  the  subarachnoid  space.  This  is  called  the 
cerebro-spinal,  or  cephalo-rachidian  liquid.  The  arachnoid  does  not 
follow  the  convolutions  and  fissures  of  the  encephalon  or  the  fissures  of 
the  cord,  but  it  simply  covers  their  surfaces.  There  is  a  longitudinal, 
incomplete,  cribriform,  fibrous  septum  in  the  cord,  passing  from  the 
inner  layer  of  the  arachnoid  to  the  pia  mater.  A  similar  arrangement 
is  found  in  certain  situations  at  the  base  of  the  skull. 

The  pia  mater  of  the  encephalon  is  a  delicate  fibrous  structure,  very 
vascular,  seeming  to  present,  indeed,  only  a  skeleton  network  of  fibres 
for  the  support  of  vessels  going  finally  to  the  nervous  substance.  This 
membrane  covers  the  surface  of  the  encephalon  immediately,  follows  the 
sulci  and  fissures,  and  is  prolonged  into  the  ventricles,  where  it  forms 
the  choroid  plexus  and  the  velum  interpositum.  From  its  internal  sur- 
face small  vessels  are  given  off  which  pass  into  the  nervous  substance. 

The  pia  mater  of  the  encephalon  is  continuous  with  the  correspond- 
ing membrane  of  the  cord ;  but  in  the  spinal  canal  the  membrane  is 
thicker,  stronger,  more  closely  adherent  to  the  subjacent  parts,  and  its 
bloodvessels  are  not  so  abundant.     In  this  situation  many  of  the  fibres 


CEPHALO-RACHIDIAN    LIQUID  547 

are  arranged  in  longitudinal  bands.  This  membrane  lines  the  anterior 
fissure  and  a  portion  of  the  posterior  fissure  of  the  cord.  At  the  fora- 
mina of  exit  of  the  cranial  and  the  spinal  nerves,  the  fibrous  structure  of 
the  pia  mater  becomes  continuous  with  the  nerve-sheaths. 

Between  the  anterior  and  posterior  roots  of  the  spinal  nerves,  on 
either  side  of  the  cord,  is  a  narrow  ligamentous  band,  the  ligamentum 
denticulatum,  which  assists  in  holding  the  cord  in  place.  This  extends 
from  the  foramen  magnum  to  the  terminal  filament  of  the  cord,  and 
is  attached  internally  to  the  pia  mater,  and  externally,  to  the  dura 
mater. 

Cephalo-rachidian  Liquid. — The  greatest  part  of  the  liquid  in  the 
cranium  and  in  the  spinal  canal  is  contained  in  the  subarachnoid  space. 
The  ventricles  of  the  encephalon  are  in  communication  with  the  central 
canal  of  the  cord,  and  also  are  connected  with  the  general  subarachnoid 
space  by  a  narrow  triangular  orifice  at  the  inferior  angle  of  the  fourth 
ventricle.  By  this  arrangement  the  liquid  in  the  ventricles  of  the 
encephalon  and  in  the  central  canal  of  the  cord  communicates  with  the 
liquid  surrounding  the  cerebro-spinal  axis,  and  the  pressure  on  these 
parts  is   equalized. 

So  far  as  is  known,  the  ofifice  of  the  cephalo-rachidian  fluid  is  simply 
mechanical,  and  its  properties  and  composition  have  no  very  definite 
physiological  significance.  Its  quantity  has  been  estimated  in  the  human 
subject  at  about  two  fluidounces  (60  cubic  centimeters);  but  this  was  the 
smallest  quantity  obtained  by  placing  the  subject  upright,  making  an 
opening  in  the  lumbar  region  and  a  counter-opening  in  the  head  to 
admit  the  pressure  of  the  atmosphere  (Magendie).  The  exact  quantity 
in  the  living  subject  could  hardly  be  estimated  in  this  way  ;  and  it  is 
difficult,  indeed,  to  see  how  anything  more  than  a  roughly  approximate 
idea  could  be  obtained.  The  quantity  indicated  probably  does  not 
represent  all  the  liquid  contained  in  the  ventricles  and  in  the  subarach- 
noid space ;  but  as  it  is  the  most  definite  estimate  that  has  been  made,  it 
is  given  as  an  approximation.  It  is  probable  that  the  quantity  is  subject 
to  considerable  variations. 

The  general  properties  and  composition  of  the  cephalo-rachidian 
liquid  are  in  brief  the  following  :  It  is  transparent  and  colorless,  free 
from  viscidity,  of  a  distinctly  saline  taste,  an  alkaline  reaction  and  it 
resists  putrefaction  for  a  long-  time.  It  is  not  affected  by  heat  or  acids. 
It  contains  a  large  proportion  of  water  (981  to  985  parts  per  thousand), 
a  considerable  quantity  of  sodium  chloride,  a  trace  of  potassium  chloride, 
sulphates,  carbonates  and  alkaline  and  earthy  phosphates.  In  addition 
it  contains  traces  of  urea,  glucose,  sodium  lactate,  fatty  matter,  choles- 
terin  and  albumin. 


548 


NERVOUS    SYSTEM 


Physiological  Anatomy  of  the  Spinal  Cord 

The  spinal  cord,  with  its  membranes,  the  roots  of  the  spinal 
nerves  and  the  surrounding  liquid,  occupies  the  spinal  canal  and  is 
continuous  with  the  encephalon.  Its  length  is  fifteen  to  eighteen 
inches  (38.1  to  45.7  centimeters)  and  its  weight  is  about  an  ounce  and 
a  half  (42.5  grams).     Its  general  form  is  cylindrical,  but  it  is  slightly 

It 


Fig.  132.  —  Transverse  sectio?i  of  the  spinal  cord  of  a  child  six  months  old,  at  the  middle  of  the  lum- 
bar enlargement,  treated  with  potassium  auric  chloride  and  uranium  nitrate ;  x  20.  By  means  of 
these  reagents,  the  direction  of  the  fibres  in  the  gray  substance  is  rendered  unusually  distinct  (Gerlach). 

a,  anterior  columns  ;  b,  posterior  columns  ;  c,  lateral  columns  ;  d,  anterior  roots  ;  e,  posterior  roots  ; 
f,  anterior  white  commissure,  in  communication  with  the  fasciculi  of  the  anterior  cornua  and  the 
anterior  columns ;  g,  central  canal,  with  its  epithelium  ;  h,  surrounding  connective  substance  of  the 
central  canal ;  i,  transverse  fasciculi  of  the  gray  commissure  in  front  of  the  central  canal ;  k,  transverse 
fasciculi  of  the  gray  commissure  behind  the  central  canal ;  /,  transverse  section  of  the  two  central 
veins;  m,  anterior  cornua;  n,  great,  lateral  cellular  layer  of  the  anterior  cornua;  o,  lesser,  anterior 
cellular  layer;  /,  smallest,  median  cellular  layer;  q,  posterior  cornua;  r,  ascending  fasciculi  in  the 
posterior  cornua ;  s,  substantia  gelatinosa. 


flattened  in  certain  portions.  It  extends  from  the  foramen  magnum  to 
the  lower  border  of  the  body  of  the  first  lumbar  vertebra.  It  presents, 
at  the  origin  of  the  brachial  nerves,  an  elongated  ovoid  enlargement 
flattened  antero-posteriorly,  and  a  corresponding  enlargement  at  the 
origin  of  the  nerves  that  supply  the  lower  extremities.  It  terminates 
below  in  a  slender  gray  filament,  called  the  filum  terminale,  at  the  lower 


THE    SPINAL   CORD  549 

border  of  the  first  lumbar  vertebra.  The  sacral  and  cocygeal  nerves, 
after  their  origin  from  the  lower  portion  of  the  cord,  pass  downward  to 
emerge  by  the  sacral  foramina  and  form  what  is  known  as  the  cauda 
equina.  The  substance  of  the  cord  is  composed  of  white  and  gray  mat- 
ter, the  white  matter  being  external.  The  pointed  inferior  extremity  of 
the  cord  consists  entirely  of  gray  m^atter. 

The  cord  presents  an  anterior  and  a  posterior  median  fissure, 
and  imperfect  and  somewhat  indistinct  anterior  and  posterior  lateral 
grooves,  from  which  latter  arise  the  anterior  and  the  posterior  roots 
of  the  spinal  nerves.  The  posterior  lateral  groove  is  fairly  well  marked, 
but  there  is  no  distinct  line  at  the  origin  of  the  anterior  roots.  The 
anterior  median  fissure  is  more  distinct.  It  penetrates  the  anterior  por- 
tion of  the  cord  in  the  median  line  for  about  one-third  of  its  thickness 
and  receives  a  highly  vascular  fold  of  the  pia  mater.  It  extends  to  the 
anterior  white  commissure.  The  posterior  fissure  is  not  so  distinct  as 
the  anterior.  It  is  not  lined  throughout  by  a  fold  of  the  pia  mater  but 
is  filled  with  connective  tissue  and  bloodvessels,  which  form  a  septum 
posteriorly  between  the  lateral  halves  of  the  cord.  The  posterior 
median  fissure  extends  nearly  to  the  centre  of  the  cord,  as  far  as  the 
posterior  gray  commissure. 

The  arrangement  of  the  white  and  the  gray  matter  in  the  cord  is 
seen  in  a  transverse  section.  The  gray  substance  is  in  the  form  of 
a  letter  H,  presenting  two  anterior  and  two  posterior  cornua  connected 
by  what  is  called  the  gray  commissure.  The  anterior  cornua  are  short 
and  broad  and  do  not  extend  to  the  surface  of  the  cord.  The  posterior 
cornua  are  longer  and  narrower,  and  they  extend  nearly  to  the  surface 
at  the  point  of  origin  of  the  posterior  roots  of  the  spinal  nerves.  In 
the  centre  of  the  gray  commissure  is  a  narrow  canal,  lined  with  cells  of 
ciliated  epithelium,  called  the  central  canal.  This  is  in  communication 
above  with  the  fourth  ventricle  and  extends  below  to  the  filum  termi- 
nale.  That  portion  of  the  gray  commissure  situated  in  front  of  this 
canal  is  sometimes  called  the  anterior  gray  commissure,  the  posterior 
portion  being  known  as  the  posterior  gray  commissure.  The  central 
canal  is  immediately  surrounded  by  connective  tissue.  In  front  of  the 
gray  commissure  is  the  anterior  white  commissure. 

The  proportion  of  the  white  to  the  gray  substance  is  variable  in 
different  portions  of  the  cord.  In  the  cervical  region,  the  white  sub- 
stance is  most  abundant,  and,  in  fact,  it  progressively  increases  in  quan- 
tity from  below  upward  throughout  the  cord.  In  the  dorsal  region,  the 
gray  matter  is  least  abundant  and  it  exists  in  greatest  quantity  in  the 
lumbar  enlargement. 

The.  white  substance  of  the  cord  is  composed  of  nerve-fibres,  con- 


550  NERVOUS    SYSTEM 

nective-tissue  elements,  neuroglia,  and  bloodvessels,  the  latter  arranged 
in  a  wide  and  delicate  plexus.  The  nerve-fibres  are  variable  in  size  and 
are  composed  of  the  axis-cylinder  and  the  medullary  substance,  without 
the  tubular  membrane. 

The  anterior  cornua  of  gray  matter  contain  bloodvessels,  connective- 
tissue  elements,  neuroglia,  very  fine  nerve-fibres,  and  large  multipolar 
nerve-cells,  which  are  sometimes  called  motor  cells.  The  posterior 
cornua  are  composed  of  the  same  elements,  the  cells  being  much 
smaller,  and  the  fibres  exceedingly  small,  presenting  very  fine  plexuses. 
The  cells  in  this  situation  are  sometimes  called  sensory  cells.  Near  the 
posterior  portion  of  each  posterior  cornu,  is  an  enlargement,  of  a  gela- 
tiniform  character,  containing  small  cells  and  fibres,  called  the  sub- 
stantia gelatinosa.  The  relations  between  the  nerve-cells  and  the 
nerve-fibres  have  already  been  described  in  connection  with  the  general 
structure  of  the  nervous  system.  The  multipolar  nerve-cells  present 
certain  prolongations  which  do  not  branch  and  are  directly  connected  with 
the  medullated  nerve-fibres.  These  are  the  neurites,  or  axis-cylinder  pro- 
longations. In  addition,  fine  branching  poles  are  described  under  the 
name  of  dendrites,  or  protoplasmic  prolongations.  The  neuroglia  is 
particularly  abundant  in  that  part  of  the  posteria  cornua  of  gray  matter 
called  the  substantia  gelatinosa  (see  Plate  XII). 

The  division  of  the  spinal  cord  into  columns  has  a  physiological 
as  well  as  an  anatomical  basis.  Anatomists  usually  recognize,  on  either 
side  of  the  cord,  an  anterior  column,  bounded  by  the  anterior  median 
fissure  and  the  line  of  origin  of  the  anterior  roots  of  the  spinal  nerves, 
a  lateral  column,  bounded  by  the  lines  of  origin  of  the  anterior  and  of 
the  posterior  roots  of  the  nerves,  and  a  posterior  column,  bounded  by 
the  line  of  the  posterior  roots  of  the  spinal  nerves  and  the  posterior 
median  fissure.  As  the  anterior  or  posterior  columns  include  either 
white  or  gray  matter,  they  are  called  respectively  anterior  or  pos- 
terior white  or  gray  columns.  Physiological  and  pathological  re- 
searches, however,  have  shown  that  the  cord  may  properly  be  further 
divided  as  follows  :  — 

1.  Columns  of  Tiirck.  — •  By  the  sides  of  the  anterior  median  fissure, 
are  two  narrow  columns  of  white  matter,  one  on  either  side,  extending 
to  the  white  commissure,  called  the  columns  of  Tiirck,  the  direct,  or  the 
uncrossed  pyramidal  tracts.  The  fibres  of  these  columns  descend; 
probably  decussate  in  the  cervical  region  of  the  cord,  and  the  columns 
are  lost  in  the  lower  dorsal  region.  Destruction  of  certain  motor  parts 
in  the  brain  is  followed  by  descending  secondary  degenerations  in  these 
columns. 

2.  Crossed  Pyramidal  Tracts.— 'Y\\q's,q  are  situated,  one  on  either 


THE    SPINAL    CORD  551 

side,  in  the  posterior  portion  of  the  lateral  columns  and  are  bounded 
internally  by  the  posterior  cornua  of  gray  matter  and  externally  by 
a  narrow  band  called  the  direct  cerebellar  tract.  In  following  the  col- 
umns upward,  it  is  found  that  they  pass  forward  in  the  upper  part  of 
the  cervical  region  and  decussate  in  the  lower  portion  of  the  anterior 
pyramids  of  the  bulb.  These  are  descending  tracts,  and  their  fibres 
undergo  descending  secondary  degenerations  as  the  result  of  destruction 
of  certain  motor  areas  in  the  brain. 

3.  Anterior  Gro2ind  Columns.- — -These  fasciculi  are  bounded  inter- 
nally by  the  columns  of  Tiirck  and  externally  by  the  anterior  cornua  of 
gray  matter  and  the  anterior  roots  of  the  spinal  nerves.  Their  fibres 
are  supposed  to  connect  the  gray  matter  of  the  anterior  cornua  of  the 
cord  with  the  gray  matter  of  the  bulb. 

4.  Lateral  Bundles.  —  These  columns  lie  in  the  lateral  portion  of 
the  cord  externally  to  the  anterior  cornua  of  gray  matter  and  the  gray 
commissure.  Their  fibres  are  supposed  to  connect  the  gray  matter  of 
the  cord  with  the  gray  matter  of  the  bulb. 

5.  Ascending  and  Descending  Cerebellar  Fasciculi.  —  These  are  situ- 
ated externally  to  the  lateral  bundles.  They  are  supposed  to  connect 
the  gray  matter  of  the  cord  with  the  cerebellum. 

The  fibres  of  the  anterior  ground  columns  and  the  lateral  bundles 
do  not  degenerate  in  either  direction  as  the  result  of  section  of  the 
cord.  Their  fibres  seem  to  connect  nerve-cells  with  each  other,  and 
their  trophic  cells  exist  at  both  extremities,  which  accounts  for  the  ab- 
sence of  degeneration  just  mentioned. 

6.  Direct  Cer'ebellar  Fasciculi. — These  fasciculi  are  situated  at  the 
outer  and  posterior  portion  of  the  lateral  columns.  Their  fibres  pass  to 
the  funiculi  graciles,  or  posterior  pyramids  of  the  bulb,  and  thence  to 
the  cerebellum,  by  the  inferior  peduncles.  They  connect  the  cells  of  the 
posterior  cornua  of  gray  matter  with  the  cerebellum.  These  columns 
make  their  appearance  first  in  the  lumbar  region  of  the  cord,  and  they 
increase  in  size  from  below  upward.  After  section  of  the  spinal  cord, 
the  fibres  of  the  direct  cerebellar  fasciculi  show  ascending  secondary 
degenerations.  Their  trophic  centres  probably  are  the  cells  of  the  pos- 
terior cornua  of  gray  matter. 

7.  Colnvins  of  Bnrdach  {Posterior  Lateral  Columns).  —  These  col- 
umns are  in  the  posterior  portion  of  the  cord,  between  the  columns  of 
Goll  and  the  posterior  cornua  of  gray  matter.  Their  fibres  connect 
certain  of  the  cells  of  the  gray  matter  of  the  posterior  cornua  with  the 
cerebellum  ;  or  at  least  the  fibres  pass  upward  and  are  connected  with 
the  restiform  bodies,  going  to  the  cerebellum  through  the  inferior  pe- 
duncles.    The  fibres  also  connect  nerve-cells  in  different  planes  of  the 


552 


NERVOUS    SYSTEM 


cord  with  each  other.  A  certain  number  of  ascending  secondary  de- 
generations has  been  noted  in  these  cohimns. 

8.  Columns  of  Goll  {^Posterior  Median  Coliivins).  —  These  delicate 
columns  are  situated  on  either  side  of  the  posterior  median  fissure. 
They  are  lost  in  the  lower  dorsal  region.  Their  fibres  pass  upward 
and  pass  into  the  funiculi  graciles  of  the  bulb.  After  section  of 
the  cord,  ascending  secondary  degenerations  are  observed  in  these 
columns. 

In  addition  to  these,  which  are  the  principal  columns  of  the  cord, 
anatomists  have  described  a  tract  called  Gower's  tract,  lying  between 
the  ascending  and  descending  cerebellar,  the  lateral  bundles  and  the 
crossed   pyramidal   tracts,   Clarke's  columns,  lying  next  the   posterior 


Fig.  133.  —  Diagram  of  the  columns  and  conducting  paths  of  the  spinal  cord  in  the  upper  dorsalregion. 

median  fissure  and  the  gray  commissure  and  limited  mainly  to  the 
dorsal  region,  and  the  tract  of  Lissauer,  lying  externally  to  the  posterior 
extremity  of  the  posterior  cornu  of  gray  matter.  Gower's  tract  passes 
to  the  bulb  by  the  periphery  of  the  anterior  pyramids  and  is  thought 
by  some  physiologists  to  contain  nerves  of  pain  and  nerves  of  tempera- 
ture, but  the  properties  of  these  columns  are  not  very  distinctly  defined. 
It  is  stated  that  the  cells  which  form  the  nucleus  of  the  pneumogastric 
in  the  bulb  are  similar  to  those  found  in  Clarke's  columns.  It  is  not 
known  that  the  fibres  of  the  tract  of  Lissauer  pass  to  the  bulb.  It 
would  seem  that  a  description  of  eight  principal  columns  renders  the 
•anatomy  of  the  cord  sufficiently  complex  without  subdividing  them  into 
fasciculi  that  are  not  as  yet  known  to  have  any  special  physiological 
significance.      Still,  degenerations  attacking  these  smaller  tracts  have 


THE    SPINAL   CORD  553 

been  observed  and  studied,  but  without  developing  distinct  and  positive 
physiological  applications. 

Directions  of  Nerve-fibres  in  the  Cord.  —  Many  of  the  points  in  the 
description  of  the  course  and  connections  of  the  fibres  in  the  cord  are 
given  as  probable.  Anatomical  observations  have  been  somewhat  con- 
tradictory, but  many  of  these  have  been  corrected  or  verified  by  follow- 
ing the  paths  of  degeneration.  What  are  called  secondary  degenerations 
are  anatomical  changes  in  the  nerve-fibres  which  follow  separation  of 
the  fibres  from  the  cells  which  act  as  their  trophic  centres,  or  the 
centres  presiding  over  their  nutrition,  these  changes  being  secondary  to 
destruction  or  degeneration  of  the  centres. 

The  fi,bres  of  the  anterior  roots  of  the  spinal  nerves,  following  these 
fibres  inward  and  upward,  pass  to  the  large  multipolar  motor  cells  of 
the  anterior  cornua  of  gray  matter  and  have  no  direct  connection  with 
the  white  columns.  Their  direction  through  the  white  columns  of  the 
cord  is  oblique  and  slightly  upward.  Surrounding  the  nerve-cells  are 
arborescent  fibrils  (synapses)  connected  with  the  fibres  that  pass  up 
the  cord  in  two  bundles,  median  and  lateral.  So  far  as  conduction  is 
concerned,  these  fibres  may  be  regarded  as  continuous  with  the  fibres 
of  the  anterior  roots.  The  fibres  of  the  median  bundle  pass  to  the  an- 
terior white  commissure,  in  which  they  decussate.  The  bundles  then 
go  each  one  to  the  column  of  Tiirck  on  the  opposite  side  and  pass  up- 
ward in  the  so-called  direct  pyramidal  tracts.  The  fibres  of  the  lateral 
bundle  go  to  the  crossed  pyramidal  tract  in  the  lateral  column  of  the 
same  side  and  pass  upward  to  decussate  at  the  bulb. 

The  fibres  of  the  columns  of  Tiirck  and  the  crossed  pyramidal 
tracts  are  the  only  fibres  of  the  cord  that  are  known  to  convey  motor 
impulses  from  the  brain.  Destruction  of  certain  parts  of  the  brain 
produces  descending  secondary  degenerations  in  these  fibres. 

It  is  probable  that  fibres  arise  from  the  cells  of  the  gray  matter  of 
the  cord,  which  connect  these  cells  with  each  other  by  means  of  synap- 
ses and  are  concerned  in  certain  reflex  phenomena  involving  the  action 
of  the  cord  alone.  These  fibres  are  in  the  anterior  fundamental  fascic- 
uli, the  anterior  ground  columns  and  the  lateral  bundle.  They  present 
no  secondary  degenerations. 

The  fibres  of  the  posterior  roots  of  the  spinal  nerves  pass  into  the 
white  substance  of  the  cord,  where  they  immediately  bifurcate,  one 
limb  passing  downward  and  the  other  upward  for  a  certain  distance, 
before  they  enter  the  gray  matter.  The  upper  limb  of  the  bifurcation 
is  the  longer.  In  their  course  they  send  off  collateral  branches  which 
penetrate  the  gray  matter  and  break  up  into  arborescent  fibrils  (synap- 
ses).    These  mingle  and  interlace  with  similar  aborescent  fibrils  from 


554 


NERVOUS    SYSTEM 


the  cell-bodies,  the  connection  between  them,  however,  being  indirect 
and  not  directly  continuous.  Some  neurites  from  the  posterior  roots 
possibly  are  directly  continuous  with  neurites  from  the  cell-bodies. 

It  is  probable  that  fibres  pass  from  the  cell-bodies  and  go  to  the  cerebel- 
lum in  the  direct  cerebellar  fasciculi,  the  columns  of  Goll  and  the  ascend- 
ing cerebellar  fasciculi,  which  show  ascending  secondary  degenerations. 

Certain  fibres  from  the  posterior  roots  of  the  spinal  nerves  pass  to  the 
cells  of  the  posterior  cornua  of  gray  matter  of  the  cord  and  are  con- 
nected by  arborizing  processes  with  arborizing  prolongations  of  these 
cells  (synapses).  Processes  from  these  cells  pass  to  the  gray  commis- 
sure and  decussate  around  the  central  canal,  conducting  sensory  im- 
pressions to  the  brain  in  the  gray  matter  of  the  opposite  side  of  the 
cord.  The  sensory  conductors,  therefore,  decussate  all  along  the  cord. 
Fibres  originating  in  the  nerve-cells  of  the  posterior  cornua  pass  in 
and  out,  along  the  cord,  and  their  synapses  connect  the  cells  with  each 
other  above  and  below.  These  may  properly  be  called  longitudinal 
commissural  fibres.  They  probably  constitute  the  greatest  part  of  the 
columns  of  Burdach. 

General  Properties  of  the  Spinal  Cord 

In  describing  the  general  properties  of  the  cord,  as  shown  by  the 
effects  of  stimulus  applied  to  its  exterior  or  to  its  cut  surface,  the 
term  "excitability"  will  be  used  to  express  a  property  indicated  by  direct 
muscular  contraction  following  stimulation  of  the  cord,  and  sensibility, 
a  property  which  enables  it  to  receive  impressions  which  produce  pain. 
In  exciting  different  parts  of  the  cord  with  electricity,  it  is  necessary  to 
guard  carefully  against  an  extension  of  the  current  beyond  the  points 
which  it  is  intended  to  stimulate.  Some  physiologists  regard  the  cord 
as  inexcitable  and  insensible,  both  on  its  surface  and  in  its  deeper  por- 
tions. With  this  view,  it  is  supposed  that  parts  of  the  cord  will  con- 
duct motor  impulses  received  from  the  centres  situated  above  but  are 
not  excited  by  a  stimulus  applied  directly.  In  the  same  way,  it  is 
thought,  parts  of  the  cord  will  convey  sensory  impressions  received 
through  the  nerves  but  are  insensible  to  direct  irritation.  Certain  of 
the  columns,  however,  react  under  direct  stimulation. 

In  experiments  made  in  1863  (Flint)  on  a  living  dog,  the  cord 
having  been  exposed  in  the  lumbar  region  and  stimulated  mechani- 
cally and  with  an  electric  current  two  hours  after  the  operation,  certain 
positive  results  were  obtained  which  led  to  the  following  conclusions  :  — 

The  gray  substance  probably  is  inexcitable  and  insensible  to  direct 
stimulation. 


THE    SPINAL   CORD  555 

The  antero-lateral  columns  are  insensible,  but  are  excitable  both  on 
the  surface  and  in  their  substance ;  and  direct  stimulation  of  these 
columns  produces  convulsive  movements  in  certain  muscles,  which 
movements  are  not  reflex  and  are  not  attended  with  pain.  The  lateral 
columns  are  less  excitable  than  the  anterior  columns. 

The  surface,  at  least,  of   the    posterior  columns    is  very  sensitive 
especially  near  the  posterior  roots  of  the  nerves.     The  deep  portion 
of  the  posterior  columns  are  probably  insensible  except  very  near  the 
origin  of  the  nerves. 

The  above  conclusions  refer  only  to  the  general  properties  of  dif- 
ferent portions  of  the  cord,  as  shown  by  direct  stimulation,  in  the 
same  way  that  the  general  properties  of  the  nerves  in  their  course 
are  demonstrated. 

Motor  Paths  in  the  Cord.  —  What  has  been  said  regarding  the 
direction  of  the  fibres  in  the  cord  and  the  situation  and  course  of  the 
degenerations  following  destruction  of  motor  centres  conveys  a  definite 
idea  of  the  motor  paths  in  the  cord.  This  idea  is  sustained  by  experi- 
ments in  which  different  columns  of  the  cord  have  been  divided  in  living 
animals. 

The  motor  paths  are  in  the  direct  pyramidal  tracts  (columns  of 
Tiirck)  and  in  the  crossed  pyramidal  tracts  of  the  lateral  columns. 
The  motor  impulses  are  conveyed  by  the  fibres  of  these  tracts  to  the 
multipolar  cells  in  the  anterior  cornua  of  gray  matter  and  are  thence 
transmitted  to  the  anterior  roots  of  certain  spinal  nerves.  In  the  lower 
dorsal  region  the  conduction  is  confined  to  the  crossed  pyramidal  tracts 
in  the  lateral  columns,  while  above,  the  direct  pyramidal  tracts  partici- 
pate in  this  action. 

The  motor  fibres  decussate  in  the  anterior  pyramids  of  the  bulb 
(crossed  pyramidal  tracts),  and  in  the  cervical  region  to  a  compara- 
tively slight  extent,  before  the  direct  pyramidal  tracts  (columns  of 
Tiirck)  pass  to  the  encephalon.  In  the  cervical  region  the  decussa- 
tion takes  place  probably  in  the  anterior  white  commissure.  The  fact 
of  this  decussation  of  motor  conductors  is  sustained  by  pathology  — 
paralysis  of  motion  following  brain-lesions,  occurring  on  the  opposite 
side  of  the  body  —  and  by  experiments  in  which  the  fibres  as  they 
cross  are  divided  by  a  longitudinal  median  section  in  the  bulb  and  in 
the  cervical  region  of  the  cord. 

Vasomotor  nerve-fibres  exist  in  the  lateral  columns  of  the  cord  and 
probably  are  connected  with  the  cells  of  the  gray  matter.  They  pass 
out  in  the  anterior  roots  of  the  spinal  nerves  and  go  to  the  bloodvessels 
either  from  the  branches  of  the  spinal  nerves  directly  or  through  fila- 
ments sent  to  the  sympathetic. 


556  NERVOUS    SYSTEM 

Sensory  Paths  in  the  Cord.  —  The  gray  matter  of  the  cord  is  the 
part  concerned  in  the  conduction  of  sensory  impressions.  This  fact  has 
been  verified  by  recent  experiments ;  but  it  is  thought  that  some  of  the 
sensory  conductors  run  in  the  columns  of  Goll.  The  cokimns  of  Goll, 
however,  exist  only  in  the  cervical  and  upper  dorsal  regions. 

The  sensory  conductors  do  not  decussate  at  any  particular  point  as 
do  the  motor  conductors  in  the  crossed  pyramidal  tracts.  The  fibres 
from  the  posterior  roots  of  the  spinal  nerves  pass  to  the  sensory  cells 
of  the  posterior  cornua  and  decussate  throughout  the  length  of  the 
cord.  If  the  cord  is  divided  longitudinally  in  the  median  line,  there  is 
complete  paralysis  of  sensation  on  both  sides  in  all  parts  below  the  sec- 
tion. In  this  section,  the  only  fibres  that  are  divided  are  those  passing 
from  one  side  of  the  cord  to  the  other.  This  decussation  is  by  fibres 
prolonged  from  the  cells  of  the  posterior  cornua,  which  cross  in  the 
gray  commissure,  around  the  central  canal. 

When  one  lateral  half  of  the  cord  is  divided  in  a  living  animal,  sen- 
sibility is  impaired  or  lost  on  the  opposite  side  of  the  body  below  the 
section,  but  there  is  hyperesthesia  on  the  side  corresponding  to  the 
section.  This  exaggeration  of  sensibility  has  not  been  satisfactorily 
explained. 

Conduction  tJirongJi  Synapses.  —  Repeated  reference  has  already 
been  made  to  the  so-called  synapses  that  connect  nerve-fibres  with  nerve- 
cells.  The  cell-bodies,  as  has  been  seen,  present  each  an  axis-cylin- 
der prolongation,  the  neurite,  and  branching,  or  arborizing  processes, 
called  dendrites.  In  the  theory  of  the  transmission  of  nerve-impulses 
or  of  centripetal  currents  through  synapses,  it  is  assumed  that  the  con- 
ducting neurite,  when  it  reaches  a  cell-body,  branches  and  arborizes 
around  the  cell,  its  branchings  interlacing  with  branchi-ng  dendrites,  but 
without  direct  connection  of  filaments.  This  is  called  a  synapse  —  from 
crvvoLTrToii,  to  join  together.  Following  out  an  impulse  from  a  motor  area 
in  the  cerebral  cortex  to  a  muscle,  it  evidently  must  pass  through  several 
collections  of  cells,  notably  in  the  corpus  striatum,  the  pons  and  the 
multipolar  cells  on  the  opposite  side  of  the  cord.  Each  synapse  has 
been  compared  to  a  relay-station  ;  and  the  passage  of  the  impulse,  which 
is  taken  up  by  the  cells  and  conveyed  onward  by  its  neurite,  involves  a 
delay  which,  in  the  frog,  is  about  0.002  of  a  second.  In  afferent  conduc- 
tion the  mechanism  of  transmission  of  impressions  is  nearly  the  same. 
In  reflex  action  involving  the  cord  only,  arborizing  filaments  from  the 
afferent  nerve-roots  form  synapses  with  the  dendrites  of  the  motor  cells 
and  impulses  are  sent  from  these  cells  to  muscles.  It  is  thought,  also, 
that  synapses  exist  in  the  ganglia  of  the  sympathetic  system  in  the 
motor  paths  of  conduction  to  non-striated  muscles.     The  same  mechan- 


THE    SPINAL   CORD  557 

ism  is  supposed  to  exist  when  different  areas  in  the  central  nervous 
system  are  connected  by  commissural,  or  association  fibres.  The  bipolar 
cells  of  the  ganglia  on  the  posterior  roots  of  the  spinal  nerves  and  of 
the  sensory  cranial  nerves,  however,  seem  to  be  merely  enlargements  in 
the  course  of  the  nerve-fibres. 

According  to  this  theory  of  nerve-conduction,  impulses  are  taken  up 
by  the  dendrites  of  the  nerve-cells  and  transmitted  onward  through  their 
neurites ;  and  this  may  involve  the  passage  of  the  current  through  a 
number  of  so-called  cell-stations.  The  cells  send  out  impulses  through 
their  neurites  and  receive  them  through  the  dendrites,  the  same  mechan- 
ism existing  for  both  centripetal  and  centrifugal  conduction,  and  "  de- 
lays "  always  occurring  at  the  cell-stations.  The  current,  therefore,  can 
move  only  in  one  direction,  this  depending  on  the  arrangement  of  the 
arborizations  of  the  neurites  and  of  the  dendrites.  Finally,  therefore, 
the  sensory  cells  of  the  cerebral  cortex  receive  impressions  through 
their  dendrites.  If  it  is  assumed  that  neurites  in  their  course  may  con- 
duct in  both  directions,  —  and  some  experiments  favor  this  view,  —  as  a 
logical  consequence  the  synapses  must  act  as  valves ;  so  that  a  centrifu- 
gal current  can  not  pass  in  the  opposite  direction  beyond  a  synapse, 
the  same  being  true  of  a  centripetal  current. 

While  the  theory  of  the  action  of  synapses  explains  many  heretofore 
obscure  phenomena  of  nerve-conduction  and  is  extremely  probable,  it 
should  be  received  as  such  and  not  as  a  matter  of  positive  and  absolute 
demonstration.  There  are  certain  properties  and  functions  of  nerve- 
cells,  connected  with  trophic  action,  degenerations  and  associations  of 
nerve-centres,  that  still  are  imperfectly  understood. 

Relations  of  the  Posterior  White  Cohivms  of  the  Cord  to  MiLSCtdar 
Coordination.  —  It  was  noticed  by  Todd,  many  years  ago  (i 839-1 847), 
in  cases  of  that  peculiar  form  of  muscular  incoordination  now  known  as 
locomotor  ataxia,  that  the  posterior  white  columns  of  the  cord  were 
diseased.  Reasoning  from  this  fact,  Todd  made  the  following  state- 
ment in  regard  to  the  office  of  these  columns :  — 

"  I  have  long  been  impressed  with  the  opinion,  that  the  office  of  the 
posterior  columns  of  the  spinal  cord  is  very  different  from  any  yet 
assigned  to  them.  They  may  be  in  part  commissural  between  the  sev- 
eral segments  of  the  cord,  serving  to  unite  them  and  harmonize  them 
in  their  various  actions,  and  in  part  subservient  to  the  function  of  the 
cerebellum  in  regulating  and  coordinating  the  movements  necessary  for 
perfect  locomotion." 

The  view  thus  early  advanced  by  Todd  has  been  sustained  by  experi- 
ments on  living  animals.  If  the  posterior  columns  are  completely  divided 
by  two  or  three  sections  made  at  intervals  of  about  three-fourths  of  an 


558  NERVOUS   SYSTEM 

inch  to  an  inch  and  a  quarter  (20  to  30  millimeters),  the  most  prominent 
effect  is  a  remarkable  trouble  in  locomotion,  consisting  in  a  want  of 
proper  coordination  of  movements.  Experiments  on  the  different 
columns  of  the  cord  in  living  animals,  however,  are  so  difficult  that 
physiologists  have  preferred  to  take  the  observations  in  cases  of  disease 
in  the  human  subject  as  the  basis  of  their  ideas  in  regard  to  the  office 
of  the  posterior  white  columns. 

The  characteristic  phenomenon  of  locomotor  ataxia  is  inability  to 
coordinate  muscular  movements,  particularly  those  of  the  extremities. 
There  is  not  of  necessity  any  impairment  of  actual  muscular  power; 
and  although  pain  and  more  or  less  disturbance  of  sensibility  are  usual, 
these  conditions  are  not  invariable  and  they  are  always  coincident  with 
disease  of  sensory  conductors.  The  characteristic  pathological  condi- 
tion is  disease  of  the  posterior  white  columns  (columns  of  Burdach). 
This  usually  is  followed  by  or  is  coexistent  with  disease  of  the  posterior 
roots  of  the  spinal  nerves  and  disease  of  the  cells  of  the  posterior  gray 
matter  of  the  cord.  As  the  cells  are  affected,  there  follow  ascending 
secondary  degenerations  in  the  columns  of  Goll.  It  is  fair  to  assume 
that  the  disease  of  the  cells  of  the  gray  matter  of  the  cord  and  of  the 
posterior  roots  of  the  spinal  nerves  is  connected  with  the  disorders  of 
general  sensibility.  The  disease  of  the  columns  of  Burdach  produces 
the  disorder  in  movements. 

Reasoning  from  the  characteristic  phenomena  and  the  essential 
pathological  conditions  of  the  cord  in  typical  cases  of  locomotor  ataxia, 
the  posterior  white  columns  of  the  cord,  connecting  cells  of  the  gray 
matter  in  different  planes  with  each  other,  assist  in  regulating  and 
coordinating  the  voluntary  movements.  The  fibres  of  these  columns 
also  connect  the  cord  with  the  cerebellum,  which  has  an  important  office 
in  muscular  coordination.  It  is  probable  that  the  appreciation  of  the 
muscular  sense  and  the  sense  of  pressure,  if  these  can  be  separated  from 
what  is  known  as  general  sensibility,  are  connected  with  the  action  of 
the  fibres  of  the  posterior  white  columns. 

Nerve-centres  in  the  Spinal  Cord 

It  has  long  been  known  that  decapitation  of  animals  does  not  arrest 
muscular  action ;  and  the  movements  observed  after  this  mutilation 
present  a  certain  degree  of  regularity  and  have  been  shown  to  be  in 
accordance  with  well-defined  laws.  Under  these  conditions,  the  regula- 
tion of  such  movements  is  effected  through  the  spinal  cord  and  the  spinal 
nerves.  If  an  animal  is  decapitated,  leaving  only  the  cord  and  its  nerves, 
there  is  no  sensation,  for  the  parts  capable  of  appreciating  sensation  are 


NERVE-CENTRES    IN    THE   SPINAL   CORD  559 

absent ;  nor  are  there  any  true  voluntary  movements,  as  the  organ  of 
the  will  is  destroyed.  Still,  in  decapitated  animals,  the  sensory  nerves 
are  for  a  time  capable  of  conducting  impressions,  and  the  motor  nerves 
can  transmit  impulses  to  the  muscles ;  but  the  only  part  capable  of 
receiving  impressions  or  of  generating  motor  impulses  is  the  gray  mat- 
ter of  the  cord.  If,  in  addition  to  the  removal  of  all  the  encephalic 
ganglia,  the  cord  itself  is  destroyed,  all  muscular  movements  are  abolished, 
except  as  they  may  be  produced  by  direct  stimulation  of  the  muscular 
tissue  or  of  individual  motor  nerves. 

The  gray  matter  of  the  brain  and  spinal  cord  is  a  connected  chain  of 
ganglia,  capable  of  receiving  impressions  through  the  sensory  nerves 
and  of  generating  motor  impulses.  The  cerebro-spinal  axis,  taken  as 
a  whole,  has  this  general  office ;  but  some  parts  have  separate  and 
distinct  properties  and  can  act  independently  of  the  others.  The  cord, 
acting  as  a  conductor,  connects  the  brain  with  the  parts  to  which  the 
spinal  nerves  are  distributed.  If  the  cord  is  separated  from  the  brain 
in  a  living  animal,  it  may  act  as  a  centre  independently  of  the  brain  ;  but 
the  encephalon  has  no  communication  with  the  parts  supplied  with 
nerves  from  the  cord,  and  it  can  act  only  on  the  parts  which  receive 
nerves  from  the  brain  itself. 

When  the  cord  is  separated  from  the  encephalon,  an  impression 
made  on  the  general  sensory  nerves  is  conveyed  to  its  gray  substance, 
and  this  gives  rise  to  a  stimulus,  which  is  transmitted  to  the  voluntary 
muscles,  producing  certain  movements  that  are  independent  of  sensa- 
tion and  volition.  This  impression  is  said  to  be  reflected  back  from  the 
cord  through  the  motor  nerves ;  and  the  movements  occurring  under 
these  conditions  are  called  reflex.  As  they  are  movements  excited  by 
stimulation  of  sensory  nerves,  they  are  sometimes  called  excitomotor. 

The  term  "  reflex,"  as  it  is  now  generally  understood,  may  properly  be 
applied  to  any  generation  of  impulses  that  occurs  as  a  consequence  of 
an  impression  received  by  a  nerve-centre  ;  and  it  is  evident  that  reflex 
phenomena  are  by  no  means  confined  to  the  action  of  the  spinal  cord. 
The  movements  of  the  iris  are  reflex,  and  yet  they  take  place  in  many 
instances  without  the  intervention  of  the  cord.  Movements  of  the 
intestines  and  of  the  involuntary  muscles  usually  are  reflex,  and  they 
involve  the  action  of  the  sympathetic  system  of  nerves.  Impressions 
made  on  the  nerves  of  special  sense,  as  those  of  smell,  sight,  hearing, 
etc.,  give  rise  to  certain  trains  of  thought.  These  involve  the  action  of 
the  brain,  but  still  they  are  reflex.  In  this  last  example  of  reflex  action, 
it  sometimes  is  difficult  to  connect  the  operations  of  the  mind  with 
external  impressions  as  an  exciting  cause ;  but  it  is  evident,  on  a  little 
reflection,  that  this  often  occurs. 


56o  NERVOUS    SYSTEM 

Reflex  Action  of  the  Spinal  Cord.  —  Simple  reflex  action  involves  the 
existence  of  an  afferent  (sensory)  nerve,  a  collection  of  nerve-cells,  and 
an  efferent  (motor)  nerve,  the  nerves  being  connected  with  the  nerve- 
cells.  In  a  decapitated  animal,  not  only  are  the  movements  independent 
of  sensation  and  volition,  but  no  movements  occur  if  the  sensory  nerves 
are  protected  from  any  kind  of  impression  or  stimulation  (Marshall  Hall, 
1832  and  1833).  If  the  cord  is  destroyed,  however,  no  movements 
follow  stimulation  of  the  surface ;  and  if  either  the  afferent  or  the 
efferent  nerves  are  divided,  no  reflex  movements  can  take  place.  Experi- 
ments on  decapitated  animals  are  in  accord  with  the  results  of  observa- 
tions on  acephalous  foetuses  and  cases  of  complete  paraplegia  from 
injury  to  the  cord. 

In  the  simplest  form  of  a  reflex  movement,  the  muscular  contraction 
is  confined  to  the  muscle  or  muscles  which  correspond,  in  their  nervous 
supply,  to  the  afferent  nerve  stimulated ;  but  when  the  stimulus  is 
sufficiently  powerful  or  when  the  cord  is  in  a  condition  of  exaggerated 
excitability,  the  impression  is  disseminated  throughout  the  gray  matter, 
and  the  entire  muscular  system  may  be  thrown  into  action.  With  feebler 
stimulation,  one  side  only  of  the  muscular  system  may  respond.  When 
the  reaction  extends  to  the  opposite  side,  it  is  called  crossed  reflex.  The 
extension  of  a  stimulus  conveyed  by  a  single  afferent  nerve  throughout 
the  cord  is  called  irradiation. 

When  a  feeble  stimulus  apphed  to  an  afferent  nerve  is  repeated 
frequently  and  at  short  intervals,  general  muscular  movements  are  pro- 
duced. This  follows  stimuli  applied  three  times  in  a  second,  and  the 
effect  is  increased  up  to  sixteen  shocks  in  a  second,  but  not  beyond  this 
number  (Rosenthal). 

In  studying  the  paths  of  conduction  in  the  cord,  it  has  been  seen 
that  sensory  conduction  takes  place  through  the  gray  matter  and  pos- 
sibly through  the  columns  of  Goll,  that  motor  impulses  are  conducted 
by  the  direct  and  the  crossed  pyramidal  tracts,  and  that  the  columns  of 
Burdach  probably  are  connected  with  muscular  coordination.  The  fibres 
of  the  cord  that  are  specially  concerned  in  reflex  action  probably  are  in 
the  anterior  ground  columns  and  the  lateral  bundles. 

It  is  well  known  that  the  reflex  excitability  of  the  cord  is  exaggerated 
by  removal  of  the  encephalon.  According  to  Setschenow,  certain  parts 
in  the  encephalon,  particularly  the  optic  lobes  in  frogs,  exert  an  inhibi- 
tory influence  over  the  reflex  acts  of  the  cord,  and  as  a  consequence, 
reflex  phenomena  are  more  marked  when  this  influence  has  been 
removed. 

Certain  poisons,  especially  strychnin,  have  a  remarkable  influence 
over   reflex   excitability.      In    a    frog    decapitated    and    poisoned    with 


REFLEX    ACTION    OF   THE    SPINAL   CORD  56 1 

Strychnin,  no  reflex  movements  occur  unless  an  impression  is  made  on 
the  sensory  nerves  ;  but  a  slight  irritation,  such  as  a  current  of  air,  throws 
the  entire  muscular  system  into  a  condition  of  violent  tetanic  spasm.  The 
same  phenomena  are  observed  in  cases  of  poisoning  with  strychnin  or  of 
tetanus  in  the  human  subject. 

The  inhalation  of  anesthetic  agents  may  abolish  all  the  ordinary 
reflex  phenomena.  Whether  this  be  due  to  an  action  on  the  cord 
itself  or  to  a  paralysis  of  the  sensory  nerves,  it  is  difficult  to  determine. 
Ordinarily,  in  animals  rendered  insensible  by  anesthetics,  the  movements 
of  respiration  continue;  but  these  also  may  be  arrested,  as  has  been  ob- 
served by  all  who  have  experimented  with  anesthetics,  especially  with 
chloroform.  A  common  way  of  determining  that  an  animal  is  completely 
under  the  influence  of  an  anesthetic  is  by  noting  an  absence  of  the  reflex 
act  of  closing  the  eyelids  when  the  cornea  is  touched. 

It  is  necessary,  after  what  has  gone  before,  only  to  indicate  in  a 
general  way  certain  phenomena  observed  in  the  human  subject,  which 
illustrate  the  reflex  action  of  the  cord.  It  is  a  common  observation,  in 
cases  of  paraplegia  in  which  the  lower  portion  of  the  cord  is  intact,  that 
movements  of  the  limbs  follow  titillation  of  the  soles  of  the  feet,  these 
movements  taking  place  independently  of  the  consciousness  or  the 
will  of  the  subject  experimented  on.  Acephalous  monsters  will  present 
general  reflex  movements  and  movements  of  respiration  and  will  even 
suck  when  the  finger  is  introduced  into  the  mouth.  Observations  of 
this  kind  are  so  familiar  that  they  need  not  be  cited  in  detail.  Experi- 
ments have  also  been  made  on  criminals  after  decapitation  ;  and  although 
the  reflex  phenomena  are  not  so  well  marked  and  can  not  be  excited  so 
long  after  death  as  in  cold-blooded  animals,  they  are  sufficiently  distinct. 

General  muscular  spasms  following  stimulation  of  sensory  nerves  are 
pathological  and  take  place  only  when  the  reflex  excitability  of  the  cord 
is  exaggerated.  Examples  of  this  action  are  the  spasms  observed  in 
tetanus  or  in  poisoning  by  strychnin.  In  experiments  on  the  lower 
animals,  particularly  frogs,  coordinate  reflex  movements  are  often  ob- 
served, such  as  the  movements  of  jumping  or  swimming.  This  is  some- 
times called  purposive  reflex  action,  as  the  movements  seem  to  have 
a  definite  purpose,  or  object.  The  following  well-known  experiment 
illustrates  a  coordinate,   or  purposive  reflex. 

Pfliiger  removed  the  entire  encephalon  from  a  frog,  leaving  only  the 
spinal  cord.  He  then  touched  the  surface  of  the  thigh  over  the  inner 
condyle  with  acetic  acid.  The  animal  thereupon  rubbed  the  irritated 
surface  with  the  foot  of  the  same  side,  apparently  appreciating  the 
seat  of  the  irritation,  and  endeavoring,  by  a  voluntary  effort,  to  remove 
it.  The  foot  of  this  side  was  then  amputated,  and  the  irritation  was 
20 


562  NERVOUS    SYSTEM 

renewed  in  the  same  place.  The  animal  made  an  ineffectual  effort  to 
reach  the  spot  with  the  amputated  member,  and  failing  in  this,  after 
some  general  movements  of  the  Hmbs,  rubbed  the  spot  with  the  foot  of 
the  opposite  side. 

It  has  been  thought  that  this  experiment  shows  a  persistence  of 
sensation  and  the  power  of  voluntary  movements  after  removal  of  the 
entire  encephalon  ;  but  it  must  be  remembered  that  the  cord  contains 
cells  collected  probably  into  groups  that  correspond  to  sets  of  muscles 
concerned  in  coordinate  movements,  and  that  many  movements  set  in 
action  by  an  effort  of  the  will  continue  in  an  automatic  manner,  as  the 
ordinarv  movements  of  progression.  It  is  more  reasonable  to  suppose 
that  a  persistent  stimulation  of  the  surface,  such  as  is  produced  by  the 
action  of  acetic  acid  on  the  skin  of  a  frog,  can  give  rise  to  coordinate 
movements  of  a  purely  reflex  character  than  to  assume  that  the  move- 
ments in  Pfliiger's  experiment  were  voluntary  efforts  to  remove  a  painful 
impression.  It  is  certain  that  in  the  higher  classes  of  animals  after  re- 
moval of  the  encephalon,  —  in  experiments  on  decapitated  criminals  and 
in  patients  suffering  from  paraplegia,  — there  is  no  evidence  of  centres 
of  true  sensation  or  volition  in  the  spinal  cord.  In  man  and  the  higher 
animals,  all  muscular  movements  that  depend  solely  on  the  reflex  action 
of  the  cord  must  be  regarded  as  automatic  and  independent  of  con- 
sciousness and  volition. 

Some  of  the  confusion  in  regard  to  the  precise  nervous  mechanism 
of  many  movements  executed  by  the  adult  man  may  be  removed  by 
an  exact  comprehension  of  the  terms  used  in  their  description.  There 
are  certain  movements  that  are  entirely  independent  of  sensation  and 
volition  and  of  practice  and  education.  Such  are  the  movements  of 
the  lower  extremities  in  paraplegia,  movements  of  the  stomach  and 
intestines  and  the  movements  of  tranquil  respiration.  These  may  be 
called  purely  reflex,  depending  entirely  on  the  action  of  the  cord  or  the 
bulb.  So-called  purposive  movements  may  be  included  in  this  category, 
at  least  when  they  occur  in  such  instances  as  that  of  the  brainless  frog 
that  swims  or  jumps.  The  nerve-impulses  there  may  be  assumed  to  be 
conducted  along  constant  and  habitual  paths  in  the  cord.  Another 
class  of  movements,  that  has  its  highest  illustration  in  man,  embraces 
those  that  are  habitual  or  highly  skilled.  These  may  be  called  auto- 
matic. They  may  be  initiated  by  an  effort  of  the  will  but  continue 
without  further  thought  or  attention.  Such  movements  are  those 
of  walking,  skating,  swimming,  in  certain  instances  playing  on  musical 
instruments  and  doing  mechanical  work.  It  seems  more  reasonable  to 
regard  such  movements  as  due  to  the  action  of  the  spinal  cord  than  to 
invoke  what  has  been  called  "unconscious  cerebration";  for  while  these 


REFLEXES    IX   MAX  563 

movements  are  executed  automatically,  the  brain  may  be  actively  en- 
gaged in  other  directions.  It  must  be  remembered,  however,  that  the 
brain  itself  often  works  automatically,  intelligent  results  occurring 
without  an  appreciation  of  the  mental  processes  by  means  of  which 
they  are  accomplished.  Examples  of  this  kind  of  action  are  often 
afforded  by  remarkable  players  at  chess  or  "  Hghtning  calculators." 

Certain  purely  reflex  movements  may  be  restrained  by  an  effort 
of  the  will,  as  is  well  known ;  provided,  always,  that  these  be  move- 
ments that  can  be  executed  by  voluntary  effort.  Nevertheless,  if  the 
sensory  impression  is  sufficiently  powerful  or  is  frequently  repeated,  it 
often  is  impossible  to  control  such  movements  by  the  will.  ^Movements 
that  are  never  in  themselves  voluntary,  such  as  the  ejaculation  of 
semen,  when  excited  by  reflex  action,  can  not  be  restrained  by  a  vol- 
untary effort;  while  the  reflex  act  of  coughing,  for  example,  may  be 
measurably  controlled.  It  is  hardly  proper  to  speak  of  inhibition  of  the 
reflexes,  in  the  sense  in  which  the  term  "inhibition  "  is  commonly  used 
in  physiology,  for  the  reason  that  probably  there  are  no  special  inhibi- 
tory nerves  for  these  movements. 

Various  reflexes  are  made  use  of  in  pathologv  as  means  of  diagnosis. 
The  superficial  reflexes  are  those  produced  by  tickling  the  soles  of  the 
feet  or  by  exciting  other  parts  of  the  skin.  The  most  prominent  of  the 
deep  reflexes  is  the  patellar  reflex,  or  the  knee-jerk,  produced  by  per- 
cussion of  the  ligamentum  patellae. 

Reflexes  m  Man.  — The  most  important  of  the  superficial  reflexes 
are  the  following  :  — 

Tickling  of  the  soles  of  the  feet  produces  movements  of  the  lower 
extremities.  In  cases  of  paraplegia  in  which  the  properties  of  the  lower 
portion  of  the  cord  are  retained,  the  reflex  movements  produced  by 
tickling  the  soles  of  the  feet  are  often  violent. 

When  the  skin  is  scratched  over  the  gluteus,  the  muscle  is  thrown 
into  contraction. 

Scratching  of  the  skin  on  the  inner  surface  of  the  thigh  produces  re- 
traction of  the  testicle  on  that  side.     This  is  called  the  cremasteric  reflex. 

The  muscles  of  the  abdomen  contract  when  the  skin  is  scratched, 
and  the  same  occurs  with  the  muscles  of  the  back  on  stimulation  of  the 
skin  of  that  part. 

The  deep  reflexes  are  sometimes  called  tendon-reflexes.  The 
"knee-jerk"  is  produced  by  contraction  of  the  quadriceps  following  a 
smart  blow  on  the  tendon  of  the  patella. 

The  "  ankle-clonus  "  is  a  contraction  of  the  gastrocnemius  when  that 
muscle  is  forcibly  put  on  the  stretch  and  maintained  in  this  condition 
for  a  short  time. 


564  NERVOUS    SYSTEM 

Both  the  superficial  and  the  deep  reflexes  often  afford  important  infor- 
mation in  regard  to  diseases  of  the  brain  and  spinal  cord. 

The  gray  matter  of  the  cord  is  not  a  single  centre,  but  consists  of  a 
number  of  centres  connected  with  each  other  and  with  the  brain. 
Some  of  these  have  already  been  described  in  connection  with  the 
history  of  various  physiological  processes,  and  others  will  be  consid- 
ered hereafter  under  appropriate  heads.  In  addition  to  those  already 
described,  are  centres  for  defecation,  at  the  fifth  lumbar  vertebra  in  dogs 
(Budge),  the  erection-centre,  in  the  lumbar  region  (Eckhard),  and  the 
parturition-centre  (Korner),  at  the  first  and  second  lumbar  vertebrae. 
Throughout  the  gray  matter  are  a  number  of  subsidiary  vasomotor  cen- 
tres that  are  subordinate  to  similar  dominant  centres  in  the  bulb.  The 
cord  also  contains  subsidiary  sweat-centres. 


CHAPTER   XXII 

THE    CEREBRUM    AND    THE    BASAL   GANGLIA 

"Weights  of  the  encephalon  and  of  certain  of  its  parts  —  The  cerebral  hemispheres  —  Cerebral 
convolutions  —  Basal  ganglia  —  Corpora  striata,  optic  thalami  and  internal  capsule  — 
Tubercula  quadrigemina  —  Crura  cerebri  —  Pons  Varolii  —  Directions  of  fibres  in  the  cere- 
brum—  Fibres  connecting  the  cerebrum  with  the  cerebellum  —  Fibres  connecting  the  two 
sides  of  the  brain  —  Fibres  connecting  different  cerebral  convolutions  on  the  same  side 
(association  fibres) — Fibres  connecting  the  brain  with  the  spinal  cord  —  Cerebral  locali- 
zation—  Motor  cortical  zone  (Rolandic  area) — General  uses  of  the  cerebrum — Extirpa- 
tion of  the  cerebrum  —  Comparative  development  of  the  cerebrum  in  the  lower  animals  — 
Development  of  the  cerebrum  in  different  races  of  men  and  in  different  individuals  —  Facial 
angle  —  Pathological  observations  —  Reaction-time  —  Centre  for  the  expressions  of  ideas 
in  language. 

The  encephalic  ganglia  are  collections  of  gray  matter  found  in  the 
encephalon,  or  what  is  commonly  known  as  the  brain.  This  part  of  the 
cerebro-spinal  axis  is  contained  in  the  cranial  cavity.  It  is  provided  with 
membranes,  which  are  similar  to  the  membranes  of  the  spinal  cord  and 
have  been  described  in  connection  with  the  cord  and  the  general  arrange- 
ment of  the  cerebro-spinal  axis.  The  gross  anatomical  divisions  of  the 
encephalon  are  the  cerebrum,  cerebellum,  pons  Varolii  and  bulb.  As 
regards  their  physiological  uses,  the  cerebellum,  pons  and  bulb  are  to  a 
certain  extent  subordinate  to  the  cerebrum.  In  treating  of  the  physi- 
ology of  these  parts,  it  will  be  convenient  to  take  up  first  the  cerebrum, 
or  the  cerebral  hemispheres,  with  their  anatomical  and  physiological 
connections  and  their  relations  to  the  other  parts  of  the  encephalon. 

All  parts  of  the  encephalon  that  act  as  nerve-centres  are  more  or  less 
intimately  connected  with  each  other  anatomically,  and  are  finally  con- 
nected, through  the  bulb,  with  the  spinal  cord.  The  exceptions  to  this 
are  the  centres  of  olfaction,  vision,  audition  and  gustation,  which  will  be 
considered  fully  in  connection  with  the  physiology  of  the  special  senses. 
The  spinal  cord,  as  has  been  seen,  is  capable  of  independent  action  as  a 
nerve-centre  or  collection  of  nerve-centres,  also  serving  as  a  means  of 
connection  between  the  brain  and  the  parts  through  the  spinal  nerves. 
The  motor  and  sensory  cranial  nerves  are  directly  connected  with  the 
encephalon. 

A  detailed  anatomical  description  of  the  brain  would  be  out  of  place 
in  this  work,  as  there  are  many  anatomical  parts,  the  exact  physiological 

565 


566 


NERVOUS    SYSTEM 


relations  of  which  are  not  understood  ;  still,  there  are  certain  parts,  which 
will  be  referred  to  by  name,  a  general  knowledge  of  the  arrangement  of 
which  is  necessary.  The  general  relations  of  these  parts  are  shown  in 
Fig.  134,  slightly  reduced  and  modified,  from  Harrison  Allen,  which 
represents  a  vertical  longitudinal  section  of  the  brain  in  the  median 
line. 

As  bearing  on  certain  points  in  the  physiology  of  the  brain,  it  is 
important  to  note  the  weight  of  the  entire  encephalon  and  of  its  great 
divisions. 

fORNIVl    PAR'   ETA  L 

CALLOSO  MARGINAL  SULCUS,  ^^nfFISr^n.    ' I' Wlllllinil 

c 


FISSURE  OFROLANDO 


SEPTUM 
L  U  C  I  D  U  M 


ANTERIOR- 
COMMISSURE 


PINEAL  GLAND. 
CORPORA  QUAORIGEMINA' 


4'"  VENTRICLE 


Fig.  134.  —  Fiew  of  the  structures  displayed  on  the  right  side  of  a  median  longitudinal  section  of  the 

brain  —  semidiagrammatic. 


Weights  of  the  Encephalon  and  of  Certain  of  its  Parts.  —  Most  of  the 
tables  of  weights  of  the  healthy  adult  brain  of  the  Caucasian,  compiled 
by  different  writers,  give  essentially  the  same  figures,  the  differences 
amounting  to  only  one  or  two  ounces  (28.3  or  56.7  grams)  for  the  entire 
encephalon.  The  average  weight  given  by  Quain,  combining  the  tables 
of  Sims,  Clendinning  and  Reid,  is  49^  ounces  (1408.3  grams)  for  the 
male,  and  44  ounces  (1247.4  grams)  for  the  female.  The.  number  of 
male  brains  weighed  was  278,  and  of  female  brains,  191.  In  males  the 
minimum  weight  was  34  ounces  (963.9  grams),  and  the  maximum,  65 
ounces  (1842.7  grams).  In  170  cases  out  of  the  278,  the  weights  ranged 
between  46  and  53- ounces  (1304. i   and   1502.5  grams),  which  maybe 


THE   CEREBRAL    HEMISPHERES 


567 


taken  as  the  average  limits.  In  females  the  minimum  was  31  ounces 
(878.8  grams),  and  the  maximum,  56  ounces  (1587.6  grams^.  In  125 
cases  out  of  the  191,  the  weights  ranged  between  41  and  47  ounces 
( 1 162.3  and   1332.4  grams). 

Quain  assumed,  from  various  researches,  that  in  new-born  infants 
the  brain  weighs  11.65  ounces  (327.8  grams),  for  the  male,  and  10 
ounces  (283.5  grams),  for  the  female.  In  both  sexes,  "  the  weight  of 
the  brain  generally  increases  rapidly  up  to  the  seventh  year,  then  more 
slowly  to  between  sixteen  and  twenty,  and  again  more  slowly  to  between 
thirty-one  and  forty,  at  which  time  it  reaches  its  maximum  point.  Beyond 
that  period,  there  appears  a  slovv^  but  progressive  diminution  in  weight 
of  about  one  ounce  (28.3  grams)  during  each  subsequent  decennial  period  ; 
thus  confirming  the  opinion,  that  the  brain  diminishes  in  advanced  life." 

The  comparative  weights  of  the  several  parts  of  the  encephalon, 
calculated  by  Reid  from  observations  on  the  brains  of  fifty-three  males 
and  thirty-four  females,  between  the  ages  of  twenty-five  and  fifty-five,  are 
as  follows  :  — 


Divisions  of  the  encephalon 


Males 


Average  weight  of  the  cerebrum 

Average  weight  of  the  cerebellum 

Average  weight  of  the  pons  and 

medulla  oblongata     .... 

Average  weight  of  the  entire  en- 
cephalon   


43.98  02.(1247.3  grams) 
5.25  oz.    (148.8  grams) 

0.98  oz.      (28.2  grams) 


38.75  oz.   (1098.6  grams) 
4.76  oz.     (134.9  grams) 

1. 01  oz.       (28.6  grams) 


50.21  oz.  (I423.5grams) 


44.52  oz.  (1262.1  grams) 


The  proportionate  weight  of  the  cerebellum  to  that  of  the  cerebrum, 
in  the  male,  is  as  i  to  81^,  and  in  the  female,  as  i  to  8|  (Quain). 

The  specific  gravity  of  the  whole  encephalon  is  about  1036,  that  of 
the  gray  matter  being  1034,  and  of  the  white,  1040  (Quain). 


The  Cerebral  Hemispheres 

Cortical  Substance.  —  The  surface  of  the  cerebral  hemispheres  is 
marked  with  fissures,  sulci  and  convolutions,  which  serve  to  increase 
the  extent  of  the  gray  substance.  The  sulci  between  the  convolutions 
vary  in  depth  in  different  parts,  the  average  being  about  an  inch  (25.4 
millimeters).  The  gray  matter,  which  is  external  and  follows  the  con- 
volutions, is  ^  to  I  of  an  inch  (2.1  to  3.2  milHmeters)  in  thickness. 
Anatomists  have  described  this  substance  as  existing  in  several  layers, 
but  these  divisions  are  largely  artificial.  In  certain  parts,  however,  par- 
ticularly in  the  posterior  portion  of  the  cerebrum,  the  gray  substance 


568 


NERVOUS    SYSTEM 


is    quite    distinctly  divided   into   two    layers,  by   a  very  delicate    inter- 
mediate layer  of  a  whitish  color. 

Histologists  usually  recognize  four  principal 
layers  in  the  cerebral  cortex.  An  external  (mo- 
lecular) layer ;  a  layer  of  small  pyramidal  cells  ; 
a  layer  of  large  pyramidal  cells  ;  a  layer  of 
stellate  cells. 

1.  The  molecular  (superficial)  layer  presents 
three  kinds  of  cells  lying  beneath  a  layer  of 
neuroglia.  The  external  cells  of  this  layer  are 
small,  and  either  bipolar  or  tripolar,  the  tripolar 
cells  resembling  the  cells 
of  the  posterior  layer  of 
gray  matter  of  the  spinal 
cord.  In  the  deepest  por- 
tion of  this  layer  are  large 
polygonal  cells.  The  neu- 
rites  of  the  cells  of  the 
molecular  layer  have  rela- 
tions with  the  teloden- 
drites  of  the  deeper  layers 
and  with  their  own  teloden- 
drites,  but  these  neurites 
do  not  extend  to  the  white 
matter. 

2.  The  layer  of  small 
cells     is     the 


s  s; 


Fig.  135.  —  Vertical  sec- 
tion of  the  ceiebral  cortex 
(R.  y  Cajal). 


I,  molecular  layer;    2,  the 
layer  of  small  pyramidal  cells; 
3,    layer    of    large    pyramidal 
cells;  4,  layer  of  large  stellate    nyramidal 
cells;  5,  white  substance.  -^ 

most  important  and  the 
thickest  of  the  three.  These  cells  present  one 
bifurcating  neurite  and  many  dendrites  and  col- 
laterals. This  layer  also  contains  a  few  large 
pyramidal  cells,  with  neurites,  dendrites,  teloneu- 
rites  and  telodendrites. 

3.  The     layer     of     large     pyramidal     cells    has     molecular  layer  of  the  cerebral 
1  1  r      ,  1,         r     ,  cortex  (R.y  Cajal). 

the  same  arrangement  as  that  of  the  cells  of  the 

A,  C,  small  spindle-shaped 

second  layer.    This  layer  also  contains  a  few  small    cells;  b,  small  stellate  cell; 
pyramidal  cells.     The  second  and  third  layers  are    ^'  l^'s^  ''^"^'^  ''^"'  ''  '' 

^  ■'  J  neurites. 

not  very  easily  separable  from  each  other. 

4.  This  layer  presents  rather  large  stellate  cells,  with  neurites,  den- 
drites and  collaterals.^ 

^  Some  histologists  describe  five  layers  in  the  cerebral  cortex,  adding  to  the  four  layers 
described  above,  a  layer  external  to  the  molecular  layer;  but  this  layer  is  composed  largely  of 
neuroglia  and  does  not  contain  nerve-cells. 


THE    CEREBRAL   CORTEX 


569 


It  may  be  said  in  general  terms  that  the  more  superficial  cells  of  the 
cerebral  cortex  are  small  and  the  deeper  cells  are  larger.  The  neurites 
of  the  molecular  layer  do  not  pass  to  the  white  matter.  The  neurites  of 
the  three  deeper  layers  extend  downward  into  the  white  matter.  The 
dendrites  and  telodendrites  pass,  some  upward  to  the  molecular  layer, 
and  some  to  interlace  with  each  other. 


Fig.    137.  —  Diagrammatic   section   tkrotigk   the 
cerebral  cortex  (R.  y  Cajal). 

A,  small  pyramidal  cell  of  the  second  layer ; 

B,  two  large  pyramidal  cells  of  the  third  layer ; 

C,  D,  stellate  cells  of  the  fourth  layer;  ii',  centrip- 
etal neurite  from  distant  centres ;  F,  collaterals 
from  the  white  substance ;  G,  bifurcated  neurite 
from  the  white  substance. 


Fig.  138. —  Cells  with  skort neurites  in  the  cerebral 
cortex  (R.  y  Cajal). 

A,  molecular  layer ;  B,  white  substance ;  a, 
cells  with  neurites  and  teloneurites ;  b,  cell  with 
a  neurite  extending  downward ;  c^  c,  cells  with 
neurites  extending  upward;  d,  small  pyramidal 

cell. 


The  cerebral  cortex  receives  centripetal  fibres  from  the  white  matter, 
which  give  off  abundant  collaterals  and  terminate  in  the  molecular 
layer  by  arborizing  filaments  (synapses)  surrounding  the  nerve-cells. 

The  white  matter  of  the  cerebrum  presents  four  groups  of  fibres  :  — 

1.  Centrifugal,  or  "  projection  "  fibres  pass  downward  from  the 
three  deeper  layers  of  the  cortex  and  finally,  with  their  collaterals, 
extend  into  the  pyramidal  tracts  of  the  cord. 

2.  Commissural  fibres  from  the  smaller  pyramidal  cells  of  the  cortex 
connect  the  two  sides  of  the  cerebrum. 


570 


NERVOUS    SYSTEM 


Fig.  139.  —  Lateral  surface  of  the  brain,  reduced  about  one-third  (Dalton). 


Fig.  140.  —  Median  section  of  the  Mz///,  reduced  about  one-third  (DaUon). 


CEREBRAL   CONVOLUTIONS 


571 


Fissure   o|    Rolando 


ssure^o^  Stjtvlus 


Fig.  T-^d)' .  —  Lateral  surface  of  the  brain,  reduced  about  one-third  (Dalton). 


Fig.  140'.  —  Median  section  of  the  brain,  reduced  about  one-third  (Dalton). 


572 


NERVOUS    SYSTEM 


3.  Association  fibres  connect  different  parts  of  the  cortex  on  the 
same  side.      These  constitute  the  greatest  part  of  the  white  substance. 

4.  Centripetal  fibres,  coming  from  the  centripetal  tracts  of  the  cord, 
go  to  the  molecular  layer  of  the  cortex. 

In  addition  to  the  above,  there  are  fibres  that  connect  the  cerebrum 
with  the  cerebellum,  which  will  be  described  later. 

Cerebral  Convolutions.  — The  cerebrum  presents  a  great  longitudinal 
median  fissure  by  which  it  is  partially  divided  into  two  lateral  halves, 
and  three  great  fissures  —  the  fissure  of  Sylvius,  the  fissure  of  Rolando 
and  the  parieto-occipital  fissure.  The  lobes  of  the  cerebrum  are  (i)  the 
frontal  lobe,  lying  in  front  of  and  above  the  fissure  of  Sylvius  and  in 
front  of  the  fissure  of  Rolando,  (2)  the  parietal  lobe,  behind  the  frontal 
lobe  and  in  front  of  and  above  the  occipital  lobe,  (3)  the  occipital  lobe, 
and  (4)  the  temporo-sphenoidal  lobe.  The  parietal  lobe  is  bounded  in 
front  by  the  fissure  of  Rolando  and  below  by  the  fissure  of  Sylvius 
and  the  parieto-occipital  fissure  (shown  in  Fig.  134).  The  occipital  lobe 
lies  below  the  parieto-occipital  fissure.  The  temporo-sphenoidal  lobe  is 
situated  below  the  fissure  of  Sylvius  and  in  front  of  the  occipital  lobe. 

While  the  convolutions  are  not  exactly  the  same  in  all  human  brains, 
or  even  in  both  sides  of  the  brain,  their  arrangement  and  relations  may 
be  described  in  a  general  way  with  sufficient  accuracy  to  enable  one  to 
recognize  easily  the  most  important  physiological  points  in  the  descrip- 
tive anatomy  of  the  cerebral  surface. 

The  first  frontal  convolution  is  bounded  internally  by  the  great  longi- 
tudinal fissure  and  externally  by  a  shallow  fissure  nearly  parallel  to  the 
longitudinal  fissure.  The  second  frontal  convolution  lies  next  the  first 
frontal  convolution,  and  is  bounded  externally  by  two  shallow  fissures 
lying  in  front  of  the  fissure  of  Sylvius.  The  third  frontal  convolution 
curves  around  the  short  branch  of  the  fissure  of  Sylvius.  On  either 
side  of  the  fissure  of  Rolando  are  the  ascending  frontal  convolution 
and  the  ascending  parietal  convolution.  Curving  around  the  posterior 
extremity  of  the  fissure  of  Sylvius,  is  the  supramarginal  convolution, 
which  is  continuous  with  the  first  temporal  convolution,  the  latter  lying 
behind  and  parallel  to  the  fissure  of  Sylvius.  Internal  to  the  posterior 
portion  of  the  intraparietal  sulcus  is  the  angular  convolution,  which  is 
continuous  with  the  second  temporal  convolution.  At  the  inferior 
border  of  the  temporo-sphenoidal  lobe,  below  the  first  and  second 
temporal  convolutions,  is  the  third  temporal  convolution.  The  superior 
parietal  convolution  lies  by  the  side  of  the  median  fissure  and  is  the 
posterior  continuation  of  the  first  frontal  convolution.  The  situation 
of  the  occipital  convolutions  is  indicated  in  Fig.  139.  In  addition 
to  these    convolutions  on  the  general  surface  of  the  cerebrum,  there 


BASAL   GANGLIA  •  573 

are  convolutions  on  the  surface  of  the  base  of  the  brain  and  in  the 
gray  matter  by  the  sides  of  the  great  longitudinal  fissure.  In  the  fissure 
of  Sylvius,  near  its  ascending  branch,  between  the  anterior  and  the 
posterior  lobes  of  the  brain  and  beneath  the  third  frontal  convolution,  is 
a  group  of  convolutions  constituting  the  island  of  Reil,  or  insula. 

Fig.  140  shows  the  most  important  parts  observed  on  the  inner  sur- 
face of  the  left  hemisphere.  These  parts  do  not  demand  any  explana- 
tion beyond  that  given  in  the  diagram  in  outline. 

Basal  Ganglia.  —  The  ganglia  at  the  base  of  the  brain  are  the 
olfactory  ganglia,  the  corpora  striata,  optic  thalami,  tubercula  quadri- 
gemina  and  the  gray  matter  of  the  pons  Varolii.  The  olfactory  ganglia 
will  be  described  in  connection  with  the  physiology  of  the  sense  of 
smell.  The  corpora  striata  and  the  optic  thalami  are  important  in  their 
relations  to  the  internal  capsule  and  the  paths  of  motor  and  sensory 
conduction. 

Corpora  Striata,  Optic  Thalami  and  Inte7'nal  Capsnle.  —  The  corpora 
striata  are  pear-shaped  bodies,  situated  at  the  base  of  the  brain,  with 
their  rounded  bases  directed  forward,  and  the  narrower  ends,  backward 
and  outward.  Their  external  surface  is  gray,  and  they  present,  on 
section,  alternate  striae  of  white  and  gray  matter.  They  present  what 
is  called  an  intraventricular  portion,  projecting  into  the  anterior  part  of 
the  lateral  ventricles,  and  an  extraventricular  portion,  which  is  embedded 
in  the  white  substance  at  the  base  of  the  brain.  The  corpora  striata  are 
to  be  regarded  as  subsidiary  centres  connected  with  motion. 

The  optic  thalami  are  oblong  bodies  situated  between  the  posterior 
extremities  of  the  corpora  striata  and  resting  upon  the  crura  cerebri  on 
the  two  sides.  These  are  white  externally,  and  in  their  interior  they 
present  a  mixture  of  white  and  gray  matter.  They  are  subsidiary  nerve- 
centres  connected  with  sensation. 

In  a  horizontal  section  made  through  the  brain,  involving  the  corpora 
striata  and  the  optic  thalami,  the  corpora  striata  present  a  division  into 
two  nuclei.  These  are  the  caudate  nucleus,  which  is  internal,  and  the 
lenticular  nucleus,  which  is  external  to  and  behind  the  caudate  nucleus. 
External  to  the  lenticular  nucleus,  is  a  layer  of  white  substance,  the 
external  capsule,  in  which  there  is  a  band  of  gray  matter,  called  the 
claustrum.  External  to  the  external  capsule,  at  its  anterior  portion,  is 
the  insula,  or  island  of  Reil. 

Between  the  caudate  nucleus  and  the  lenticular  nucleus  in  front,  is 
a  broad  band  of  white  fibres,  continuous  with  a  band  of  white  fibres 
lying  posteriorly,  between  the  lenticular  nucleus  and  the  optic  thalamus 
on  either  side.  This  band  is  the  internal  capsule.  The  portion  of  the 
internal  capsule  that  lies  between  the  caudate  nucleus  and  the  lenticu- 


574 


NERVOUS    SYSTEM 


lar  nucleus    is  called    its    anterior   division  ;    and  the    portion   situated 
between  the  lenticular  nucleus  and  the  optic  thalamus  is  its  posterior 


Fig.  141.  —  Horizontal  section  of  the  brain,  reduced  about  one-quarter  (Dalton). 


division.     The  bend    where    the   posterior   division   joins  the  anterior 
division  is  called  the  knee  of  the  capsule. 

The  directions  of  the  fibres  of  the  internal  capsule  are  in  general 


BASAL    GANGLIA  575 

terms  the  following :  Fibres  from  the  crura  cerebri  go  directly  into  the 
corpora  striata  in  front  and  into  the  optic  thalami  behind.  This  is 
the  course  of  the  greatest  part  of  the  fibres,  but  some  fibres  go  directly 


Fig.  141'.  —  Horizontal  section  of  the  brain,  reduced  about  one-quarter  fDalton). 
CS,  corpus  striatum  (caudate  nucleusj  ;   LX,  lenticular  nucleus;   OT,  optic  thalamus. 

through  the  internal  capsule,  and  thence  to  the  gray  matter  of  the 
cerebral  convolutions.  Most  of  the  fibres,  however,  which  form  the 
internal  capsule  come  from  the  gray  matter  of  the  corpora  striata 
and  optic  thalami  and  curve  outward  and  upward  to  go  to  the  gray 
matter  of  the  hemispheres.      As  they  pass  from  the  internal  capsule 


576 


NERVOUS   SYSTEM 


to  the  internal  surface    of    the    cerebral  convolutions,    they  form  the 
corona  radiata. 

In  the  human  subject,  lesions  affecting  the  anterior  two-thirds  of 
the  posterior  division  of  the  internal  capsule  produce  paralysis  of 
motion  only  and  are  followed  by  descending  degenerations.  The 
fibres  in  this  part  are  connected  with  the  corpora  striata.  Lesions 
affecting  both  the  anterior  two-thirds  and  the  posterior  third  of  the 
posterior  division  of  the  internal  capsule  produce  paralysis  of  motion 
and  sensation.      The  fibres  in  the  posterior  third  are  connected  with 


Fig.  142. —  I'ertical  section  of  the  brain,  reduced  about  one-quarter  (Dalton). 


the  optic  thalami.     Ascending  degenerations  have  not  been  observed 
in  the  fibres  of  the  cerebrum. 

Ttibercida  Qiiadrige7nina.  —  These  little  bodies,  sometimes  called 
the  optic  lobes,  are  rounded  eminences,  two  on  either  side,  situated  just 
below  the  third  ventricle.  The  anterior,  called  the  nates,  are  the  larger. 
These  are  oblong  and  of  a  grayish  color  externally.  The  posterior 
called  the  testes,  are  situated  just  behind  the  anterior.  They  are 
rounded  and  are  rather  lighter  in  color  than  the  anterior.  Both  contain 
gray  matter  in  their  interior.  They  are  the  main  points  of  apparent 
origin  of  the  optic  nerves  and  are  connected  by  commissural  fibres  with 
the  optic  thalami.  In  birds  the  tubercles  are  two  in  number,  instead 
of  four,  and  are  called  tubercula  bigemina. 


BASAL   GANGLIA 


577 


Crura  Cerebri.  —  The  crura  are  short,  thick,  rounded  bands  which 
pass  from  the  cerebral  hemispheres  to  the  upper  border  of  the  pons 
Varohi.  They  are  rather  broader  above  than  below  and  are  about  three- 
quarters  of  an  inch  (19  millimeters)  in  length.  They  are  composed  of 
longitudinal  white  fibres  connecting  various  parts  with  the  cerebrum. 
Each  crus  is'  divided  into  a  superficial  and  a  deep  band,  by  a  layer  of 
gray  substance  called  the  locus  niger.  The  locus  niger  contains  small 
multipolar  nerve-cells  and  abundant  pigmentary  granules.  The  lower, 
or  superficial  band  of  the  crus  is  called  the  crusta.     The  deep  band  is 


Fig.  142'. —  Vertical  section  of  the  brain,  reduced  about  one-quarter  (Daiton). 

I,  I,  I,  I,  first  frontal  convolution ;  II,  II,  second  frontal  convolution  ;  III,  III,  third  frontal  convo- 
lution ;  CC,  corpus  callosum ;  CS,  corpus  striatum ;  IC,  internal  capsule ;  LN,  lenticular  nucleus ; 
/«,  insula;  6',  fissure  of  Sylvius. 

called  the  tegmentum.     The  crusta  consists  of  white  fibres  only.     In 
the  tegmentum  the  fibres  are  mixed  with  masses  of  gray  matter. 

Pojis  Varolii.  —  The  pons  Varolii,  called  the  tuber  annulare,  cr  the 
Tnesocephalon,  is  situated  at  the  base  of  the  brain  just  above  the  bulb. 
It  is  white  externally  and  contains  in  its  interior  a  large  admixture  of 
gray  matter.  It  presents  both  transverse  and  longitudinal  white  fibres. 
Its  transverse  fibres  connect  the  two  halves  of  the  cerebellum.  Its 
longitudinal  fibres  are  connected  below  with  the  anterior  pyramidal 
bodies  and  the  olivary  bodies  of  the  bulb,  the  lateral  columns  of  the 
cord  and  a  certain  portion  of  the  posterior  columns.  The  fibres  are  con- 
nected above  wdth  the  crura  cerebri  and  pass  to  the  brain. 


578  NERVOUS    SYSTEM 

If  the  cerebral  hemispheres,  the  olfactory  ganglia,  the  optic  lobes, 
the  corpora  striata  and  the  optic  thalami  are  removed,  the  animal 
loses  the  special  senses  of  smell  and  sight  and  the  intellectual  facul- 
ties, there  is  a  certain  degree  of  enfeeblement  of  the  muscular  system, 
but  voluntary  motion  and  general  sensibility  are  retained.  So  far  as 
voluntary  motion  is  concerned,  an  animal  operated  on  irt  this  way  is 
nearly  in  the  condition  of  one  simply  deprived  of  the  cerebral  hemi- 
spheres. There  are  no  voluntary  movements  that  show  any  degree  of 
intelligence,  but  the  animal  can  stand,  and  various  consecutive  move- 
ments are  executed,  which  are  different  from  the  simple  reflex  acts 
depending  exclusively  on  the  spinal  cord.  The  coordination  of  move- 
ments is  perfect  unless  the  cerebellum  has  been  removed.  As  regards 
general  sensibility,  an  animal  deprived  of  all  the  encephalic  ganglia 
except  the  pons  Varolii  and  the  bulb  undoubtedly  feels  pain.  In 
rabbits,  rats  and  other  animals,  after  removal  of  the  cerebrum,  corpora 
striata  and  optic  thalami,  pinching  of  the  ear  or  foot  is  immediately 
followed  by  prolonged  and  plaintive  cries.  Physiologists  have  insisted 
on  the  character  of  these  cries  as  indicating  actual  perception  of  pain- 
ful impressions  and  as  different  from  cries  that  are  purely  reflex. 
Voluntary  movements  and  cries  are  observed  in  persons  subjected  to 
painful  surgical  operations,  when  incompletely  under  the  influence  of 
an  anesthetic,  concerning  the  character  of  which  there  can  be  no  doubt. 
The  movements  are  voluntary,  and  the  cries  are  evidence  of  the  acute 
perception  of  pain  ;  but  such  patients  have  no  recollection  of  any  pain- 
ful sensation.  So  far  as  can  be  judged  from  what  is  known  of  the 
action  of  the  encephalic  centres,  the  pain  under  these  conditions  is  per- 
ceived by  some  nerve-centre,  probably  in  the  pons  Varolii,  but  the  im- 
pression is  not  conveyed  to  the  cerebrum  and  is  not  recorded  by  the 
memory. 

Taking  all  the  experimental  facts  into  consideration,  the  following 
seems  to  be  the  most  reasonable  view  in  regard  to  the  action  of  the 
pons  Varolii  as  a  nerve-centre :  — 

It  is  an  organ  capable  of  originating  impulses  that  give  rise  to  volun- 
tary movements,  when  the  cerebrum,  corpora  striata  and  the  optic 
thalami  have  been  removed ;  and  probably  it  regulates  the  automatic 
voluntary  action  in  station  and  progression.  Many  voluntary  move- 
ments, the  result  of  intellectual  effort,  are  made  in  obedience  to  impulses 
transmitted  from  the  cerebrum,  through  conducting  fibres  in  the  pons 
Varolii,  to  the  cord  and  the  general  motor  nerves. 

The  gray  matter  of  the  pons  Varolii  is  also  capable  of  receiving 
painful  impressions,  which,  when  all  the  encephalic  ganglia  are  in- 
tact, are   conducted  to  and  are    perceived  by  the  cerebrum  and  are 


FIBRES    OF    THE    CEREBRUM  ♦  579 

remembered ;  but  there  are  distinct  evidences  of  the  perception  of  pain, 
even  when  the  cerebrum  has  been  removed. 

Directions  of  tJie  Fibres  iji  the  Cerebrum.  —  Fibres  pass  from  the 
cerebral  hemispheres  to  the  cerebellum.  Commissural  fibres  connect 
the  cerebrum  and  certain  of  the  basal  ganglia  on  the  two  sides.  Fibres 
connect  the  gray  matter  of  cerebral  convolutions  on  the  same  side. 
Fibres  pass  from  the  inner  surface  of  the  gray  matter  of  the  cerebrum 
to  the  internal  capsule,  corpora  striata,  optic  thalami  and  pons  Varolii, 
the  bulb  and  thence  to  the  spinal  cord.  The  directions  of  these  four 
sets  of  fibres  have  been  quite  accurately  described. 

1.  Fibres  connecting  the  Cerebmvi  with  the  Cerebelbitn. — (A)  Fibres 
from  the  gray  matter  of  the  frontal  lobe,  in  front  of  the  anterior  central 
convolution,  pass  through  the  anterior  division  of  the  internal  capsule 
and  thence  through  the  inner  portion  of  the  outer  layer  of  the  crus 
cerebri  (crusta)  to  the  pons,  where  they  seem  to  go  to  the  cells  of  the 
gray  matter,  forming  synapses.  From  the  pons,  fibres  go  to  the  lateral 
and  posterior  regions  of  the  cerebellum  on  the  opposite  side.  (B)  Fibres 
from  the  occipital  and  temporo-sphenoidal  lobes  pass  in  the  outer  portion 
of  the  crusta  and  go  to  the  upper  portion  of  the  cerebellum,  near  the 
middle  lobe.  This  connection  probably  is  crossed.  (C)  Above  the 
pyramidal  tract  of  the  crusta,  is  a  small  tract  of  fibres  which  connects 
the  caudate  nucleus  of  the  corpus  striatum,  through  synapses  in  the 
pons,  with  the  cerebellum  on  the  opposite  side  ( Gowers). 

2.  Fibres  cojinecting  the  Two  Sides  of  the  Brain.  —  (A)  Fibres 
from  the  inner  surface  of  the  gray  matter  of  the  convolutions  pass  from 
one  side  to  the  other,  through  the  corpus  callosum,  and  connect  the  two 
hemispheres.  These  are  the  transverse  fibres  of  the  corpus  callosum. 
(B)  Fibres  from  the  gray  matter  of  the  temporo-sphenoidal  lobes  pass 
through  the  corpora  striata  to  the  anterior  commissure.  These  connect 
the  temporo-sphenoidal  lobes,  and  probably  the  corpora  striata,  on  the 
two  sides.  (C)  Fibres  from  the  deeper  portion  of  the  crus  cerebri 
(tegmentum)  pass  to  the  optic  thalamus  on  either  side  and  thence  to  the 
temporo-sphenoidal  lobes.  They  form  the  posterior  commissure  and  con- 
nect the  temporo-sphenoidal  lobes  and  the  optic  thalami  of  the  two  sides. 

3.  Fibres  connecting  Different  Cerebral  Convohitions  on  the  Same  Side 
{^Association  Fibres). — (A)  Arcuate  fibres,  passing  from  one  convolution 
to  another,  connect  adjacent  convolutions.  (B)  Longitudinal  fibres  con- 
nect distant  convolutions.  The  fibres  of  the  fornix  connect  the  optic 
thalamus  with  the  hippocampus  major  and  the  uncinate  gyrus.  Fibres 
in  the  corpus  callosum  connect  the  anterior  and  posterior  extremities  of 
the  gyrus  fornicatus.  These  are  the  longitudinal  fibres  of  the  corpus 
callosum.     Other  longitudinal  fibres,  connecting  parts  more  or  less  dis- 


580 ■  NERVOUS    SYSTEM 

tant,  are  found  in  the  tenia  semicircularis,  the  uncinate  fasciculus,  the 
fillet  of  the  gyrus  fornicatus  and  the  inferior  longitudinal  fasciculus. 
The  last-mentioned  fasciculus  connects  the  gray  matter  of  the  tem- 
poro-sphenoidal  and  occipital  lobes. ^ 

4.  Fibres  connecting  the  Brain  zvith  the  Spinal  Cord.  —  Arising 
from  the  internal  concave  surface  of  the  cortical  substance  of  the 
cerebrum,  converging  fibres,  at  first  running  side  by  side  with  the 
curved  commissural  fibres,  separate  as  the  latter  curve  backward  to 
pass  again  to  the  cortical  substance,  and  are  directed  toward  the 
corpora  striata  and  the  optic  thalami.  The  limits  of  the  irregular 
planes  of  separation  of  the  commissural  and  the  converging  fibres 
contribute  to  form  the  boundaries  of  the  ventricular  cavities  of  the 
brain.  In  studying  the  course  of  the  converging  fibres  arising  from 
all  points  in  the  concave  surface  of  the  cerebral  gray  matter,  it  is  found 
that  they  take  various  directions.  The  fibres  from  the  anterior  region 
of  the  cerebrum  pass  backward  and  form  distinct  fasciculi  which  con- 
verge to  the  gray  substance  of  the  corpora  striata.  The  fibres  from  the 
middle  portion  converge  regularly  to  the  middle  region  of  the  external 
portions  of  the  optic  thalami.  The  fibres  from  the  posterior  portion 
pass  from  behind  forward  and  are  distributed  in  the  posterior  portion  of 
the  optic  thalami.  The  fibres  from  the  convolutions  of  the  hippocampi 
and  the  fascia  dentata  are  lost  in  the  gray  substance  lining  the  internal 
borders  of  the  optic  thalami.  In  the  course  of  most  of  these  fibres 
toward  the  corpora  striata  and  the  optic  thalami,  they  pass  through  the 
internal  capsule. 

The  fibres  from  the  middle  and  anterior  portions  of  the  cerebrum, 
especially  the  middle  portion,  contribute  largely  to  the  formation  of  the 
anterior  two-thirds  of  the  posterior  division  of  the  internal  capsule. 
The  fibres  from  the  posterior  portion  of  the  cerebrum  are  found  in  the 
posterior  third  of  the  posterior  division  of  the  internal  capsule.  The 
middle  and  anterior  fibres  undergo  descending  degenerations  following 
lesions  of  motor  areas.  A  few  of  the  converging  fibres  from  the  hemi- 
spheres pass  directly  through  the  internal  capsule  and  have  no  connec- 
tion with  the  corpora  striata  and  optic  thalami. 

1  Recent  researches  by  Flechsig,  made  by  a  new  process  called  the  embryological  method, 
though  incomplete,  probably  will  lead  to  important  results.  It  has  been  ascertained  that  vari- 
ous tracts  of  fibres  receive  medullary  sheaths  at  different  stages  of  intra-uterine  development, 
the  axis-cylinders  appearing  first  without  coverings.  As  the  medullary  substance  appears,  the 
fibres  are  said  to  become  "  myelinated."  Association  fibres  are  myelinated  later  than  projec- 
tion fibres,  the  latter  receiving  the  sheath  at  about  the  fifth  month.  In  studying  embryos  by  this 
method,  Flechsig  assumes  to  have  demonstrated  the  exact  course  of  various  association  tracts, 
and  their  connections  with  "  association  centres."  The  theoretical  deduction  from  these  ob- 
servations are  interesting,  but  can  not  as  yet  be  accepted  as  conclusive.  They  relate  largely  to 
the  voluntary  action  of  groups  of  muscles  following  sensory  impressions  of  various  kinds,  cutane- 
ous, auditory,  visual,  etc. 


CEREBRAL    LOCALIZATION 


581 


From  the  internal  capsule,  the  fibres  pass  in  the  crus  cerebri  to  the 
upper  border  of  the  pons  Varolii.  The  motor. fibres  pass  through  the 
pons  as  longitudinal  fibres,  go  to  the  anterior  pyramids  of  the  bulb, 
where  most  of  them  decussate,  and  thence  to  the  pyramidal  tracts  of 
the  spinal  cord.  The  sensory  fibres  go  to  the  posterior  part  of  the 
cord.  The  converging  cerebral  fibres  are  reenforced,  in  their  downward 
course,  by  fibres  from  the  tubercular  quadrigemina  and  the  gray  matter 
of  the  pons  Varolii.     Certain  fibres  go  to  the  olivary  bodies  in  the  bulb. 


Fig.  143.  —  Diagrammatic  representation  of  the  direction  of  some  of  the  fibres  in  the  cerebrum  (Le  Bon) , 


A  more  extended  description  of  these  fibres  will  be  given  in  connection 
with  the  physiological  anatomy  of  the  bulb.  As  fibres  pass  through 
parts  containing  nerve-cells,  they  often  are  "  reenforced  "  in  a  way  that 
is  somewhat  obscure.  It  is  probable,  however,  that  this  is  by  fibres 
originating  in  arborescent  filaments  (synapses)  surrounding  the  cells. 

Cerebral  Localization.  —  The  observations  of  Flourens  (1822  and 
1823)  and  his  immediate  followers,  which  seemed  to  show  that  the 
cerebrum  was  neither  excitable  nor  sensible  to  direct  stimulation,  have 
been  so  completely  contradicted   by  the    experiments  of    Fritsch    and 


582 


NERVOUS   SYSTEM 


Hitzig  (1870),  Ferrier,  Munk,  Horsley  and  many  others,  that  the  ques- 
tion of  the  existence  of  motor  and  sensory  centres  —  especially  motor 
centres  —  hardly  admits  of  discussion.  The  negative  results  obtained 
by  Flourens  were  probably  due  to  severe  hemorrhage,  which,  according 
to  Ferrier,  rapidly  destroys  the  excitability  of  the  motor  cortical  areas. 
Some  of  the  experiments  of  Goltz,  by  which  it  was  attempted  to  prove 
that  circumscribed  and  invariable  motor  areas  do  not  exist,  are  answered 
by  observations  showing  descending  secondary  degenerations  following 
injury  of  certain  parts  of  the  cerebral  cortex.  The  earlier  observations 
on  cerebral  localization  were  made  on  dogs.  Later,  experiments  have 
been  made  on  monkeys,  and  the  results  of  these  have  been  to  a  certain 
extent  confirmed  by  pathological  observations  on  the  human  subject. 
Beginning  with  the  observations  in  which  descending  degenerations 
have  been  noted  as  a  consequence  of  destruction  of  parts  of  the  cerebral 
cortex,  it  may  be  assumed  that  distinct  areas  exist  which  preside  over 
certain  localized  muscular  movements. 

Motor  Cortical  Zone  {Ro/andic  A7'ea).  —  The  motor  cortical  zone  is  on 
either  side  of  the  fissure  of  Rolando.  It  usually  is  described  as  including 
the  ascending  frontal  and  ascending  parietal  convolutions  (see  Fig.  139), 
and  the  paracentral  lobule  (see  Fig.  140).  Faradization  of  parts  in  and 
adjacent  to  this  zone  is  followed  by  localized  muscular  movements.  In 
fact,  the  motor  areas  seem  to  be  subject  to  nearly  the  same  laws,  as 
regards  their  reactions  to  faradic  stimulation,  as  are  the  motor  nerves. 
Forty  faradic  shocks  per  second  produce  a  corresponding  number  of 
single  muscular  contractions.  Forty-six  shocks  per  second  produce  a 
tetanic  contraction  (Franck  and  Pitres).  Destruction  of  motor  areas  is 
followed  by  partial  loss  of  power  in  certain  sets  of  muscles  and  by 
secondary  descending  degeneration  of  nerve-fibres  extending  through 
the  corona  radiata,  the  internal  capsule,  the  crura  cerebri,  the  anterior 
pyramids  of  the  bulb  and  finally  the  pyramidal  tracts  of  the  spinal 
cord. 

While  it  can  not  be  doubted  that  the  Rolandic  area  is  made  up  of  a 
number  of  motor  centres,  it  is  now  thought  by  many  physiologists  that 
it  receives  sensory  fibres  from  the  skin  and  the  muscular  system  ;  and 
therefore  it  is  sometimes  called  the  sensori-motor  area.  The  physio- 
logical basis  of  this  view  is  the  close  association  of  sensations  and 
voluntary  movements ;  and  it  has  been  proved  that  extirpation  of  the 
Rolandic  area  in  monkeys  is  followed  by  impaired  sensibility.  Recent 
anatomical  researches,  made  by  means  of  the  staining  methods  of  Golgi 
and  Ramon  y  Cajal,  seem  to  favor  this  idea,  although  the  tracing  of  the 
fibres  presents  difficulties  which  render  the  results  somewhat  unsatis- 
factory. 


CEREBRAL   LOCALIZATION 


583 


It  remains  now  to  locate  the  distinct  motor  areas.  This  has  been 
done  on  the  brain  of  the  monkey  by  Ferrier,  Horsley  and  others,  who 
have  applied  their  observations  as  nearly  as  possible  to  the  human  brain. 
While  the  divisions  now  recognized  can  not  be  taken  as  absolute,  experi- 
ments on  monkeys  have  been  followed  by  results  so  nearly  constant, 
that  the  most  important  localizations  may  be  accepted  as  correct. 

I.  The  centre  for  movements  of  the  upper  extremities  is  on  the 
outer  surface  of  the  brain  and  includes  the  superior  portion  of  the  as- 
cending frontal  convolution  and  nearly  all  the  ascending  parietal  con- 


Fig.    144. — Motor  cortical  zone  {Rolandic  area)  on  the  outer  surface  of  the  cerebrum  (Exner). 


volution,  except  the  very  uppermost  portion  of  these  convolutions,  next 
the  great  longitudinal  fissure. 

2.  The  centre  for  movements  of  the  leg  and  foot  is  on  the  mesial 
surface  of  the  brain,  including  the  paracentral  lobule. 

3.  The  centre  for  movements  of  the  trunk  and  shoulders  is  mainly 
on  the  mesial  surface  of  the  brain,  in  front  of  the  upper  part  of  the 
centre  for  the  leg  and  foot. 

4.  The  centre  for  movements  of  the  head,  eyes  and  lids  is  on  the 
outer  surface  of  the  brain,  including  the  posterior  portion  of  the  first  and 
second  frontal  convolutions  and  extending  to  the  mesial  surface. 

5.  The  centre  for  the  muscles  of  the  mouth  includes  the  lower  por- 
tion of  the  ascending  frontal  convolution. 

The  action  of  all  these  motor  centres  is  crossed. 


584 


NERVOUS    SYSTEM 


Fig.   145.  —  Diagram  of  a  median  section  of  the  brain. 


Attempts  have  been  made  to  subdivide  the  centres  just  indicated, 
but  most  of  these  are  hardly  justified  by  experimental  results,  even  in 
monkeys.  Still  less  can  it  be  assumed  that  more  restricted  centres  can 
be  accurately  mapped 
out  in  the  human  sub- 
ject. It  has  been 
thought  proper,  there- 
fore, to  describe  in  this 
work  those  centres 
only,  the  localization 
of  which  admits  of  lit- 
tle doubt.  It  is  proba- 
ble, however,  judging 
from  the  very  recent 
experiments  of  Sher- 
rington and  Griinbaum 
on  certain  anthropoid  apes,  that  the  cortical  motor  areas  are  more 
extensive  than  has  been  supposed.  The  method  employed  by  these 
observers  was  to  place  one  electrode   of   a  feeble  faradic  current  on 

certain  parts  of  the  ex- 
posed cortex  and  the 
other  on  an  indifferent 
point.  This  was  thought 
to  limit  the  motor  areas 
much  more  accurately 
than  the  older  method 
with  the  two  elec- 
trodes applied  to  the 
brain. 

In  man,  lesions  of 
parts  of  the  motor-cor- 
tical zone  produce  local- 
ized paralysis,  or  what  is 
called  monoplegia,  the 
action  being  crossed. 
The  following  are  some 
of  the  more  common 
forms  of  monoplegia 
that  have  been  observed  to  attend  localized  cortical  lesions  :  i,  oculo- 
motor monoplegia  (isolated  ptosis) ;  2,  facial  monoplegia,  sometimes 
associated  with  paralysis  of  the  hypoglossal  nerve ;  3,  brachial  mono- 
plegia,   or   paralysis   of  the    opposite    arm ;    4,   crural   monoplegia,  or 


Tvunk^and 


5hO'jlde\'S 


Fig.  146.  —  Diagram  of  certain  motor  cortical  areas. 


GENERAL   USES    OF    THE   CEREBRUM  585 

paralysis  of  the  opposite  leg;  5,  brachio-facial  monoplegia,  or  paralysis 
of  the  arm  and  face. 

In  addition  to  the  motor  areas  just  described,  there  probably  is  a 
group  of  sensory  areas  on  the  mesial  surface  of  t|ie  brain  that  has  been 
called  the  tactile  centre.  This  is  in  the  gyrus  fornicatus,  just  above  the 
corpus  callosum.  The  centres  for  the  special  senses,  which  will  be 
more  fully  considered,  however,  farther  on,  are  the  following  :  olfactory 
centre  and  taste  centre,  at  the  anterior  extremity  of  the  temporal  lobe ; 
the  simple  visual  centre,  on  the  mesial  surface  of  the  cerebrum  above 
and  below  the  calcarine  fissure;  the  psychical  visual  centre,  on  the  con- 
vex surface  of  the  occipital  lobe,  behind  the  auditory  centre  and  on 
the  left  side  only ;  the  simple  auditory  centre,  in  the  superior  and  mid- 
dle temporal  convolutions  ;  the  psychical  auditory  centre,  in  the  superior 
temporal  convolution,  on  the  left  side  only. 

One  of  the  most  important  of  the  cerebral  centres  is  the  centre  for 
speech,  which  will  be  described  after  the  consideration  of  the  general 
uses  of  thfe  cerebral  hemispheres. 

General  Uses  of  the  Cerebrum 

The  cortical  substance  of  the  cerebral  hemispheres  not  only  is  capa- 
ble of  generating  motor  impulses  of  the  kind  known  as  voluntary  and  of 
receiving  sensory  impressions,  including  those  connected  with  the  special 
senses,  but  its  anatomical  and  physiological  integrity,  and  its  connec- 
tions, especially  with  sensory  conductors,  are  essential  to  what  are 
known  as  mental  operations.  The  existence  of  the  mind  and  the  possi- 
bility of  normal  operations  of  the  intelligence  depend  on  the  existence 
of  the  gray  matter  of  the  cerebral  cortex  and  its  normal  physiological 
condition  and  relations.  Mental  operations  involve  a  slight  elevation  of 
temperature  and  slightly  increase  some  of  the  excretions.  It  is  prob- 
able, therefore,  that  they  involve  changes  of  matter  ;  and  these  changes, 
if  they  occur,  can  be  effected  only  by  the  cells  of  the  brain.  Without 
defining  or  analyzing  the  intellectual  faculties  or  attempting  to  locate 
different  faculties  in  special  parts,  it  is  sufficient  to  state  that  certain  of 
them  reside  probably  in  that  portion  of  the  brain  which  is  anterior  to 
the  motor-cortical  zone ;  that  is,  in  the  frontal  lobes.  These  lobes,  so 
far  as  is  known,  do  not  present  motor  or  sensory  areas ;  and  recent 
observations  have  shown  that  lesions  of  the  frontal  lobes  especially  are 
attended  with  marked  impairment  of  the  intellectual  faculties  and  little 
or  no  motor  disturbance. 

The  brain  and  the  intellectual  power  of  man  are  so  far  superior  in 
their  development  to  this  organ  and  its  properties  in  the  lower  animals. 


586  NERVOUS    SYSTEM 

that  some  psychologists  have  regarded  the  human  intelligence  as  distinct 
in  nature  as  well  as  in  degree.  Although  physiologists  do  not  commonly 
accept  this  proposition,  regarding  the  intelligence  of  man  as  simply  su- 
perior in  degree  to  that  of  the  lower  animals,  it  is  evident  that  this  dif- 
ference in  the  degree  of  development  is  so  great  as  to  render  the  human 
mind  hardly  comparable  with  the  intellectual  attributes  of  animals  low 
in  the  scale.  Still,  there  can  be  no  doubt  in  regard  to  the  identity  of 
the  nature  of  the  faculties  of  the  brain  in  man  and  in  some  of  the  lower 
animals,  however  much  these  faculties  may  differ  in  their  development. 
If  this  proposition  be  true,  it  is  reasonable  to  apply  experiments  on 
the  brain  in  the  lower  animals  to  the  physiology  of  corresponding  parts 
in  the  human  subject. 

Exti^'pation  of  the  Cerebjum.  —  Experiments  on  different  classes  of 
animals  show  clearly  that  the  brain  is  less  important,  as  regards  the 
ordinary  manifestations  of  animal  life,  in  proportion  as  its  relative 
development  is  smaller.  For  example,  if  the  cerebral  hemispheres  are 
removed  from  fishes  or  reptiles,  the  movements  that  are  called  voluntary 
may  be  but  little  affected ;  while  if  the  same  mutilation  is  performed  in 
birds  or  certain  of  the  mammalia,  the  diminished  power  of  voluntary 
motion  is  much  more  marked.  It  would  be  plainly  unphilosophical  to 
assume,  because  a  fish  or  a  frog  will  swim  in  water  and  execute  move- 
ments after  removal  of  the  hemispheres  very  like  those  of  the  uninjured 
animal,  that  their  feeble  intelligence  is  not  destroyed  by  the  operation. 
It  is  not  only  possible  but  probable  that  in  the  very  lowest  of  the 
vertebrates,  the  operations  of  the  nervous  centres  are  not  the  same  as 
in  higher  animals.  There  is,  for  example,  a  fish  (the  lancet-fish,  amphi- 
oxus  lanceolatus)  that  has  no  brain,  all  the  functions  of  animal  life 
being  regulated  by  the  gray  substance  of  the  spinal  cord.  It  is 
essential,  therefore,  in  endeavoring  to  apply  the  results  of  experiments 
on  the  brain  in  the  lower  animals  to  human  physiology,  to  separate,  so 
far  as  possible,  distinct  manifestations  of  intelligence  from  automatic 
acts. 

Flourens  (1822  and  1823)  made  a  series  of  observations  on  the 
different  parts  of  the  encephalon.  As  regards  the  cerebral  hemispheres, 
he  found  that  complete  removal  of  these  parts  in  living  animals  (frogs, 
pigeons,  fowls,  mice,  moles,  cats  and  dogs)  was  invariably  followed  by 
stupor,  apparent  loss  of  intelligence  and  absence  of  even  the  ordinary 
instinctive  acts.  Animals  thus  mutilated  retained  general  sensibility 
and  the  power  of  voluntary  movements,  but  were  thought  to  be  deprived 
of  the  special  senses  of  sight,  hearing,  smell  and  taste.  As  regards 
general  sensibihty  and  voluntary  movements,  Flourens  was  of  the  opin- 
ion that  animals    deprived  of  their  cerebral  lobes  possessed  sensation 


GENERAL    USES    OF    THE    CEREBRUM  587 

but  had  lost  the  power  of  perception  ;  and  that  they  could  execute 
voluntary  movements  when  an  irritation  was  applied  to  any  part,  but 
had  lost  the  power  of  making  such  movements  in  obedience  to  a  spon- 
taneous effort  of  the  will.  One  of  the  most  remarkable  phenomena 
observed  was  entire  loss  of  memory  and  of  the  power  of  connecting 
ideas.  The  voluntary  muscular  system  was  enfeebled  but  not  paralyzed. 
Removal  of  one  hemisphere  produced,  in  the  higher  classes  of  animals 
experimented  on,  enfeeblement  of  the  muscles  of  the  opposite  side, 
but  the  intellectual  faculties  were  in  part  or  entirely  retained. 

The  observations  of  Flourens  have  been  repeated  by  many  physi- 
ologists, and  in  the  main  confirmed,  except  as  regards  the  special 
senses.  Bouillaud  (1826)  made  a  large  number  of  observations  on 
pigeons,  fowls,  rabbits  and  other  animals,  in  which,  after  removal  of  the 
hemispheres,  he  noted  the  persistence  of  the  senses  of  sight  and  hear- 
ing. Longet  finally  demonstrated  the  fact  that  both  sight  and  hearing 
are  retained  after  extirpation  of  the  hemispheres,  even  more  clearly 
than  Bouillaud,  by  the  following  experiments :  he  removed  the  hemi- 
spheres from  a  pigeon,  the  animal  surviving  the  operation  eighteen 
days.  When  this  animal  was  placed  in  a  dark  room  and  a  light  was 
suddenly  brought  near  the  eyes,  the  iris  contracted  and  the  animal 
winked  ;  "  but  it  was  remarkable,  that  when  a  lighted  candle  was  moved 
in  a  circle,  and  at  a  sufficient  distance,  so  that  there  should  be  no  sensa- 
tion of  heat,  the  pigeon  executed  an  analogous  movement  of  the  head." 
An  examination  after  death  showed  that  the  removal  of  the  cerebrum 
had  been  complete.  An  animal  deprived  of  the  hemispheres  also  opened 
the  eyes  at  the  report  of  a  pistol  and  gave  other  evidence  that  the  sense 
of  hearing  was  retained. 

In  regard  to  the  senses  of  smell  and  taste,  it  is  more  difficult  to 
determine  their  presence  than  to  ascertain  that  the  senses  of  sight  and 
hearing  are  retained.  It  is  probable,  however,  that  the  sense  of  smell 
is  not  abolished,  if  the  hemispheres  are  carefully  removed,  leaving  the 
olfactory  ganglia  intact ;  and  there  is  no  direct  evidence  that  extirpation 
of  the  cerebrum  affects  the  sense  of  taste ;  indeed,  in  young  cats  and 
dogs,  Longet  noted  evidences  of  a  disagreeable  impression  following 
the  introduction  of  a  concentrated  solution  of  colocynth  into  the  mouth, 
as  distinctly  as  in  the  same  animals  under  normal  conditions. 

Comparative  Development  of  the  Cerebrum  in  tJie  Lower  Animals.  —  It 
is  necessary  only  to  refer  briefly  to  the  development  of  the  cerebrum  in 
the  lower  animals  as  compared  with  the  human  subject,  to  show  the 
connection  of  the  hemispheres  with  intelHgence.  In  man  the  cerebrum 
presents  a  large  preponderance  in  weight  over  other  portions  of  the 
encephalon  ;  but  in  some  of  the  lower  animals  the  cerebrum  is  even  less 


588  NERVOUS    SYSTEM 

in  weight  than  the  cerebellum.  In  man,  also,  not  only  the  relative  but 
the  absolute  weight  of  the  brain  is  greater  than  in  the  lower  animals, 
with  but  two  exceptions.  Todd  has  cited  a  number  of  observations 
made  on  the  brains  of  elephants,  in  which  the  weights  ranged  between 
nine  and  ten  pounds  (about  4000  and  4500  grams).  Rudolphi  gave 
the  weight  of  the  encephalon  of  a  whale,  seventy-five  feet  long  (about 
23  meters),  as  considerably  over  five  pounds  (about  2300  grams).  With 
the  exception  of  these  animals,  man  possesses  the  largest  brain  in  the 
zoological  scale. 

Another  interesting  point  in  this  connection  is  the  development  of 
cerebral  convolutions  in  certain  animals,  by  which  the  relative  quantity 
of  gray  matter  is  increased.  In  fishes,  reptiles  and  birds,  the  surface 
of  the  hemispheres  is  smooth  ;  but  in  many  mammals,  especially  in 
those  remarkable  for  intelligence,  the  cerebrum  presents  a  greater  or 
less  number  of  convolutions,  as  it  does  in  the  human  subject. 

Development  of  the  CerebriLni  in  Different  Races  of  Men  and  in 
Different  Individuals.  —  It  may  be  stated  as  a  general  proposition,  that 
in  the  different  races  of  men,  the  cerebrum  is  developed  in  proportion 
to  their  intellectual  power ;  and  in  different  individuals  of  the  same 
race,  the  same  general  rule  obtains.  Still,  this  presents  marked  excep- 
tions. Certain  brains  in  an  inferior  race  may  be  larger  than  the 
average  in  the  superior  race  ;  and  it  is  frequently  observed  that  unusual 
intellectual  vigor  is  coexistent  with  a  small  brain,  and  the  reverse. 
These  exceptions,  however,  do  not  take  away  from  the  force  of  the 
original  proposition.  As  regards  races,  the  rule  is  found  to  be  invari- 
able, when  a  sufficient  number  of  observations  are  analyzed ;  and  the 
same  holds  true  in  comparing  a  large  number  of  individuals  of  the  same 
race.  Average  men  have  an  advantage  over  average  women  of  about 
six  ounces  (170  grams)  of  cerebral  substance;  and  while  many  women 
are  far  superior  in  intellect  to  many  men,  such  instances  are  not  suffi- 
ciently frequent  to  invalidate  the  general  proposition,  that  the  greatest 
intellectual  capacity  and  mental  vigor  is  coincident  with  the  greatest 
quantity  of  cerebral  substance.  If  the  view  —  which  is  in  every  way 
reasonable  — be  accepted,  that  the  gray  substance  alone  of  the  cerebral 
hemispheres  is  directly  connected  with  the  mind,  it  would  be  necessary, 
in  comparing  different  individuals  with  the  view  of  establishing  a 
definite  relation  between  brain-substance  and  intelligence,  to  estimate 
the  quantity  of  gray  matter ;  but  it  is  not  easy  to  see  how  this  can  be 
done  with  any  degree  of  accuracy. 

It  is  undoubtedly  true  that  proper  training  and  exercise  develop  and 
increase  the  vigor  of  the  intellectual  faculties,  and  that  thereby  the  brain 
is  increased  in  power,  as  are  the  muscles  under  analogous  conditions. 


GENERAL    USES    OF    THE    CEREBRUM  589 

This  will  perhaps  explain  some  of  the  exceptions  above  indicated ;  but 
an  additional  explanation  may  be  found  in  differences  in  the  quality  of 
brain-substance  in  different  individuals,  irrespective  of  the  size  of  the 
cerebral  hemispheres.  One  evidence  that  these  differences  in  the 
quality  of  intellectual  working  matter  exist  is  that  some  small  brains 
actually  accomplish  more  and  better  work  than  some  large  brains. 
This  may  be  due  to  differences  in  training,  to  the  extraordinary  develop- 
ment, in  some  individuals,  of  certain  qualities,  to  intensity  and  pertinacity 
of  purpose,  capacity  for  persistent  labor  in  certain  directions,  a  fortu- 
nate direction  of  the  mental  efforts,  opportunity  and  circumstances,  etc. ; 
but  aside  from  these  considerations,  it  is  probable  that  there  are 
important  individual   differences  in  the   quality   of   nervous   matter. 

Facial  Angle.  —  It  is  not  necessary  to  enter  into  an  extended  discus- 
sion of  the  relations  of  the  facial  angle  to  intelligence.  It  was  proposed 
by  Camper  to  take  the  angle  made  at  the  junction  of  two  lines,  one 
drawn  from  the  most  projecting  part  of  the  forehead  to  the  alveolae  of 
the  teeth  of  the  upper  jaw,  and  another  passing  horizontally  backward 
from  the  lower  extremity  of  the  first  line,  as  the  facial  angle.  This 
angle  is  to  a  certain  extent  a  measure  of  the  projection  of  the  anterior 
lobes  of  the  brain.  A  number  of  observations  on  the  facial  angle  in 
different  races  has  been  made  by  Camper  and  by  other  physiologists 
and  ethnologists.  These  show,  in  general  terms,  that  the  angle  is 
larger  in  man  than  in  any  of  the  inferior  animals  and  is  largest  in  those 
races  that  possess  the  greatest  intellectual  development. 

Pathological  Observations.  —  It  is  a  fact  now  generally  admitted  in 
pathology,  that  loss  of  cerebral  substance  from  repeated  hemorrhage 
is  sooner  or  later  followed  by  impairment  of  the  intellectual  faculties. 
This  point  frequently  is  difficult  to  determine  in  an  individual  instance  ; 
but  an  analysis  of  a  sufficient  number  of  cases  shows  impaired  memory, 
tardy,  inaccurate  and  feeble  connection  of  ideas,  abnormal  irritability  of 
temper  with  childish  susceptibility  to  petty  or  imaginary  annoyances, 
easily-excited  emotional  manifestations  and  a  variety  of  phenomena  de- 
noting abnormally  feeble  intellectual  power  following  any  considerable 
disorganization  of  cerebral  substance.  In  short,  pathological  conditions 
of  the  brain  all  go  to  show  that  the  intellectual  faculties  are  directly 
connected  with  the  cerebral  hemispheres. 

In  idiots  the  brain  usually  is  of  small  size,  although  there  are  excep- 
tions to  this  rule.  In  two  cases  of  adult  idiots,  reported  by  Tiedemann, 
the  brain  was  about  one-half  of  the  normal  weight.  The  brain  of  an 
idiotic  woman,  forty-two  years  of  age,  reported  by  Gore,  weighed  ten 
ounces  and  five  grains  (about  284  grams).  It  has  been  obser\-ed,  also, 
that  the  cerebellum  is    not  proportionally  diminished  in  size  in  idiots 


590  NERVOUS    SYSTEM 

(Bradley).  In  one  instance  reported,  the  proportion  of  the  cerebellum 
to  the  cerebrum  was  as  i  to  5.5.  In  the  healthy  adult  male  of  ordinary 
weight,  the  proportion  is  as  i  to  8|.  The  statements  just  made  in 
regard  to  the  brains  of  idiots  refer  to  cases  characterized  by  complete 
absence  of  intelligence,  and  furthermore,  probably,  by  very  small  de- 
velopment of  the  body.  On  the  other  hand,  there  are  instances  of 
idiocy,  the  body  being  of  ordinary  size,  in  which  the  weight  of  the 
encephalon  is  little  if  any  below  the  average.  Lelut  has  reported 
several  cases  of  this  kind.  In  one  of  these,  a  deaf-mute  idiot,  forty- 
three  years  of  age,  a  little  above  the  ordinary  stature,  presenting  "  idiocy 
of  the  lowest  degree  ;  almost  no  sign  of  intelligence ;  no  care  of  cleanli- 
ness," the  encephalon  weighed  48.32  ounces  (1369.8  grams).  Other 
cases  of  idiots  of  medium  stature  are  given,  in  which  the  brain  weighed 
but  little  less  than  the  normal  average.  In  the  IVc-st  Riding  Ltuiatic 
Asylum  Reports,  London,  1876,  is  a  report  of  the  case  of  a  congenital 
imbecile,  aged  thirty  years,  height  five  feet  and  eight  inches  (172.7  cen- 
timeters), died  of  phthisis,  whose  brain  weighed  7o|^  ounces  (2000 
grams).  This  is  heavier  than  the  heaviest  normal  brain  on  record. 
The  normal  brain-weight  is  49^^  ounces  (1408.3  grams). 

Rcactioti-tiine .  —  The  time  that  elapses  between  the  application  of 
sensory  stimulus  and  its  appreciation  by  the  sensorium  is  known  as 
reaction-time.  In  experiments  with  reference  to  this  point,  the  person 
observed  makes  an  electric  signal  when  the  sensation  is  perceived.  The 
reaction-time  is  0.12  of  a  second  for  a  shock  on  the  hand,  0.13  for  the 
forehead,  o.  1 7  for  the  toe  and  o.  1 3  for  a  sudden  noise  (Exner).  The  dura- 
tion is  about  0.16  of  a  second  for  impressions  made  on  the  nerves  of 
special  sense.  This  is  the  time  of  conduction  of  the  impression  to  the 
brain,  its  appreciation  by  the  individual,  the  generation  of  the  voluntary 
impulse  and  the  conduction  of  this  impulse  to  the  muscles  concerned 
in  making  the  signal.  It  probably  is  subject  to  variations  analogous  to 
those  observed  in  the  "  personal  equation." 

Centre  for  the  Expression  of  Ideas  in  Language.  —  The  location  of 
this  centre  depends  entirely  on  the  study  of  cases  of  disease  in  the 
human  subject.  It  is  evident  that  there  must  be  a  comprehension  of 
the  significance  of  words,  the  formation  of  an  idea  more  or  less  complex 
and  a  coordinate  action  of  the  muscles  concerned  in  speech  as  condi- 
tions essential  to  expression  in  spoken  language.  One  or  more  of  these 
conditions  may  be  absent  in  cases  of  disease  ;  and  the  general  absence 
of  the  power  of  verbal  expression,  when  this  depends  on  cerebral  lesion, 
is  known  as  aphasia.  This  is  quite  different  from  aphonia,  which  is 
simply  loss  of  voice.  If  the  comprehension  of  the  meaning  of  words 
is  absent,  the  individual  is  incapable  of  receiving  ideas  expressed  in 


CENTRES    FOR   THE    EXPRESSION    OF    IDEAS    IN    LANGUAGE        591 

language.  In  cases  of  aphasia  it  often  is  difficult  to  determine  this 
point.  In  certain  cases  it  is  possible  that  the  individual  may  under- 
stand what  is  said  and  may  form  ideas  to  which  he  is  unable  to  give 
verbal  expression.  In  such  instances  he  can  neither  speak  nor  write. 
There  are  certain  cases  in  which  written  or  printed  words  convey  no 
idea,  while  spoken  words  are  understood,  but  there  is  no  loss  of  intelli- 
gence and  words  are  spoken  without  difficulty.  This  condition  is  called 
word-blindness.  If  there  is  simple  want  of  coordination  of  the  muscles 
concerned  in  speech,  words  are  spoken  that  may  have  no  connection 
with  the  idea  to  be  conveyed,  but  the  individual  may  be  able  to  express 
himself  in  writing.  This  condition  is  known  as  ataxic  aphasia.  The 
inability  to  express  ideas  in  writing  is  called  agraphia,  and  this  usually 
is  an  indication  of  the  condition  known  as  amnesic  aphasia,  in  which  it 
is  impossible  to  put  ideas  into  words  in  any  way.  In  this  condition 
there  is  loss  of  memory  for  words,  as  its  name  implies.  Persons  affected 
with  purely  ataxic  aphasia  may  understand  and  write  perfectly,  but  they 
can  not  read  aloud  or  repeat  words  or  sentences  spoken  to  them.  In 
cases  of  simple  amnesic  aphasia,  patients  can  sometimes  repeat  dictated 
words.  In  cases  in  which  hemiplegia  is  marked,  the  aphasia  usually  is 
ataxic.  In  cases  in  which  there  is  no  hemiplegia,  the  aphasia  usually 
is  amnesic.  The  ataxic  and  amnesic  forms  of  aphasia  may  be  combined. 
A  full  description,  however,  of  the  many  and  varied  forms  of  aphasia 
would  be  out  of  place  in  this  work. 

In  1766  Pourfour  du  Petit  reported  a  case  of  aphasia,  with  lesion  of 
the  left  frontal  lobe  of  the  cerebrum,  in  which  the  patient  could  pro- 
nounce nothing  but  "  11011.'' 

Marc  Dax  (1836)  indicated  loss  or  impairment  of  speech  in  one  hun- 
dred and  forty  cases  of  right  hemiplegia.  These  observations  attracted 
little  attention,  until  1861,  when  the  subject  was  studied  by  Broca.  Since 
then,  many  cases  of  aphasia  with  lesion  of  the  left  frontal  lobe  have  been 
reported  by  various  writers.  In  1863  M.  G.  Dax,  a  son  of  Marc  Dax, 
limited  the  lesion  to  the  middle  portion  of  the  left  frontal  lobe.  It  was 
further  stated  by  Broca  and  Hughlings  Jackson  to  be  that  portion  of  the 
brain  nourished  by  the  left  middle  cerebral  artery  (the  inferior  frontal 
branch).  According  to  recent  observers,  the  most  frequent  lesion  is  in 
the  parts  supplied  by  the  left  middle  cerebral  artery,  particularly  the 
lobe  of  the  insula,  or  the  island  of  Reil ;  and  it  is  a  curious  fact  that  this 
part  is  found  only  in  man  and  monkeys,  being  in  the  latter  but  slightly 
developed. 

While  the  cerebral  lesion  in  aphasia  involves  the  left  frontal  lobe  in 
the  great  majority  of  cases,  there  are  instances  in  M^hich  the  right  lobe 
alone  is  affected,  and  these  occur  in  left-handed  persons.     Aside  from 


592  NERVOUS    SYSTEM 

the  anatomical  arrangement  of  the  arteries,  which  seem  to  furnish 
a  greater  quantity  of  blood  to  the  left  hemisphere,  it  is  e\-ident  that  so 
far  as  voluntary  movements  are  concerned,  the  right  hand,  foot,  eye  etc., 
are  used  in  preference  to  the  left,  and  that  the  motor  operations  of  the 
left  hemisphere  are  superior  in  activity  to  those  of  the  right.  Bateman 
has  quoted  two  cases  of  aphasia  dependent  on  lesion  of  the  right  side 
of  the  brain,  and  consequent  left  hemiplegia,  in  which  the  persons  were 
left-handed  ;  and  these,  few  as  they  are,  are  important,  as  showing  that 
a  person  may  use  the  right  side  of  the  brain  in  speech,  as  in  the  other 
motor  acts. 

Broadbent  has  reported  an  examination  of  the  encephalon  of  a  deaf 
and  dumb  woman.  In  this  case  the  brain  was  found  to  be  of  about  the 
usual  weight,  but  the  left  third  frontal  convolution  was  of  "  comparatively 
small  size  and  simple  character."' 

Taking  into  consideration  all  the  pathological  facts  bearing  on  the 
question,  it  seems  certain  that  in  the  great  majority  of  persons  the  organ 
or  part  presiding  over  the  faculty  of  language  is  situated  on  the  left 
side,  at  or  near  the  third  frontal  convolution  and  the  island  of  Reil, 
mainly  in  the  parts  supplied  by  the  middle  cerebral  artery.  In  some 
few  instances  the  organ  seems  to  be  in  the  corresponding  part  on  the 
right  side.  It  is  possible  that  originally  both  sides  preside  over  speech, 
and  the  superiority  of  the  left  side  of  the  brain  over  the  right  and  its 
more  constant  use  by  preference  in  right-handed  persons  may  lead  to 
a  gradual  abolition  of  the  action  of  the  right  side  of  the  brain,  in  con- 
nection with  speech,  simply  from  disuse.  This  view,  however,  is  purely 
hvpothetical.  In  some  cases  of  aphasia  from  lesion  of  the  speech- 
centre  in  the  left  hemisphere,  recovery  takes  place,  and  occasionally 
"  speech  has  been  again  lost  when  a  fresh  lesion  occurred  in  this  part 
of  the  right  hemisphere"  (Gowersj.  In  the  ataxic  form  of  aphasia,  the 
idea  and  memory  of  words  remain,  and  there  is  loss  of  speech  simply 
from  inability  to  coordinate  the  muscles  concerned  in  articulate  lan- 
guage. Patients  affected  in  this  way  can  not  speak  but  can  write  with 
ease  and  correctness.  In  the  amnesic  form  of  the  disease,  the  idea  and 
memory  of  language  are  lost ;  patients  can  not  speak,  and  are  affected 
with  agraphia,  or  inability  to  write.  The  motor  tracts  from  the  centre 
for  speech  pass  to  the  anterior  portion  of  the  posterior  division  of  the 
internal  capsule  and  thence  through  the  left  crus,  into  the  pons  Varolii, 
where  they  decussate  and  go  to  the  right  side  of  the  bulb. 

Recently  the  curious  fact  has  been  noted  that  in  the  deaf  and  dumb, 
who  use  a  sign-language  made  with  the  fingers,  lesion  of  the  speech- 
centre  is  attended  with  aphasia,  in  which  the  power  of  expressing  ideas 
bv  means  of  the  sign-language  is  lost. 


CHAPTER   XXIII 

THE    CEREBELLUM    AND    THE    BULB 

The  cerebellum  —  Physiological  anatomy  —  Extirpation  of  the  cerebellum  —  Pathological  ob- 
servations—  The  bulb  —  Physiological  anatomy  —  Uses  of  the  bulb  —  Nerve-centres  in 
the  bulb  —  Respiratory  centre  —  Vital  point  (so  called)  —  RoUing  and  turning  move- 
ments following  injury  of  certain  parts  of  the  encephalon  (forced  movements;. 


The  Cerebellum 

A  FULL  description  of  the  anatomy  of  the  cerebellum  is  not  necessary 
to  a  comprehension  of  its  uses,  so  far  as  these  are  known.  The  points, 
in  this  connection, 
that  are  most  im- 
portant are  the 
following  :  the  di- 
vision of  the  sub- 
stance of  the  cere- 
bellum into  gray 
and  white  matter ; 
the  connections  be- 
tween the  cells  and 
the  fibres  ;  the  con- 
nections of  the 
fibres  with  the  cere- 
brum and  with  cer- 
tain prolongations 
of  the  columns  of 
the      spinal      cord 


Cerebellum  and  bulb  (Hirschfeld). 


Fig.    147. 

I,  I,  corpus  dentatum  ;  2,  pons  Varolii;  3,  section  of  the  middle  pe- 
duncle ;  4,  4,  4,4,  4,  4,  laminae  forming  the  arbor  vitas;  5,  5,  olivary  body 
thrOUSrh    the    bulb  ■    °^  ^^^  bulb;  6,  anterior  pyramid  of  the  bulb;  7,  upper  extremity  of  the 
spinal  cord. 

and  the  passage  of 

fibres  between  the  two  lateral  lobes.     These  are  the  only  anatomical 

points  that  wall  be  considered. 

Physiological  Anatomy.  —  The  cerebellum,  situated  beneath  the  oc- 
cipital lobes  of  the  cerebrum,  weighs  about  5.25  ounces  (148.8  grams) 
in  the  male,  and  4.7  ounces  (135  grams)  in  the  female.  The  propor- 
tionate weight  to  that  of  the  cerebrum  is  as  i  to  8-i  in  the  male,  and  as 
I  to  8^  in  the  female.  It  is  separated  from  the  cerebrum  by  a  strong 
2Q  593 


594 


NERVOUS    SYSTEM 


process  of  the  dura  mater,  called  the  tentorium.  Like  the  cerebrum, 
the  cerebellum  presents  an  external  layer  of  gray  matter,  the  interior 
being  formed  of  white,  or  fibrous  nerve-tissue.  The  extent  of  the  gray 
substance  is  much  increased  by  convolutions  and  by  the  penetration 
from  the  surface  of  arborescent  processes  of  gray  matter.  Near  the 
centre  of  each  lateral  lobe,  embedded  in  the  white  substance,  is  an 


Fig.  148.  —  Section  of  a  cerebellar  lamina  perpendicular  to  its  axis  (R.  y  Cajal). 

^,  molecular  layer;  5,  granular  layer ;  C",  white  substance  ;  a,  cell  of  Purkinje  ;  <?,  its  neurite  with 
two  collaterals;  (^,  (5,  stellate  cells  of  the  molecular  layer ;  d,  basket-like  arrangement  of  teloneurites 
around  a  cell  of  Purkinje;  e,  superficial  stellate  cell;  /,  large  stellate  cell  of  the  granular  layer;  g,  small 
stellate  cell  of  the  granular  layer;  h,  centripetal  neurite ;  n,  centripetal  neurite  distributed  in  the  molec- 
ular layer;  J,  m,  neuroglia.  The  arborescent  dendrites  of  one  only  of  the  cells  of  Purkinje  are  repre- 
sented in  the  figure. 


irregularly-dentated  mass  of  gray  matter,  called  the  corpus  dentatum. 
The  convolutions  are  finer  and  more  abundant  and  the  gray  substance 
is  deeper  in  the  cerebellum  than  in  the  cerebrum.  These  convolutions, 
also,  are  present  in  many  of  the  inferior  animals  in  which  the  surface 
of  the  cerebrum  is  smooth. 

The  cerebellum  consists  of  two  lateral   hemispheres,  more  largely 
developed  in  man  than  in  the  inferior  animals,  and  a  median  lobe.     The 


PHYSIOLOGICAL   ANATOMY    OF    THE    CEREBELLUM 


595 


hemispheres  are  subdivided  into  smaller  lobes,  which  it  is  unnecessary 
to  describe.  Beneath  the  cerebellum,  bounded  in  front  and  below  by 
the  bulb  and  pons  Varolii,  laterally,  by  the  superior  peduncles,  and 
above,  by  the  cerebellum  itself,  is  a  lozenge-shaped  cavity,  called  the 
fourth  ventricle. 

The  gray  substance  of  the  cerebellum  is  divided  quite  distinctly 
into  two  layers.  The  external  layer  is  called  the  molecular  layer,  and 
the  internal,  the  granular  layer. 

The  molecular  layer  contains  the  large  cells  of  Purkinje.  These 
send  off  arborescent  dendrites  that  extend  toward  the  surface,  giving 
off  small  telodendrites   in  their  course.     The  neurites   pass   downward 


Fig.   149.  —  Section  of  a  cerebellar  lamina  parallel  to  its  axis  (R.  y  Cajal). 

^,  molecular  layer;  5,  granular  layer ;  C,  white  substance;  a,  small  stellate  cell  of  the  granular 
layer,  with  its  bifurcating  neurite ;  b,  bifurcation  ;  e,  bulbous  end  of  a  neurite ;  f,  neurite  of  a  cell  of 
Purkinje. 

into  the  white  substance.  In  passing  through  the  white  matter,  they 
give  off  collaterals,  which  reascend  to  the  molecular  layer.  The  mo- 
lecular layer  also  contains  small  stellate  cells,  which  give  off  neurites 
that  send  collaterals  to  form  a  basket-like  arrangement  around  the  cells. 

The  granular  layer  presents  small  stellate  cells  which  have  a  few 
short  dendrites  and  long  bifurcating  neurites,  the  latter  extending  into 
the  molecular  layer.  This  layer  also  has  large  stellate  cells  that  send 
their  dendrites  into  the  molecular  layer  and  distribute  their  neurites 
in  the  granular  layer. 

The  histology  of  the  structures  found  in  the  cerebellum  is  complex ; 
and  its  physiological  significance  is  as  yet  so  obscure  that  it  does  not 
seem  necessary  here  to  describe  it  more  in  detail. 


596 


NERVOUS    SYSTEM 


In  the  white  substance  are  found  arcuate  fibres  that  connect 
different  adjacent  areas  of  gray  matter. 

The  superior  peduncles  of  the  cerebellum  pass  to  the  cerebrum 
through  the  longitudinal  tract  of  the  pons  Varolii.  The  middle  pe- 
duncles connect  the  two  lateral  lobes  through  the  transverse  tract  of 


Fig.    150.—   CeH of  PurkinJe,X  170  {l^fia.mmg).'^ 

This  figure  shows  the  arborizing  dendrites  extending  upward  from  the  cell-body  and  a  neurite,  with 
one  collateral  passing  to  the  left  in  the  granular  layer. 

1  This  figure  is  an  exact  reproduction  of  an  actual  object  stained  by  the  method  of  Golgi. 
The  dendrites  extend  upward  toward  the  border  of  the  gray  matter.  The  cell-body  lies  near 
the  granular  layer.  From  the  cell-body,  a  neurite  passes  into  the  granular  layer  toward  the 
white  matter.  The  dendrites  belong  to  a  cell-body  that  has,  superimposed,  another  cell-body 
with  a  neurite.  The  two  cell-bodies  are  fused  as  well  as  the  granular  substance  below.  The 
dendrites  of  the  superimposed  cell-body  were  wiped  away.  Aside  from  the  fusing  of  the 
cell-bodies  and  of  the  granular  layers,  the  picture  has  not  been  touched  and  is  an  exact  repro- 
duction of  the  actual  appearances.  It  is  unusual  to  see  a  neurite  extending  for  any  considerable 
distance  from  a  Purkinje  cell. 


EXTIRPATION    OF   THE   CEREBELLUM  597 

the  pons.  The  inferior  peduncles  are  connected  with  the  restiform 
bodies  of  the  bulb  and  through  the  bulb  with  the  posterior  columns  of 
the  cord. 

Extirpation  of  the  Cerebellum.  —  When  its  greatest  part  or  the  entire 
cerebellum  is  removed  from  a  bird  or  a  mammal,  the  animal  being 
before  the  operation  in  a  normal  condition  and  no  other  parts  being 
injured,  there  are  no  phenomena  constantly  and  invariably  observed 
except  certain  modifications  of  the  voluntary  movements  (Flourens). 
The  intelligence,  general  and  special  sensibility,  the  involuntary  move- 
ments and  the  simple  faculty  of  voluntary  motion  remain.  The  move- 
ments, however,  are  irregular  and  incoordinate  ;  the  animal  can  not 
maintain  its  equilibrium  ;  and  on  account  of  the  impossibility  of  making 
regular  movements,  it  can  not  feed.  This  want  of  equilibrium  and  of 
the  power  of  coordinating  the  muscles  of  the  general  voluntary  system 
causes  the  animal  to  assume  remarkable  postures,  which,  to  one 
accustomed  to  these  experiments,  are  characteristic.  Later  experiments 
on  the  inferior  animals,  as  well  as  pathological  observations  on  the 
human  subject,  have  shown  that  muscular  coordination  is  disturbed 
when  the  median  lobe  is  extirpated,  while  removal  of  the  lateral  lobes 
has  no  such  effect.  It  is  well  known  that  many  muscular  acts  are  more 
or  less  automatic,  as  in  standing,  and,  to  a  certain  extent,  in  walking. 
These  acts,  as  well  as  nearly  all  voluntary  movements,  require  a  certain 
coordination  of  the  muscles,  and  this,  and  this  alone,  is  affected  by 
destruction  of  the  middle  lobe  of  the  cerebellum. 

Pathological  Obset'vations.  —  Records  of  cases  of  lesion  of  the  cere- 
bellum in  the  human  subject  have  accumulated  until  the  number  is 
quite  large.  A  study  of  cases  in  which  the  phenomena  referable  to 
cerebellar  injury  were  not  complicated  by  paralysis,  coma  or  convulsions, 
shows  that  serious  lesion  of  the  middle  lobe  is  almost  always  attended 
with  marked  muscular  incoordination  ;  but  cases  in  which  only  a  por- 
tion of  one  or  of  both  hemispheres  is  involved  may  not  present  any 
disorder  in  the  muscular  movements.  These  facts  are  in  accord  with 
the  results  of  experiments  on  the  lower  animals. 

The  phenomena  observed  in  cases  of  cerebellar  incoordination  are 
notably  different  from  those  presented  in  simple  locomotor  ataxia.  In 
cerebellar  disease,  the  gait  is  staggering,  much  as  it  is  in  alcoholic  intoxi- 
cation. The  chief  difficulty  seems  to  be  in  maintaining  the  equilibrium 
in  progression,  even  with  great  care  and  close  attention  on  the  part  of 
the  patient.  With  the  idea  in  mind  that  there  is  a  coordinating  centre 
for  the  muscles  of  progression,  and  that  this  centre  acts  imperfectly,  it 
seems  as  though  an  efficient  effort  at  coordination  were  impossible.  In 
locomotor  ataxia,  patients  seem  to  make  coordinating   efforts,  but  the 


598  NERVOUS    SYSTEM 

paths  by  which  these  efforts  find  their  way  to  the  muscles  are  disturbed, 
and  the  coordinating  process,  which  is  more  or  less  automatic  in  health, 
requires  peculiar  care  and  attention  ;  but  with  the  aid  of  the  sense  of 
sight  and  artificial  supports,  progression  may  be  safely  though  irregu- 
larly accomplished.  The  movements  are  jerky,  and  each  step  seems  to 
require  a  distinct  act  of  volition.  It  is  possible  to  imagine  that  in 
disorganization  of  the  paths  of  coordination  in  the  spinal  cord,  the 
coordinating  centre  may  act  in  some  degree  through  the  motor  paths  in 
the  direct  and  crossed  pyramidal  tracts.  It  is  certain  that  the  want  of 
normal  coordinating  power  is  supplemented  by  ordinary  voluntary  acts 
and  by  the  sense  of  sight. 

Vertigo  is  not  a  necessary  accompaniment  of  cerebellar  ataxia. 
Disease  of  the  semicircular  canals  of  the  internal  ear  (Meniere's 
disease)  is  attended  with  vertigo,  and  this  is  the  main  cause  of  the 
disturbances  of  equilibrium. 

The  Bulb 

The  medulla  oblongata,  or  bulb,  connects  the  spinal  cord  with  the 
encephalic  ganglia.  It  is  composed  of  white  and  gray  matter  and  pre- 
sents in  its  substance  a  number  of  important  nerve-centres.  It  is  not 
necessary  to  give  anything  like  a  complete  anatomical  description  of 
the  bulb.  Its  most  important  conducting  parts  are  those  which  are  con- 
tinuous with  the  columns  of  the  cord  and  pass  to  the  cerebrum  and 
cerebellum.  The  nuclei  of  origin  of  certain  of  the  cranial  nerves  in  the 
floor  of  the  fourth  ventricle  have  already  been  mentioned. 

Physiological  Anatomy. — The  bulb  is  pyramidal  in  form,  with  its 
broad  extremity  above,  and  rests  in  the  basilar  groove  of  the  occipital 
bone,  extending  from  the  lower  border  of  the  pons  Varolii  to  the  atlas. 
It  is  about  an  inch  and  a  quarter  (31.8  millimeters)  in  length,  three- 
quarters  of  an  inch  (19.  i  millimeters)  broad  at  its  widest  portion  and 
half  an  inch  (12.7  millimeters)  thick.  It  is  flattened  antero-posteriorly. 
Like  the  cord,  it  has  an  anterior  and  a  posterior  median  fissure. 

Apparently  continuous  with  the  anterior  columns  of  the  cord,  are 
the  two  anterior  pyramids,  one  on  either  side.  Viewed  superficially,  the 
innermost  fibres  of  these  pyramids  are  seen  to  decussate  in  the  median 
line ;  but  if  the  fibres  are  traced  from  the  cord,  it  is  found  that  they 
come  from  the  crossed  pyramidal  tracts  of  the  lateral  columns  and  that 
none  are  derived  from  the  anterior  columns.  The  fibres  of  the  external 
portion  of  the  anterior  pyramids  come  from  the  direct  pyramidal  tracts 
of  the  cord.  At  the  site  of  the  decussation,  the  pyramids  are  composed 
entirely  of  white  matter ;  but  as  the  fibres  spread  out  to  pass  to  the 


PHYSIOLOGICAL  ANATOMY   OF   THE   BULB 


599 


encephalon  above,  they  present  nodules  of  gray  matter   between    the 
fasciculi  of  fibres. 

External  to  the  anterior  pyramids,  are  the  corpora  olivaria.  These 
are  oval  and  are  surrounded  by  a  distinct  groove.  They  are  white 
externally  and  contain  a  gray  nucleus 
called  the  corpus  dentatum. 

External  to  the  corpora  olivaria,  are 
the  restiform  bodies,  formed  chiefly  of 
white  matter  and  constituting  the  postero- 
lateral portion  of  the  bulb.  They  are  con- 
tinuous with  the  posterior  white  columns 
of  the  cord.  The  restiform  bodies  spread 
out  as  they  ascend,  and  pass  to  the  cere- 
bellum, forming  a  large  portion  of  the 
inferior  peduncles.  Some  fibres  from  the 
restiform  bodies  pass  to  the  cerebrum. 

Beneath  the  olivary  bodies  and  be- 
tween the  anterior  pyramids  and  the 
restiform  bodies,  are  the  lateral  tracts  of 
the  bulb,  sometimes  called  the  intermedi- 
ary or  lateral  fasciculi,  or  the  funiculi  of 
Rolando.  These  are  composed  of  an  in- 
timate mixture  of  white  and  gray  matter 
and  have  a  yellowish  gray  color.  They 
receive  all  that  portion  of  the  antero- 
lateral columns  of  the  cord  which  does 
not  enter  into  the  composition  of  the 
anterior  pyramids.  They  usually  are  de- 
scribed as  parts  of  the  restiform  bodies ; 
but  they  are  peculiarly  important,  from 
the  fact  that  they  contain  the  gray  centres 

■>  o      y  11,  arciform  fibres ;   12,  upper  extremity 

presiding  over  respiration;    and  for  that    of  the  spinal  cord ;  13,  ligamentum  den- 
reason  they  are  here  described  as  distinct     "^"^""^'  ^4.  14.    uia  maer  o 
fasciculi. 

The  posterior  pyramids  (funiculi  gra- 
ciles)  are  the  smallest  of  all.  They  pass 
upward  to  the  cerebellum,  without  decus- 
sating, joining  the  restiform  bodies  above. 
They  are  composed  chiefly  of  white  matter. 
As  they  pass  upward  in  the  bulb,  they  diverge,  leaving  a  space  called 
the  fourth  ventricle. 

The   fourth  ventricle  is  the  cavity  between   the    pons  Varolii,  the 


Fig.  151- 


Anterior  view   of  the   bulb 
(Sappey). 

I,  infundibulum  ;  2,  tuber  cinereum  ; 
3,  corpora  albicantia ;  4,  cerebral  pe- 
duncle; 5,  pons  Varolii;  6,  origin  of 
the  middle  peduncle  of  the  cerebel- 
lum ;  7,  anterior  pyramids  of  the  bulb 

8,  decussation  of  the  anterior  pyramids 

9,  olivary  bodies ;    10,   restifort)i   bodies 


cord;  15,  optic  tracts;  16,  chiasm  of 
the  optic  nerves;  17,  inotor  oculi  com- 
munis; 18,  patheticus;  19,  fifth  nerve; 
20,  motor  oculi  externus ;  21,  facial 
nerve  ;  22,  auditory  nerve  ;  23,  nerve  of 
Wrisberg ;  24,  glosso-pharyngeal  nerve ; 
25,  pneumogastric ;  26,  26,  spinal  acces- 
sory; 27,  sublingual  nerve;  28,  29,  30, 
cervical  nerves. 


6oo 


NERVOUS    SYSTEM 


bulb  and  the  cerebellum.  It  is  lozenge-shaped,  the  acute  angles  being 
above  and  below.  The  upper  angle  extends  to  the  upper  border  of  the 
pons,  and  the  lower  angle,  to  the  lower  border  of  the  olivary  bodies. 
The  triangles  which  form  this  lozenge  are  of  nearly  equal  size.  The 
superior  triangle  is  bounded  laterally  by  the  superior  peduncles  of  the 
cerebellum,  as  they  converge  to  meet  at  the  corpora  quadrigemina. 
The  inferior  triangle  is  bounded  laterally  by  the  funiculi  graciles  and 
the  restiform  bodies  of  the  medulla,  which  diverge  at  its  lower  angle. 
The  arched  roof  of  the  ventricle  is  formed  by  the  valve  of  Vieussens, 
which  is  stretched  between  the  superior  peduncles  of  the  cerebellum 
and  covers  the  anterior  triangle,  and  the  cerebellum,  which  covers  the 

posterior    triangle.      Beneath 


the  cerebellum  is  a  reflection 
of  the  pia  mater.  The  fourth 
ventricle  communicates  above 
with  the  third  ventricle  by  the 
aqueduct  of  Sylvius ;  below 
with  the  subarachnoid  space, 
by  the  foramen  of  Magendie  ; 
and  by  a  small  opening  below, 
with  the  central  canal  of  the 
cord.  The  floor  of  the  ventri- 
cle is  formed  by  the  posterior 
surface  of  the  pons  above  and 
the  bulb  below.  It  presents 
a  fissure  in  the  median  line, 
which  terminates  below  in  the 
calamus  scriptorius.  By  the 
sides  of  the  median  fissure 
are  the  fasciculi  teretes,  which 
correspond  to  the  intermediary  fasciculi  of  the  bulb.  Little  eminences 
in  the  floor  indicate  the  situation  of  nuclei  of  origin  of  cranial  nerves. 
The  floor  is  composed  mainly  of  a  layer  of  gray  matter,  continuous 
with  the  gray  commissure  of  the  cord.  The  lower  portion  of  the  floor 
is  marked  by  transverse  lines  of  white  matter  emerging  from  the  median 
fissure. 

The  two  lateral  halves  of  the  posterior  portion  of  the  bulb  are  con- 
nected together  by  fibres  arising  from  the  gray  matter  of  the  lateral 
tracts,  or  intermediary  fasciculi,  passing  obliquely,  in  a  curved  direction 
from  behind  forward,  to  the  raphe  in  the  median  line.  There  also  are 
fibres  passing  from  before  backward  to  form  a  posterior  commissure, 
and  fibres  arising  from  the  cells  of  the  olivary  bodies,  which  connect 


Fig.  152.  —  Floor  of  the  fourth  ventricle  (Hirschfeld). 

I,  median  fissure,  between  the  fasciculi  teretes; 
2,  transverse  white  striae;  3,  inferior  peduncle  of  the 
cerebellum;    4,  posterior  pyramid   (funiculus  gracilis); 

5,  5,  superior  peduncles  (divided)  of  the  cerebellum ;  6, 

6,  bands  to  the  side  of  the  crura  cerebri;  7,7,  lateral 
grooves  of  the  crura  cerebri ;   8,  corpora  quadrigemina. 


PHYSIOLOGICAL   ANATOMY    OF  THE   BULB  6oi 

the  gray  substance  of  the  lateral  halves.  Commissural  fibres  also  con- 
nect the  gray  matter  of  the  lateral  tracts  with  the  corpora  dentata  of 
the  olivary  bodies,  and  the  olivary  bodies  with  the  cerebellum,  their 
fibres  forming  part  of  the  inferior  peduncles  of  the  cerebellum.  In 
addition,  it  is  probable  that  fibres,  taking  their  origin  from  all  the  gray 
nodules  of  the  bulb,  pass  to  the  parts  of  the  encephalon  situated  above. 

So  far  as  the  fibres  of  origin  of  the  cranial  nerves  are  concerned,  it 
may  be  stated  in  general  terms  that  a  number  of  the  motor  roots  arise 
from  the  gray  matter  of  the  floor  of  the  fourth  ventricle,  the  roots  of 
sensory  nerves  arising  from  gray  nuclei  in  the  posterior  portions. 

It  is  hardly  necessary  to  discuss  the  action  of  the  bulb  as  a  con- 
ductor of  sensory  impressions  and  of  motor  stimulus  to  and  from  the 
brain.  It  is  evident  that  there  is  conduction  of  this  kind  from  the  spinal 
cord  to  the  ganglia  of  the  encephalon,  and  this  must  take  place  through 
the  medulla :  a  fact  which  is  inevitable,  from  its  anatomical  relations, 
and  which  is  demonstrated  by  its  section  in  living  animals. 

The  action  of  the  bulb  as  a  reflex  nerve-centre  depends  on  its  gray 
matter.  When  the  gray  substance  is  destroyed,  certain  important  reflex 
phenomena  are  instantly  abolished.  From  its  connection  with  the 
cranial  nerves,  one  would  expect  it  to  play  an  important  part  in  the 
movements  of  the  face,  in  deglutition,  in  the  action  of  the  heart  and  of 
various  glands,  important  points  that  are  fully  considered  under  ap- 
propriate heads. 

The  connections  of  the  bulb  with  the  different  columns  of  the  cord 
are  as  follows  :  — 

The  columns  of  Tiirck  pass  directly  from  the  cord  to  the  cerebrum 
by  fibres  at  the  outer  borders  of  the  anterior  pyramids. 

The  crossed  pyramidal  tracts  pass  to  the  anterior  pyramids  and 
there  decussate. 

The  anterior  ground  columns  and  the  lateral  bundles  connect  the 
gray  matter  of  the  cord  with  the  gray  matter  of  the  bulb. 

The  direct  cerebellar  fascicuH  and  the  columns  of  Goll  pass  to  the 
cerebellum  through  the  funiculi  graciles,  next  the  posterior  fissure. 

The  columns  of  Burdach  and  the  descending  and  ascending  cerebel- 
lar tracts  pass  to  the  restiform  bodies. 

The  fibres  of  the  funiculi  graciles  and  some  of  the  fibres  of  the  col- 
umns of  Burdach  go  to  the  cerebellum  without  decussating.  A  few 
fibres  of  the  restiform  bodies  go  directly  to  the  cerebrum. 

Nerve-centres  in  the  Bulb.  — •  The  following  centres  have  been 
located  in  the  bulb :  — 

I.  The  centre  for  closure  of  the  eyelids  is  related  to  the  nuclei  of 
origin  of  the  facial  and  the  trifacial. 


6o2  NERVOUS    SYSTEM 

2.  The  sneezing  centre  is  related  to  the  trifacial  and  certain  expira- 
tory muscles. 

3.  The  centre  for  coughing  is  related  to  the  pneumogastric  and 
certain  expiratory  muscles. 

4.  The  centre  for  swallowing  is  related  to  the  glosso-pharyngeal,  the 
trifacial,  the  pneumogastric  and  the  muscles  of  deglutition. 

The  bulb  also  contains  (5)  the  vomiting  centre,  (6)  the  glycogenic 
centre,  (7)  the  dominant  sweat-centre,  (8)  the  salivary  centre,  and  (9) 
the  dominant  vasomotor  centres. 

10.  The  bulb  probably  contains  inhibitory  and  accelerator  cardiac 
centres.  The  fibres  of  the  inhibitory  nerves,  in  the  human  subject,  are 
contained  in  the  sheath  of  the  pneumogastric.  Arising  from  the  bulb, 
passing  into  the  cord  and  out  of  the  cord  with  the  communicating 
branches  of  the  lower  cervical  and  upper  dorsal  nerves  to  the  sympa- 
thetic and  thence  to  the  cardiac  plexus,  are  the  so-called  accelerator 
nerves  of  the  heart.  The  inhibitory  and  accelerator  nerves  are  con- 
nected with  the  cardiac  centre  in  the  bulb.  The  inhibitory  fibres 
restrain,  or  inhibit  the  heart's  action,  and  the  action  of  the  accelerator 
nerves  is  to  increase  the  number  of  pulsations. 

11.  Respiratory  Centres.  — There  are  two  respiratory  centres  in  the 
bulb,  one  on  either  side  of  the  median  line  and  connected  together  by 
commissural  fibres.  These  centres  preside  over  the  respiratory  move- 
ments. They  do  not,  however,  occupy  all  that  portion  of  the  bulb 
included  between  the  two  planes  first  indicated  by  Flourens,  but  are 
confined  to  the  gray  matter  of  the  lateral  tracts,  or  the  intermediary 
fasciculi.  This  is  shown  by  the  fact  that  respiration  persists  in  animals 
after  division  of  the  anterior  pyramids  and  the  restiform  bodies. 
Nearly  all  experimenters  have  found  that  the  spinal  cord  may  be 
divided  below  the  bulb,  and  that  all  the  encephalic  ganglia  above  may 
be  removed,  respiratory  movements  still  persisting.  It  is  a  common 
thing  in  vivisection  to  kill  an  animal  by  breaking  up  the  bulb.  When 
this  is  done  there  are  no  struggles  and  no  manifestations  of  the  distress 
of  asphyxia.  The  respiratory  muscles  simply  cease  their  action,  and  the 
animal  loses  instantly  the  sense  of  want  of  air.  A  striking  contrast  to 
this  is  presented  when  the  trachea  is  tied  or  when  all  the  respiratory 
muscles  are  paralyzed  without  touching  the  medulla. 

Under  normal  conditions  the  centres  on  the  two  sides  probably 
operate  through  the  pneumogastric  nerves,  and  the  respiratory  move- 
ments on  the  two  sides  are  synchronous.  That  there  is  a  respiratory 
centre  on  either  side  is  shown  by  the  experiment  of  dividing  the  bulb 
longitudinally  in  the  median  line,  the  respiratory  movements  afterward 
continuing  with  regularity.     If,  now,  the  pneumogastric  is  divided  on 


RESPIRATORY    NERVE-CENTRES  603 

one  side,  the  respiratory  movements  on  that  side  become  slower  and  are 
no  longer  synchronous  with  the  movements  on  the  opposite  side.  This 
shows  that  while  the  respiratory  centres  on  the  two  sides  normally  act 
together,  being  connected  with  each  other  by  commissural  fibres,  each 
one  has  independent  connections  with  the  pneumogastric  on  the  corre- 
sponding side  of  the  body. 

In  ordinary  tranquil  respiration  the  act  of  inspiration  is  reflex  and 
is  due  to  an  impression  conveyed  to  the  bulb  through  the  pulmonary 
branches  of  the  pneumogastrics.  It  has  lately  been  asserted  that  the 
impression  which  gives  rise  to  inspiratory  movements  is  due  to  partial 
collapse  of  the  air-vesicles,  and  that  when  the  vesicles  are  distended,  an 
impression  is  received  by  the  bulb  that  gives  rise  to  movements  of  expi- 
ration. It  is  difficult,  however,  to  reconcile  this  theory  with  the  facts. 
It  does  not  account  for  the  absence  of  respiratory  movements  in  the 
foetus,  when  the  air-cells  are  entirely  collapsed,  or  for  certain  phenomena 
that  follow  inflation  of  the  lungs  with  irrespirable  gases.  It  is  more 
reasonable  to  assume  that  the  impression,  in  tranquil  respiration,  is  due 
to  the  carbon  dioxide  contained  in  the  air-cells,  and  that  the  movements 
of  expiration  are  almost  entirely  passive. 

In  difficult  respiration  attended  with  a  sense  of  suffocation  and 
violent  inspiratory  efforts,  the  sense  is  due  to  the  circulation  of  non- 
oxygenated  blood  in  the  respiratory  centres.  This  was  shown  by  a 
number  of  experiments  (Flint)  begun  in  1861  and  carried  on  up  to  1880. 

]^ital  Poijit  {so  called).  —  Since  it  has  been  definitely  ascertained  that 
destruction  of  a  restricted  portion  of  the  gray  substance  of  the  bulb 
produces  instantaneous  and  permanent  arrest  of  the  respiratory  move- 
ments, Flourens  and  others  have  called  this  centre  the  vital  knot,  de- 
struction of  which  is  immediately  followed  by  death.  With  the  existing 
knowledge  of  the  properties  and  uses  of  the  different  tissues  and  organs 
of  which  the  body  is  composed,  it  is  almost  unnecessary  to  present  any 
arguments  to  show  the  unphilosophical  character  of  such  a  proposition. 
One  can  hardly  imagine  such  a  thing  as  instantaneous  death  of  the 
entire  organism  ;  and  still  less  can  it  be  assumed  that  any  restricted 
portion  of  the  nervous  system  is  the  one  essential  vital  point.  Probably, 
a  very  powerful  electric  discharge  passed  through  the  entire  cerebro- 
spinal axis  produces  the  nearest  approach  to  instantaneous  death ;  but 
even  then  it  is  by  no  means  certain  that  some  parts  do  not  for  a  time 
retain  their  physiological  properties.  In  apparent  death  the  ner\'es  and 
the  heart  may  be  shown  to  retain  their  characteristic  properties ;  the 
muscles  will  contract  under  stimulus,  and  will  appropriate  oxygen  and 
give  off  carbon  dioxide,  or  respire ;  the  glands  may  be  made  to  secrete ; 
and  no  one  can  assume  that  under  these  conditions  the  entire  orsianism 


604  NERVOUS    SYSTEM 

is  dead.  There  seems  to  be  no  such  thing  as  death,  except  as  the  various 
tissues  and  organs  which  go  to  make  up  the  entire  body  become  so 
altered  as  to  lose  their  physiological  properties  beyond  the  possibility 
of  restoration  ;  and  this  does  not  occur  for  all  parts  of  the  organism  in 
an  instant.  A  person  drowned  may  be  to  all  appearances  dead,  and 
certainly  would  die  without  measures  for  restoration  ;  yet  in  such  in- 
stances, restoration  may  be  accomplished,  the  period  of  apparent  death 
being  simply  a  blank,  so  far  as  the  recollection  of  the  individual  is 
concerned.  It  is  as  impossible  to  determine  the  exact  instant  when 
the  vital  principle,  or  whatever  it  may  be  called,  leaves  the  body  in 
death,  as  to  indicate  the  time  when  the  organism  becomes  a  living 
being.  Death  is  nothing  more  than  a  permanent  destruction  of  so-called 
vital  physiological  properties  ;  and  this  occurs  successively  and  at  differ- 
ent times  for  different  tissues  and  organs. 

When  it  is  seen  that  frogs  will  live  for  weeks,  and  sometimes  for 
months,  after  destruction  of  the  bulb,  and  that  in  mammals,  by  keep- 
ing up  artificial  respiration,  many  of  the  most  important  physiological 
acts,  such  as  the  movements  of  the  heart,  may  be  prolonged  for  hours 
after  decapitation,  one  can  understand  the  physiological  absurdity  of 
the  proposition  that  there  is  any  such  thing  as  a  vital  point,  either  in 
the  bulb  or  in  any  other  part  of  the  nervous  system. 

Rolling  and   Turning    Movements  following    Injury  of  Certain 
Parts  of  the  Encephalon  (Forced  Movements) 

The  remarkable  movements  of  rolling  and  turning,  produced  by 
section  or  injury  of  certain  of  the  commissural  fibres  of  the  encephalon, 
are  not  very  important  in  their  bearing  on  the  uses  of  the  brain,  and  they 
are  rather  to  be  classed  among  the  curiosities  of  experimental  physiology. 
The  movements  follow  unilateral  lesions  and  are  dependent,  to  a  certain 
extent,  on  a  consequent  inequality  in  the  power  of  the  muscles  on  one 
side,  without  actual  paralysis.  These  have  been  called  forced  move- 
ments. Injury  to  the  following  parts  usually  determines  movements  of 
rotation :  — 

"  I. 

"2. 

"3. 
"4- 
"5. 
"6. 

"7- 


Cerebral  hemispheres  ; 

Corpora  striata ; 

Optic  thalami  (Flourens,  Longet,  Schiff); 

Cerebral  peduncles  (Longet); 

Pons  Varolii ; 

Tubercula  quadrigemina,  or  bigemina  (Flourens); 

Peduncles  of   the  cerebellum,  especially  the    middle,  and    the 


lateral  portions  of  the  cerebellum  (Magendie); 


FORCED    MOVEMENTS  605 

"8.    Olivary  bodies,  restiform  bodies  (Magendie); 

"9.    External  part  of  the  anterior  pyramids  (Magendie); 

"  10.  Portion  of  the  bulb  from  which  the  facial  nerve  arises  (Brown- 
Sequard) ; 

"II.    Optic  nerves ; 

"12.  Semicircular  canals  (Flourens);  auditory  nerve  (Brown- 
Sequard)." 

The  movements  that  follow  unilateral  injury  of  the  parts  mentioned 
above  are  of  two  kinds ;  namely,  roUing  of  the  entire  body  on  its  longi- 
tudinal axis,  and  turning,  always  in  one  direction,  in  a  small  circle,  called 
by  the  French  the  movement  of  manege.  A  capital  point  to  determine 
in  these  phenomena  is  whether  the  movements  are  due  to  paralysis  or 
enfeeblement  of  certain  muscles  upon  one  side  of  the  body,  to  a  direct  or 
reflex  irritation  of  the  parts  of  the  nervous  system  involved  or  to  both 
these  causes  combined.  The  experiments  of  Brown-Sequard  and  others 
show  that  the  movements  may  be  due  to  irritation  alone,  for  thev  occur 
when  parts  of  the  encephalon  and  the  upper  portions  of  the  cord  are 
simply  pricked,  without  section  of  fibres.  When  there  is  extensive 
division  of  fibres,  it  is  probable  that  the  effects  of  the  enfeeblement  of 
certain  muscles  are  added  to  the  phenomena  produced  by  simple  irrita- 
tion. The  most  satisfactory  explanation  of  these  movements  is  the  one 
proposed  by  Brown-Sequard,  who  attributed  them  to  a  more  or  less  con- 
vulsive action  of  muscles  on  one  side  of  the  body,  produced  by  irritation 
of  the  nerve-centres.  He  regarded  the  rolling  as  simply  an  exaggera- 
tion of  the  turning  movements,  and  places  both  in  the  same  category. 

It  is  not  necessary  to  enter  into  an  extended  discussion  of  these 
experiments.-  In  some  of  them,  the  movements  have  been  observed 
toward  the  side  operated  on,  and  in  others,  toward  the  sound  side. 
These  differences  probably  depend  on  the  fact  that  in  certain  experi- 
ments the  fibres  are  involved  before  their  decussation,  and  in  others, 
after  they  have  crossed  in  the  median  line.  In  some  instances  the 
movements  may  be  due  to  a  reflex  action,  from  stimulation  of  afferent 
fibres,  and  in  others  the  action  of  the  irritation  may  be  direct. 


CHAPTER   XXIV 

SYMPATHETIC    SYSTEM —SLEEP 

Cranial  ganglia  —  Cervical  ganglia  —  Thoracic  ganglia  —  Ganglia  in  the  abdominal  and  the 
pelvic  cavities  —  General  properties  of  the  sympathetic  ganglia  and  nerves  —  Direct 
experiments  on  the  sympathetic  —  Vasomotor  centres  and  nerves  —  Reflex  vasomotor 
phenomena  —  Vaso-inhibitory  nerves  —  Trophic  centres  and  nerves  —  Sleep  —  Dreams  — 
Condition  of  the  brain  and  nervous  system  during  sleep. 

Like  the  cerebro-spinal  system,  the  sympathetic  is  composed  of 
centres,  or  ganglia,  and  nerves.  The  ganglia  contain  nerve-cells,  most 
of  which  differ  but  little  from  the  cells  of  the  encephalon  and  spinal 
cord.  The  nerves  are  composed  of  fibres,  some  of  which  are  nearly 
identical  in  structure  with  the  ordinary  motor  and  sensory  fibres,  while 
many  are  the  so-called  gelatinous  fibres.  The  nerve-fibres  are  con- 
nected with  the  cells  in  the  ganglia,  and  the  ganglia  are  connected  with 
each  other  by  commissural  fibres. 

The  sympathetic  ganglia  constitute  a  continuous  chain  on  either 
side  of  the  body,  beginning  above  with  the  ophthalmic  ganglia  and  ter- 
minating below  in  the  ganglion  impar.  It  is  important  to  note,  how- 
ever, that  the  chain  of  ganglia  is  not  independent,  but  that  each  ganglion 
receives  motor  and  sensory  filaments  from  the  cerebro-spinal  nerves,  and 
that  filaments  pass  from  the  sympathetic  to  the  cerebro-spinal  system. 
The  general  distribution  of  the  sympathetic  filaments  is  to  mucous  mem- 
branes—  and  possibly  to  integument,  —  to  the  heart,  to  non-striated 
muscular  fibres,  and  particularly  to  the  muscular  coat  of  the  arteries. 
So  far  as  has  been  shown  by  anatomical  investigations,  there  are  no 
fibres  derived  exclusively  from  the  sympathetic  that  are  distributed  to 
striated  muscles  except  those  which  pass  to  the  muscular  tissue  of  the 
heart.  Near  the  terminal  filaments  of  the  sympathetic,  in  most  of  the 
parts  to  which  these  fibres  are  distributed,  there  exist  large  numbers  of 
ganglionic  cells. 

The  general  arrangement  of  the  sympathetic  ganglia  and  the  distri- 
bution of  the  nerves  may  be  stated  very  briefly  ;  but  a  knowledge  of 
certain  anatomical  points  is  indispensable  as  an  introduction  to  an  intel- 
ligent study  of  the  physiology  of  this  system. 

Jn  the  cranium,  are  the  four  cranial  ganglia  —  the  ophthalmic,  the 
spheno-palatine,  the  otic  and  the  submaxillary.     In  the  neck,  are  the 

606 


SYMPATHETIC    GANGLIA  607 

three  cervical  ganglia  —  the  superior,  middle,  and  inferior.  In  the  chest, 
are  the  twelve  thoracic  ganglia,  corresponding  to  the  twelve  ribs.  The 
great  semilunar  ganglia,  the  largest  of  all  and  sometimes  called  the  ab- 
dominal brain,  are  in  the  abdomen,  by  the  side  of  the  coeliac  axis.  In 
the  lumbar  region,  in  front  of  the  spinal  column,  are  the  four  lumbar 
ganglia.  In  front  of  the  sacrum  are  the  four  or  five  sacral,  or  pelvic 
ganglia ;  and  finally,  in  front  of  the  coccyx,  is  a  small  single  ganglion, 
the  last  of  the  sympathetic  chain,  called  the  ganglion  impar.  Thus,  the 
sympathetic  cord,  as  it  is  sometimes  called,  consists  of  twenty-eight  to 
thirty  ganglia  on  either  side,  terminating  below  in  a    single  ganglion. 

Cranial  Ganglia.  —  The  ophthalmic,  lenticular,  or  ciliary  ganglion  is 
situated  deeply  in  the  orbit,  is  of  a  reddish  color  and  about  the  size  of 
a  pin's-head.  It  receives  a  motor  branch  from  the  third  pair  and  sensory 
filaments  from  the  nasal  branch  of  the  ophthalmic  division  of  the  fifth.  It 
also  is  connected  with  the  cavernous  plexus  and  with  Meckel's  gan- 
glion. Its  so-called  motor  and  sensory  roots  from  the  third  and  the 
fifth  pair  have  already  been  described  in  connection  with  these  nerves. 
Its  filaments  of  distribution  are  the  ten  or  twelve  short  ciliary  nerves, 
which  pass  to  the  ciliary  muscle  and  the  iris.  A  dehcate  filament  from 
this  ganglion  passes  to  the  eye,  with  the  central  artery  of  the  retina,  in 
the  canal  in  the  centre  of  the  optic  nerve. 

The  uses  of  the  ophthalmic  ganglion  relate  mainly  to  the  action  of 
the  ciliary  muscle  and  iris ;  and  it  is  necessary  here  only  to  indicate  its 
anatomical  relations,  leaving  its  function  to  be  taken  up  in  connection 
with  the  physiology  of  vision. 

The  spheno-palatine,  or  Meckel's  ganglion,  is  the  largest  of  the 
cranial  ganglia.  It  is  triangular  in  shape,  reddish  in  color,  and  situated 
in  the  spheno-maxillary  fossa,  near  the  spheno-palatine  foramen.  It 
receives  a  motor  root  from  the  facial,  by  the  Vidian  nerve.  Its  sensory 
roots  are  the  two  spheno-palatine  branches  from  the  superior  maxillary 
division  of  the  fifth.  It  has  a  large  number  of  branches  of  distri- 
bution. Two  or  three  small  filaments  enter  the  orbit  and  go  to  its 
periosteum.  Its  other  branches,  which  it  is  unnecessary  to  describe 
fully  in  detail,  are  distributed  to  the  gums,  the  membrane  covering  the 
hard  palate,  the  soft  palate,  the  uvula,  the  roof  of  the  mouth,  the  tonsils, 
the  mucous  membrane  of  the  nose,  the  middle  auditory  meatus,  a  portion 
of  the  pharyngeal  mucous  membrane  and  the  levator  palati  and  azygos 
uvulae  muscles.  It  is  probable  that  the  filaments  sent  to  these  two 
striated  muscles  are  derived  from  the  facial  nerve  and  do  not  properly 
belong  to  the  sympathetic  system.  The  ganghon  sends  also  a  short 
branch  of  a  reddish  gray  color  to  the  carotid  plexus. 

The  otic  ganglion,  sometimes  called  Arnold's  ganghon,  is  a  small, 


6o8 


NERVOUS    SYSTEM 


Fig.  153.  —  Cervical  and  thoracic  portions  of  the  sympathetic  (Sappey). 

I,  I,  I,  chain  of  ganglia  of  the  sympathetic  ;  2,  superior  cervical  ganglion  ;  3,  branches  to  the 
carotid;  4,  filaments  from  the  facial  to  the  spheno-palatine  and  to  the  otic  ganglion;  5,  ophthalmic 
ganglion;  6,  spheno-palatine  ganglion  ;  7,  otic  ganglion  ;  8,  submaxillary  ganglion;  9,  middle  cervical 
ganglion;  10,  cord  connecting  the  two  ganglia ;  11,  inferior  cervical  ganglion;  12,  13,  filaments  con- 
necting this  with  the  middle  ganglion  ;  14,  superior  cardiac  nerve ;  15,  middle  cardiac  nerve ;  16,  in- 
ferior cardiac  nerve;  17,  17,  cardiac  plexus;  18,  ganglion  of  the  cardiac  plexus;  19,  nerve  following 
the  right  coronary  artery;  20,21,  22,  great  splanchnic  nerve;  23,  lesser  splanchnic  nerve;  24,  24,  solar 
plexus, 


SY.MPATHETIC    GANGLIA 


609 


oval,   reddish   gray  body,   situated  just    below   the    foramen    ovale.     It 
receives   a  motor  filament  from  the  facial  and  sensorv  filaments  from 


branches  of  the  fifth 
and  of  the  glosso-phar- 
yngeal.  Its  filaments  of 
distribution  go  to  the 
mucous  menibrane  of 
the  tympanic  cavity  and 
Eustachian  tube  and  to 
the  tensor  tympani  and 
tensor  palati  muscles. 
Reasoning  from  the  gen- 
eral mode  of  distribu- 
tion of  the  sympathetic 
filaments,  those  going  to 
the  striated  muscles  are 
derived  from  the  facial. 
It  also  sends  branches 
to  the  carotid  plexus. 

The  submaxillary  gan- 
glion, which  is  situated  on 
the  submaxillary  gland, 
is  small,  rounded,  and 
reddish  gray  in  color.  It 
receives  motor  filaments 
from  the  chorda  tympani 
nerve  and  sensory  fila- 
ments from  the  lingual 
branch  of  the  fifth.  Its 
filaments  of  distribution 
go  to  Warton's  duct,  to 
the  mucous  membrane 
of  the  mouth  and  to  the 
submaxillary  gland. 

Cervical  Gajiglia.  — 
The  three  cer\'ical    o-an- 


v3^ 


Fig.  154.  —  Lumbar  and   sacral  parfions  of  the    sympathetic 
(Sappey). 


I,  solar  plexus  ;  2,  lower  end  of  the  great  splanchnic  nerve: 
3,  lower  end  of  the  lesser  splanchnic  nei^'e ;  4,  4,  last  two  thoracic 
glia  are  situated  opposite  gangUa;  5,  5,  the  four  lumbar  ganglia ;  6,  6,  7,  7,  branches  from 
4-V,       <-Vi'    r1     -PH^^-V,  A  the  lumbar  ganglia ;  8,  superior  mesenteric  plexus ;  9,11,12,13, 

tne    iniru,    nitn    ana    SeV-      aortic   lumbar  plexus;    10,  inferior  mesenteric  plexus;  14,  14, 
enth      Cers-ical      vertebrae      sacral  portion  of  the  sympathetic;    15,  15,  16,  16,  17.  17,  hypo- 

gastric  plexus. 

respectively,    i  he  middle 

ganglion  sometimes  is  wanting,  and  the  inferior  ganglion  occasionally  is 

fused  with  the  first  thoracic    ganglion.     These  ganglia  are  connected 


6lO  NERVOUS    SYSTEM 

together  by  the  so-called  sympathetic  cord.  They  have  a  number  of 
filaments  of  communication  above  with  the  cranial  and  the  cervical 
nerves  of  the  cerebro-spinal  system.  Branches  from  the  superior 
ganglion  go  to  the  internal  carotid  to  form  the  carotid  and  the  cavern- 
ous plexuses,  following  the  vessels  as  they  branch  to  their  distribution. 
Branches  from  this  ganglion  pass  to  the  cranial  ganglia.  There  also 
are  branches  that  unite  with  filaments  from  the  pneumogastric  and  the 
glosso-pharyngeal  to  form  the  pharyngeal  plexus,  and  branches  that 
form  a  plexus  on  the  external  carotid,  the  vertebral  and  the  thyroid 
arteries,  following  the  ramifications  of  these  vessels. 

From  the  cervical  portion  of  the  sympathetic,  the  three  cardiac 
nerves  arise  and  pass  to  the  heart,  entering  into  the  formation  of  the 
cardiac  plexus.  The  superior  cardiac  nerve  arises  from  the  superior 
ganglion ;  the  middle  nerve,  the  largest  of  the  three,  arises  from  the 
middle  ganglion,  or  from  the  sympathetic  cord  when  this  ganglion  is 
wanting  ;  and  the  inferior  nerve  arises  from  the  inferior  cervical  ganglion 
or  the  first  thoracic.  These  nerves  present  frequent  communications 
with  various  of  the  adjacent  cerebro-spinal  nerves,  penetrate  the  tho- 
rax and  form  the  deep  and  superficial  cardiac  plexuses  and  the  pos- 
terior and  the  anterior  coronary  plexuses.  In  these  plexuses  there  are 
found  ganglioform  enlargements ;  and  on  the  surface  and  in  the  sub- 
stance of  the  heart,  are  collections  of  nerve-cells  connected  with  the 
fibres. 

Thoracic  Ganglia.  —  The  thoracic  ganglia  are  situated  in  the  chest, 
beneath  the  pleura,  and  rest  on  the  heads  of  the  ribs.  They  usually 
are  twelve  in  number,  but  occasionally  two  are  fused  into  one.  They 
are  connected  together  by  the  sympathetic  cord.  They  each  communi- 
cate by  two  filaments  with  the  cerebro-spinal  nerves.  One  of  these  is 
white,  like  the  spinal  nerves,  and  probably  passes  to  the  sympathetic, 
and  the  other,  of  a  grayish  color,  is  thought  to  contain  the  true  sympa- 
thetic filaments.  From  the  upper  six  ganglia  filaments  pass  to  the  aorta 
and  its  branches.  The  branches  that  form  the  posterior  pulmonary 
plexus  arise  from  the  third  and  fourth  ganglia.  The  great  splanchnic 
nerve  arises  mainly  from  the  seventh,  eighth  and  ninth  ganglia,  receiv- 
ing a  few  filaments  from  the  upper  six  ganglia.  This  is  a  large,  white, 
rounded  cord,  which  penetrates  the  diaphragm  and  passes  to  the  semi- 
lunar ganglion,  sending  a  few  filaments  to  the  renal  plexus  and  the 
suprarenal  capsules.  The  lesser  splanchnic  nerve  arises  from  the  tenth 
and  eleventh  ganglia,  passes  into  the  abdomen  and  joins  the  coeliac 
plexus.  The  renal  splanchnic  nerve  arises  from  the  last  thoracic 
ganglion  and  passes  to  the  renal  plexus.  The  three  splanchnic  nerves 
present  frequent  anastomoses  with  each   other. 


SYMPATHETIC    GANGLIA  6ll 

Ganglia  in  the  Abdominal  and  the  Pelvic  Cavities.  —  The  semilunar 
ganglia  on  the  two  sides  send  off  radiating  branches  to  form  the  solar 
plexus.  They  are  situated  by  the  side  of  the  coeKac  axis  and  near  the 
suprarenal  capsules.  These  are  the  largest  of  the  sympathetic  ganglia. 
From  these  arise  plexuses  distributed  to  various  parts  in  the  abdomen,  as 
follows  :  The  phrenic  plexus  follows  the  phrenic  artery  and  its  branches 
to  the  diaphragm.  The  coeliac  plexus  subdivides  into  the  gastric,  hepatic 
and  splenic  plexuses,  which  are  distributed  to  organs  as  their  names 
indicate.  From  the  solar  plexus  different  plexuses  are  given  off,  which 
pass  to  the  kidneys,  the  suprarenal  capsules,  the  testes  in  the  male  and 
the  ovaries  in  the  female,  the  intestines  (by  the  superior  and  inferior 
mesenteric  plexuses),  the  upper  part  of  the  rectum,  the  abdominal  aorta 
and  the  vena  cava.  The  filaments  follow  the  distribution  of  the  blood- 
vessels in  the  solid  viscera. 

The  lumbar  ganglia,  four  in  number,  are  situated  in  the  lumbar 
region,  on  the  bodies  of  the  vertebree.  They  are  connected  with  the 
ganglia  above  and  below  and  with  each  other  by  the  sympathetic 
cord,  receiving,  like  the  other  ganglia,  filaments  from  the  spinal 
nerves.  Their  branches  of  distribution  form  the  aortic  lumbar  plexus 
and  the  hypogastric  plexus  and  follow  the  course  of  the  blood- 
vessels. 

The  four  or  five  sacral  ganglia  and  the  ganglion  impar  are  situated 
by  the  inner  side  of  the  sacral  foramina  and  in  front  of  the  coccyx. 
These  are  connected  with  the  ganglia  above  and  with  each  other  and 
receive  filaments  from  the  sacral  nerves,  there  being  usually  two 
branches  of  communication  for  each  ganglion.  The  filaments  of  distri- 
bution go  to  all  the  pelvic  viscera  and  bloodvessels.  The  inferior  hypo- 
gastric, or  pelvic  plexus  is  a  continuation  of  the  hypogastric  plexus 
above  and  receives  a  few  filaments  from  the  sacral  ganglia.  The  uterine 
nerves  go  to  the  uterus  and  the  Fallopian  tubes.  In  the  substance  of 
the  uterus  the  nerves  are  connected  with  small  collections  of  ganglionic 
cells.  The  sympathetic  filaments  are  prolonged  into  the  upper  and 
lower  extremities,  following  the  course  of  the  bloodvessels  and  ter- 
minating  in   their  muscular  coat. 

The  filaments  of  the  sympathetic,  at  or  near  their  terminations,  are 
connected  with  ganglionic  cells,  not  only  in  the  heart  and  the  uterus,  but 
in  the  bloodvessels,  lymphatics,  the  coccygeal  gland,  the  submucous  and 
the  muscular  layer  of  the  entire  alimentary  canal,  the  salivary  glands, 
pancreas,  excretory  ducts  of  the  liver  and  pancreas,  the  larynx,  trachea, 
pulmonary  tissue,  bladder,  ureters,  the  entire  generative  apparatus, 
suprarenal  capsules,  thymus,  lachrymal  canals,  ciliary  muscle  and  the 
iris.     In  these  situations  nerve-cells  have  been  demonstrated,  and  it  is 


6i2  NERVOUS    SYSTEM 

probable  that  they  exist  everywhere  in  connection  with  the  terminal 
filaments  of  this  system  of  nerves. 

General  Properties  of  the  Sympathetic  Ganglia  and  Nerves.  —  The 
sympathetic  gangha  and  nerves  possess  a  dull  sensibility,  which  is 
particularly  marked  in  the  ganglia.  That  the  nerves  contain  afferent 
fibres  is  shown  by  certain   reflex  phenomena. 

Stimulation  of  the  sympathetic  produces  muscular  movements,  but 
these  are  confined  usually  to  non-striated  muscular  fibres,  to  which 
these  nerves  are  largely  distributed.  The  muscular  movements  do  not 
immediately  follow  stimulation  of  the  nerves,  but  there  is  a  long  latent 
period.  The  muscular  contraction,  also,  persists  for  a  time  and  the 
subsequent  relaxation  is  slow.  The  properties  of  the  vasomotor  nerves 
will  be  considered  separately. 

The  sympathetic  ganglia  are  connected  with  the  motor  and  sensory 
divisions  of  the  cerebro-spinal  system.  Some  of  the  ganglia  and  nerve- 
plexuses  are  directly  dependent  for  their  action  on  the  cerebro-spinal 
system,  while  others  are  capable,  at  least  for  a  time,  of  independent 
action.  Among  the  latter,  are  the  ganglia  of  the  heart,  the  intestinal 
plexuses,  the  plexuses  of  the  uterus  and  Fallopian  tubes,  of  the  ureters 
and  of  the  bloodvessels. 

Direct  Experiments  on  the  Sympathetic.  ■ —  The  experiments  of  Pour- 
four  du  Petit  (1712-1725)  were  the  first  to  give  any  positive  information 
regarding  the  action  of  the  sympathetic  system ;  and  these  observa- 
tions mav  be  taken  as  the  starting-point  of  a  definite  knowledge  of  the 
physiology  of  the  sympathetic,  although  they  showed  only  the  influence 
of  the  cervical  portion  on  the  eye.  In  18 16  Dupuy  removed  the  supe- 
rior cervical  ganglia  in  horses,  with  the  effect  of  producing  injection  of 
the  conjunctiva,  elevation  of  temperature  in  the  ear  and  an  abundant 
secretion  of  sweat  on  one  side  of  the  head  and  neck.  These  experiments 
showed  that  the  sympathetic  has  an  important  influence  on  nutrition, 
calorification  and  secretion.  In  1851  Bernard  divided  the  sympathetic 
in  the  neck  on  one  side  in  rabbits  and  noted  on  the  corresponding  side 
of  the  head  and  the  ear  increased  vascularity  and  an  elevation  in  tem- 
perature of  7°  to  11°  Fahr.  (4°  to  6°  C).  This  condition  of  increased 
heat  and  vascularity  continues  for  several  months  after  division  of  the 
nerve.  In  1852  Brown-Sequard  repeated  these  experiments  and  attrib- 
uted the  elevation  of  temperature  directly  to  an  increase  in  the  supply 
of  blood  to  the  parts  affected.  He  made  an  important  advance  in  the 
history  of  the  sympathetic  by  demonstrating  that  its  section  paralyzed 
the  muscular  coat  of  the  arteries,  and  further,  that  faradization  of  the 
nerve  in  the  neck  caused  the  vessels  to  contract.  This  was  the  discov- 
ery of  the  vasomotor  nerves,  and  it  belongs  without  question  to  Brown- 


DIRECT    EXPERIMENTS    ON    THE    SYMPATHETIC  613 

Sequard,  who  published  his  observations  in  August,  1852.  A  few 
months  later  in  the  same  year,  Bernard  made  similar  experiments  and 
presented  the  same  explanation  of  the  phenomena  observed. 

The  important  points  developed  by  the  first  experiments  of  Bernard 
and  of  Brown-Sequard  were  that  the  sympathetic  system  influences  the 
general  process  of  nutrition,  and  that  many  of  its  filaments  are  distributed 
to  the  muscular  coat  of  the  bloodvessels.  Before  these  experiments,  it 
had  been  shown  that  filaments  from  this  system  influenced  the  contrac- 
tions of  the  muscular  coat  of  the  alimentary  canal. 

When  the  sympathetic  is  divided  in  the  neck,  the  local  increase  in 
temperature  is  attended  with  a  considerable  increase  in  the  supply  of 
blood  to  the  side  of  the  head  corresponding  to  the  section.  The  increased 
temperature  is  due  to  a  local  exaggeration  of  the  nutritive  processes, 
apparently  dependent  on  the  hyperemia.  There  are  many  instances 
in  pathology  of  local  increase  in  temperature  attending  increased  supply 
of  blood  to  restricted  parts.  In  an  experiment  by  Bidder,  after  excis- 
ing about  half  an  inch  (12.7  millimeters)  of  the  cervical  sympathetic  in 
a  half-grown  rabbit,  the  ear  on  that  side,  in  the  course  of  about  two 
weeks,  became  distinctly  longer  and  broader  than  the  other. 

It  is  easy  to  observe  the  effects  of  dividing  the  sympathetic  in  the 
neck,  but  similar  phenomena  have  been  noted  in  other  parts.  Among 
the  most  striking  of  these  experiments  are  those  reported  by  Samuel, 
who  described  an  intense  hyperemia  of  the  mucous  membrane  of  the 
stomach  and  intestines  following  extirpation  of  the  coeliac  plexus.  By 
comparative  experiments  it  was  shown  that  this  did  not  result  from 
peritonitis  produced  by  the  operation. 

As  regards  secretion,  the  influence  of  the  sympathetic  is  very  marked. 
When  the  sympathetic  filaments  distributed  to  a  gland  are  divided,  the 
supply  of  blood  is  much  increased  and  an  abundant  flow  of  the  secre- 
tion follows  (Bernard).  Peyrani  has  shown  that  the  sympathetic  has 
an  influence  on  the  secretion  of  urine.  When  the  nerves  in  the  neck 
are  stimulated,  the  quantity  of  urine  and  of  urea  is  increased,  and  this 
increase  is  greater  with  the  induced  than  with  the  constant  current. 
When  the  sympathetic  is  divided,  the  quantity  of  urine  and  of  urea 
sinks  to  the  minimum. 

Moreau  published  in  1870  a  series  of  observations  on  the  influence 
of  the  sympathetic  nerves  on  the  secretion  of  liquid  by  the  intestinal 
canal,  which  are  important  as  affording  a  possible  explanation  of  the 
sudden  occurrence  of  watery  diarrhoea.  In  these  experiments  the  abdo- 
men was  opened  in  a  fasting  animal,  and  three  loops  of  intestine,  each 
loop  four  to  eight  inches  (100  to  200  millimeters)  long,  were  isolated 
by  ligatures.     All  the  nerves  passing  to  the  middle  loop  were  divided. 


6 14  NERVOUS    SYSTEM 

taking  care  to  avoid  the  bloodvessels.  The  intestine  was  then  replaced, 
and  the  wound  in  the  abdomen  was  closed  with  sutures.  The  next  day 
the  animal  was  killed.  The  two  loops  with  the  nerves  intact  were  found 
empty,  as  is  normal  in  fasting  animals,  and  the  mucous  membrane  was 
dry ;  but  the  loop  with  the  nerves  divided  was  found  filled  with  a  clear, 
alkaline  liquid,  colorless  or  slightly  opaline,  which  precipitated  a  few 
fiocculi  of  organic  matter  on  boiling. 

Vasomotor  Centres  and  Nerves.  — The  principal  or  dominating  vaso- 
motor centres  are  situated  in  the  bulb,  one  on  either  side,  about  one- 
tenth  of  an  inch  (2.5  miUimeters)  from  the  median  line.  Each  centre, 
in  the  rabbit,  is  about  one-eighth  of  an  inch  (3  millimeters)  long  and 
about  one-sixteenth  of  an  inch  (1.5  millimeters)  wide.  Its  lower  border 
is  about  one-fifth  of  an  inch  (5  millimeters)  above  the  calamus  scriptorius. 
Each  side  of  the  body  has  its  special  vasomotor  centre,  and  very  few 
if  any  of  the  vasomotor  fibres  decussate.  The  situation  of  the  vaso- 
motor centres  in  the  bulb  has  been  determined  by  successive  removal 
of  the  nerve-centres  above.  If  the  central  end  of  a  large  cerebro-spinal 
nerve  is  stimulated  in  an  animal  poisoned  with  curare,  the  vasomotor 
nerves  produce  contraction  of  the  bloodvessels  by  reflex  action  and  there 
is  a  rise  in  the  bjood-pressure.  The  action  is  not  interfered  with  by 
removal  of  the  encephalic  ganglia  from  above  downward,  until  the 
part  of  the  medulla  containing  the  vasomotor  centres  is  reached.  When 
these  centres  are  destroyed,  the  reflex  vasomotor  action  is  permanently 
arrested. 

Subordinate  vasomotor  centres  exist  in  the  spinal  cord.  When  the 
vasomotor  centre  in  the  bulb  is  destroyed,  there  is  a  fall  in  the  blood- 
pressure  ;  but  if  the  circulation  is  continued,  after  a  time  the  bloodves- 
sels regain  their  "tone  "  and  the  pressure  may  then  be  affected  by  reflex 
action.  It  is  probable  that  these  spinal  centres  exist  throughout  the 
dorsal  and  lumbar  regions  of  the  cord. 

All  the  vasomotor  nerves  are  derived  from  the  bulb  and  the  spinal 
cord.  Some  of  the  vasomotor  fibres  to  the  head  pass  in  the  trunks  of 
the  motor  cranial  nerves,  but  most  of  them  come  from  the  anterior  roots 
of  some  of  the  spinal  nerves  and  pass  to  the  head  by  the  filaments  of 
distribution  of  the  cervical  sympathetic.  The  vasomotor  fibres  pass  in 
the  lateral  columns  of  the  cord,  and  from  the  cord,  in  the  anterior  roots 
of  the  spinal  nerves,  in  the  dog,  as  far  down  as  the  second  pair  of 
lumbar  nerves.  These  fibres  are  medullated  but  are  of  small  size. 
They  pass  to  the  bloodvessels  either  through  branches  from  the  sympa- 
thetic ganglia  or  through  the  ordinary  cerebro-spinal  nerves.  They 
therefore  are  not  confined  to  branches  of  the  sympathetic. 

The  vasomotor  nerves  are  capable  of  influencing  local  circulations, 


REFLEX  VASOMOTOR  PHENOMENA  615 

probably  through  distinct  centres  for  different  parts.  Direct  stimula- 
tion of  the  principal  vasomotor  centre  (10  to  12  or  more  single  induction 
shocks  per  second  for  strong  currents  or  20  to  25  for  moderate  currents) 
increases  the  blood-pressure  to  the  maximum. 

The  contractile  coats  of  the  veins  and  lymphatics  probably  are  influ- 
enced by  vasomotor  nerves,  but  little  is  known  of  the  mechanism  of  this 
action. 

Reflex  Vasomotor  Phenomena. — The  most  important  physiological 
processes  connected  with  the  vasomotor  nerves  are  reflex.  It  is  evident 
from  experiments  on  the  inferior  animals  and  observations  on  the  human 
subject  that  there  are  afferent  as  well  as  efferent  nerves.  The  reflex 
acts  connected  with  secretion  have  already  been  considered ;  but  there 
are  other  phenomena  that  demand  a  brief  description. 

As  regards  animal  heat,  the  production  of  which  is  intimately  con- 
nected with  the  supply  of  blood  to  the  parts,  it  is  important  to  note  the 
observations  of  Brown-Sequard  and  of  Lombard,  who  found  that  pinch- 
ing of  the  skin  on  one  side  was  attended  with  a  diminution  in  the  tem- 
perature in  the  corresponding  member  of  the  opposite  side,  and  that 
sometimes,  when  the  irritation  w^as  applied  to  the  upper  extremities, 
changes  were  produced  in  the  temperature  of  the  lower  limbs.  Tholozan 
and  Brown-Sequard  found,  also,  that  lowering  the  temperature  of  one 
hand  produced  a  considerable  depression  in  the  heat  of  the  other  hand, 
without  any  notable  diminution  in  the  general  heat  of  the  body. 
Brown-Sequard  showed  that  by  immersing  one  foot  in  water  at  41° 
Fahr.  (5°  C.)  the  temperature  of  the  other  foot  was  diminished  by  about 
7°  Fahr.  (4°  C)  in  the  course  of  eight  minutes.  These  experiments 
show  that  certain  impressions  made  on  the  sensory  nerves  affect  the 
animal  heat  by  reflex  action.  As  section  of  the  sympathetic  filaments 
increases  the  heat  in  particular  parts  with  an  increase  in  the  supply  of 
blood,  and  their  faradization  reduces  the  quantity  of  blood  and  diminishes 
the  temperature,  it  is  reasonable  to  infer  that  the  reflex  action  takes 
place  through  the  vasomotor  nerves.  If  it  is  assumed  that  the  impres- 
sion is  conveyed  to  the  centres  by  the  nerves  of  general  sensibility, 
and  that  the  vessels  are  modified  in  their  calibre  and  the  heat  is  affected 
through  the  sympathetic  fibres,  it  remains  only  to  determine  the  situa- 
tion of  the  centres  that  receive  the  impression  and  generate  the  stimulus. 
These  centres  are  situated  in  the  cerebro-spinal  axis. 

The  existence  of  vasomotor  nerves  and  their  connection  with  centres 
in  the  cerebro-spinal  axis  are  now  sufficiently  well  established.  It  is 
certain,  also,  that  centres  presiding  over  particular  acts  may  be  dis- 
tinctly located,  as  the  genito-spinal  centre,  in  the  spinal  cord  opposite 
the  fourth  lumbar  vertebra,  and  the  cilio-spinal  centre,  in  the  cerncal 


6l6  NERVOUS    SYSTEM 

region  of  the  cord.  Impulses  generated  in  these  centres,  sometimes  as 
the  result  of  impressions  received  through  the  nerves  of  general  sensi- 
bility, produce  contraction  of  the  non-striated  muscular  fibres  of  the  iris, 
vasa  deferentia  etc.,  including  the  muscular  coats  of  the  bloodvessels. 
The  contraction  of  the  muscular  walls  of  the  vessels  is  tonic ;  and  when 
their  nerves  are  divided,  relaxation  takes  place  and  the  vessels  are 
dilated  by  the  pressure  of  blood.  By  this  action  the  local  circulations 
are  regulated  in  accordance  with  impressions  made  on  sensory  nerves, 
the  physiological  requirements  of  certain  parts,  mental  emotions  etc. 
Secretion,  the  peristaltic  movements  of  the  alimentary  canal,  the  move- 
ments of  the  iris  etc.,  are  influenced  in  this  way.  This  action  also  is 
illustrated  in  cases  of  reflex  paralysis,  in  inflammations  as  the  result  of 
"  taking  cold,"  and  in  many  other  pathological  conditions. 

It  remains  only  to  show  that  the  phenomena  following  section  of 
the  sympathetic  in  animals  are  illustrated  in  certain  cases  of  disease  or 
injury  in  the  human  subject.  It  is  rare  to  observe  traumatic  injury 
confined  to  the  sympathetic  in  the  neck.  A  single  case,  however, 
apparently  of  this  kind,  has  been  reported  by  Mitchell.  A  man  received 
a  gunshot-wound  in  the  neck.  Among  the  phenomena  observed  a  few 
weeks  after,  were  contraction  of  the  pupil  on  the  side  of  the  injury,  and 
after  exercise,  flushing  of  the  face  on  that  side.  There  was  no  differ- 
ence in  the  temperature  of  the  two  sides  during  repose,  but  no  thermo- 
metric  observations  were  made  when  half  of  the  face  was  flushed  by 
exercise.  Bartholow  has  reported  several  cases  of  unilateral  sweating 
of  the  head  (two  observed  by  himself),  in  some  of  which  there  prob- 
ably was  compression  of  the  sympathetic  by  an  aneurism.  In  the  cases 
in  which  the  condition  of  the  eye  was  observed,  the  pupil  was  found 
contracted  in  some  and  dilated  in  others.  In  none  of  these  cases  were 
there  any  accurate  thermometric  observations.  In  a  series  of  observa- 
tions by  Wagner,  on  the  head  of  a  woman,  eighteen  minutes  after 
decapitation,  strong  stimulation  of  the  sympathetic  produced  enlarge- 
ment of  the  pupil.  In  such  a  case  as  this,  it  would  not  be  possible 
to  make  observations  on  the  influence  of  the  sympathetic  on  the  tem- 
perature. 

Vaso-inJiibitory  Nc7'i.'es.  —  There  are  certain  nerves  the  direct  action 
of  which  under  faradic  stimulation  is  to  dilate  certain  bloodvessels. 
These  nerves  may  also  be  excited  by  reflex  action  through  the  sensory 
nerves.  In  many  nerves,  as  the  chorda  tympani,  the  nervi  erigentes 
etc.,  the  existence  of  inhibitory  fibres  has  been  demonstrated.  For 
example,  division  of  the  nervi  erigentes  has  no  immediate  effect  on  the 
penis,  but  faradization  of  the  peripheral  ends  of  the  nerves  dilates  the 
bloodvessels  and  produces  erection.     Fibres  possessing  this  property 


TROPHIC   CENTRES    AND    NERVES  617 

undoubtedly  exist  throughout  the  body,  in  the  sympathetic  and  in  the 
motor  and  mixed  nerves ;  and  it  is  possible  that  there  are  vasomotor 
inhibitory  centres,  although  such  centres  have  not  been  located.  The 
mode  of  action  of  these  nerves  is  analogous  to  that  of  the  inhibitory 
nerve  of  the  heart,  restraining  and  regulating  the  action  of  vasomotor 
nerves  and  allowing  the  pressure  of  blood  to  dilate  the  vessels.  It  does 
not,  however,  seem  proper  to  call  them  "  vaso-dilator  "  nerves,  any  more 
than  it  would  be  correct  to  call  the  inhibitory  nerve  of  the  heart  the 
cardiac  dilator  nerve. 

Trophic  Centres  and  Nerves.  —  Collections  of  nerve-cells  act  as  cen- 
tres, presiding  over  the  nutrition  of  the  nerve-fibres  with  which  they  are 
connected ;  but  it  has  been  found  that  the  nutrition  of  other  parts  may 
be  profoundly  affected  through  the  nervous  system.  Many  patholo- 
gists, relying  on  the  presence  of  lesions  of  cells  in  the  cord,  in  con- 
nection with  cases  of  progressive  muscular  atrophy,  admit  the  existence 
of  trophic  cells  and  nerves.  These  views,  however,  rest  almost  entirely 
on  pathological  observations.  Experiments  on  the  sympathetic  do 
not  positively  show  any  influence  on  nutrition,  except  as  this  system 
of  nerves  affects  the  supply  of  blood  to  the  parts.  When  a  sympa- 
thetic nerve  is  divided,  there  is  an  exaggeration  of  the  nutritive  processes 
in  particular  parts,  and  there  may  be  inflammatory  phenomena,  but 
atrophy  of  muscles  is  not  observed.  Atrophy  of  muscles,  indeed,  fol- 
lows division  of  cerebro-spinal  nerves  only,  or,  as  cases  of  disease  have 
shown,  disorganization  of  cells  belonging  to  what  are  recognized  as 
motor'centres.  As  regards  this  condition,  there  can  be  no  doubt  of  the 
fact  that  progressive  muscular  atrophy  is  attended  with  disorganization 
of  certain  of  the  motor  cells  of  the  spinal  cord. 

Without  fully  discussing  this  subject  —  which  properly  belongs  to 
pathology  —  the  facts  may  be  briefly  stated  as  follows:  There  may  be 
progressive  atrophy  of  certain  muscles,  uncompHcated  with  paralysis 
except  in  so  far  as  there  is  weakness  of  these  muscles  due  to  partial  and 
.progressive  destruction  of  their  contractile  elements.  The  only  constant 
pathological  condition  in  these  cases,  aside  from  the  changes  in  the 
muscular  tissue,  is  destruction  of  certain  cells  in  the  antero-lateral  por- 
tions of  the  cord,  with  more  or  less  atrophy  of  the  corresponding 
anterior  roots  of  the  nerves.  It  has  not  been  assumed  that  there  are 
cells  in  the  cord,  presenting  anatomical  peculiarities  by  which  they  may 
be  distinguished  from  the  ordinary  motor  or  sensory  elements ;  but  the 
fact  of  the  degeneration  of  certain  cells  (a  pigmentary  and  sclerotic 
atrophy),  others  remaining  normal,  has  led  to  the  distinction  by  writers, 
of  trophic  cells,  and  of  course  these  must  be  connected  with  the  parts 
by  trophic  nerves. 


6i8  NERVOUS    SYSTEM 

Sleep 

When  it  is  remembered  that  about  one-third  of  each  day  is  passed  in 
sleep,  and  that  at  this  time,  voluntary  motion,  sensation,  the  special 
senses  and  various  of  the  functions  of  the  organism  are  greatly  modified, 
the  importance  of  a  physiological  study  of  this  condition  is  sufficiently 
apparent.  The  subject  of  sleep  is  most  appropriately  considered  in 
connection  with  the  nervous  system,  for  the  reason  that  the  most 
important  modifications  in  function  are  observed  in  the  cerebro-spinal 
axis  and  nerves.  Repose  is  as  necessary  to  the  nutrition  of  the  mus- 
cular system  as  proper  exercise  ;  but  repose  of  the  muscles  relieves  the 
fatigue  due  to  exercise,  without  sleep.  It  is  true  that  after  violent  and 
prolonged  exertion  there  frequently  is  a  desire  for  sleep,  but  simple 
repose  often  will  restore  the  muscular  power.  After  the  most  violent 
exertions,  a  renewal  of  muscular  vigor  is  most  easily  and  completely 
effected  by  rest  without  sleep,  a  fact  familiar  to  all  who  are  accustomed 
to  athletic  exercises.  After  prolonged  and  severe  mental  exertion, 
however,  or  after  long-continued  muscular  effort  involving  excessive 
expenditure  of  the  so-called  nerve-force,  sleep  becomes  an  imperative 
necessity.  If  the  nervous  system  is  not  abnormally  excited  by  effort, 
sleep  follows  moderate  exertion  as  a  natural  consequence,  and  it  is  the 
only  physiological  means  of  complete  restoration ;  but  the  two  most 
important  muscular  acts,  namely,  those  concerned  in  circulation  and 
respiration,  are  not  completely  arrested,  sleeping  or  walking,  although 
they  undergo  certain  modifications. 

In  infancy  and  youth,  when  the  organism  is  in  process  of  develop- 
ment, sleep  is  more  important  than  in  adult  life  or  in  old  age.  The 
infant  does  little  but  sleep,  eat  and  digest.  In  adult  life,  under  physi- 
ological conditions,  a  person  requires  about  eight  hours  of  sleep ; 
some  need  less,  but  few  require  more.  In  old  age,  unless  after  extraor- 
dinary exertion,  less  sleep  is  required  than  in  adult  life.  Each  indi- 
vidual learns  by  experience  how  much  sleep  is  necessary  in  perfect 
health  ;  and  there  is  nothing  which  more  completely  incapacitates  one 
for  mental  or  muscular  effort,  especially  the  former,  than  loss  of  natural 
rest. 

Sleeplessness  is  one  of  the  most  important  of  the  predisposing 
causes  of  certain  forms  of  brain-disease,  a  fact  that  is  well  recog- 
nized by  practical  physicians.  One  of  the  most  severe  methods  of 
torture  is  long-continued  deprivation  of  sleep ;  and  persons  have  been 
known  to  sleep  when  subjected  to  acutely  painful  impressions.  Severe 
muscular  effort,  even,  may  be  continued  during  sleep.  In  forced 
marches,   regiments    have  been  known  to  sleep  while  walking  ;    men 


SLEEP  619 

have  slept  soundly  in  the  saddle ;  persons  will  sometimes  sleep  during 
the  din  of  battle;  and  other  instances  illustrating  the  imperative  demand 
for  sleep  after  prolonged  vigilance  might  be  cited.  It  is  remarkable, 
also,  how  noises  to  which  one  has  become  accustomed  may  fail  to  dis- 
turb natural  rest.  Those  who  have  been  long  habituated  to  the  noise 
of  a  crowded  city  frequently  find  difficulty  in  sleeping  in  the  stillness  of 
the  country.  Prolonged  exposure  to  intense  cold  induces  excessive 
somnolence;  and  if  this  is  not  resisted,  the  sleep  passes  into  stupor,  the 
power  of  resistance  to  cold  rapidly  diminishes  and  death  is  the  result. 
Intense  heat  often  produces  drowsiness,  but,  as  is  well  known,  is  not 
favorable  to  natural  sleep. 

Sleep  is  preceded  by  a  feeling  of  drowsiness,  an  indisposition  to 
mental  or  physical  exertion,  and  a  general  relaxation  of  the  muscular 
system.  It  then  requires  a  decided  effort  to  keep  awake.  In  sleep  the 
voluntary  muscles  are  inactive,  the  lids  are  closed,  the  ordinary  impres- 
sions of  sound  are  not  appreciated,  and  sometimes  there  is  a  dreamless 
condition,  in  which  the  consciousness  of  existence  is  lost. 

Dj-eavis.  —  There  may  be,  during  sleep,  mental  operations  of  which 
there  is  no  consciousness  or  recollection,  unconscious  cerebration,  as  it 
has  been  called.  It  is  well  known  that  dreams  are  vividly  remembered 
immediately  on  awakening,  but  that  the  recollection  of  them  rapidly 
fades  away,  unless  they  are  brought  to  mind  by  an  effort  to  recall  and 
relate  them.  Whatever  may  be  the  condition  of  the  mind  in  sleep,  if 
the  sleep  is  normal,  there  is  repose  of  the  cerebro-spinal  system  and  an 
absence  of  voluntary  effort,  which  restore  the  capacity  for  mental  and 
physical  exertion. 

The  impressionability  and  the  activity  of  the  human  mind  are  so 
great,  most  of  the  animal  functions  are  so  far  subordinate  to  its 
influence  and  the  organism  is  so  subject  to  unusual  mental  conditions, 
that  it  is  difficult  to  determine  with  exactness  the  phenomena  of  sleep 
that  are  physiological  and  to  separate  those  that  are  slightly  abnor- 
mal. It  can  not  be  assumed,  for  example,  that  a  dreamless  sleep, 
in  which  existence  is,  as  it  were,  a  blank,  is  the  only  normal  condition 
of  repose  of  the  system  ;  nor  is  it  possible  to  determine  what  dreams  are 
due  to  previous  trains  of  thought,  to  impressions  from  the  external 
world  received  during  sleep,  and  are  purely  physiological,  and  what  are 
due  to  abnormal  nervous  influences,  disordered  digestion  etc.  It  may 
be  assumed,  however,  that  an  entirely  refreshing  sleep  is  normal. 

That  reflex  ideas  originate  during  sleep,  as  the  result  of  external  im- 
pressions, there  can  be  no  doubt ;  and  many  remarkable  experiments  on 
the  production  of  dreams  of  a  definite  character,  by  subjecting  a  person 
during  sleep  to  peculiar  influences,  have  been  recorded.     The  halluci- 


620  NERVOUS    SYSTEM 

nations  produced  in  this  way  are  called  hypnagogic,  and  they  occur 
usually  when  the  subject  is  not  in  a  condition  favorable  to  sound  sleep. 

As  regards  dreams  due  to  external  impressions,  it  is  a  curious  fact, 
which  has  been  noted  by  many  observers  and  is  one  that  accords  with 
the  personal  experience  of  all  who  have  reflected  on  the  subject,  that 
trains  of  thought  and  imaginary  events,  which  seem  to  pass  over  a  long 
period  of  time  in  dreams,  actually  occur  in  the  brain  within  a  few  sec- 
onds. A  person  is  awakened  by  a  certain  impression,  which  undoubt- 
edly has  given  rise  to  a  dream  that  seemed  to  occupy  hours  or  days,  and 
yet  the  period  of  time  between  the  impression  and  the  awakening  was 
hardly  more  than  a  few  seconds  ;  and  persons  will  drop  asleep  for  a 
few  minutes,  and  yet  have  dreams  with  elaborate  details  and  appar- 
ently of  great  length. 

Condition  of  the  Brain  and  Nervous  System  during  Sleep.  —  During 
sleep  the  brain  may  be  in  a  condition  of  absolute  repose  —  at  least,  so 
far  as  there  is  any  subjective  knowledge  of  mental  operations  —  or  there 
may  be  more  or  less  connected  trains  of  thought.  There  is,  also,  as  a 
rule,  absence  of  voluntary  effort,  although  movements  may  be  made  to 
relieve  discomfort  from  position  or  external  irritation,  without  awakening. 
The  sensory  nerves  retain  their  properties,  although  the  general  sensi- 
bility is  somewhat  blunted ;  and  the  same  may  be  said  of  the  special 
senses  of  hearing,  smell  and  probably  of  taste.  There  is  every  reason 
to  believe  that  the  action  of  the  sympathetic  system  is  not  disturbed  or 
affected  by  sleep,  if  the  iniluence  of  the  vasomotor  nerves  on  the  circu- 
lation in  the  brain  be  excepted. 

Two  opposite  theories  were  formerly  held  in  regard  to  the  immediate 
cause  of  sleep.  In  one,  this  condition  was  attributed  to  venous  conges- 
tion and  increased  pressure  of  blood  in  the  brain,  and  this  view  probably 
had  its  origin  in  the  fact  that  cerebral  congestion  induces  stupor  or  coma. 
Stupor  and  coma,  however,  are  distinct  from  natural  sleep ;  for  in  the 
former  the  action  of  the  brain  is  suspended,  there  usually  is  no  conscious- 
ness, no  dreaming,  and  the  condition  is  manifestly  abnormal.  In  animals 
rendered  comatose  by  opium,  the  brain  when  exposed  is  found  deeply 
congested  with  venous  blood.  The  same  condition  often  obtains  in  pro- 
found anesthesia  by  chloroform,  but  a  state  of  the  brain  nearly  resem- 
bling normal  sleep  is  observed  in  anesthesia  by  ether.  These  facts  have 
been  demonstrated  by  experiments  on  living  animals  and  have  been 
observed  in  the  human  subject  in  cases  of  injury  of  the  head.  When 
opium  is  administered  in  large  doses,  the  brain  is  congested  during  the 
condition  of  stupor  or  coma ;  but  this  congestion  is  relieved  when  the 
animal  passes,  as  sometimes  happens,  from  the  effects  of  the  agent  into 
a  natural  sleep.     In  view  of  these  facts  and  others  that  will  be  stated 


SLEEP  621 

hereafter,  it  is  unnecessary  to  discuss  further  the  theory  that  sleep  is 
attended  with  or  is  produced  by  congestion  of  the  cerebral  vessels. 

The  idea  that  the  circulation  in  the  brain  is  diminished  during  sleep  has 
been  entertained  by  some  physiologists,  but  it  has  rested  chiefly  on  theo- 
retical considerations.  The  experiments  of  Durham  (i860)  seem  to  dem- 
onstrate that  the  supply  of  blood  to  the  brain  is  always  greatly  diminished 
during  sleep.  These  experiments  were  made  on  dogs.  A  piece  of  the 
skull  was  removed  with  a  trephine,  and  a  watch  glass  was  accurately 
fitted  to  the  opening  and  cemented  at  the  edges  with  Canada  balsam. 
When  the  animals  operated  on  were  awake,  the  vessels  of  the  pia  mater 
were  seen  moderately  distended  and  the  circulation  was  active ;  but  dur- 
ing natural  sleep,  the  brain  retracted  and  became  pale.  "  The  contrast 
between  the  appearance  of  the  brain  during  its  period  of  functional 
activity  and  during  its  state  of  repose  or  sleep  was  most  remarkable." 
There  can  hardly  be  a  doubt,  after  these  experiments,  that  during  sleep 
the  cerebral  circulation  is  considerably  diminished  in  activity. 

The  influence  of  diminished  supply  of  blood  to  the  brain  has  been 
illustrated  by  compression  of  both  carotid  arteries.  In  an  experiment 
performed  on  his  own  person,  Fleming  produced  immediate  and  pro- 
found sleep  in  this  way,  and  this  result  invariably  followed  in  subse- 
quent trials  on  himself  and  others.  Waller  produced  anesthesia  in 
patients  by  pressure  on  both  pneumogastric  nerves ;  but  the  nerves 
are  so  near  the  carotid  arteries  that  they  could  hardly  be  compressed, 
in  the  human  subject,  without  interfering  with  the  current  of  blood,  and 
such  experiments  do  not  positively  show  whether  the  loss  of  sensibility 
be  due  to  pressure  on  the  nerves  or  on  the  vessels.  In  some  rare 
instances  in  which  both  carotid  arteries  have  been  tied  in  the  human 
subject,  it  has  been  stated  that  there  is  an  unusual  drowsiness  following 
the  consequent  diminution  in  the  activity  of  the  cerebral  circulation ; 
but  this  result  is  by  no  means  constant,  and  the  morbid  conditions 
involved  in  so  serious  an  operation  usually  are  such  as  to  interfere  with 
their  value  as  facts  bearing  on  the  question  under  consideration.  So 
far  as  the  human  subject  is  concerned,' the  most  important  facts  are 
the  results  of  compression  of  both  carotids  in  healthy  persons.  These, 
as  well  as  experiments  on  animals,  all  go  to  show  that  the  supply  of 
blood  to  the  brain  is  diminished  during  natural  sleep,  and  that  sleep 
may  be  induced  by  retarding  the  cerebral  circulation  by  compressing 
the  vessels  of  supply.  When  the  circulation  is  interfered  with  by  com- 
pressing the  veins,  congestion  is  the  result,  and  there  is  stupor  or  coma. 

If  diminished  flow  of  blood  through  the  cerebral  vessels  is  the  cause 
of  natural  sleep,  it  becomes  important  to  inquire  how  this  condition  of 
physiological  anemia  is  brought  about.     It  must  be  that  when  the  system 


622  NERVOUS    SYSTEM 

requires  sleep,  the  vessels  of  the  brain  contract  in  obedience  to  a  stimu- 
lus received  through  the  sympathetic  system  of  nerves,  diminishing  the 
supply  of  blood  here  as  in  other  parts  under  varied  physiological  con- 
ditions. The  vessels  of  the  brain  are  provided  with  vasomotor  nerves, 
and  it  is  sufficient  to  have  noted  that  the  arteries  are  contracted  during 
sleep,  the  mechanism  of  this  action  being  well  established  by  observa- 
tions on  other  parts  of  the  circulatory  system. 

Little  is  known  of  the  intimate  nature  of  the  processes  of  nutrition 
of  the  brain  during  its  activity  and  in  repose ;  but  there  can  be  no 
doubt  of  the  fact  that  there  is  more  or  less  cerebral  action  at  all  times 
when  one  is  awake.  Although  the  mental  processes  are  much  less 
active  during  sleep,  even  at  this  time  the  operations  of  the  brain  are 
not  always  suspended.  It  is  equally  well  established  that  exercise  of 
the  brain  is  attended  with  physiological  wear  of  nervous  tissue,  and  like 
other  parts  of  the  organism,  its  tissue  requires  periodic  repose  for  regen- 
eration of  the  substance  consumed.  Analogies  to  this  are  to  be  found 
in  parts  that  are  more  easily  subjected  to  direct  observation.  The  mus- 
cles require  repose  after  exertion,  and  the  glands,  when  not  actively 
engaged  in  discharging  their  secretions,  present  intervals  of  so-called 
rest.  As  regards  the  glands,  during  the  intervals  of  rest  the  supply  of 
blood  to  their  tissue  is  much  diminished.  It  is  probable,  also,  that  mus- 
cles in  action  receive  more  blood  than  during  rest ;  but  it  is  mainly 
when  these  parts  are  not  active,  and  when  the  supply  of  blood  is 
smallest,  that  the  processes  of  regeneration  of  tissue  seem  to  be 
most  efficient.  As  a  rule  the  activity  of  parts,  while  it  is  attended  with 
an  increased  supply  of  blood,  is  a  condition  more  or  less  opposed  to  the 
processes  of  repair,  the  hyperemia  being,  apparently,  a  necessity  for 
the  marked  and  powerful  manifestations  of  their  peculiar  action.  When 
the  parts  are  active,  the  blood  seems  to  be  required  to  keep  at  the  proper 
standard  the  so-called  irritability  of  the  tissues  and  to  increase  their 
power  of  action  under  proper  stimulus.  Exercise  increases  the  power 
of  regeneration  and  favors  full  development  in  the  repose  that  follows ; 
but  during  rest,  the  tissues  have  time  to  appropriate  new  matter,  and 
this  does  not  seem  to  involve  a  large  supply  of  blood.  A  muscle  is 
exhausted  by  prolonged  exertion ;  and  the  large  quantity  of  blood  pass- 
ing through  the  tissue  carries  away  carbon  dioxide  and  other  products  of 
katabolism,  which  are  increased  in  quantity,  until  it  gradually  uses  up  its 
capacity  for  work.  Then  follows  repose ;  the  supply  of  blood  is 
reduced,  but  under  normal  conditions,  the  tissue  repairs  the  waste 
which  has  been  excited  by  action,  the  blood  furnishing  nutritive 
matter  and  carrying  away  a  comparatively  small  quantity  of  effete 
products. 


SLEEP  623 

It  may  safely  be  assumed  that  processes  analogous  to  those  just 
described  take  place  in  the  brain.  By  absence  of  voluntary  effort,  the 
muscles  have  time  for  rest  and  for  the  repair  of  physiological  waste, 
and  their  action  is  for  the  time  suspended.  As  the  activity  of  the  brain 
involves  consciousness,  volition,  the  generation  of  thought,  and,  in  short, 
the  mental  condition  observed  while  awake,  complete  repose  of  the  brain 
is  characterized  by  the  opposite  conditions.  It  is  true  that  the  brain 
may  be  rested  without  sleep,  by  abstaining  from  mental  effort,  by  the 
gratification  of  certain  of  the  senses  and  by  mental  distraction  of  various 
kinds,  and  that  the  mind  may  work  to  some  extent  during  sleep  ;  but 
during  the  period  of  complete  repose  —  a  condition  necessary  to  perfect 
health  and  full  mental  vigor  —  consciousness  and  volition  are  lost,  there 
is  no  thought,  and  the  brain,  which  does  not  receive  blood  enough 
to  stimulate  it  to  action,  is  simply  occupied  in  the  insensible  repair  of 
its  substance  and  is  preparing  itself  for  renewed  work.  Exhaustion  of 
the  muscles  produces  a  sense  of  fatigue  of  the  muscular  system,  indis- 
position to  muscular  exertion,  and  a  desire  for  rest,  not  necessarily 
involving  drowsiness.  Fatigue  of  the  brain  is  manifested  by  indisposi- 
tion to  mental  exertion,  dulness  of  the  special  senses  and  a  desire  for  sleep. 
Simple  repose  will  relieve  physiological  fatigue  of  muscles ;  and  when 
a  particular  set  of  muscles  has  been  used,  the  fatigue  often  disappears 
when  these  muscles  alone  are  at  rest,  although  others  be  brought  into 
action.     Sleep,  and  sleep  alone,  relieves  fatigue  of  the  brain. 

During  sleep  nearly  all  the  physiological  processes,  except  those 
directly  under  the  control  of  the  sympathetic  nervous  system,  are  dimin- 
ished in  activity.  The  circulation  is  slower,  and  the  pulsations  of  the 
heart  are  less  frequent,  as  well  as  the  respiratory  movements.  These 
points  have  already  been  considered  in  connection  with  the  physiology 
of  circulation  and  respiration.  Physiologists  have  little  positive  infor- 
mation in  regard  to  the  relative  activity  of  the  processes  of  digestion, 
absorption  and  secretion  during  sleep.  The  drowsiness  which  many 
persons  experience  after  a  full  meal  may  be  due  in  part  to  a  determi- 
nation of  blood  to  the  alimentary  canal  and  a  consequent  diminution  in 
the  supply  to  the  brain. 

It  must  be  that  fatigue,  as  well  as  sleep,  has  a  physical  basis.  While 
fatigue  may  be  in  part  explained  by  the  assumption  that  during  exer- 
cise the  reparative  processes  are  for  the  time  unequal  to  the  wear  or 
waste,  this  does  not  fully  account  for  the  nervous  phenomena  observed. 
It  has  been  shown,  indeed,  by  Ranke,  and  later  by  Mosso,  that  the 
blood  of  a  fatigued  animal  injected  into  an  animal  at  rest  will  produce 
promptly  all  the  phenomena  of  fatigue.  This  is  explained  by  the 
assumption  that  exercise  involves  the  production  of  what  may  be  called 


624  NERVOUS    SYSTEM 

"  fatigue-products  "  ;  but  the  characters  of  these  products  have  not  been 
ascertained.  Nevertheless,  they  probably  exist  in  the  blood  and  affect 
the  nerve-cells. 

When  fatigue  is  followed  by  sleep,  it  is  certain  that  the  supply  of 
blood  to  the  brain  is  considerably  diminished.  The  only  explanation  of 
this  is  that  in  some  way  the  somniferous  agent  in  the  blood  operates 
through  the  vasomotor  system.  The  fatigue-product  or  products  induce 
a  desire  for  sleep  ;  but  the  necessity  for  sleep  is  represented  by  certain 
structural  changes  that  have  taken  place,  probably  in  the  nerve-cells  of 
the  brain.  These  changes  are  degenerative  and  their  repair  requires 
a  more  or  less  extended  period  of  functional  rest.  Studies  of  these 
changes  by  Hodge,  Mann,  Vas,  Lambert  and  others  have  afforded  a 
reasonable  physical  basis  of  sleep. 

Following  nervous  cell-activity  or  repeated  stimulation  of  nerve-cells 
through  the  nerves,  the  cells  undergo  marked  changes  in  size  and  con- 
figuration. The  cells  become  shrunken,  vacuolated  and  crenated ;  and 
the  nuclei  are  even  more  shrunken  and  irregular  in  form,  the  diminu- 
tion in  size  sometimes  amounting  to  fifty  per  cent.  These  changes  have 
been  observed  in  cats,  dogs,  birds  and  other  animals  lower  in  the  scale. 
That  they  may  occur  in  the  human  subject  is  inferred.  After  a  num- 
ber of  hours  of  repose  —  about  equal  to  the  daily  period  of  sleep  in  the 
human  subject  —  the  cells  and  nuclei  are  found  to  have  returned  to  their 
original  condition. 

In  addition  to  the  changes  just  indicated,  it  is  more  than  probable 
that  alterations  occur  in  the  Nissl  bodies.  If  the  view  can  be  accepted 
that  these  bodies  contain  stored-up  nervous  energy  that  is  consumed  in 
the  production  of  nerve-impulses  and  may  be  restored  by  rest,  it  may 
be  assumed  that  the  necessity  for  sleep  is  due  —  in  part,  at  least  —  to 
destruction  of  chromatoplasm  by  active  chromatolysis.  There  is,  how- 
ever, what  may  be  called  a  passive  chromatolysis  in  "  disuse  atrophy  " 
of  nerve-cells.  This  has  been  shown  in  the  cell-degeneration  that 
occurs  after  nerve-fibres  attached  to  cells  have  been  divided. 

While  the  views  of  physiologists  in  regard  to  the  office  of  Nissl 
bodies  are  to  some  extent  speculative,  it  is  certain  that  nerve-cells 
undergo  degenerative  changes  during  wakefulness  and  activity  and  that 
during  sleep  they  are  gradually  restored  to  their  normal  condition  and 
resume  their  normal  appearance,  calling  normal  the  condition  following 
repose.  By  these  restorative  processes  the  nervous  system  becomes 
capable  of  renewed  activity.  It  is  to  be  remembered,  however,  that 
this  restoration  may  be  in  a  measure  produced  by  rest  without  sleep, 
and  that  sleep  may  follow  a  period  of  nervous  and  muscular  inactivity 
as  nearly  complete  as  is  possible  in  a  waking  condition. 


CHAPTER   XXV 

SENSE  OF  TOUCH  — OLFACTION  — GUSTATION 

Muscular  sense  —  Sense  of  touch  —  Appreciation  of  temperature  —  Olfaction  —  Olfactory 
(first  nerve) — Properties  and  uses  of  the  olfactory  nerves  —  Mechanism  of  olfaction  — 
Relations  of  olfaction  to  the  sense  of  taste  —  Gustation — Nerves  of  taste  —  Chorda 
tympani  —  Glosso-pharyngeal  (ninth  nerve)  — General  properties  of  the  glosso-pharyngeal 
—  Relations  of  the  glosso-pharyngeal  to  gustation  —  Mechanism  of  gustation — Physio- 
logical anatomy  of  the  organs  of  taste — Taste-beakers. 

The  senses  of  smell,  taste,  sight  and  hearing  involve  peculiar 
organs,  provided  with  nerves  having  special  properties  that  usually  are 
not  endowed  with  what  is  described  as  general  sensibility.  These 
nerves  have  been  omitted  in  the  general  description  of  the  nervous 
system,  as  well  as  the  organs  in  which  they  are  distributed. 

Sensations  of  pain,  touch,  contact  (localization),  temperature,  weight, 
pressure  and  the  so-called  muscular  sense,  are  all  conveyed  to  the  senso- 
rium  by  what  have  been  described  as  centripetal  nerves,  the  sense  of 
touch  being  perfected  in  certain  parts  by  peculiar  structures  at  the  end- 
ings of  the  nerves.  The  muscular  sense,  by  which  weight  and  resistance 
are  appreciated,  undoubtedly  depends  largely  on  the  muscular  nerves. 
The  above  subdivisions  are  sufficiently  distinct  so  far  as  the  character 
of  the  sensations  are  concerned  ;  and  it  remains  to  see  whether  they 
pass  to  distinct  centres  by  special  paths  of  conduction  or  are  conveyed 
hy  what  are  known  as  nerves  of  general  sensibility.  As  regards  this 
question,  physiologists  have  to  rely  mainly  on  experiments  on  the  human 
subject,  and  pathological  observations. 

The  general  sensory  nerves  are  sufficiently  distinct  in  their  proper- 
ties from  the  true  nerves  of  special  sense.  The  latter  convey  peculiar 
impressions  only,  such  as  those  of  sight,  hearing,  smell  and  taste.  The 
former,  when  strongly  stimulated  or  irritated,  always  convey  impressions 
of  pain.  Separating,  then,  all  other  senses,  except  the  venereal  sense, 
from  the  true  special  senses,  it  is  proper  to  inquire  whether  it  be  reason- 
able to  assume  that  any  of  the  varieties  of  general  sensation  require 
special  nerves  for  their  conduction. 

It  is  well  known  that  a  relatively  strong  stimulation  of  a  sensory 
nerve  or  of  sensitive  parts  is  necessary  for  the  production  of  a  painful 
impression  ;  and  it  is  also  well  known  that  very  painful  impressions 
2s  625 


626  SPECIAL    SENSES 

overpower  impressions  of  touch,  weight,  pressure,  temperature  and  the 
so-called  muscular  sense.  In  cases  of  disease,  it  is  sometimes  observed 
that  tactile  sensibility  is  retained  in  parts  that  are  insensible  as  regards 
pain.  It  is  possible  that  sensory  nerve-fibres  may  become  so  altered  in 
their  properties  as  to  be  incapable  of  conducting  painful  impressions, 
while  they  still  conduct  sensations  that  are  appreciated  only  as  im- 
pressions of  contact.  This  is  observed  in  certain  cases  of  artificial 
anesthesia.  In  hyperesthesia,  or  exaggerated  sensibility  to  painful  im- 
pressions, the  tactile  sense  is  necessarily  overpowered  in  a  greater  or 
less  degree.  Impressions  made  on  a  sensory  nerve  in  its  course  are 
always  appreciated  as  painful,  and  the  pain  is  referred  to  the  terminal 
distribution  of  the  nerve,  this  being  a  law  of  sensory  perception.  There 
is  no  sense  of  contact  at  the  ends  of  the  nerve,  and  there  is  no  contact. 
The  impression,  in  order  to  be  perceived  at  all,  must  be  painful.  These 
facts  may  be  in  a  measure  applied  to  local  impressions  produced  by 
extremes  of  heat  and  cold  or  by  chemical  or  electric  stimulation  of  sensi- 
tive parts. 

The  internal  organs  have  as  a  rule  no  tactile  sensibility,  although 
they  may  be  sensitive;  and  feeble  impressions  may  not  be  appreciated, 
while  stronger  impressions  are  painful. 

Titillation  is  produced  by  unusual  feeble  impressions  or  slight  im- 
pressions frequently  repeated  on  the  peripheral  ends  of  certain  sensory 
nerves.  These  impressions  are  not  precisely  tactile  nor  are  they  painful. 
They  produce  peculiar  sensations,  and  they  frequently  give  rise  to  vio- 
lent reflex  movements,  by  what  is  known  as  a  summation  of  sensory 
stimulations. 

Musailar  Sense  (so  called^.  —  It  is  difficult  to  define  exactly  what  is 
meant  by  the  term  "  muscular  sense,"  as  it  is  used  by  some  physiologists. 
In  all  probability  the  sense  which  enables  one  to  appreciate  the  resist- 
ance, immobility  or  elasticity  of  substances  that  are  grasped  or  stood 
upon,  or  which  are  in  any  way  opposed  to  the  exertion  of  muscular 
effort,  may  be  greatly  modified  by  education  and  habit.  It  is  undoubt- 
edly true,  however,  that  general  sensibility  regulates  the  action  of 
muscles  to  a  considerable  extent.  If,  for  example,  the  lower  extremi- 
ties are  paralyzed  as  regards  sensation,  the  muscular  power  remaining 
intact,  frequently  the  person  so  affected  can  not  w^alk  unless  able  to  see 
the  ground. 

Those  who  regard  the  muscular  sense  as  distinct  from  the  sense  of 
touch,  weight  or  pressure,  connect  it  with  the  neuro-muscular  spindles, 
that  have  already  been  described  in  treating  of  the  terminations  of  nerves 
in  voluntary  muscles. 

In  general  the  parts  that  are  most  sensitive  to  the  impressions  of 


SENSE    OF   TOUCH  627 

touch,  as  the  fingers,  enable  one  to  appreciate  differences  in  pressure 
and  weight  with  greatest  accuracy.  The  sense  of  simple  pressure,  un- 
aided by  the  estimation  of  weight  by  muscular  effort,  usually  is  more 
acute  on  the  left  side.  Differences  in  weight  can  be  accurately  distin- 
guished when  they  amount  to  only  one-sixteenth,  by  estimating  the  mus- 
cular effort  in  lifting,  in  addition  to  the  sense  of  pressure ;  but  the  sense 
of  pressure  alone  enables  most  persons  to  appreciate  a  difference  of  not 
less  than  one-eighth.  When  weights  are  tested  by  lifting  with  the  hand, 
the  appreciation  of  slight  differences  is  more  delicate  if  the  weights  are 
successively  tested  with  the  same  hand  than  when  two  weights  are 
placed,  one  in  either  hand.  When  the  interval  between  the  two  trials 
is  more  than  forty  seconds,  slight  differences  in  weight  —  the  difference 
between  fourteen  and  a  half  and  fifteen  ounces  (411  and  425  grarhs),  for 
example — can  not  be  accurately  appreciated.  In  such  trials,  it  is  neces- 
sary to  have  the  metals  used  of  the  same  temperature,  for  cold  metals 
seem  heavier  than  warm. 

Sense  of  Touch 

The  different  modes  of  termination  of  the  sensory  nerves  have 
already  been  described;  and  in  many  instances  it  is  possible  to  explain, 
by  the  anatomical  characters  of  the  nerves,  the  differences  that  have 
been  observed  in  the  delicacy  of  the  tactile  sensibility  and  sense  of  con- 
tact in  different  parts  —  differences  which  are  vtr/  important  patho- 
logically as  well  as  physiologically. 

Variations  in  the  Sense  of  Contact  in  Differerit  Parts  {Localization 
of  Impressions).  —  In  certain  parts  of  the  cutaneous  surface  the  general 
sensibility  is  much  more  acute  than  in  others.  For  example,  a  sharp 
blow  on  the  face  is  more  painful  than  a  similar  injury  to  other  parts; 
and  the  eye,  as  is  well  known,  is  peculiarly  sensitive.  The  appreciation 
of  temperature  varies  in  different  parts,  this  probably  depending  to  a 
great  extent  on  habitual  exposure.  Some  parts,  as  the  soles  of  the 
feet  or  the  axilla,  are  peculiarly  sensitive  to  titillation.  The  sense  of 
touch,  also,  by  which  the  size,  form,  character  of  the  surface,  consistence 
etc.,  of  objects  are  appreciated,  is  developed  in  a  greater  degree  in  some 
parts  than  in  others.  The  tips  of  the  fingers  commonly  are  used  to 
ascertain  those  properties  of  objects  revealed  by  the  sense  of  touch. 
This  sense  is  capable  of  education  and  is  almost  always  extraordinarily 
developed  in  persons  who  are  deprived  of  some  other  special  sense,  as 
sight  or  hearing.  The  blind  learn  to  recognize  individuals  by  feeling  of 
the  face.  A  remarkable  instance  of  this  is  quoted  in  works  on  physi- 
ology, of  the  blind  sculptor,  Giovanni  Gonelli,  who  was  said  to  model 
excellent  likenesses,  being  guided  by  the  sense  of  touch  alone.      Other 


628  SPECIAL    SENSES 

instances  of  this  kind  are  on  record.  The  blind  have  been  known  to 
become  proficients  in  conchology  and  botany,  depending  entirely  on  the 
touch.  It  is  well  known  that  the  blind  learn  to  read  with  facihty  by 
passing  the  fingers  over  raised  letters  but  little  larger  than  the  letters  in 
an  ordinary  folio  Bible. 

An  easy  method  of  determining  the  relative  delicacy  of  the  sense  of 
contact  in  different  parts  of  the  cutaneous  surface  was  devised  a  num- 
ber of  years  ago  (1829)  by  E.  H.  Weber.  This  method  consists  in 
the  application  to  the  skin,  of  two  fine  points,  separated  from  each 
other  by  a  known  distance.  The  individual  experimented  on  should 
be  blindfolded,  and  the  points  applied  to  the  skin  simultaneously.  By 
carefully  adjusting  the  distance  between  the  points,  a  limit  will  be 
reached  where  the  two  impressions  upon  the  surface  are  appreciated 
as  one;  and  by  gradually  approximating  them,  the  subject  will  sud- 
denly feel  both  points  as  one,  when  an  instant  before,  with  the  points  a 
little  farther  removed  from  each  other,  he  distinctly  felt  two  impres- 
sions. This  gives  a  measure  of  the  delicacy  of  the  sense  of  contact  in 
different  parts.  An  instrument,  consisting  of  a  pair  of  dividers  with 
a  graduated  bar  giving  a  measure  of  the  separation  of  the  points,  com- 
bines simplicity,  convenience  of  use  and  portability.  This  instrument 
is  called  an  esthesiometer.  The  experiments  of  Weber  were  made  on 
his  own  person.  They  showed  some  slight  variations  with  the  direction 
of  the  line  of  the  two  points,  but  these  are  not  important.  The  follow- 
ing table  is  made  of  selections  from  the  observations  of  Weber,  taking 
those  that  are  most  likely  to  be  useful  as  a  guide  in  pathological  investi- 
gations. The  experiments  of  Valentin  and  others  on  different  persons 
do  not  vary  much  in  their  results  from  the  figures  given  in  the  table  on 
opposite  page. 

By  comparing  the  distribution  of  the  tactile  corpuscles  with  the 
results  given  in  the  table,  it  will  be  seen  that  the  sense  of  contact  is  most 
delicate  in  those  situations  in  which  the  tactile  corpuscles  are  most 
abundant.  In  the  space  of  a  little  more  than  yV  of  an  inch  (2.2  millime- 
ters) square,  on  the  palmar  surface  of  the  third  phalanx  of  the  index 
finger,  Meissner  counted  the  greatest  number  of  corpuscles ;  namely, 
one  hundred  and  eight.  In  this  situation  the  tactile  sensibility  is  more 
acute  than  in  any  other  part  of  the  skin,  the  mean  distance  indicated 
by  the  esthesiometer  being  0.603  of  a  line,  or  1.27  millimeter  (Valentin). 
In  the  same  space  on  the  second  phalanx,  forty  corpuscles  were  counted, 
the  esthesiometer  marking  1.558  line,  or  3.27  millimeters  (Valentin), 
this  part  ranking  next  in  tactile  sensibility  after  the  red  surface  of  the 
lips.  One  can  readily  understand  how  the  tactile  corpuscles,  embedded 
in  the  amorphous  substance  of  the  cutaneous  papillae,  might  increase 


SENSE    OF   TOUCH 


629 


the  delicacy  of  appreciation  of  slight  impressions,  by  presenting  hard 
surfaces  against  which  the  nerve-filaments  can  be  pressed. 


TABLE  OF  VARIATIONS  IN  THE  SENSE  OF  CONTACT  IN  DIFFERENT 
PORTIONS  OF  THE  SKIN  (WEBER) 

The  sensibility  is  measured  by  the  greatest  distance  between  two  points  at  which  they  convey  a  single  impression 
when  applied  simultaneously.  The  measurements  are  given  in  lines  (^5  of  an  inch,  or  a  little  more  than 
2  millimeters). 


PART  OF   SURFACE 

Lines 

Mm. 

Tip  of  tongue        ........ 

0.50 

1.05 

Palmar  surface  of  third  phalanx  of  forefinger 

1. 00 

2.10 

Red  surface  of  lower  lip         ...         . 

2.00 

4.20 

Palmar  surface  of  second  phalanges  of  fingers 

2.00 

4.20 

Dorsal  surface  of  third  phalanges  of  fingers    . 

3.00 

6.30 

Tip  of  nose  ....... 

3.00 

6.30 

Palmar  surface  of  metacarpus 

3.00 

6.30 

End  of  great  toe   ...... 

5.00 

10.50 

Palm  of  hand        ...... 

5.00 

10.50 

Skin  of  cheek,  over  buccinator 

5.00 

10.50 

Skin  of  cheek,  over  anterior  part  of  malar  bone 

7.00 

14.70 

Dorsal  surface  of  first  phalanges  of  fingers     . 

7.00 

14.70 

Lower  part  of  forehead           .... 

10.00 

21.00 

Back  of  hand 

14.00 

29.40 

Patella  and  surrounding  part  of  thigh    . 

16.00 

33-6o 

Dorsum  of  foot  near  toes       .... 

18.00 

37.80 

Upper  and  lower  extremities  of  forearm 

18.00 

37.80 

Upper  and  lower  extremities  of  leg 

Penis 

18.00 
18.00 

37.80 
37.80 

18.00 

37.80 

Gluteal  region  and  neighboring  part  of  thigh 

18.00 

37.80 

Middle  of  forearm  where  its  circumference  is  greatest 

30.00 

63.00 

Middle  of  thigh  where  its  circumference  is  greatest 

30.00 

63.00 

As  regards  those  portions  of  the  general  cutaneous  surface  in  which 
no  tactile  corpuscles  have  been  demonstrated,  it  is  not  easy  to  connect 
the  variations  in  the  sense  of  contact  with  the  nervous  distribution,  as 
little  is  known  of  the  comparative  richness  of  the  terminal  nervous 
filaments  in  these  situations. 

There  is  much  uncertainty  in  regard  to  the  location  of  a  cerebral 
tactile  centre.  Ferrier  described  a  diffused  centre  in  the  "  hippocampal 
region,"  the  action  of  which  is  crossed ;  but  the  observations  to  deter- 
mine loss  of  the  sense  of  contact  after  destruction  of  this  part,  made  on 
monkeys,  are  by  no  means  satisfactory.     It  may  be  stated  provisionally 


630 


SPECIAL   SENSES 


that  the  centre  for  this  sense  probably  is  in  the  gyrus  fornicatus,  which 
is  on  the  mesial  surface  of  the  brain,  above  the  corpus  callosum.  How- 
ever, Munk  and  many  others  locate  this  centre  in  the  Rolandic  area,  a 
part  containing  several  motor  centres.  These  differences  of  opinion 
illustrate  the  evident  difficulty  of  studying  tactile  sensibility  in  the  infe- 
rior animals. 

Appreciation  of  Temperatin^e.  —  As  regards  the  general  temperature, 
the  sense  is  relative  and  is  much  modified  by  habit.  This  statement 
needs  no  explanation.  As  is  well  known,  what  is  cold  for  an  inhabitant 
of  the  torrid  zone  would  be  warm  for  one  accustomed  to  an  excessively 
cold  chmate.  Habitual  exposure  also  modifies  the  sense  of  temperature. 
Many  persons  not  in  the  habit  of  dressing  warmly  suffer  but  little  in 


Fig.  lec. Map  showing  the  relative  distribution  of  the  sensitivity  to  touch,  warmth  and  cold  in  the 

palm  of  the  left  hand  (Goldscheider) . 

"  In  A,  the  whole  surface  is,  when  tested  by  a  small  cork  applied  by  a  spring,  found  of  approxi- 
mately equal  sensitivity  except  in  the  areas  marked  black;  these  are  relatively  insensible  for  touch. 

"  In  B,  the  areas  of  sensitivity  to  warmth  stimuli  are  represented  by  degrees  of  shading,  the  most 
sensitive,  by  the  black  shading ;  the  next,  by  the  lined  areas  ;  the  next,  by  the  dotted  areas ;  and  those 
of  least  sensitiveness,  by  the  blank  spaces. 

"  In  C,  the  topography  of  sensitivity  to  cold  stimuli  is  indicated  in  the  same  way  as  that  to  warm 
stimuli  in  B." 


extremely  cold  weather.  Those  who  habitually  expose  the  hands  or 
even  the  feet  to  cold,  render  these  parts  comparatively  insensible  to 
temperature ;  and  the  same  is  true  of  those  who  often  expose  the  hands, 
face  or  other  parts  to  heat.  The  variations  in  the  sensibility  of  different 
parts  of  the  surface  to  temperature  depend,  also,  on  special  properties 
of  the  parts  themselves. 

The  experiments  of  Weber  and  others  show  that  the  skin  is  the 
chief  organ  for  the  appreciation  of  temperature,  if  the  mouth,  palate, 
vagina  and  rectum,  by  which  the  differences  between  warm  and  cold 
substances  are  readily  distinguished,  are  excepted.  In  several  instances 
in  which  large  portions  of  the  skin  were  destroyed  by  burns  and  other 
injuries,  experiments  have  been  made  by  applying  spatulas  of  different 


OLFACTION  .631 

temperatures.  In  one  of  these,  a  spatula,  plunged  in  water  at  48°  to 
55°  Fahr.  (9°  to  12°  C),  was  applied  to  a  denuded  surface,  and  again,  a 
spatula  at  113°  to  122°  Fahr.  (45°  to  50°  C).  When  the  patient  was 
requested  to  tell  which  was  the  warmer,  the  answers  were  as  frequently 
incorrect  as  they  were  correct;  but  the  discrimination  was  easy  and 
certain  when  the  applications  were  made  to  the  surrounding  healthy 
skin.  When  applications  at  a  higher  temperature  were  made  to  the 
denuded  part,  the  patient  suffered  only  pain. 

Recent  experiments  have  shown  that  there  are  distinct  areas  of  the 
skin  which  are  sensible  to  heat  and  others  sensible  to  cold.  These  are 
called  heat  and  cold  spots.  They  are  irregularly  intercommingled 
with  other  areas,  some  of  which  are  sensitive  to  painful  and  some  to 
tactile  impressions.  Figure  155  shows  the  arrangement  of  the  heat  and 
cold  areas. 

The  venereal  sense  is  unlike  any  other  sensation  and  is  general  as 
well  as  referable  to  the  organs  of  generation.  In  this  connection,  how- 
ever, it  is  interesting  to  note  that  the  tactile  sensibiHty  of  the  palmar 
surface  of  the  third  phalanx  of  the  fingers,  measured  by  the  esthesiome- 
ter,  compared  with  the  sensibility  of  the  penis,  is  as  0.802  to  0.034,  or 
between  twenty-three  and  twenty-four  times  greater. 

Olfaction 

The  nerves  directly  connected  with  the  senses  of  olfaction,  vision 
and  audition  have  little  or  no  general  sensibility.  As  regards  the 
olfactory  nerves,  the  parts  to  which  they  are  distributed  are  so  largely 
supplied  with  branches  from  the  fifth,  that  it  is  somewhat  difficult  to 
determine  the  fact  of  their  sensibility  or  insensibility  to  ordinary  impres- 
sions. These  nerves,  however,  are  distributed  to  the  mucous  membrane 
of  that  portion  only  of  the  nasal  cavity  that  is  endowed  with  the  special 
sense  of  srnell. 

Nasal  FosscB. — The  two  irregularly-shaped  cavities  in  the  middle 
of  the  face,  opening  in  front  by  the  anterior,  nares  and  connected  with 
the  pharynx  by  the  posterior  nares,  are  called  the  nasal  fossae.  The 
membrane  lining  these  cavities  usually  is  called  the  Schneiderian  mucous 
membrane,  and  sometimes,  the  pituitary  membrane.  This  membrane 
is  closely  adherent  to  the  fibrous  coverings  of  the  bones  and  car- 
tilages by  which  the  nasal  fossae  are  bounded,  and  it  is  thickest  over 
the  turbinated  bones.  It  is  continuous  with  the  membrane  lining  the 
pharynx,  the  nasal  duct  and  lachrymal  canals,  the  Eustachian  tube,  the 
frontal,  ethmoidal  and  sphenoidal  sinuses  and  the  antrum.  There  are 
openings  leading  from  the  nasal  fossae  to  all  these  cavities. 


632 


SPECIAL    SENSES 


The  essential  organ  of  olfaction  is  the  mucous  membrane  lining  the 
upper  half  of  the  nasal  fossae.  Not  only  has  it  been  shown  anatomi- 
cally that  this  part  alone  receives  the  terminal  filaments  of  the  olfactory 
nerves,  but  experiments  have  demonstrated  that  it  is  the  only  part  capa- 
ble of  appreciating  odorous  impressions.  If  a  tube  is  introduced  into 
the  nostril,  placed  horizontally  over  an  odorous  substance  so  that  the 
emanations  can  not  penetrate  its  calibre,  no  odor  is  perceived,  though 
the  membrane  below  the  end  of  the  tube  might  receive  the  emanations ; 
but  if  the  tube  is  directed  toward  the  odorous  substance,  so  that  the 

emanations  can  pene- 
trate to  the  upper  por- 
tion of  the  nares,  the 
odor  is  immediately 
appreciated. 

That  portion  of  the 
lining  of  the  nasal 
fossae,  prop'erly  called 
the  olfactory  mem- 
brane, extends  from 
the  cribriform  plate 
of  the  ethmoid  bone 
downward  a  little  less 
than  an  inch  (25  milli- 

Fig.  \^fi.  —  Olfactory  ganglion  and  nerves  (Hirschfeld).  mCtCrs).      It  is  Soft  and 

1,  olfactory  ganglion  and  nerves  ;  2,  branch  of  the  nasal  nerve;  friable,    Very    VaSCUlar, 

3.  spheno-palat.ne  ganglion;   4.  7.  branches  of  the  great  palatine  thicker     than     the     rCSt 
nerve;  5,  posterior  palatine  nerve;  6,  middle  palatine  nerve;  8,9, 

branches   from  the   spheno-palatine   ganglion;    10,   11,  12,  Vidian  of       the       SchncideriaU 

nerve  and  its  branches ;   i^,  external  carotid  branch  from  the  supe-  ,                       ,   . 

rior  cervical  ganglion.  membrane,  and  m  man 

it  has  rather  a  yellow- 
ish color.  It  is  covered  with  long,  delicate,  columnar  cells,  nucleated, 
and  each  one  provided  with  three  to  eight  ciliary  processes,  the  move- 
ments of  which  are  from  before  backward.  The  olfactory  membrane 
is  provided  with  a  large  number  of  long  racemose  mucous  glands,  which 
produce  a  secretion  that  keeps  the  surface  moist,  a  condition  essential 
to  the  accurate  perception  of  odorous  impressions.  The  olfactory  organ 
in  some  of  the  lower  animals,  in  which  the  sense  of  smell  is  very  delicate, 
is  relatively  larger  than  in  man.     In  dogs  it  is  much  larger. 


Olfactory  (First  Nerve) 

The  apparent  origin  of  the  olfactory  nerve  is  by  three  roots  from 
the  inferior  and  internal  portion  of  the  frontal  lobe  of  the  cerebrum,  in 


OLFACTORY    NERVE  633 

front  of  the  anterior  perforated  space.  The  three  roots  are  an  external 
and  an  internal  white  root,  and  a  middle  root  composed  of  gray  matter. 
The  external  white  root  is  long  and  delicate,  passing  outward,  across  the 
fissure  of  Sylvius,  to  the  temporo-sphenoidal  lobe.  The  internal  white 
root  is  thicker  and  shorter  than  the  external  root  and  arises  from  the 
most  posterior  portion  of  the  frontal  lobe.  The  middle,  or  gray  root 
arises  from  a  little  eminence  of  gray  matter  situated  on  the  posterior 
and  inner  portion  of  the  inferior  surface  of  the  frontal  lobe. 

The  deep  origin  of  the  roots  of  the  olfactory  nerves  is  still  a  matter 
of  discussion.  The  external  root  passes  through  the  gray  substance  of 
the  island  of  Reil,  to  a  gray  nucleus  in  the  temporo-sphenoidal  lobe,  in 
front  of  the  pes  hippocampi.  The  fibres  of  the  middle  root  have  not 
been  traced  farther  than  the  gray  eminence  from  which  they  arise.  The 
fibres  of  the  internal  root  probably  are  con- 
nected with  the  fibres  of  the  gyrus  fornicatus. 
The  three  roots  converge  to  form  a  single 
cord  at  the  inner  boundary  of  the  fissure  of 
Sylvius.  This  cord  passes  forward  and  slightly 
inward,  in  a  deep  groove  between  two  convo- 
lutions on  the  under  surface  of  the  frontal  lobe 
covered  by  the  arachnoid    membrane,  to   the  R 

ethmoid  bone.      This  portion  of  the  nerve  is    ,  Fig.  157. - Vertuai seaio,,  0/ 

the  olfactory  viembrane  of  an  exe- 
Soft  and  friable.       It  is  composed  of  both  white    cuted    criminal,  x  250  (Zimmer- 

and  gray  matter,  the  proportions  being  about  m^nn  and  Sobotta). 
two-thirds  of   the  former  to  one-third  of   the  J^X^r,  S^^.^"^' 
latter.     The  gray  substance,  derived  from  the 

gray  root,  is  at  the  upper  portion  of  the  nerve,  the  white  substance 
occupying  the  inferior  and  the  lateral  portions. 

By  the  side  of  the  crista  gaUi  of  the  ethmoid  bone,  the  nerve-trunk 
expands  into  an  oblong  ganglion  called  the  olfactory  bulb.  This  is 
grayish  in  color,  very  soft,  and  contains  the  ordinary  ganglionic  ele- 
ments. From  the  olfactory  bulb,  fifteen  to  eighteen  nervous  filaments 
are  given  off,  which  pass  through  foramina  in  the  cribriform  plate 
of  the  ethmoid  bone.  These  filaments  are  composed  entirely  of  nerve- 
fibres,  and  are  quite  resisting,  owing  to  fibrous  elements  prolonged  from 
the  dura  mater.  It  is  strictly  correct,  perhaps,  to  regard  these  as  the 
true  olfactory  nerves,  the  cord  leading  from  the  olfactory  bulb  to 
the  cerebrum  being  properly  a  commissure.  Having  passed  through 
the  cribriform  plate,  the  olfactory  nerves  are  distributed  to  the  olfactory 
membrane,  in  three  groups  :  an  inner  group,  distributed  to  the  mucous 
membrane  of  the  upper  third  of  the  septum ;  a  middle  group,  to  the 
upper  portion  of  the  nasal  fossae  ;  and  an  outer  group,  to  the  mucous 


634  SPECIAL    SENSES 

membrane  covering  the  superior  and  middle  turbinated  bones  and  a  por- 
tion of  the  ethmoid. 

The  mode  of  termination  of  the  olfactory  nerves  differs  from  that  of 
the  ordinary  sensory  nerves,  and  is  peculiar  and  characteristic,  as  it  is  in 
the  other  organs  of  special  sense.  The  olfactory  mucous  membrane  con- 
tains terminal  nerve-cells,  called  olfactory  cells,  which  are  situated  be- 
tween the  cells  of  epithelium.  These  are  long,  dehcate,  spindle-shaped, 
varicose  structures,  each  one  containing  a  clear  round  nucleus.  In  the 
frog  there  is  a  fine  hair-like  process  projecting  from  each  cell  beyond 
the  mucous  membrane,  which  has  not  been  observed  in  man  or  in  the 
mammalia. 

Properties  and  Uses  of  the  Olfactory  Nerves.  —  It  is  almost  certain 
that  the  olfactory  nerves  possess  none  of  the  general  properties  of 
ordinary  nerves  belonging  to  the  cerebro-spinal  system  and  are  endowed 
with  the  special  sense  of  smell  alone.  The  filaments  coming  from  the 
olfactory  bulbs  and  distributed  to  the  pituitary  membrane  have  not  been 
exposed  and  stimulated  in  living  animals ;  but  experiments  on  the 
nerves  behind  the  olfactory  bulbs  show  that  they  are  insensible  to 
ordinary  impressions.  Attempts  have  been  made  to  demonstrate,  in 
the  human  subject,  the  special  properties  of  these  nerv^es,  by  passing  an 
electric  current  through  the  nostrils ;  but  their  situation  is  such  that 
these  observations  are  of  necessity  indefinite  and  unsatisfactory. 

Among  the  experiments  on  the  higher  orders  of  animals,  in  which 
the  olfactory  nerves  have  been  divided,  may  be  cited,  as  open  to  no  ob- 
jections, those  of  Vulpian  and  Philipaux,  on  dogs.  It  is  well  known 
that  the  sense  of  smell  usually  is  very  acute  in  these  animals.  On 
dividing  or  extirpating  the  olfactory  bulbs,  "  after  the  animal  had 
completely  recovered,  it  was  deprived  of  food  for  thirty-six  or  forty- 
eight  hours  ;  then,  in  its  absence,  a  piece  of  cooked  meat  was  concealed 
in  a  corner  of  the  laboratory.  Animals,  successfully  operated  on, 
then  taken  into  the  laboratory,  never  found  the  bait ;  and,  neverthe- 
less, care  had  been  taken  to  select  hunting-dogs."  This  experiment  is 
conclusive;  more  so  than  those  in  which  animals  deprived  of  the  olfac- 
tory bulbs  w^ere  shown  to  eat  feces  without  disgust,  for  this  sometimies 
occurs  in  dogs  that  have  not  been  mutilated. 

Comparative  anatomy  shows  that  the  olfactory  bulbs  usually  are 
developed  in  proportion  to  the  acuteness  of  the  sense  of  smell.  Patho- 
logical facts  show,  in  the  human  subject,  that  impairment  or  loss  of 
the  olfactory  sense  is  coincident  with  injury  or  destruction  of  these 
ganglia.  Cases  have  been  reported  in  which  the  sense  of  smell  was 
lost  or  impaired  from  injury  to  the  olfactory  nerves.  In  nearly  all  the 
cases  on  record,  the  general  sensibiUty  of  the  nostrils  was  not  affected. 


MECHANISM    OF   OLFACTION  635 

The  delicacy  of  the  sense  of  smell,  measured  by  the  possible  tenuity 
of  odorous  particles  that  can  be  recognized  through  the  olfactory  organs, 
is  very  great,  even  in  man,  in  whom  olfaction  is  much  inferior  to  this 
sense  in  some  of  the  lower  animals.  Fischer  and  Penzoldt,  experi- 
menting with  ethyl  mercaptan  (C2HgSH)  in  1885,  were  able  to  recog- 
nize the  peculiar  and  disgusting  odor  of  this  substance  in  a  dilution 
of  one  part  in  fifty  billions  of  air,  the  weight  of  mercaptan  distributed 
in  three  cubic  inches  (about  50  cubic  centimeters)  being  estimated  at 
30,00 o,U 0,000  of  a  gram  (460,0^0,000  ^i  a  milligram),  containing  4.7 
trillion  molecules.  It  is  said  that  the  odor  of  iodoform  can  be  recog- 
nized in  quantities  as  small  as  e,^ o'o,"o'oo",'oFo  ^^  ^  grain,  or  the  one  hun- 
dred billionth  of  a  gram  (Berthelot). 

Mechanism  of  Olfaction.  —  In  experimenting  on  the'  sense  of  smell 
it  has  been  found  difficult  to  draw  an  exact  line  of  distinction  between 
impressions  of  general  sensibility  and  those  which  attack  the  special 
sense,  or,  in  other  words,  between  irritating  and  odorous  emanations ; 
and  the  vapors  of  ammonia,  acetic  acid,  nitric  acid  etc.,  undoubtedly 
possess  irritating  properties  that  overpower  their  odorous  qualities.  It 
is  unnecessary  in  this  connection  to  discuss  the  different  varieties  of 
odors  recognized  by  some  of  the  earlier  writers,  as  the  fragrant,  aro- 
matic, fetid,  nauseous  etc.,  distinctions  sufficiently  evident  from  their 
mere  enumeration ;  and  it  is  plain  enough  that  there  are  emanations, 
like  those  from  delicately-scented  flowers,  that  are  easily  recognizable 
by  the  sense  of  smell,  while  they  make  no  impression  on  the  ordinary 
sensory  nerves.  The  marked  individual  differences  in  the  delicacy  of 
the  olfactory  organs  in  the  human  subject  and  in  different  animals  are 
evidence  of  this  fact.  Hunting-dogs  recognize  odors  to  which  most 
persons  are  insensible ;  and  certain  races  of  men  are  said  to  possess 
a  remarkable  delicacy  of  the  sense  of  smell.  Like  the  other  special 
senses,  olfaction  may  be  cultivated  by  attention  and  practice,  as  is 
exemplified  in  the  delicate  discrimination  of  wines,  qualities  of  drugs 
etc.,  by  experts. 

After  what  has  been  said  concerning  the  situation  of  the  olfactory 
organ  in  the  upper  part  of  the  nasal  fossae  and  the  necessity  of  particles 
impinging  upon  this  membrane  in  order  that  their  odorous  properties" 
may  be  appreciated,  it  is  almost  unnecessary  to  state  that  the  passage 
of  odorous  emanations  to  this  membrane  by  inspiring  through  the 
nostrils  is  essential  to  olfaction,  so  that  animals  or  men,  after  divi- 
sion of  the  trachea,  being  unable  to  pass  the  air  through  the  nostrils, 
are  deprived  of  the  sense  of  smell.  The  act  of  inhalation  through  the 
nose  is  an  illustration  of  the  mechanism  by  which  the  odorous  particles 
may  be  brought  at  will  in  contact  with  the  olfactory  membrane. 


636  SPECIAL   SENSES 

It  is  a  curious  point  to  determine  whether  the  sense  of  smell  is 
affected  by  odors  passing  from  within  outward  through  the  nasal  fossae. 
Persons  who  have  offensive  emanations  from  the  respiratory  organs 
usually  are  not  aware,  from  their  own  sensations,  of  any  disagreeable 
odor.  This  fact  has  been  explained  by  the  assumption  that  the  olfac- 
tory membrane  gradually  becomes  accustomed  to  the  odorous  impres- 
sion. This  is  an  apparently  satisfactory  explanation ;  for  it  can  hardly 
be  supposed  that  the  direction  of  the  emanations,  provided  they  come 
in  contact  with  the  membrane,  could  modify  their  effects.  In  a 
case  of  cancer  of  the  stomach,  with  vomiting  of  fetid  matters,  the 
patient  at  first  perceived  an  offensive  odor  when  the  gases  from  the 
stomach  were  expired  through  the  nostrils ;  but  this  gradually  disap- 
peared (Longet). 

Relations  of  Olfaction  to  the  Sense  of  Taste.  —  The  relations  of  the 
sense  of  smell  to  the  sense  of  taste  are  very  intimate.  In  the  apprecia- 
tion of  delicate  shades  of  flavor,  it  is  well  known  that  olfaction  plays  so 
important  a  part  that  it  can  hardly  be  separated  from  gustation.  The 
common  practice  of  holding  the  nose  when  disagreeable  remedies  are 
swallowed  is  an  illustration  of  the  connection  between  the  two  senses. 
In  most  cases  of  anosmia,  there  is  inability  to  distinguish  delicate 
flavors,  and  patients  can  distinguish  by  the  taste,  only  sweet,  saline, 
acid  and  bitter  impressions. 

It  undoubtedly  is  true  that  the  delicacy  of  the  sense  of  taste  is  im- 
paired when  the  sense  of  smell  is  lost.  The  experiment  of  tasting 
wines  blindfolded  and  with  the  nostrils  plugged,  and  the  partial  loss 
of  taste  during  a  severe  coryza,  are  sufficiently  familiar  illustrations  of 
this.  In  the  great  majority  of  cases,  when  there  is  complete  anosmia, 
the  taste  is  sensibly  blunted ;  and  in  cases  in  which  this  does  not  occur, 
it  is  probable  that  the  savory  emanations  pass  from  the  mouth  to  the 
posterior  portion  of  the  nasal  fossae,  and  that  here  the  mucous  mem- 
brane is  not  entirely  insensible  to  special  impressions. 

It  is  unnecessary,  in  this  connection,  to  describe  fully  the  reflex 
phenomena  that  follow  impressions  made  on  the  olfactory  membrane. 
The  odor  of  certain  sapid  substances,  under  favorable  conditions,  will 
produce  an  abundant  secretion  of  saliva  and  even  of  gastric  juice,  as  has 
been  shown  by  experiments  on  animals.  Other  examples  of  the  effects 
of  odorous  impressions  of  various  kinds  are  sufficiently  familiar. 

According  to  Ferrier  and  others,  the  olfactory  centre  is  on  the 
mesial  surface  of  the  brain,  near  the  anterior  extremity  of  the  uncinate 
gyrus ;  but  this  location  of  the  centre  can  not  be  regarded  as  definitely 
determined.  Stimulation  of  this  part  in  monkeys  produces  peculiar 
movements  of  the  nostril  and  lip  of  the  same  side. 


GUSTATION  637 


Gustation 


The  special  sense  of  taste  gives  the  appreciation  of  what  is  known 
as  the  savor  of  certain  substances  introduced  into  the  mouth  ;  and  this 
sense  exists,  in  general  terms,  in  parts  supplied  by  filaments  from  the 
lingual  branch  of  the  fifth  and  the  glosso-pharyngeal  nerves. 

It  is  assumed  by  some  physiologists,  that  the  true  tastes  are  quite 
simple,  presenting  the  qualities  that  are  recognized  as  sweet,  acid, 
bitter  and  saline ;  while  the  more  delicate  shades  of  what  are  called 
flavors  nearly  always  involve  olfactory  impressions  which  it  is  difficult 
to  separate  entirely  from  gustation.  Flavors,  indeed,  are  regarded  sim- 
ply as  odors.  Applying  the  term  "savor"  exclusively  to  the  quality  that 
makes  an  impression  on  the  nerves  of  taste,  it  is  evident  that  the  sensa- 
tion is  special  in  its  character  and  different  from  the  tactile  sensibility 
of  the  parts  involved  and  from  the  sensation  of  temperature.  The 
terminal  filaments  of  the  gustatory  nerves  are  impressed  by  the  actual 
contact  of  savory  substances,  which  must  of  necessity  be  soluble.  To 
a  certain  extent  there  is  a  natural  classification  of  savors,  some  of  which 
are  agreeable,  and  others,  disagreeable ;  but  even  this  distinction  is 
modified  by  habit,  education,  and  various  other  circumstances.  Articles 
that  are  unpleasant  in  early  life  often  become  agreeable  in  later  years. 
Inasmuch  as  the  taste  is  to  some  extent  an  expression  of  the  nutritive 
demands  of  the  system,  it  is  found  to  vary  under  different  conditions. 
Chlorotic  females,  for  example,  frequently  crave  the  most  unnatural 
articles,  and  their  morbid  taste  may  disappear  under  appropriate  treat- 
ment. Inhabitants  of  the  frigid  zone  crave  fatty  articles  of  food  and 
often  drink  rancid  oils  with  avidity.  Patients  often  become  accustomed 
to  the  most  disagreeable  remedies  and  take  them  without  repugnance. 
Again,  the  most  savory  dishes  may  even  excite  disgust,  when  the 
appetite  has  become  cloyed ;  while  abstinence  sometimes  lends  a 
delicious  flavor  to  the  simplest  articles  of  food.  The  taste  for  certain 
articles  certainly  is  acquired ;  and  this  is  almost  always  true  of  tobacco, 
now  so  largely  used  in  civilized  countries. 

Anything  more  than  the  simplest  classification  of  savors  is  difficult 
if  not  impossible.  It  is  easy  to  recognize  that  certain  articles  are  bitter 
or  sweet,  empyreumatic  or  insipid,  acid  or  alkaline  etc.,  but  beyond 
these  simple  distinctions,  the  shades  of  difference  are  closely  connected 
with  olfaction  and  are  too  delicate  and  too  many  for  detailed  description. 
Some  persons  are  comparatively  insensible  to  nice  distinctions  of  taste, 
while  others  recognize  with  facility  the  most  delicate  differences. 
Strong  impressions  may  remove  for  a  time  the  appreciation  of  less 
powerful   and   decided    flavors.     The   tempting   of   the   appetite  by  a 


638  SPECIAL   SENSES 

proper  gradation  of  gustatory  and  odorous  impressions  is  illustrated  in 
the  modern  cuisine,  which  aims  at  an  artistic  combination  and  succes- 
sion of  dishes  and  wines,  so  that  the  agreeable  sensations  are  prolonged 
to  the  utmost  limit.  This  may  often  be  regarded  as  a  violation  of 
strictly  hygienic  principles,  but  it  none  the  less  exemplifies  the  cultiva- 
tion of  the  sense  of  taste. 

Nei"i'es  of  Taste.  —  Two  nerves,  the  chorda  tympani  and  the  glosso- 
pharyngeal, are  endowed  with  the  sense  of  taste.  These  nerves  are 
distributed  to  distinct  portions  of  the  gustatory  organ.  The  chorda 
tympani  has  already  been  referred  to  as  one  of  the  branches  of  the 
facial ;  the  glosso-pharyngeal  has  not  yet  been  described. 

Chorda  Tyuipani.  —  In  the  description  already  given  of  the  facial, 
the  chorda  tympani  is  spoken  of  as  the  fourth  branch.  It  passes 
through  the  tympanum,  between  the  ossicles  of  the  ear,  and  joins  the 
inferior  maxillary  division  of  the  fifth  at  an  acute  angle,  between  the 
two  pterygoid  muscles,  becoming  so  closely  united  with  it  that  it  can 
not  be  followed  farther  by  dissection.  The  filaments  of  this  branch 
probably  originate  from  the  intermediary  nerve  of  Wrisberg,  which 
some  anatomists  describe  as  arising  from  the  glosso-pharyngeal.  The 
course  of  the  filaments  of  the  chorda  tympani,  after  this  nerve  has 
joined  the  fifth,  is  shown  by  the  effect  on  the  sense  of  taste  and  the 
alteration  of  the  nerve-fibres  following  its  division ;  and  observations  on 
the  sense  of  taste  show  that  this  nerve  is  distributed  to  the  anterior 
two-thirds  of  the  tongue.  The  general  properties  of  the  chorda  tym- 
pani have  been  ascertained  only  by  observations  made  after  its  paralysis 
or  division.  All  experiments  in  which  a  stimulus  has  been  applied 
directly  to  the  nerve  in  living  animals  have  been  negative  in  their 
results. 

In  paralysis  of  the  facial  in  which  the  lesion  affects  the  root  so  deeply 
as  to  involve  the  chorda  tympani,  there  is  loss  of  taste  in  the  anterior 
two-thirds  of  the  tongue,  general  sensibility  being  unaffected  ;  and  many 
cases  illustrating  this  fact  have  been  recorded.  Aside  from  cases  of 
paralysis  of  the  facial  with  impairment  of  taste,  in  which  the  general 
sensibility  of  the  tongue  is  intact,  instances  are  on  record  of  affections 
of  the  fifth  pair,  in  which  the  tongue  was  insensible  to  ordinary  impres- 
sions, the  sense  of  taste  remaining. 

Passing  from  the  consideration  of  pathological  facts  to  experiments 
on  living  animals,  the  results  are  equally  satisfactory.  Although  it  is 
somewhat  difficult  to  observe  impairment  of  taste  in  animals,  experi- 
menters have  succeeded  in  training  dogs  and  cats  so  as  to  observe  the 
effects  of  colocynth  and  various  sapid  substances  applied  to  the  tongue. 
In  a  number  of  experiments  of  this  kind,  it  has  been  observed  that  after 


GLOSSO-PHARYNGEAL    NERVES  639 

section  of  the  chorda  tympani —  or  of  the  facial  so  as  to  involve  the 
chorda  tympani  —  the  sense  of  taste  is  abolished  in  the  anterior  two- 
thirds  of  the  tongue  on  the  side  of  the  section.  In  a  number  of  cases 
the  introduction  of  an  artificial  membrana  tympani  in  the  human  subject 
has  been  followed  by  loss  of  taste  on  the  corresponding  side  of  the 
tongue,  and  on  both  sides,  when  membranes  were  introduced  into 
both  ears.  This  disappears  when  the  membranes  are  removed  ;  and 
the  phenomena  may  properly  be  referred  to  pressure  on  the  chorda 
tympani. 

As  regards  the  gustatory  properties  of  the  anterior  two-thirds  of  the 
tongue,  certainly  in  the  human  subject,  it  may  be  stated  without  reserve 
that  these  properties  depend  on  the  chorda  tympani,  its  gustatory  fila- 
ments taking  their  course  to  the  tongue  with  the  lingual  branch  of  the 
inferior  maxillary  division  of  the  fifth.  In  addition,  the  lingual  branch 
of  the  fifth  contains  filaments  derived  from  the  large  root  of  this  nerve, 
which  give  general  sensibihty  to  the  mucous  membrane. 

Glosso-Pharyngeal  (Ninth  Nerve) 

The  glosso-pharyngeal  is  distributed  to  those  portions  of  the  gusta- 
tory mucous  membrane  not  supplied  by  filaments  from  the  chorda 
tympani.  It  undoubtedly  is  a  nerve  of  taste  ;  and  the  question  of  its 
other  uses  will  be  considered  in  connection  with  its  general  proper- 
ties, as  well  as  the  differences  between  this  nerve  and  the  chorda 
tympani. 

Physiological  Anatomy.  —  The  apparent  origin  of  the  glosso-pharyn- 
geal is  from  the  groove  between  the  olivary  and  restiform  bodies  of  the 
medulla  oblongata,  between  the  roots  of  the  auditory  nerve  above  and 
the  pneumogastric  below.  The  deep  origin  is  in  a  gray  nucleus  in  the 
lower  part  of  the  floor  of  the  fourth  ventricle,  between  the  nucleus  of 
the  auditory  nerve  and  the  nucleus  of  the  pneumogastric.  From  this 
origin,  the  nerve  passes  forward  and  outward,  to  the  posterior  foramen 
lacerum,  by  which  it  emerges  with  the  pneumogastric,  the  spinal  acces- 
sory and  the  internal  jugular  vein.  At  the  upper  part  of  the  fora- 
men, is  a  small  ganglion,  the  jugular  ganglion,  including  only  a  portion 
of  the  root.  Within  the  foramen,  is  the  main  ganglion,  including  all 
the  filaments  of  the  trunk,  called  the  petrous  ganglion,  or  the  ganglion 
of  Andersch. 

At  or  near  the  ganglion  of  Andersch  the  glosso-pharyngeal  usually 
receives  a  small  filament  from  the  pneumogastric.  This  communication 
is  sometimes  wanting.  The  same  may  be  said  of  a  filament  passing  to 
the  glosso-pharyngeal  from  the  facial,  which  is  not  constant.     Branches 


640 


SPECIAL   SENSES 


from  the  glosso-pharyngeal  go  to  the  otic  gangUon  and  to  the  carotid 
plexus  of  the  sympathetic. 

The  distribution  of  the  glosso-pharyngeal  is  quite  extensive.  The 
tympanic  branch  (the  nerve  of  Jacobson)  arises  from  the  anterior  and 
external  parts  of  the  ganglion  of  Andersch,  and  enters  the  cavity  of  the 
tympanum,  where  it  divides  into  six  branches.     Of  these  six  branches, 


Fig.  158.  —  Glosso-pharyngeal  nerve  (Sappey"). 

I,  large  root  of  the  fifth  nerve;  2,  ganglion  of  Gasser ;  3,  ophthalmic  division  of  the  fifth;  4,  supe- 
rior maxillary  division;  5,  inferior  maxillary  division  ;  6,  10,  lingual  branch  of  the  fifth,  containing  the 
filaments  of  the  chorda  tywpani ;  7,  branch  from  the  sublingual  to  the  lingual  branch  of  the  fifth; 
8,  chorda  tympa?ii ;  9,  inferior  dental  nerve;  11,  submaxillary  ganglion  ;  12,  mylo-hyoid  branch  of  the 
inferior  dental  nerve;  13,  anterior  belly  of  the  digastric  muscle;  14,  section  of  the  mylo-hyoid  muscle; 
15,  1%,  glosso-pharyngeal  nerve  ;  \b,  ganglion  of  Andersch  ;  17,  branches  from  the  glosso-pharyngeal  to 
the  stylo-glossiis  and  the  sfylo-pharyngeus  7nuscles  ;  ig,  19,  pneumogastric ;  20,  21,  ganglia  of  the  pneu- 
mogastric;  22,  22,  superior  laryngeal  nerve;  23,  spinal  accessory;  24,  25,  26,  27,  28,  sublingual  nerve 
and  branches. 


two  posterior  are  distributed  to  the  mucous  membrane  of  the  fenestra 
rotunda  and  the  membrane  surrounding  the  fenestra  ovalis ;  two  an- 
terior are  rlistributed,  one  to  the  carotid  canal,  where  it  anastomoses 
with  a  branch  from  the  superior  cervical  ganglion,  and  the  other  to  the 
mucous  membrane  of  the  Eustachian  tube ;  two  superior  branches  are 
distributed  to  the  otic  ganglion  and,  as  is  stated  by  some  anatomists,  to 


GENERAL    PROPERTIES    OF    THE    GLOSSO-PHARYNGEAL         641 

the  spheno-palatine  ganglion.  In  addition  to  these,  a  branch  has  been 
described  as  going  to  the  geniculate  ganglion  of  the  intermediary  nerve 
of  Wrisberg. 

A  little  below  the  posterior  foramen  lacerum,  the  glosso-pharyngeal 
sends  branches  to  the  posterior  belly  of  the  digastric  and  to  the  stylo- 
hyoid muscle.  There  is  also  a  branch  which  joins  a  filament  from  the 
facial  to  the  stylo-glossus. 

Opposite  the  middle  constrictor  of  the  pharynx,  three  or  four  branches 
join  branches  from  the  pneumogastric  and  the  sympathetic,  to  form 
together  the  pharyngeal  plexus.  This  plexus  contains  a  number  of 
ganglionic  points,  and  filaments  of  distribution  from  the  three  nerves 
go  to  the  mucous  membrane  and  to  the  constrictors  of  the  pharynx. 
The  mucous  membrane  probably  is  supplied  by  the  glosso-pharyngeal. 
It  is  probable,  also,  that  the  muscles  of  the  pharynx  are  supplied  by  fila- 
ments from  the  pneumogastric,  which  are  derived  originally  from  the 
spinal  accessory. 

Near  the  base  of  the  tongue,  branches  are  sent  to  the  mucous  mem- 
brane covering  the  tonsils  and  the  soft  palate. 

The  lingual  branches  penetrate  the  tongue  about  midway  between 
its  border  and  centre,  are  distributed  to  the  mucous  membrane  at  its 
base  and  are  connected  with  certain  of  the  papillae. 

General  Properties  of  the  Glosso-Pharyngeal.  —  To  ascertain  the  gen- 
eral properties  of  this  nerve,  it  must  be  stimulated  at  its  root  before  it 
has  contracted  anastomoses  with  other  nerves ;  and  the  nerve  must  be 
divided  in  order  to  avoid  reflex  phenomena.  Taking  these  precautions  it 
has  been  found  that  stimulation  of  the  peripheral  end  of  the  nerve  does 
not  give  rise  to  muscular  movements.  There  can  be  no  doubt  of  the  fact 
that  the  nerve  is  sensory,  although  its  sensibility  is  dull.  In  experi- 
ments in  which  the  nerve  has  seemed  to  be  insensible  to  ordinary  im- 
pressions, it  is  probable  that  the  animals  operated  on  had  been  exhausted 
more  or  less  by  pain  and  loss  of  blood  in  the  operation  of  exposing  the 
nerve,  which,  it  is  well  known,  abolish  the  sensibility  of  some  of  the 
nerves. 

Experiments  on  the  glosso-pharyngeal  are  not  very  definite  and  sat- 
isfactory in  their  results  as  regards  the  general  sensibility  of  the  base  of 
the  tongue,  the  palate  and  the  pharynx.  The  sensibility  of  these  parts 
seems  to  depend  chiefly  on  branches  of  the  fifth,  passing  to  the  mucous 
membrane  through  Meckel's  ganglion.  Experiments  show,  also,  that  the 
reflex  phenomena  of  deglutition  take  place  mainly  through  these  branches 
of  the  fifth,  and  that  the  glosso-pharyngeal  has  little  or  nothing  to  do 
with  the  process.  In  fact,  after  division  of  both  glosso-pharyngeal 
nerves,  deglutition  does  not  seem  to  be  affected.     Stimulation  of  the 


642 


SPECIAL   SENSES 


glosso-pharyngeal   by  electricity  inhibits  respiration  for  a  short  time. 

This  action  is  reflex. 

Relations  of  the  Glosso-Pharyngeal  Nerves  to  Gustation.  —  Relying 

on    experiments    on    the    inferior    animals,  particularly   dogs,  it  seems 

certain  that  there  are 
two  nerves  presiding 
over  the  sense  of 
taste :  The  chorda- 
tympani  nerve  gives 
this  sense  to  the 
anterior  two-thirds  of 
the  tongue  exclusive- 
ly ;  and  the  glosso- 
pharyngeal supplies 
this  sense  to  the  pos- 
terior portion  of  the 
tongue.  The  chorda 
tympani  seems  to 
have  nothing  to  do 
with  general  sensibil- 
ity ;  while  the  glosso- 
pharyngeal is  an  or- 
dinary sensory  nerve, 
as  well  as  a  nerve 
of  special  sense. 

MeeJianism  of  Gus- 
tation. —  Articles  that 
make  the  special  im- 
pression on  the  gus- 
tatory organ  are  in 
solution ;  introduced 
■p\g.ie^^.  —  Papiii(B  of  the  tongue  {^^■^T^^y').  into  the  mouth,  they 

I,  I,  circumvallate  papillae;  2,  median  circumvallate  papilla,  which  inCrCaSC    the     floW    of 

entirely  fills  the  foramen  caecum;    3,  3,  3,  3,  fungiform  papillae;   4,  4,  y           .1^        r^flpv    ar 

filiform  papillse;  5,  5,  vertical  folds  and  furrows  of  the  border  of  the  ^auva,    Liic     iciiCA    ctc- 

tongue;    6,  6,  6,  6,  glands  at  the  base  of  the  tongue;  7,  7,  tonsils;  tion    involving   chicfly 

8,  epiglottis;    o,  median  glosso-epiglottidean  fold.  ,              1              .,1                    1 

^^  ^  s         Fs  ^j^g  submaxillary  and 

sublingual  glands  ;  there  usually  is  more  or  less  mastication,  which 
increases  the  flow  of  the  parotid  saliva ;  and  during  the  acts  of  mas- 
tication and  the  first  stages  of  deglutition,  the  sapid  substances  are 
distributed  over  the  gustatory  membrane,  so  extensively,  indeed,  that 
it  is  difficult  to  locate  exactly  the  seat  of  the  special  impression.  In 
this  way,  by  the  movements  of  the  tongue,  aided  by  an  increased  flow 


PHYSIOLOGICAL   ANATOMY   OF   THE   ORGANS    OF    TASTE       643 


Fig.  160.  —  Afeduun-sized   circum- 
vallate  papilla,  X  20  (SappeyJ. 

I,  papilla,  the  base  only  being 
apparent  (it  is  seen  that  the  base  is 
covered  with  secondary  papillae)  ; 
2,  groove  between  the  papilla  and 
the  surrounding  wall  ;  3,  3,  wall  of 
the  papilla. 


of  saliva,  the  actual  contact  of  the  savory  articles  is  rapidly  effected. 

The  thorough  distribution  of  these  substances  over  the  tongue  and  the 

mucous  membrane  of  the  general  buccal 
cavity  leads  to  some  confusion  in  the  appre- 
ciation of  the  special  impressions  ;  and  in 
order  to  ascertain  if  different  portions  of  the 
membrane  possess  different  properties,  it  is 
necessary  to  make  careful  experiments,  limit- 
ing the  points  of  contact  as  exactly  as  possi- 
ble. This  has  been  done,  with  the  result  of 
showing  that  the  true  gustatory  organ  is  quite 
restricted  in  its  extent. 

It  has  been  found  that  certain  gustatory 
impressions  attack  readily  the  parts  supplied 
by  the  chorda  tympani,  while  others  attack 
the  terminal  filaments  of  the  glosso-pharyn- 
geal.  Classifying  savors  as  sweets,  acids, 
bitters  and  salines, 
it     appears      that 

sweets  attack  especially  the  tip  of  the  tongue  ; 

acids  and  salines,  the   sides  of  the  tongue ; 

bitters,  the  back  of  the  tongue.     It  is  said  that 

an  acid  taste  may  be  recognized  in  a  solution 

equivalent  to  one  part  of  sulphuric  acid  in  one 

thousand  of  water.     Chewiiig  the  leaves  of 

the  gymnema  sylvestre  abolishes  for  a  time 

the  sense  of  bitters  and  sweets,  but  sensibility 

to  acids  and  salines  remains.     This  plant  is 

used  by  the  natives  in  India  as  a  remedy  for 

snake-bite. 

Physiological  Anatomy  of  the  Organs  of 

Taste. — Anatomical    and    physiological    re- 
searches   have  shown    that,  at   least  in   the 

human  subject,  the  organ  of    taste  probably 

is    confined    to    the    dorsal    surface    of    the 

tongue    and  the  lateral   portion    of   the  soft 

palate.       The  upper  surface   of    the  tongue 

presents  a  large  number  of  special  papillae, 

called    in    contradistinction    to    the    filiform 

papillae,  fungiform  and  circumvallate.    These 

are  not  found  on  its  under  surface  or  anywhere   except  on  the  supe- 
rior portion ;  and  it  is  now  well  established  that  the  circumvallate  and 


Fig.  161.  —  FuJigiform ,  filiform. , 
and  hemispherical  papillce,  X  20 
(Sappey). 

I,  I,  two  fungiform  papillae  cov- 
ered with  secondary  papillee  ;  2,  2, 
2,  filiform  papillae;  3,  a  filiform  pa- 
pilla, the  prolongations  of  which 
are  turned  outward  ;  4,  a  filiform 
papilla  with  vertical  prolongations  ; 
5, 5,  small  filiform  papillce  with  the 
prolongations  turned  inward  ;  6,  6, 
filiform  papillce  with  striations  at 
their  bases  ;  7,  7,  hemispherical  pa- 
pillae, slightly  apparent,  situated 
between  the  fungiform  and  the 
filiform  papillae. 


644  SPECIAL  SENSES 

fungiform  papillae  alone  contain  the  organs  of  taste.  Experiments  on 
the  gustatory  organs,  by  the  application  of  solutions  to  different  parts 
through  fine  glass  tubes,  have  shown  that  the  mucous  membrane  around 
a  papilla  has  no  gustatory  sensibility,  but  that  different  savors  can  be 
distinguished  when  a  single  papilla  is  touched  (Camerer). 

In  Fig.  159,  which  represents  the  dorsal  surface  of  the  tongue,  the 
large  circumvallate  papillae,  usually  seven  to  twelve  in  number,  are  seen 
in  the  form  of  an  inverted  V,  occupying  the  base  of  the  tongue.  The 
fungiform  papillae  are  scattered  over  the  surface  but  are  most  abundant 
at  the  point  and  near  the  borders.  Both  varieties  of  papillae  are  distin- 
guishable by  the  naked  eye. 

The  circumvallate  papillae  simply  are  enlarged  fungiform  papillae, 
each  one  surrounded  with  a  circular  ridge,  or  wall,  and  covered  with 
small  secondary  papillae.  The  fungiform  papillae  have  each  a  short 
thick  pedicle  and  an  enlarged  rounded  extremity.  One  hundred  and 
fifty  to  two  hundred  of  these  can  easily  be  counted.  These,  also,  pre- 
sent small  secondary  papillae  on  their  surfaces.  When  the  mucous 
membrane  of  the  tongue  is  examined  with  a  low  magnifying  power,  par- 
ticularly after  maceration  in  acetic  or  in  dilute  hydrochloric  acid,  their 
structure  is  readily  observed.  They  are  abundantly  supplied  with 
bloodvessels  and  nerves. 

Several  glandular  structures  are  found  beneath  the  mucous  mem- 
brane of  the  tongue.  On  either  side  of  the  frenum,  near  the  point,  is 
a  gland  about  three-quarters  of  an  inch  (20  millimeters)  long  and  one- 
third  of  an  inch  (8.5  millimeters)  broad,  which  has  five  or  six  little  open- 
ings on  the  under  surface  of  the  tongue.  Near  the  taste-buds,  are  small 
racemose  glands,  which  discharge  a  watery  secretion  by  minute  ducts 
that  open  into  the  grooves  within  the  walls  of  the  circumvallate  papillae 
(Ebner). 

Taste-Buds. —  Loven  and  Schvvalbe  (1867)  described  under  this 
name  peculiar  structures  that  are  supposed  to  be  the  true  organs  of 
taste.  They  are  found  on  the  lateral  slopes  of  the  circumvallate  papillae 
and  occasionally  on  the  fungiform  papillae.  They  consist  of  flask-like 
collections  of  spindle-shaped  cells,  which  are  received  into  little  excava- 
tions in  the  epithelial  covering  of  the  mucous  membrane,  the  bottom 
resting  on  the  connective-tissue  layer.  Their  form  is  ovoid,  and  at  the 
neck  of  each  flask  is  a  rounded  opening  called  the  taste-pore.  Their 
length  is  ^\^  to  3^  of  an  inch  (71  to  83  /a),  and  their  transverse 
diameter,  about  g^^  of  an  inch  (41  tx).  The  cavity  of  the  taste-buds  is 
filled  with  cells,  of  which  two  kinds  are  described.  The  first  variety,  the 
outer  cells,  or  the  cover-cells,  are  spindle-shaped  and  curved  to  corre- 
spond to  the  wall  of  the  beaker.     These  come  to  a  point  at  the  taste- 


TASTE-BUDS  645 

pore.  In  the  interior  are  elongated  cells,  with  large  clear  nuclei,  which 
are  called  taste-cells.  Delicate  hair-like  processes  are  connected  with 
the  taste-cells  and  extend  through  the  taste-pores,  in  the  form  of  line 
filaments.  Bodies  similar  to  the  taste-buds  have  been  found  on  the 
papillae  of  the  soft  palate  and  uvula,  the  mucous  membrane  of  the  epi- 
glottis and  some  parts  of  the  top  of  the  larynx.  As  regards  these  struc- 
tures in  the  tongue,  it  has  been  found  that  four  or  iive  months  after 
section  of  the  glosso-pharyngeal  on  one  side  in  rabbits,  the  taste-buds 


gzr= 


ep 


Fig.   162.  —  Transverse   section    of  a    taste-        Fig.    163.  —  Vertical    section   of  a    taste-bud,  X  500 
bud  from  a  rabbit,  X  500  (Sobotta).  (Sobotta). 

stg,  taste-pore  ;  dz,  lining  epithelium,  ep,   stratified  epithelium  ;    dz,  lining  epithelium  ; 

gz,    gustatory    cells;  pg,  taste-pore;    stg,  taste-fila- 
ments (gustatory  rods) . 

on  the  corresponding  side  of  the  posterior  portion  of  the  tongue  disap- 
pear, while  they  remain  perfect  on  the  sound  side. 

According  to  the  views  of  those  who  have  described  the  so-called 
taste-buds,  sapid  solutions  find  their  way  into  the  interior  of  these  struc- 
tures through  the  taste-pores  and  come  in  contact  with  the  taste-cells, 
these  cells  being  directly  connected  with  the  terminal  filaments  of  the 
gustatory  nerves. 

Ferrier  and  others  have  described  a  taste-centre  near  the  so-called 
olfactory  centre  in  the  uncinate  gyrus ;  but  their  observations  are  not 
very  definite,  and  the  location  of  a  centre  for  gustation  must  still  be 
regarded  as  uncertain. 


CHAPTER   XXVI 

THE    ORGAN    OF   VISION 

Optic  (seconri  nerve)  — General  properties  of  the  optic  nerves  —  Physiological  anatomy  of  the 
eyeball  —  Sclerotic  coat  —  Cornea  —  Choroid  coat  —  Ciliary  processes  —  Iris  —  Pupillary 
membrane  —  Retina — Layer  of  rods  and  cones  (Jacob's  membrane,  or  bacillar  mem- 
brane)—  Crystalline  lens  —  Suspensory  ligament  of  the  lens  (zone  of  Zinn) — Aqueous 
humor  —  Vitreous  humor  —  Summary  of  the  anatomy  of  the  globe  of  the  eye. 

The  chief  points  to  be  considered  in  the  physiology  of  vision  are  the 
following :  — 

1.  The  physiological  anatomy  and  the  general  properties  and  uses 
of  the  optic  nerves. 

2.  The  physiological  anatomy  of  the  parts  essential  to  normal  vision, 

3.  The  laws  of  refraction,  diffusion  etc.,  bearing  on  the  physiology 
of  vision. 

4.  The  action  of  the  different  parts  of  the  eye  in  the  production  and 
appreciation  of  correct  images. 

5.  Binocular  vision. 

6.  The  physiological  anatomy  and  uses  of  accessory  parts,  as  the 
muscles  that  move  the  eyeball. 

7.  The  physiological  anatomy  and  uses  of  the  parts  that  protect  the 
eye,  as  the  lachrymal  glands,  eyelids  etc. 

Optic  (Second  Nerve) 

The  bands  that  pass  from  the  tubercula  quadrigemina  to  the  eyes 
are  divided  into  the  optic  tracts,  which  extend  from  the  tubercula  on 
either  side  to  the  chiasm,  or  commissure;  the  chiasm,  or  the  decussat- 
ing portion  ;  and  the  optic  nerves,  which  pass  from  the  chiasm  to  the 
eyes. 

The  optic  tracts  arise  each  by  two  roots,  internal  and  external.  The 
internal  roots,  which  are  the  smaller,  arise  from  the  anterior  tubercula 
quadrigemina  and  pass  through  the  internal  corpora  geniculata  to  the 
optic  chiasm.  The  external  roots,  which  are  the  larger,  arise  from  the 
posterior  part  of  the  optic  thalami,  pass  to  the  external  corpora  geni- 
culata, from  which  they  receive  fibres,  and  thence  to  the  chiasm. 

Partly  by  anatomical  researches  and  partly  by  experiments  on  the 

646 


THE   OPTIC   NERVE 


647 


cerebral  cortex  in  the  lower  animals  and  pathological  observations  on 
the  human  subject,  it  has  been  shown  that  fibres  from  the  apparent 
origin  of  the  optic  tracts  pass  backward  to  the  gray  matter  of  the  occipi- 
tal lobes  of  the  cerebrum.  They  then  pass  to  the  bulb,  extend  down 
as  far  as  the  decussation  of  the  pyramids  and  probably  are  concerned 
in  the  reflex  movements  of  the  iris. 

The  two  roots  of  each  optic  tract  unite  above  the  external  corpus 
geniculatum,  forming  a  flattened  band,  which  takes  an  oblique  course 
around  the  under  surface  of  the  crus  cerebri 
to  the  optic  commissure. 

The  optic  commissure,  or  chiasm,  is 
situated  just  in  front  of  the  corpus  cine- 
reum,  resting  upon  the  olivary  process  of 
the  sphenoid  bone.  As  its  name  implies, 
this  is  the  point  of  union  between  the  nerves 
of  the  two  sides.  At  the  commissure  the 
fibres  from  the  optic  tracts  take  three  direc- 
tions ;  and  in  addition,  the  commissure  con- 
tains filaments  passmg  from  one  eye  to  the 
other,  which  have  no  connection  with  the 
optic  tracts.  The  four  sets  of  fibres  in 
the  optic  commissure  are  the  following:  — 

1.  Decussating  fibres,  passing  from  the 
optic  tract  on  either  side  to  the  eye  of  the  Fig-  164.— o///c  tracts,  commissure 

.  .  _,,  ^    ,        -,  and  nerves  (Hirschfeld). 

opposite  Side.    1  he  greatest  part  01  the  fibres 

I,  infundibulum  ;  2,  corpus  xine- 
reum  ;  3,  corpora  albicantia  ;  4,  cere- 
bral peduncle  ;  5,  pons  Varolii ;  b,  optic 
tracts  atid  nerves,  decussating  at  the 

2.  External  fibres,  fewer  than  the  pre-  comm issure,  or  chiasm  :j,mo'iQToc\x\\ 
ceding,  which  pass  from  the  optic  tract  to 
the  eye  on  the  same  side. 


10/ 


take  this  direction, 
is  internal. 


Their  relative  situation 


communis;     B,     pathelicus;    9,    fifth 

nerve ;     10,    motor     oculi     externus ; 

II,  facial   nerve;   12,  auditory  nerve; 

T^.,  •,        ,      1  1  -13,   nerve   of    Wrisberg;    14,   glosso- 

3.  Fibres       situated       on       the       posterior    pharyngeal  nerve;  15,  pneumogastric; 

border  of  the  commissure,  which  pass  from    ^6,  spinal  accessory;   17,  sublingual 

,  ,  ,       ,  nerve. 

one  optic   tract   to  the  other   and   do    not 

go  to  the  eyes.      These  fibres  are   scanty  and  sometimes  wanting. 

4.  Fibres  situated  on  the  anterior  border  of  the  commissure,  greater 
in  number  than  the  preceding,  which  pass  from  one  eye  to  the  other  and 
which  have  no  connection  with  the  optic  tracts. 

The  fibres  of  the  optic  tracts  on  the  two  sides  are  connected  with 
distinct  portions  of  the  retina.  This  fact  is  illustrated  in  cases  of  hemi- 
anopsia, which  show  that  the  decussating  fibres  have  the  following 
directions  and  distribution  :  — 

From  the  left  side  of  the  encephalon,  fibres  pass  to  the  right  eye, 


648  SPECIAL    SENSES 

supplying  the  inner,  or  nasal  mathematical  half  of  the  retina,  from  a 
vertical  line  passing  through  the  macula  lutea.  Fibres  also  pass  to  the 
left  eye,  supplying  the  outer,  or  temporal  half  of  the  retina.  The  ma- 
cula lutea,  then,  and  not  the  point  of  entrance  of  the  optic  nerve,  is  in  the 
true  vertical  line  of  division  of  the  retina. 

With  the  exception  of  a  few^  grayish  filaments,  the  fibres  of  the  optic 
tracts  and  the  optic  nerves  are  of  the  ordinary  medullated  variety  and 
present  no  differences  in  structure  from  the  general  cerebro-spinal 
nerves. 

The  optic  commissure  is  covered  with  a  fibrous  membrane  and  is 
more  resisting  than  the  optic  tracts.  The  optic  nerves  are  rounded  and 
are  enclosed  in  a  double  sheath  derived  from  the  dura  mater  and  the 
arachnoid.     They  pass  into  the  orbit  on  either  side  and  penetrate  the 

sclerotic  at  the  posterior,  inferior  and  internal 
portion  of  the  globe.  As  the  nerves  enter 
the  globe  they  lose  their  coverings  from  the 
dura  mater  and  arachnoid.  The  sheath  de- 
rived from  the  dura  mater  is  adherent  to  the 
periosteum  of  the  orbit  at  the  sphenoidal 
fissure,  and  when  it  reaches  the  globe,  it  fuses 
with  the  sclerotic  coat.  Just  before  the 
Fig.  z(^s.- Diagram  of  the  de-  "crves  penetrate  the  globe,  they  each  present 
cussation  of  fibres  at  the  optic    a  wcll-markcd  constriction.     At  the  point  of 

cotnniissure.  .  ,  .  ,   .        , 

penetration  there  is  a  thm  but  strong  mem- 

The  dotted  lines  show  the  four      ,  .  i  r  r  •  r 

directions  of  the  fibres.  brane,  presenting  a  number  01  perforations  tor 

the  passage  of  the  nervous  filaments.  This 
membrane,  the  lamina  cribrosa,  is  in  part  derived  from  the  sclerotic,  and 
in  part,  from  the  coverings  of  the  individual  nerve-fibres,  which  lose  their 
investing  membranes  at  this  point.  In  the  interior  of  each  eye  there 
is  a  little  mammillated  eminence,  formed  by  the  united  fibres  of  the 
nerve.  The  retina,  with  which  the  optic  nerve  is  connected,  will  be 
described  as  one  of  the  coats  of  the  eye. 

In  the  centre  of  the  optic  nerve  is  a  minute  canal,  lined  with  fibrous 
tissue,  in  which  are  lodged  the  central  artery  of  the  retina  and  its  corre- 
sponding vein,  with  a  delicate  nervous  filament  from  the  ophthalmic  gan- 
glion. The  vessels  penetrate  the  optic  nerve  ^  to  |  of  an  inch  (8.5  to 
19. 1  millimeters)  behind  the  globe.  The  central  canal  does  not  e.xist 
behind  these  vessels. 

General  Pr'operties  of  the  Optic  Nerves.  —  There  is  little  to  be  said 
regarding  the  general  properties  of  the  optic  nerves,  except  that  they 
are  the  only  nerves  capable  of  conveying  to  the  cerebrum  the  special 
impressions   of    sight   and   are    not    endowed  with    general    sensibility. 


PHYSIOLOGICAL   ANATOMY  OF    THE    EYEBALL  649 

Their  mechanical  or  electric    stimulation    produces    luminous    impres- 
sions. , 

Physiological  Anatomy  of  the  Eyeball 

The  eyeball  is  a  spheroidal  body,  partly  embedded  in  a  cushion  of  fat 
in  the  orbit,  protected  by  the  surrounding  bony  structures  and  the  eye- 
lids, its  surface  bathed  with  the  secretion  of  the  lachrymal  gland  and 
movable  in  various  directions  by  the  action  of  certain  muscles.  It  is 
surrounded  with  a  thin  serous  sac,  the  capsule  of  Tenon,  which  exists 
in  two  layers.  The  outer  layer  lies  next  the  fat  in  which  the  globe  is  em- 
bedded and  the  inner  layer  invests  the  sclerotic  coat.  When  the  axis 
of  the  eye  is  directed  forward,  the  globe  has  the  form  of  a  sphere  in  its 
posterior  five-sixths,  with  the  segment  of  a  smaller  sphere  occupying  its 
anterior  sixth.  The  segment  of  the  smaller  sphere,  bounded  externally 
by  the  cornea,  is  more  prominent  than  the  rest  of  the  globe. 

The  eyeball  is  made  up  of  several  coats  enclosing  certain  refracting 
media.  The  external  coat  is  the  sclerotic,  covering  the  posterior  five- 
sixths  of  the  globe,  which  is  continuous  with  the  cornea,  covering  the 
anterior  sixth.  This  is  a  dense,  opaque,  fibrous  membrane,  for  the  pro- 
tection of  the  inner  coats  and  the  contents  of  the  globe.  The  cornea  is 
dense,  resisting  and  transparent.  The  muscles  that  move  the  globe  are 
attached  to  the  sclerotic  coat. 

Were  it  not  for  the  prominence  of  the  cornea,  the  eyeball  would  pre- 
sent very  nearly  the  form  of  a  perfect  sphere,  as  will  be  seen  by  the 
following  measurements  of  its  various  diameters  ;  but  the  prominence  of 
its  anterior  sixth  gives  the  greatest  diameter  in  the  antero-posterior 
direction. 

In  measurements  made  by  Sappey,  one  to  four  hours  after  death,  of 
the  eyes  of  twelve  adult  females  and  fourteen  adult  males,  of  different 
ages,  the  following  mean  results  were  obtained  :  — 


Subjects  examined 

Diameters  (inch,  and  millimeters  in  parentheses) 

Antero-posterior 

Transverse                Vertical 

Oblique 

Mean  of  12  females,  18  to  81  years  of  age   . 
Mean  of  14  males,  20  to  79  years  of  age 

0.941  (23.9  mm.) 
0.968  (24.6  mm.) 

0.911  (23  4  mm.)  0.905  (23.0  mm.) 
0.941  (23.9  mm.)io.925  (23.5  mm.) 

0.937  (23.8  mm.) 
0.949  (24.1  mm.) 

From  these  results  it  is  seen  that  all  the  diameters  are  less  in  the 
female  than  in  the  male.  The  antero-posterior  diameter  is  the  great- 
est of  all,  and  the  vertical  diameter  is  the  shortest.  The  measurements 
at  different  ages,  not  cited  in  the  table  just  given,  show  that  the  excess 
of  the  antero-posterior  diameter  over  the  others  diminishes  with  age. 


650  SPECIAL    SENSES 

Sclerotic  Coat.  —  The  sclerotic  is  the  dense,  opaque,  fibrous  covering 
of  the  posterior  five-sixths  of  the  eyeball.  Its  thickness  is  different  in 
different  portions.  At  the  point  of  penetration  of  the  optic  nerve,  it 
measures  ^^  of  an  inch  ( i  millimeter).  It  is  thinnest  at  the  middle 
portion  of  the  eye,  measuring  about  g^^  of  an  inch  (0.5  millimeter),  and 
is  a  little  thicker  again  near  the  cornea.  This  membrane  is  composed 
chiefly  of  bundles  of  ordinary  connective  tissue.  The  fibres  are  slightly 
wavy,  and  are  arranged  in  flattened  bands,  which  are  alternately  longi- 
tudinal and  transverse,  giving  the  membrane  a  lamellated  appearance, 
although  it  can  not  be  separated  into  distinct  layers.  Mixed  with  these 
bands  of  connective-tissue  fibres  are  small  fibres  of  elastic  tissue.  The 
vessels  of  the  sclerotic  are  scanty.  They  are  derived  from  the  ciliary 
vessels  and  the  vessels  of  the  muscles  of  the  eyeball.  The  tissue  of  the 
sclerotic  yields  gelatin  on  boiling. 

Cornea.  —  The  cornea  is  the  transparent  membrane  that  covers  about 
the  anterior  sixth  of  the  globe  of  the  eye.  As  before  remarked,  this  is 
the  most  prominent  portion  of  the  eyeball.  It  is  in  the  form  of  a  seg- 
ment of  a  sphere,  attached  by  its  borders  to  the  segment  of  the  larger 
sphere  formed  by  the  sclerotic.  The  thickness  of  the  corneals  about  g^^ 
of  an  inch  (0.8  millimeter),  in  its  central  portion,  and  about  ^-^  of  an  inch 
(i  millimeter)  near  its  periphery.  Its  substance  is  composed  of  trans- 
parent fibres,  arranged  in  complete  layers  something  like  the  layers  of 
the  sclerotic.     It  yields  chondrin  instead  of  gelatin  on  boiling. 

On  the  external,  or  convex  surface  of  the  cornea,  are  several  layers 
of  delicate,  transparent,  nucleated  epithelium.  The  most  superficial 
cells  are  flattened,  the  middle  cells  are  rounded,  and  the  deepest  cells 
are  elongated  and  arranged  perpendicularly.  These  cells  become 
slightly  opaque  and  whitish  after  death.  Just  beneath  the  epithelial 
covering  of  the  cornea,  is  a  very  thin,  transparent  membrane,  described 
by  Bowman  under  the  name  of  the  "anterior  elastic  lamella."  This 
membrane,  with  its  cells,  is  a  continuation  of  the  conjunctiva.  It  is 
sometimes  called  Bowman's  membrane. 

The  proper  corneal  structure  is  composed  of  flattened  bundles  of 
very  pale  fibres  interlacing  with  each  other  in  every  direction.  Their 
arrangement  is  lamellated,  although  they  can  not  be  separated  into 
complete  and  distinct  layers.  Between  the  bundles  of  fibres,  lie  a  great 
number  of  stellate,  anastomosing,  connective-tissue  corpuscles.  In  these 
cells  and  in  the  intervals  between  the  fibres,  there  is  a  considerable 
quantity  of  transparent  liquid.  The  fibres  constituting  the  substance  of 
the  cornea  are  continuous  with  the  fibrous  structure  of  the  sclerotic, 
from  which  they  can  not  be  separated  by  maceration.  At  the  margin 
of  the  cornea  the  opaque  fibres  of  the  sclerotic  abruptly  become  trans- 


PHYSIOLOGICAL   ANATOMY   OF   THE    EYEBALL 


651 


parent.     The  corneal  substance  is  very  tough  and  will  resist  a  pressure 
sufficient  to  rupture  the  sclerotic. 

On  the  posterior,  or  concave  surface  of  the  cornea,  is  the  membrane 
of  Descemet  or  of  Demours.  This  is  elastic,  transparent,  structureless, 
rather  loosely  attached,  and  covered  with  a  single  layer  of  regularly 
polygonal,  nucleated  epithelium.  At  the  circumference  of  the  cornea  a 
portion  of  this  membrane  passes  to  the  anterior  surface  of  the  iris,  in 
the  form  of  a  number  of  processes  which  constitute  the  ligamentum  iridis 
pectinatum,  a  portion  passes  into  the  substance  of  the  ciliary  muscle  and 
a  portion  is  continuous 
with  the  fibrous  structure 
of  the  sclerotic. 

In  the  adult  the  cornea 
is  almost  without  blood- 
vessels, but  in  foetal  life 
it  presents  a  rich  plexus 
extending  nearly  to  the 
centre.  These  disappear, 
however,  before  birth, 
leaving  a  very  few  deli- 
cate looped  vessels  at  the 
extreme  edge. 

In  the  cornea,  fine 
nerve-fibres  terminate  in 
the  nuclei  of  the  posterior 
layer  of  the  epithelium  of 
its  convex  surface.  The 
cornea  also  contains 
lymph-spaces  and  the  so- 
called  "  wandering  cells." 
The  surface  of  the  cornea 
is  exquisitely  sensitive. 

Choroid  Coat.  —  Calling  the  sclerotic  and  the  cornea  the  first  coat  of 
the  eyeball,  the  second  is  the  choroid,  with  the  ciliary  processes,  the 
ciliary  muscle  and  the  iris.  This  was  called  by  the  older  anatomists  the 
uvea,  a  name  which  was  later  applied,  sometimes  to  the  entire  iris  and 
sometimes  to  its  posterior,  or  pigmentary  layer.  The  choroid  and 
ciliary  processes  will  be  described  together  as  the  second  coat.  The 
ciliary  muscle  and  the  iris  will  be  described  separately. 

The  choroid  is  distinguished  from  the  other  coats  by  its  dark  color  and 
its  great  vascularity.  It  occupies  that  portion  of  the  eyeball  correspond- 
ing to  the  sclerotic.     It  is  perforated  posteriorly  by  the  optic  nerve  and  is 


Fig.   166.  —  Choroid  coat  of  the  eye  (Sappey). 

I,  optic  nerve  ;  2,  2,  2,  2,  3,  3,  3,  4,  sclerotic  coat,  divided  and 
turned  back  to  show  the  choroid;  5,  5,  5,  5,  the  cornea,  divided 
into  four  portions  and  turned  back  ;  6,  6,  canal  of  Schlemm  ;  7, 
external  surface  of  the  choroid,  traversed  by  the  ciliary  nerves 
and  one  of  the  long  ciliary  arteries;  8,  central  vessel,  into 
which  open  the  vasa  vorticosa ;  9,  9,  10,  10,  choroid  zone;  11, 
II,  ciliary  nerves;  12,  long  ciliary  artery;  13,  13,  13,  13,  ante- 
rior ciliary  arteries ;  14,  iris;  15,  15,  vascular  circle  of  the  iris; 
16,  pupil. 


652  SPECIAL    SENSES 

connected  in  front  with  the  iris.  It  is  delicate  in  structure  and  com- 
posed of  two  or  three  distinct  layers.  Its  thickness  is  -^^  to  ^^  of  an 
inch  (0.3  to  I  millimeter).  Its  thinnest  portion  is  at  about  the  middle 
of  the  eye.  Posteriorly  it  is  a  little  thicker.  Its  thickest  portion  is  at 
its  anterior  border. 

The  external  surface  of  the  choroid  is  connected  with  the  sclerotic 
by  vessels  and  nerves  (the  long  ciliary  arteries  and  the  ciliary  nerves) 
and  very  loose  connective  tissue.  This  is  sometimes  called  the  mem- 
brana  fusca,  although  it  can  hardly  be  regarded  as  a  distinct  layer.  It 
contains,  in  addition  to  bloodvessels,  nerves  and  fibrous  tissue,  a  few 
irregularly-shaped  pigment-cells. 

The  vascular  layer  of  the  choroid  consists  of  arteries,  veins  and 
capillaries,  arranged  in  a  peculiar  manner.  The  layer  of  capillary 
vessels,  which  is  internal,  is  sometimes  called  the  tunica  Ruyschiana. 
The  arteries,  which  are  derived  from  the  posterior  short  ciliary  arteries 
and  are  connected  with  the  capillary  plexus,  lie  just  beneath  the  pig- 
mentary layer  of  the  retina.  The  plexus  of  capillaries  is  closest  at  the 
posterior  portion  of  the  membrane.  The  veins  are  external  to  the 
other  vessels.  They  are  very  abundant  and  are  disposed  in  curves 
converging  to  four  trunks.  This  arrangement  gives  the  veins  a  peculiar 
appearance,  and  they  have  been  called  vasa  vorticosa.  The  pigmentary 
portion  is  composed,  over  the  greatest  part  of  the  choroid,  of  a  single 
layer  of  regularly-polygonal  cells,  somewhat  flattened,  measuring  20^00 
to  y-500  of  an  inch  (12  to  16  /jl)  in  diameter.  These  cells  are  filled  with 
pigmentary  granules  of  uniform  size  and  give  to  the  membrane  its 
characteristic  dark-brown  or  chocolate  color.  The  pigmentary  granules 
in  the  cells  are  less  abundant  near  their  centre,  where  a  clear  nucleus 
can  readily  be  observed.  In  the  anterior  portion  of  the  membrane,  in 
front  of  the  anterior  limit  of  the  retina,  the  cells  are  smaller,  more 
rounded,  more  completely  filled  with  pigment  and  present  several 
layers.  Beneath  the  layer  of  hexagonal  pigment-cells,  the  intervascular 
spaces  of  the  choroid  are  occupied  by  stellate  pigment-cells.  The 
cells  next  the  layer  of  rods  and  cones  are  regarded  as  constituting  the 
outer,  or  pigmentary  layer  of  the  retina.  These  cells  send  little  hair- 
like processes  inward  between  the  rods  and  cones. 

Ciliary  Processes.  —  The  anterior  portion  of  the  choroid  is  arranged 
in  the  form  of  folds  or  plaits  projecting  internally,  called  the  ciliary 
processes.  The  largest  of  these  folds  are  about  -^  of  an  inch  (2.5  milli- 
meters) in  length.  They  are  sixty  to  eighty  in  number.  The  larger 
folds  are  of  nearly  uniform  size  and  are  arranged  regularly  around  the 
margin  of  the  crystalline  lens.  Between  these  folds,  which  constitute 
about  two-thirds  of  the  entire  number,  are  smaller  folds,  lying,  without 


PHYSIOLOGICAL   ANATOMY    OF   THE   EYEBALL 


653 


regular  alternation,  between  the  larger.  Within  the  folds,  are  received 
corresponding  folds  of  the  thick  membrane,  continuous  anteriorly  with 
the  hyaloid  membrane  of  the  vitreous  humor,  called  the  zone  of  Zinn. 

The  ciliary  processes  present  bloodvessels,  which  are  somewhat 
larger  than  those  of  the  rest  of  the  choroid.  The  pigmentary  cells  are 
smaller  and  are  arranged  in  several  layers.  The  anterior  border  of 
the  processes  is  free  and  contains  little  or  no  pigment. 

Ciliary  Muscle.  —  This  muscle,  formerly  known  as  the  ciliary  liga- 
ment and  now  sometimes  called  the  tensor  of  the  choroid,  is  the  agent 
for  the  accommodation  of  the  eye  to  vision  at  different  distances.  Under 
this  view,  the  ciliary  muscle  is  an  organ 
of  great  importance ;  and  it  is  essential, 
in  the  study  of  accommodation,  to  have 
an  exact  idea  of  its  relations  to  the  coats 
of  the  eye  and  to  the  crystalline  lens. 

The  form  and  situation  of  the  ciliary 

muscle  are  as  follows  :  It  surrounds  the 

anterior  margin   of   the  choroid,  in   the 

form  of  a  ring  about  \  of  an  inch  (3.2 

millimeters)  wide  and  -^-^  of  an  inch  (0.5 

millimeter)  in   thickness  at  its  thickest 

portion,  which  is  its  anterior  border.     It 

I 
becomes  thmner  from  before  backward,   bran 

until    its    posterior    border   apparently  *^/ .""^""y  P''°'^^^^f  =  ^' ^' '■^^*^^'"sfi^''.^' 

■^  ^  ^  -'of  the  ciliary  muscle ;  7,  section  01  the  cir- 

f  uses   with    the    fibrous    structure    of    the    cularportionoftheciliary  muscle;  8,  venous 

1  •!         Ti    •  'i.  i.  J       r    plexus  of  the  ciliary  process ;  Q,  lo,  sclerotic 

choroid.       It    is    Semitransparent    and    of    l^^^.   „,  i,,  cornea;   13,  epithelial  layer  of 

a    grayish    color.         Its    situation    is     just    the   cornea;   14,  membrane  of  Descemet; 

,    .  ,  c    ,^  •^•  .1  i^,  liramentum  iridis  pectinatum ;   i6,  epi- 

outside    of    the     ciliary     processes,    these    thelium    of  the    membrane   of   Descemet; 

processes  projecting  in  front  of  its  an-  ^7,  union  of  the  sclerotic  coat  with  the 

.        cornea;  18,  section  of  the  canal  of  Schlemm. 

tenor  border,  about  2V  of  S-^^  i^^ch  ( i  mil- 
limeter). Regarding  the  anterior  border  of  this  muscle  as  its  origin  and 
the  posterior  border  as  its  insertion,  it  arises  in  front  from  the  circular 
line  of  junction  of  the  cornea  and  sclerotic,  the  border  of  the  membrane 
of  Descemet,  and  the  ligamentum  iridis  pectinatum.  Its  fibres,  which 
are  chiefly  longitudinal,  pass  backward  and  are  lost  in  the  choroid,  ex- 
tending somewhat  farther  back  than  the  anterior  limit  of  the  retina. 
In  addition,  a  network  of  circular  muscular  fibres  has  been  described, 
lying  over  the  anterior  portion  of  the  ciliary  body,  at  the  periphery  of 
the  iris,  beneath  the  longitudinal  fibres.  Some  of  these  fibres  have  an 
oblique  direction. 

The  ciliary  muscle  is  composed  mainly  of  muscular  fibres.  These 
fibres,    anatomically    considered,    belong    to    the    non-striated    variety. 


Fig.  167.  —  Ciliary  muscle,  X  5  (Sappey). 

crystalline  lens ;  2,  hyaloid  mem- 
3,  zone  of  Zinn  ;  4,  iris ;  5,  5,  one  of 


654  SPECIAL    SENSES 

They  are  pale,  present  a  number  of  oval  longitudinal  nuclei  and  have 
no  striae. 

It  is  evident,  from  the  arrangement  of  the  fibres  of  the  ciliary  mus- 
cle, that  its  action  must  be  to  approximate  the  border  of  connection  of 
the  sclerotic  and  cornea  and  the  circumference  of  the  choroid,  com- 
pressing the  vitreous  humor  and  relaxing  the  suspensory  ligament  of 
the  lens.  This  action  enables  the  lens  to  change  its  form ;  and  it  adapts 
the  curvature  of  the  lens  to  vision  at  different  distances.  The  nerves 
of  the  ciliary  muscle  are  derived  from  the  long  and  the  short  ciliary. 

Iris.  —  The  iris  corresponds  to  the  diaphragm  of  optical  instruments. 
It  is  a  circular  membrane,  situated  just  in  front  of  the  crystalline  lens, 
with  a  round  perforation  (the  pupil)  near  its  centre. 

The  attachment  of  the  greater  circumference  of  the  iris  is  to  the 
line  of  junction  of  the  cornea  and  sclerotic,  near  the  origin  of  the  ciliary 
muscle,  the  latter  passing  backward  to  be  inserted  into  the  choroid,  and 
the  former  passing  directly  over  the  crystalline  lens.  The  diameter  of 
the  iris  is  about  half  an  inch  (12.5  millimeters).  The  pupil  is  subject  to 
considerable  variations  in  size.  When  at  its  medium  of  dilatation,  the 
diameter  of  the  pupil  is  \  to  \  of  an  inch  (3.2  to  4.2  millimeters).  The 
pupillary  orifice  is  not  in  the  mathematical  centre  of  the  iris  but  is  situ- 
ated a  little  toward  the  nasal  side.  The  thickness  of  the  iris  is  a  little 
greater  than  that  of  the  choroid,  but  it  is  unequal  in  different  parts,  the 
membrane  being  thinnest  at  its  great  circumference  and  its  pupillary 
border,  and  thickest  at  about  the  junction  of  its  inner  third  with  the 
outer  two-thirds.  It  slightly  projects  anteriorly  and  divides  the  space 
between  the  lens  and  the  cornea  into  two  chambers,  anterior  and  poste- 
rior, the  anterior  chamber  being  much  the  larger.  Taking  advantage 
of  a  property  of  the  crystalline  lens  called  fluorescence,  which  enables 
an  observer,  by  concentrating  on  it  a  blue  light,  to  see  the  boundaries 
in  the  living  eye,  Helmholtz  has  demonstrated  that  the  posterior  surface 
of  the  iris  and  the  anterior  surface  of  the  lens  are  actually  in  contact, 
except,  perhaps,  for  a  certain  distance  near  the  periphery  of  the  iris. 
This  being  the  case,  the  posterior  chamber  is  very  small  and  exists  only 
near  the  margins  of  the  lens  and  the  iris. 

The  color  of  the  iris  is  different  in  different  individuals.  Its  ante- 
rior surface  usually  is  very  dark  near  the  pupil  and  presents  colored 
radiations  toward  its  periphery.  Its  posterior  surface  is  of  a  dark- 
purple  color  and  is  covered  with  pigment-cells. 

The  iris  presents  three  layers.  The  anterior  layer  is  continuous 
with  the  membrane  of  the  aqueous  humor.  At  the  greater  circumfer- 
ence, it  presents  little  fibrous  prolongations,  forming  a  delicate  dentated 
membrane   continuous  with    the    ligamentum    iridis    pectinatum.     The 


PHYSIOLOGICAL   ANATOMY   OF   THE   EYEBALL  655 

membrane  covering  the  general  anterior  surface  of  the  iris  is  extremely 
thin  and  is  covered  with  cells  of  tessellated  epithelium.  Just  beneath 
this  membrane  are  a  number  of  irregularly-shaped  pigment-cells. 

The  posterior  layer  of  the  iris  is  thin,  easily  detached  from  the 
middle  layer,  and  contains  a  number  of  small  cells  rich  in  pigmentary 
granules.     Some  anatomists  recognize  this  membrane  only  as  the  uvea. 

The  middle  layer  constitutes  by  far  the  greatest  part  of  the  substance 
of  the  iris.  It  is  composed  of  connective  tissue,  muscular  fibres  of  the 
non-striated  variety,  many  bloodvessels  and  probably  nerve-terminations. 
Directly  surrounding  the  pupil,  forming  a  band  about  -^  of  an  inch 
(0.5  millimeter)  in  width,  is  a  layer  of  non-striated  muscular  fibres, 
called  the  sphincter  of  the  iris.  In  addition  to  the  sphincter,  are  radi- 
ating fibres,  which  can  be  traced  from  near  the  circumference  of  the 
iris  almost  to  its  pupillary  border,  lying  both  in  front  of  and  behind  the 
circular  fibres. 

The  bloodvessels  of  the  iris  are  derived  from  the  arteries  of  the 
choroid,  from  the  long  posterior  ciliary  and  from  the  anterior  ciliary 
arteries.  The  long  ciliary  arteries  are  two  branches,  running  along  the 
sides  of  the  eyeball,  between  the  sclerotic  and  choroid,  to  form  finally  a 
circle  surrounding  the  iris.  The  anterior  ciliary  arteries  are  derived 
from  the  muscular  branches  of  the  ophthalmic.  They  penetrate  the 
sclerotic  a  little  behind  the  iris  and  join  the  long  ciliary  arteries  in 
the  vascular  circle.  From  this  circle,  the  vessels  branch  and  pass  into 
the  iris,  to  form  a  smaller  arterial  circle  around  the  pupil.  The  veins 
of  the  iris  empty  into  a  circular  sinus  situated  at  the  junction  of  the 
cornea  with  the  sclerotic.  This  is  called  the  circular  venous  sinus,  or  the 
canal  of  Schlemm. 

The  nerves  of  the  iris  are  the  long  ciliary,  from  the  fifth,  which  are 
sensory,  and  the  short  ciliary,  from  the  ophthalmic  ganglion.  The  cir- 
cular fibres  are  animated  by  filaments  from  the  third  nerve,  which  pass 
through  the  ophthalmic  ganglion.  The  radiating  fibres  receive  filaments 
derived  from  the  cervical  sympathetic,  probably  through  the  carotid 
plexus  and  the  ganglion  of  Gasser. 

Pupillary  Membrane.  —  At  a  certain  period  of  foetal  life  the  pupil  is 
closed  with  a  membrane  connected  with  the  lesser  circumference  of  the 
iris,  called  the  pupillary  membrane.  This  is  not  distinct  during  the  first 
months ;  but  between  the  third  and  the  fourth  months,  it  is  readily  seen. 
It  is  most  distinct  at  the  sixth  month.  The  membrane  is  thin  and  trans- 
parent and  completely  separates  the  anterior  from  the  posterior  chamber 
of  the  eye.  It  is  provided  with  vessels  derived  from  the  arteries  of  the 
iris,  anastomosing  with  each  other  and  turning  back  in  the  form  of 
loops  near  the  centre.     At  about  the  seventh  month  it  begins  to  give 


656  SPECIAL    SENSES 

way  at  the  centre,  gradually  atrophies  and  scarcely  a  trace  of  it  can 
be  seen  at  birth.  The  presence  and  condition  of  the  pupillary  mem- 
brane often  are  important  as  an  aid  in  determining  the  age  of  a 
foetus. 

Retina.  —  The  retina  is  described  by  anatomists  as  the  third  tunic  of 
the  eye.  It  is  closely  connected  with  the  optic  nerve,  and  the  most 
important  structures  entering  into  its  composition  are  continuous  with 
prolongations  from  the  nerve-cells.  This  is  the  membrane  endowed 
with  the  special  sense  of  sight,  the  other  structures  in  the  eye  being 
accessory. 

If  the  sclerotic  and  choroid  are  removed  from  the  eye  under  water, 
the  retina  is  seen,  in  perfectly  fresh  specimens,  in  the  form  of  a  delicate 
transparent  membrane  covering  the  posterior  portion  of  the  vitreous 
humor.  A  short  time  after  death  it  becomes  slightly  opaline.  It  ex- 
tends over  the  posterior  portion  of  the  eyeball  to  a  distance  of  about  ^^g- 
of  an  inch  (1.7  milHmeter)  behind  the  ciliary  processes.  When  torn 
from  its  anterior  attachment,  it  presents  a  finely-serrated  edge,  called 
the  ora  serrata.  This  edge  adheres  very  closely,  by  mutual  interlace- 
ment of  fibres,  to  the  zone  of  Zinn.  In  the  middle  of  the  membrane, 
its  thickness  is  about  y^  of  an  inch  (200  ^x).  It  becomes  thinner  nearer 
the  anterior  margin,  where  it  measures  only  about  g^Q-  of  an  inch  (80  fx). 
Its  external  surface  is  in  contact  with  the  choroid,  and  its  internal,  with 
the  hyaloid  membrane  of  the  vitreous  humor. 

The  optic  nerve  penetrates  the  retina  about  \  of  an  inch  (3.2  milli- 
meters) within,  and  yV  o^  ^^^  \n<z\i  (2.1  millimeters)  below  the  antero- 
posterior axis  of  the  globe,  presenting  at  this  point  a  small  rounded 
elevation  on  the  internal  surface  of  the  membrane,  perforated  in  its 
centre  for  the  passage  of  ,the  central  artery  of  the  retina.  At  a 
point  -^2  to  5  o^  ^^  ^^ch  (2.1  to  3.2  millimeters)  external  to  the  point  of 
penetration  of  the  nerve,  is  an  elliptic  spot,  its  long  diameter  being 
horizontal,  about  ^  of  an  inch  (2.1  millimeters)  long  and  -^^  of  an  inch 
(0.7  millimeter)  broad,  called  the  yellow  spot  of  Sbmmerring,  or  the 
macula  lutea.  In  the  centre  of  this  spot  is  a  depression  called  the 
fovea  centralis.  This  depression  is  in  the  axis  of  distinct  vision.  The 
yellow  spot  exists  only  in  man  and  the  quadrumana. 

The  structures  in  the  retina  that  present  the  greatest  physiological 
importance  are  the  layer  of  pigment-cells,  the  layer  of  rods  and  cones, 
the  layer  of  nerve-cells,  and  the  filaments  that  connect  the  rods  and 
cones  with  the  cells.  These  are  the  only  anatomical  elements  of  the 
retina,  so  far  as  is  known,  that  are  directly  concerned  in  the  reception 
of  optical  impressions  ;  and  they  will  be  described  rather  minutely, 
while  the  intermediate  layers  will  be  considered  more  briefly. 


THE    RETINA  657 

Most  anatomists  reco2:nize  ten  laA'ers  in  the  retina  :  — 


r.    Inner  limitary  membrane.  6 

2.  Expansion    of    fibres    of  the        7, 

optic  nerve.  8 

3.  Layer  of  ganglion-cells.  9 

4.  Inner  molecular  layer.  10 

5.  Inner  nuclear  layer. 


Outer  molecular  1 


ayer. 


Outer  nuclear  layer. 
Outer  limitary  membrane. 
Layer  of  rods  and  cones. 
Layer  of  pigment-cells. 


1.  The  inner  limitary  membrane  is  a  delicate  structure,  with  fine  striae 
and  nuclei,  composed  of  connective-tissue  elements.  It  is  about  0-5-^-5- 
of  an  inch  (i  /a)  in  thickness.  From  this  membrane,  connective-tissue 
elements  (fibres  of  Miiller)  are  sent  into  the  various  layers  of  the  retina, 
where  they  form  a  framework  for  the  support  of  the  other  structures. 

2.  The  layer  formed  by  the  expansion  of  the  optic  nerve  is  composed 
of  pale  transparent  nerve-fibres,  -g^o'iT  ^^  25^0"  °^"  ^^  ^^^^  ('^•5  ^o  ^  /^) 
in  diameter.     These  do  not  require  special  description. 

3.  The  layer  of  ganglion-cells  is  composed  of  multipolar  nerve-cells, 
measuring  ^ihii  ^°  Tso"  ^^  ^^  ^^^^  (8  to  32  /-t)  in  diameter.  In  the  centre 
of  the  retina,  at  the  macula  lutea,  the  cells  present  eight  layers,  and  they 
diminish  to  a  single  layer  near  the  periphery.  The  smaller  cells  are 
situated  near  the  centre,  and  the  larger,  near  the  periphery.  Each  cell 
sends  off  several  filaments  (two  to  twenty-five),  probably  going  to  the 
layer  of  rods  and  cones,  and  a  single  filament  which  becomes  continuous 
with  one  of  the  filaments  of  the  optic  nerve. 

4.  The  inner  molecular  layer  consists  of  a  plexus  of  minute  fibrils 
and  fine  granules. 

5.  The  inner  nuclear  layer  is  composed  of  nuclear  bodies,  rather 
large  and  some  of  them  stellate  in  form. 

6.  The  outer  molecular  layer  consists  of  a  plexus  of  fine  fibrils  and. 
nuclei. 

7.  The  outer  nuclear  layer  presents  clear,  oval,  nuclear  bodies,  con- 
nected with  the  rods  and  cones  by  one  process  to  each  rod  or  cone,  and 
sending  fibrils  to  the  adjacent  molecular  layer. 

8.  The  outer  limitary  membrane  is  composed  of  delicate  connective- 
tissue  elements. 

9.  The  layer  of  rods  and  cones  is  the  most  important  of  all  and  will 
receive  special  description. 

10.  The  layer  of  pigment-cells  has  already  been  described  in  con- 
nection with  the  choroid  coat. 

Layer  of  Rods  and  Cones  {Jacob' s  Membrane  —  tJie  Bacillar  2Iemb7'ane\ 
—  The  layer  of  rods  and  cones  is  composed  of  rods,  or  cylinders,  ex- 
tending through  its  entire  thickness,  closely  packed,  and  giving  to  the 

2U 


658 


SPECIAL    SENSES 


external  surface  a  regular  mosaic  appearance ;  and  between  these,  is  a 
greater  or  less  number  of  flask-shaped  bodies,  the  cones.  This  layer  is 
about  3^Q  of  an  inch  {^6  /x)  in  thickness  at  the  middle  of  the  retina; 
;j^-g-  of  an  inch  (62  /i),  about  midway  between  the  centre  and  the  periph- 
ery;  and  near  the  periphery,  about  -^\-^  of  an  inch  (55  \x).  At  the 
macula  lutea  the  rods  are  wanting.  Over  the  rest  of  the  membrane,  the 
rods  predominate  and  the  cones  become  less  and  less  frequent  toward 
the  periphery. 

The  rods  are  regular  cylinders,  their  length  corresponding  to  the 
thickness  of  the  layer,  terminating  above  in  truncated  extremities,  and 


IX. 


VIII. 
VII. 


VI. 

V. 

IV. 

III. 
II. 


Fig.  168.  —  Diagram  of  the  retina  (Kallius). 

I,  inner  limitary  membrane  ;  II,  expansion  of  fibres  of  the  optic  nerve;  III,  layer  of  ganglion- 
cells;  IV,  inner  molecular  layer  ;  V,  inner  nuclear  layer  ;  VI,  outer  molecular  layer;  VII,  outer 
nuclear  layer  ;  VIII,  outer  limitary  membrane  ;  IX,  layer  of  rods  and  cones  ;  X,  layer  of  pigment- 
cells. 

Note.  —  The  small  letters  in  this  figure  refer  to  minute  details  of  structure  that  have  not  been  con- 
sidered in  the  text.  The  lower  border  of  the  cut  may  be  taken  as  representing  the  inner  limitary 
membrane.  The  numbering  of  the  layers  is  from  below  upward,  reversing  the  order  in  the  original 
diagram,  and  a  number  for  the  inner  limitarv  membrane  has  been  added. 


below  in  points  which  probably  are  continuous  with  the  filaments  of  con- 
nection with  the  nerve-cells.  Their  diameter  is  about  ^3^0^  ^'^  ^^^  ^"^^ 
(2  //.).  They  are  clear,  of  rather  a  fatty  lustre,  soft  and  pliable,  but 
somewhat  brittle,  and  so  alterable  that  they  are  with  difficulty  seen  in  a 
natural  state.  They  should  be  examined  in  perfectly  fresh  preparations, 
moistened  with  hquid  from  the  vitreous  humor  or  with  serum.     When 


THE    RETINA  659 

perfectly  fresh  it  is  difficult  to  make  out  anything  but  an  entirely  homo- 
geneous substance  ;  but  shortly  after  death  each  rod  seems  to  be  divided 
by  a  delicate  line  into  an  outer  and  an  inner  segment,  the  outer  being 
a  little  the  longer.  At  the  upper  extremity  of  the  inner  segment,  is  a 
hemispherical  body,  with  its  convexity  presenting  inward,  called  the 
lentiform  body.  The  entire  inner  segment  is  somewhat  granular  and 
often  presents  a  granular  nucleus  at  its  inner  extremity.  The  outer  seg- 
ment apparently  differs  in  its  constitution  from  the  inner  segment  and 
is  not  similarly  affected  by  reagents.  Treated  with  dilute  acetic  acid 
the  outer  segment  becomes  broken  up  transversely  into  thin  disks. 

The  cones  probably  are  of  the  same  constitution  as  the  rods,  but  the 
portion  called  the  inner  segment  is  pyriform.  The  straight  portion 
above  (the  outer  segment)  is  sometimes  called  the  cone-rod.  The  entire 
cones  are  about  half  the  length  of  the  rods  and  occup};  the  inner  por- 
tion of  the  layer.  The  outer  segment  is  in  its  constitution  precisely  like 
the  outer  segment  of  the  rods.  The  inner  segment  is  slightly  granular 
and  contains  a  nucleus.  The  cones  are  connected  below  with  filaments 
passing  into  the  deeper  layers  of  the  retina. 

At  the  fovea  centralis,  Jacob's  membrane  is  composed  entirelv  of 
elongated  cones  with  no  rods.  These  are  slightly  increased  in  thick- 
ness at  the  macula  lutea,  but  are  diminished  again  in  thickness,  by 
about  one-half,  at  the  fovea  centralis.  At  the  fovea  the  optic  nerve- 
fibres  are  wanting ;  and  the  ganglion-cells,  which  exist  in  a  single  laver 
over  other  portions  of  the  retina,  here  present  six  to  eight  layers,  ex- 
cept at  the  very  centre,  where  there  are  but  three  layers.  Of  the 
layers  between  the  cones  and  the  ganglion-cells,  the  outer  nuclear  laver 
and  the  outer  molecular  layer  remain  in  the  fovea,  while  the  inner 
nuclear  layer  and  the  inner  molecular  layer  are  wanting.  xA.t  the  fovea, 
indeed,  those  elements  of  the  retina  which  may  be  regarded  as  purely 
accessory  disappear,  leaving  only  the  structures  that  are  concerned 
directly  in   the  reception   of  visual   impressions. 

The  retina  becomes  progressively  thinner  from  the  centre  to  the 
periphery.  The  molecular  and  granular  layers  and  the  nervous  layers 
are  lost  in  the  anterior  half  of  the  membrane. 

The  following  is  the  probable  mode  of  connection  between  the  rods 
and  cones  and  the  ganglion-cells  :  The  filaments  from  the  bases  of  the 
rods  and  cones  pass  inward,  presenting  in  their  course  the  corpuscles 
which  have  been  described  in  the  molecular  and  granular  lavers,  and 
finally  become,  as  is  thought,  directly  continuous  with  the  poles  of  the 
ganglion-cells.  The  cells  send  filaments  to  the  layer  formed  bv  the 
expansion  of  the  optic  nerve,  which  are  continuous  with  the  nerve- 
fibres. 


66o 


SPECIAL    SENSES 


The  following  description,  with  Fig.  169,  was  furnished  by  Loring  :  — • 
"  The  arteries  and  veins  of  the  retina  are  subdivisions  of  the  arteria 
and  vena  centraUs.  The  larger  branches  run  in  the  nerve-fibre  layer 
and  are  immediately  beneath  the  inner  limitary  membrane.  The  vessels 
lie  so  superficially  that  in  a  cross-section  examined  with  the  microscope, 
they  are  seen  to  project  above  the  general  level  of  the  retina,  toward  the 
vitreous  humor.  While  the  large  vessels  are  in  the  plane  of  the  inner 
surface  of  the  retina,  the  smaller  branches  penetrate  the  substance  of 
the  retina,  to  the  inner  nuclear  layer.  They  do  not  extend,  however, 
as  far  as  the  outer  nuclear  and  the  layer  of  rods  and  cones.  These 
two  layers,  therefore,  have  no  bloodvessels. 

"The  ramifications  of  the 
vessels  present  an  arborescent 
appearance  when  seen  with  the 
ophthalmoscope.  The  manner 
in  which  the  vessels  are  distrib- 
uted and  the  way  in  which  the 
circulation  is  carried  on  can  be 
better  understood  by  a  study  of 
Fig.  169  than  by  any  detailed  de- 
scription. The  figure  represents 
the  ophthalmoscopic  appearance 
of  a  normal  eye  in  young  adult 
life.  The  darker  vessels  are  the 
veins,  and  the  lighter  vessels,  the 
arteries.  The  dotted  oval  line  is 
diagrammatic  and  indicates  the 
position  and  extent  of  the  macula  lutea.  It  is  seen  that  this  oval  space 
contains  a  number  of  fine  vascular  twigs  which,  coming  from  above  and 
below,  extend  toward  the  spot  in  the  centre  of  the  oval,  which  marks 
the  position  of  the  fovea  centralis.  In  opposition,  then,  to  the  general 
opinion,  which  is  that  the  macula  lutea  has  no  bloodvessels,  it  is  the 
spot  of  all  others  in  the  retina  which  is  most  abundantly  supplied  with 
minute  vascular  branches.  These  vessels  can  be  distinctly  seen  even 
with  the  ophthalmoscope  ;  and  microscopical  examination  shows  that 
the  capillary  plexus  in  the  macula  lutea  is  closer  and  richer  than  in  any 
other  part  of  the  retina."  (The  figure  shows  an  inverted  image  of  the 
right  fundus.) 

The  arteries  of  the  retina  send  branches  to  the  periphery,  where 
they  supply  a  wide  plexus  of  small  capillaries  in  the  ora  serrata.  These 
capillaries  empty  into  an  incomplete  venous  circle,  branches  from  which 
pass  back  by  the  sides  of  the  arteries,  to  the  vena  centralis. 


Fig.   169. —  Bloodvessels  of  the  retina,  X  7^  (Loring). 


CRYSTALLINE    LENS 


66  r 


Crystalline  Lens.  —  The  crystalline  is  a  double-convex  lens,  which  is 
transparent  and  very  elastic.  Its  action  in  the  refraction  of  the  rays 
of  light  is  analogous  to  that  of  convex  lenses  in  optical  instruments.  It 
is  situated  behind  the  pupil  in  what  is  called  the  hyaloid  fossa  of  the 
vitreous  humor,  which  is  exactly  moulded  to  its  posterior  convexity. 
In  the  foetus  the  capsule  of  the  lens  receives  a  branch  from  the  arteria 
centralis,  but  it  is  non-vascular  in  the  adult.  The  anterior  convexity 
of  the  lens  is  just  behind  the  iris,  and  its  borders  are  in  relation  with 
what  is  known  as  the  suspensory  ligament.  The  convexities  do  not 
present  regular  curvatures,  and  they  are  so  subject  to  variations  after 
death  that  measurements,  post  mortem,  are  of  little  value.     During  Ufe, 


Fig.  170.  —  Crystalline  lens,  anterior  view 
(Babuchin). 


Fig.  171.  —  Section  of  the  crystalline 
lens  (Babuchin). 


however,  they  have  been  exactly  measured  in  different  conditions  of  ac- 
commodation. The  diameters  of  the  lens  in  the  adult  are  about  \  of 
an  inch  (8.5  millimeters)  transversely  and  \  of  an  inch  (6.4  millimeters) 
antero-posteriorly.  The  convexity  is  greater  on  its  posterior  than  on 
its  anterior  surface.  In  foetal  life  the  convexities  of  the  lens  are  greater 
than  in  the  adult  and  its  structure  is  much  softer.  In  old  age  the  con- 
vexities are  diminished  and  the  lens  becomes  harder  and  less  elastic. 
The  substance  of  the  lens  is  made  up  of  layers  of  fibres  of  different 
degrees  of  density,  and  the  whole  is  enveloped  in  a  delicate  membrane 
called  the  capsule. 

The  capsule  of  the  lens  is  a  thin  transparent  membrane  and  is  very 
elastic.      It  usually  is  from  o-g^Qo  to  15V0  of  '^'^  inch  (10  to  17/x)  thick, 


662  SPECIAL    SENSES 

but  is  much  thinner  at  the  periphery,  measuring  here  only  g  J^ ^  of  an 
inch  (4  fi).  Its  thickness  is  increased  in  old  age.  The  anterior  portion 
of  the  capsule  is  lined  on  its  inner  surface  with  a  layer  of  delicate  nu- 
cleated epithelium.  The  posterior  half  of  the  capsule  has  no  epithelial 
lining.  The  cells  are  regularly  polygonal,  measuring  2A0  ^^  250  o^ 
an  inch  (12  to  20  yu.)  in  diameter,  with  large  round  nuclei.  After  death 
they  are  said  to  break  down  into  a  liquid,  known  as  the  liquid  of  Mor- 
gagni,  though  by  some  this  liquid  is  supposed  to  be  exuded  from  the 
substance  of  the  lens.  At  all  events,  the  cells  disappear  soon  after 
death. 

If  the  lens  is  viewed  entire  with  a  low  magnifying  power,  it  pre- 
sents upon  either  of  its  surfaces,  a  star  with  nine  to  sixteen  radiations 
extending  from  the  centre  to  about  one-half  or  two-thirds  of  the  distance 
to  the  periphery.  The  stars  seen  on  the  two  surfaces  are  not  coinci- 
dent, the  rays  of  one  being  situated  between  the  rays  of  the  other.  In 
the  foetus  the  stars  are  more  simple,  presenting  only  three  radiations  on 
either  surface.  These  stars  are  not  fibrous,  like  the  rest  of  the  lens, 
but  are  composed  of  a  homogeneous  substance,  which  extends,  also, 
between  the  fibres. 

The  greatest  part  of  the  substance  of  the  lens  is  composed  of  deli- 
cate, soft  and  pliable  fibres,  which  are  transparent  but  perfectly  dis- 
tinct. These  fibres  are  flattened  six-sided  prisms,  closely  packed 
together,  so  that  their  transverse  section  presents  a  regularly-tessellated 
appearance.  They  are  50V0  ^^  25^00  ^^  ^^  ^^^^  ^5  ^°  10  /^)  broad,  and 
T3W0  ^°  90V0  °^  ^^  ^'^^^  (2  to  3  ft)  in  thickness.  Their  flat  surfaces 
are  parallel  with  the  surface  of  the  lens.  The  direction  of  the  fibres  is 
from  the  centre  and  from  the  rays  of  the  stellate  figures  to  the  periph- 
ery, where  they  turn  and  pass  to  the  star  of  the  opposite  side.  The 
outer  layers  of  fibres  near  the  equator,  or  circumference  of  the  lens, 
contain  distinct  oval  nuclei  with  one  or  two  nucleoli.  These  become 
smaller  in  passing  more  deeply  into  the  substance  of  the  lens  and  grad- 
ually disappear. 

The  regular  arrangement  of  the  fibres  of  the  lens  makes  it  possible 
to  separate  its  substance  into  laminae,  which  have  been  compared  by 
anatomists  to  the  layers  of  an  onion  ;  but  this  separation  is  artificial, 
and  the  number  of  apparent  layers  depends  largely  on  the  dexterity  of 
the  manipulator.  It  is  to  be  noted,  however,  that  the  exernal  portions 
of  the  lens  are  soft,  even  gelatinous,  and  that  the  central  layers  are 
much  harder,  forming  a  sort  of  central  kernel,  or  nucleus. 

The  lens  is  composed  of  a  globulin,  called  crystallin,  combined  with 
various  inorganic  salts.  One  of  the  constant  constituents  of  this  body 
is  cholesterin.     In  an  examination  of  four  fresh  crystalline  lenses  of  the 


CRYSTALLINE    LENS  663 

OX,  cholesterin  was  found  in  the  proportion  of  0.907  of  a  part  per  1000 
(Flint).  In  some  cases  of  cataract,  cholesterin  exists  in  the  lens  in  a 
crystalline  form ;  but  under  normal  conditions  it  is  united  with  the 
other  constituents. 

Suspensory  Ligament  of  the  Lens  {Zone  of  Zinn).  —  The  vitreous 
humor  occupies  about  the  posterior  two-thirds  of  the  globe  and  is 
enveloped  in  a  delicate  capsule  called  the  hyaloid  membrane.  In  the 
region  of  the  ora  serrata  of  the  retina  this  membrane  divides  into  two 
layers.  The  posterior  layer  lines  the  depression  in  the  vitreous  humor 
into  which  the  lens  is  received.  The  anterior  layer  passes  forward 
toward  the  lens  and  divides  into  two  secondary  layers,  one  of  which 
passes  forward  to  become  continuous  with  the  anterior 
portion  of  the  capsule  of  the  lens,  while  the  other 
passes  to  the  posterior  surface  of  the  lens  to  become 
continuous  with  this  portion  of  its  capsule.  The 
anterior  of  these  layers  is  corrugated  or  thrown  into 
folds  that  correspond  with  the  ciliary  processes,  with 
which  it  is  in  contact.  This  corrugated  portion  is  Fig.172.  — Z(W(7/zi«« 
called  the  zone  of  Zinn.     The  two  layers  thus  sur-  ..."  ' 

''  I,  crystalline  lens;  2, 

round  the  lens  and  are  properly  called  its  suspensory    2,  vitreous  humor;  3,3, 

T  j_  A       ii        i  1  r   j_i  T  zone  of  Zinn ;  4, 4,- pos- 

ligament.  As  the  two  layers  of  the  suspensory  hga-  ^^^j^^  portion  of  the 
ment  separate  a  certain  distance  from  the  lens,  one    zone  of  zinn,  thrown 

.  ,  ,  ,  .  into  folds ;  5,  6,  6,  an- 

passing  to  the  anterior  and  the  other  to  the  posterior  ^erjor  and  middle  por- 
portion   of   the   capsule,   there    remains   a  triangular    *i°"s  ^^  ^^^  2°"^^  *^^ 

\         •  1  Zinn. 

canal,    about  -^-^   of   an   inch   (2.5    millimeters)  wide, 
surrounding  the  border  of  the  lens,  called  the  canal  of  Petit.     Under 
natural  conditions  the  walls  of  this  canal  are  nearly  in  apposition,  and 
it  contains  a  small  quantity  of  clear  liquid. 

The  membrane  forming  the  suspensory  hgament  is  composed  of  pale 
longitudinal  and  transverse  fibres  of  rather  a  peculiar  appearance,  which 
are  much  less  affected  by  acetic  acid  than  fibres  of  ordinary  connective 
tissue. 

Agueons  Humor.  —  The  space  bounded  in  front  by  the  cornea, 
posteriorly,  by  the  crystalline  lens  and  the  anterior  face  of  its  suspen- 
sory Hgament,  and  at  its  circumference,  by  the  tips  of  the  ciHary  pro- 
cesses, is  known  as  the  aqueous  chamber.  This  contains  a  clear  liquid 
called  the  aqueous  humor.  The  iris  separates  this  space  into  two 
divisions,  which  communicate  with  each  other  through  the  pupil ; 
namely,  the  anterior  chamber,  situated  between  the  anterior  face  of  the 
iris  and  the  cornea,  and  the  posterior  chamber,  between  the  posterior 
face  of  the  iris  and  the  crystalline.  It  is  evident,  from  the  position  of 
the  iris,  that  the  anterior  chamber  is  much  the  larger  ;  and,  indeed,  the 


664  SPECIAL    SENSES 

posterior  surface  of  the  iris  and  the  anterior  surface  of  the  lens  are  in 
contact,  except,  perhaps,  near  their  periphery  or  when  the  iris  is  much 
dilated.  The  liquid  filling  the  chambers  of  the  eye  is  rapidly  reproduced 
after  it  has  been  evacuated,  as  occurs  in  many  surgical  operations. 

The  aqueous  humor  is  colorless  and  transparent,  faintly  alkaline,  of 
a  specific  gravity  of  about  1005,  and  with  nearly  the  same  index  of 
refraction  as  that  of  the  cornea  and  the  vitreous  humor.  It  contains  a 
small  quantity  of  an  albuminous  matter,  but  it  is  not  rendered  turbid  by 
heat  or  other  agents  that  coagulate  albumin.  Various  inorganic  salts 
(the  chlorides,  sulphates,  phosphates  and  carbonates)  exist  in  small  pro- 
portions in  this  liquid.      It  contains  also  traces  of  urea  and  glucose. 

The  anterior  and  the  posterior  chambers  of  the  eye  are  regarded  as 
lymph-spaces  communicating  with  the  lymphatics  of  the  conjunctiva, 
corjiea,  iris  and  ciliary  processes.  In  addition  a  lymph-space  is  described 
as  existing  between  the  choroid  and  the  sclerotic.  This  space  is  sup- 
posed to  communicate  with  a  perivascular-canal  system  around  the  vasa 
vorticosa,  and  through  these  vessels,  with  the  space  between  the  capsule 
of  Tenon  and  the  sclerotic  (Schwalbe).  The  latter  is  connected  with 
lymph-channels  that  surround  the  optic  nerve  (Key  and  Retzius). 

Vitreous  Hiiuior.  — The  vitreous  humor  is  a  clear  glassy  substance, 
occupving  about  the  posterior  two-thirds  of  the  globe.  It  is  enveloped 
in  a  delicate  structureless  capsule,  called  the  hyaloid  membrane,  which 
is  about  gyoo^  of  an  inch  (4  ix)  in  thickness.  This  membrane  adheres 
rather  strongly  to  the  limitary  membrane  of  the  retina.  In  front,  at  the 
ora  serrata,  the  hyaloid  membrane  is  thickened  and  becomes  continuous 
with  the  suspensory  ligament  of  the  lens. 

The  vitreous  humor  itself  is  gelatinous,  of  feeble  consistence  and 
slightly  alkaline  in  its  reaction,  with  a  specific  gravity  of  about  1005. 
On  section  there  oozes  from  it  a  watery  and  slightly  mucilaginous  liquid. 
This  humor  is  not  affected  bv  heat  or  alcohol  but  is  coagulated  bv  cer- 
tain  mineral  salts,  especially  lead  acetate.  When  thus  solidified  it  pre- 
sents regular  layers,  like  the  white  of  an  &gg  boiled  in  its  shell ;  but 
these  are  artificial.  In  the  embryo  the  vitreous  humor  is  divided  into 
a  number  of  little  cavities  and  contains  cells  and  leucocytes.  It  is  also 
penetrated  by  a  branch  from  the  central  artery  of  the  retina,  which 
passes  through  its  centre  to  ramify  on  the  posterior  surface  of  the  lens. 
This  structure,  however,  is  not  found  in  the  adult,  the  vitreous  humor 
being  then  without  bloodvessels.  The  vitreous  humor  is  divided  into 
compartments  formed  by  delicate  membranes  radiating  from  the  point 
of  penetration  of  the  optic  ner\'e  to  the  anterior  boundary  where  the 
hyaloid  membrane  is  in  contact  with  the  capsule  of  the  lens.  In  this 
way  the  humor  is  divided  up,  something  like  the  half  of  an  orange, 


SUMMARY    OF  THE    AXATO.MY   OF    THE    EYEBALL 


665 


into  about  one  hundred  and  eighty  membranous  processes  of  extreme 
deUcacy,  which  do  not  interfere  with  its  transparency. 


Summary  of  the  Anatomy  of  the  Globe  of  the  Eye  ' 

This  summary  is  intended  simply  to  indicate  the  relations  and  the 
physiological  importance  of  the  various  parts  of  the  eye,  in  connection 
with  Fig.  173. 

The  eyeball  is  nearly  spherical  in  its  posterior  five-sixths,  its  anterior 
sixth  being  formed  of  the  segment  of  a  smaller  sphere,  which  is  slightly 
projecting.     It  presents  the  following  parts,  indicated  in  the  figure :  — 


SUPERIOR  RECTL'S 


CHOROID 


-INFERIOR  RECTUS 


Fig.  173.  —  Diagrammatic  section  of  the  eye. 

The  sclerotic ;  a  dense  fibrous  membrane,  chiefly  for  the  protection 
of  the  more  delicate  structures  of  the  globe,  and  giving  attachment  to 
the  muscles  that  move  the  eyeball.  Attached  to  the  sclerotic  are  the 
tendons  of  the  recti  and  the  oblique  muscles. 

The  cornea ;  a  transparent  structure,  forming  the  anterior  projecting 
sixth  of  the  globe  ;  dense  and  resisting,  allowing,  however,  the  passage 
of  light ;  covered,  on  its  convex  surface,  with  several  layers  of  trans- 
parent epithelial  cells. 

The  choroid  coat ;  lining  the  sclerotic  and  extending  only  as  far  for- 
ward as  the  cornea ;  connected  with  the  sclerotic  by  loose  connective 
tissue,  in  which  ramify  bloodvessels  and  nerves,  and  presenting  an  ex- 
ternal vascular  layer  and  an  internal  pigmentary  layer  (described  with 
retina),  which  latter  gives  its  characteristic  dark-brown  color. 


666  SPECIAL    SENSES 

The  ciliary  processes ;  folds  of  the  choroid,  which  form  its  anterior 
border  and  which  embrace  the  folds  of  the  suspensory  ligament  of  the 
lens. 

The  ciliary  muscle;  situated  just  outside  of  the  ciliary  processes, 
arising  from  the  circular  line  of  junction  of  the  sclerotic  with  the  cornea, 
passing  over  the  ciliary  processes,  and  becoming  continuous  with  the 
fibrous  tissue  of  the  choroid.  The  action  of  this  muscle  is  to  tighten 
the  choroid  over  the  vitreous  humor  and  to  relax  the  ciliary  processes 
and  the  suspensory  ligament  of  the  lens,  when  the  lens,  by  virtue  of  its 
elasticity,  becomes  more  convex.  This  action  is  indicated  by  the  dotted 
lines  in  the  figure. 

The  iris ;  dividing  the  space  in  front  of  the  lens  into  two  chambers 
occupied  by  the  aqueous  humor.  The  anterior  chamber  is  much  the 
larger.  The  iris,  in  its  central  portion  surrounding  the  pupil,  is  in  con- 
tact with  the  lens.  Its  circumference  is  just  in  front  of  the  line  of  origin 
of  the  ciliary  muscle. 

The  retina  ;  a  delicate  transparent  membrane,  lining  the  choroid 
and  extending  to  about  -^^  of  an  inch  (1.7  millimeters)  behind  the 
ciliary  processes,  the  anterior  margin  forming  the  ora  serrata.  The 
optic  nerve  penetrates  the  retina  a  little  internal  to  and  below  the 
antero-posterior  axis  of  the  globe.  The  layer  of  rods  and  cones  is  situ- 
ated next  the  pigmentary  layer,  which  is  external.  Internal  to  the 
layer  of  rods  and  cones  and  the  outer  limitary  membrane,  are  the 
molecular  and  nuclear  layers ;  next,  the  layer  of  nerve-cells  ;  next, 
the  expansion  of  the  fibres  of  the  optic  nerve ;  and  next,  in  apposition 
with  the  hyaloid  membrane  of  the  vitreous  humor,  is  the  inner  limitary 
membrane. 

The  crystalline  lens  ;  elastic,  transparent,  enveloped  in  its  capsule 
and  surrounded  by  the  suspensory  ligament. 

The  suspensory  ligament;  the  anterior  layer  connected  with  the  an- 
terior portion  of  the  capsule  of  the  lens,  and  the  posterior,  with  the 
posterior  portion  of  the  capsule.  The  folded  portion  of  this  ligament, 
which  is  received  between  the  folds  of  the  ciliary  processes,  is  the  zone 
of  Zinn.  The  triangular  canal  between  the  anterior  and  the  posterior 
layers  of  the  suspensory  ligament  and  surrounding  the  equator  of  the 
lens  is  the  canal  of  Petit. 

The  vitreous  humor ;  enveloped  in  the  hyaloid  membrane,  which 
membrane  is  continuous  in  front  with  the  suspensory  ligament  of  the 
lens. 


CHAPTER    XXVII 
REFRACTION    IX    THE    EYE  —  ACCO.M.MODATIOX 

Refraction  in  the  eye  —  Certain  laws  of  refraction,  dispersion  etc.,  bearing  on  the  physiology  of 
vision — Refraction  by  lenses  —  Spherical  monochromatic  aberration  —  Chromatic  aberra- 
tion—  Formation  of  images  in  the  eye  —  Visual  purple  and  visual  yellow  and  accommoda- 
tion of  the  eye  for  different  degrees  of  illumination  —  Mechanism  of  refraction  in  the  eye  — 
Astigmatism  —  Movements  of  the  iris  —  Direct  action  of  light  on  the  iris  —  Accommodation 
of  the  eye  for  vision  at  different  distances  —  Changes  in  the  crj'stalline  lens  in  accommoda- 
tion—  Changes  in  the  iris  in  accommodation  —  Erect  impressions  produced  by. images  in- 
verted upon  the  retina  —  Field  of  indirect  vision  —  Binocular  vision  —  Corresponding  points 
—  The  horopter  —  Duration  of  luminous  impressions  (after-images)  —  Irradiation. 

In  applying  some  of  the  laws  of  refraction  of  light  to  the  action  of 
the  transparent  media  of  the  eye,  it  is  necessary  to  have  in  mind  certain 
general  facts  in  regard  to  vision,  that  have  as  yet  been  considered  very 
briefly  or  have  been  omitted.  The  eye  is  not  a  perfect  optical  instrument, 
looking  at  it  from  a  purely  physical  point  of  view.  This  statement, 
however,  should  not  be  understood  as  implying  that  the  arrange- 
ment of  the  parts  is  not  such  as  to  adapt  them  perfectly  to  their  uses  in 
connection  with  the  appreciation  of  visual  impressions.  By  physical 
tests  it  can  be  demonstrated  that  the  eye  is  not  entirely  achromatic  ;  but 
in  ordinary  vision  the  dispersion  of  colors  is  not  appreciated.  There 
is  but  a  single  point  in  the  retina,  the  fovea  centralis,  where  vision  is 
absolutely  distinct ;  and  it  is  upon  this  point  that  images  are  made  to 
fall  when  the  eye  is  directed  toward  any  particular  object. 

The  refracting  apparatus  is  not  exactly  centred,  —  a  condition  essen- 
tial to  the  satisfactory  performance  of  perfect  optical  instruments.  For 
example,  in  a  compound  microscope  or  a  telescope,  the  centres  of  the 
different  lenses  entering  into  the  construction  of  the  instrument  are 
situated  in  a  straight  line.  Were  the  eye  a  perfect  optical  instrument, 
the  line  of  vision  would  coincide  exactly  with  the  optical  axis ;  but  this 
is  not  the  case.  The  visual  line  —  a  line  drawn  from  an  object  to  its 
image  on  the  fovea  centralis  —  deviates  from  the  optical  axis,  in  normal 
eyes,  to  the  nasal  side.  The  visual  line,  therefore,  forms  an  angle  with 
the  optical  axis,  which  is  known  as  the  angle  alpha.  This  deviation  of 
the  visual  line  is  observed  both  in  the  horizontal  and  in  the  vertical 
planes.  The  horizontal  deviation  varies  by  two  to  eight  degrees,  and  the 
vertical,  by  one  to  three  degrees.     Of  course  this  want  of  exact  centring 

667 


668  SPECIAL    SENSES 

of  the  dioptric  apparatus  in  normal  eyes  does  not  practically  affect  dis- 
tinct vision;  for  when  the  eyes  are  directed  toward  any  object,  this 
object  is  brought  in  the  line  of  the  visual  axis  ;  but  the  angle  alpha  is 
an  important  element  to  be  taken  into  account  in  certain  mathematical 
calculations  connected  with  the  physics  of  the  eye. 

The  area  of  distinct  vision  is  quite  restricted  ;  but  were  it  larger,  it  is 
probable  that  the  mind  would  become  confused  by  the  extent  and  variety 
of  the  impressions,  and  that  it  would  not  be  so  easy  to  observe  minute 
details  and  fix  the  attention  on  small  objects. 

Although  certain  objects  are  seen  with  distinctness  only  in  a 
restricted  field,  the  angle  of  vision  is  very  wide,  and  rays  of  light  are 
admitted  from  an  area  equal  to  nearly  the  half  of  a  sphere.  Such  a 
provision  .is  eminently  adapted  to  visual  requirements.  The  eyes  are 
directed  to  a  particular  point  and  a  certain  object  is  seen  distinctly,  with 
the  advantage  of  an  image  in  the  two  eyes,  exactly  at  the  points  of  dis- 
tinct vision  ;  the  rays  coming  from  without  the  area  of  distinct  vision 
are  received  upon  different  portions  of  the  surface  of  the  retina  and 
produce  an  impression  more  or  less  indistinct,  not  interfering  with  the 
observation  of  the  particular  object  to  which  the  attention  is  for  the 
moment  directed ;  but  even  while  looking  intently  at  any  object, 
the  attention  may  be  attracted  by  another  object  of  an  unusual  charac- 
ter, which  might,  for  example,  convey  an  idea  of  danger,  and  the  point 
of  distinct  vision  can  be  turned  in  its  direction.  Thus,  while  but  few 
objects  are  seen  distinctly  at  one  time,  the  area  of  indistinct  vision  is 
large  ;  and  the  attention  may  readily  be  directed  to  unexpected  or  unusual 
objects  that  come  within  any  part  of  the  field  of  view.  The  small  extent 
of  the  area  of  distinct  vision,  especially  for  near  objects,  may  readily  be 
appreciated  in  watching  a  person  who  is  reading,  when  the  eyes  will  be 
seen  to  follow  the  lines  from  one  side  of  the  page  to  the  other. 

Certain  Lmvs  of  Refraction,  Dispersion  etc.,  bearing  on  the  Physiology 
of  Vision.  —  Physiologists  have  little  to  do  with  the  theory  of  light, 
except  as  regards  the  modifications  of  luminous  rays  in  passing  through 
the  refracting  media  of  the  eye.  It  will  be  sufficient  to  state  that  nearly 
all  physicists  of  the  present  day  agree  in  accepting  what  is  known  as  the 
theory  of  undulation,  rejecting  the  emission-theory  proposed  by  Newton. 
It  is  necessary  to  the  theory  of  undulation  to  assume  that  all  space  and 
all  transparent  bodies  are  permeated  with  what  has  been  called  a  lumi- 
niferous  ether  ;  and  that  light  is  propagated  by  vibration  or  undulation  of 
this  hypothetical  substance.  This  theory  assimilates  light  to  sound  in 
the  mechanism  of  its  propagation  ;  but  in  sound  the  waves  are  longitudi- 
nal, following  the  line  of  propagation,  while  in  light  the  particles  vibrate 
transversely,  or  at  right  angles  to  the  line  of  propagation. 


REFRACTION    IN    THE    EYE  669 

The  different  calculations  of  physicists  in  regard  to  the  velocity  of 
light  have  been  remarkably  uniform  in  their  results.  The  lowest  calcu- 
lations put  it  at  about  185,000  miles  (297,725  kilometers)  in  a  second, 
and  the  highest,  at  about  195,000  miles  (313,818  kilometers).  The  rate 
of  propagation  usually  is  assumed  to  be  about  192,000  miles  (309,000 
kilometers). 

The  intensity  of  light  is  in  proportion  to  the  amplitude  of  the  vibra- 
tions. The  intensity  diminishes  in  inverse  ratio  to  the  square  of  the 
distance. 

In  the  theory  of  the  colors  into  which  white  light  maybe  decomposed 
by  prisms,  it  is  a  matter  of  demonstration  that  the  waves  of  the  different 
colors  are  not  of  the  same  length.  The  decomposition  of  Hght  is  due  to 
differences  in  the  ref rangibility  of  the  different  colored  rays  as  they  pass 
at  an  angle  through  a  medium  denser  than  the  air. 

The  analysis  of  white  light  into  the  colors  of  the  spectrum  shows 
that  it  is  compound;  and  by  synthesis,  the  colored  rays  may  be 
brought  together,  producing  white  light.  Colors  m.ay  be  obtained  by 
decomposition  of  light  by  transparent  bodies,  the  different  colored  rays 
being  refracted,  or  bent,  by  a  prism,  at  different  angles.  It  is  not  in 
this  way,  however,  that  the  colors  of  different  objects  are  produced. 
Certain  objects  have  the  property  of  reflecting  the  rays  of  light.  A 
smooth  polished  surface,  like  a  mirror,  may  reflect  all  the  rays  ;  and  the 
object  then  has  no  color,  only  the  reflected  light  being  appreciated  by 
the  eye.  Certain  other  objects  do  not  reflect  all  the  rays  of  light,  some 
of  them  being  lost  to  view,  or  absorbed.  When  an  object  absorbs  all  the 
rays  it  has  no  color  and  is  called  black.  When  an  object  absorbs  the 
rays  equally  and  reflects  a  portion  of  these  rays  without  decomposition, 
it  is  gray  or  white.  There  are  many  objects,  however,  that  decompose 
white  light,  absorbing  certain  rays  of  the  spectrum  and  reflecting  others. 
The  rays  not  absorbed,  but  returned  to  the  eye  by  reflection,  give  color 
to  the  object.  Thus,  if  an  object  absorbs  aU  the  rays  of  the  spectrum 
except  the  red,  the  red  rays  strike  the  eye,  and  the  color  of  the  object  is 
red.  So  it  is  with  objects  of  different  shades,  the  colors  of  which  are 
given  by  the  unabsorbed  rays. 

A  mixture  of  different  colors  in  certain  proportions  will  result  in 
white.  Two  colors,  which,  when  mixed,  result  in  white,  are  called  com- 
plementary. The  following  colors  of  the  spectrum  bear  such  a  relation 
to  each  other :  Red  and  greenish  blue  ;  orange  and  cyanogen-blue ; 
yellow  and  indigo-blue  ;  greenish  yellow  and  violet. 

The  fact  that  impressions  made  on  the  retina  persist  for  an  appre- 
ciable length  of  time  affords  an  illustration  of  the  law  of  complementary 
colors.     If  a  disk,  presenting  divisions  with  two  complementary  colors,  is 


6/0  SPECIAL    SENSES 

made  to  revolve  so  rapidly  that  the  impressions  made  by  the  two  colors 
are  blended,  the  resulting  impression  is  of  white. 

Refraction  by  Lenses.  —  A  ray  of  light  is  an  imaginary  pencil  so 
small  as  to  present  but  a  single  line  ;  and  the  hght  admitted  to  the  in- 
terior of  the  eye  by  the  pupil  is  supposed  to  consist  of  an  infinite  num- 
ber of  such  rays.  In  studying  the  physiology  of  vision,  it  is  important 
to  recognize  the  lav/s  of  refraction  of  rays  by  transparent  bodies  bounded 
by  curved  surfaces,  with  particular  reference  to  the  action  of  the  crystal- 
line lens. 

The  action  of  a  double-convex  lens,  like  the  crystalline,  in  the  refrac- 
tion of  light,  may  be  readily  understood  by  an  application  of  the  well- 
known  laws  of  refraction  by  prisms.  A  ray  of  light  falling  on  the  side 
of  a  prism  at  an  angle  is  deviated  toward  a  line  perpendicular  to  the  sur- 
face of  the  prism.  As  the  ray  passes  from  the  prism  to  the  air,  it  is 
again  refracted,  but  the  deviation  is  then  from  the  perpendicular  of  the 
second  surface  of  the  prism.  In  passing  through  a  prism,  therefore, 
the  pencil  of  light  is  bent,  or  refracted,  toward  the  base. 

A  circle  is  equivalent  to  a  polygon  with  an  infinite  number  of  sides. 
A  regular  double-convex  lens  is  a  transparent  body  bounded  by  seg- 
ments of  a  sphere.  Theoretically,  a  double-convex  lens  may  be  assumed 
to  be  composed  of  an  infinite  number  of  sections  of  prisms  (Fig.  174,  I), 
or  to  make  the  comparison  with  prisms  more  striking,  though  less  accu- 
rate, the  lens  may  be  assumed  to  be  composed  of  prisms.  Fig.  174,  II 
(Weinhold). 

If  these  prisms  or  sections  of  prisms  are  infinitely  small,  so  that  the 
surface  of  each  receives  but  a  single  infinitely  small  pencil  of  light,  these 
pencils  will  be  refracted  toward  the  bases  of  the  prisms,  and  different 
rays  of  light  from  all  points  of  an  object  may  be  brought  to  an  infinite 
number  of  foci,  all  these  foci,  for  a  plane  object,  being  in  the  same 
plane.  If  the  number  of  sections  is  equal  on  every  side  of  the  centre  of 
the  lens,  the  bases  looking  toward  the  axis  of  the  lens,  the  rays  of  light 
will  cross  at  a  certain  point  and  the  image  will  be  inverted.  This  is 
illustrated  in  Fig.  174,  which  represents  a  section  of  a  lens  theoretically 
dissected  into  six  sections  of  prisms. 

If  the  lens  A  B  (Fig.  174)  is  assumed  to  be  free  from  what  is  known 
as  spherical  aberration,  the  rays  from  the  point  C  will  be  refracted  and 
brought  to  a  focus  at  the  point  D.  In  the  same  vv^ay  the  rays  from  E 
will  be  brought  to  a  focus  at  F,  the  two  sets  of  rays  crossing  before  they 
reach  their  focal  points.  The  same  is  true  for  all  the  rays  from  every 
point  in  the  image  C  E,  which  strike  the  lens  at  an  angle,  but  the  ray  G 
H,  which  is  perpendicular  to  the  lens,  is  not  deviated.  The  rays  of  light 
are  refracted  in  this  way  by  the  cornea  and  by  the  crystalline  lens.     The 


REFRACTION    IN    THE    EYE 


671 


retina  is  normally  at  such  a  distance  from  the  lens  that  the  lays  are 
brought  to  a  focus  exactly  at  its  surface.  Inasmuch  as  the  rays  cross 
before  they  reach  the  retina,  the  image  is  inverted. 

Supposing  the  crystalline  lens  to  be  free  from  spherical  and  chro- 
matic aberration,  the  formation  of  a  perfect  image  depends  on  the  fol- 
lowing conditions  :  — 

The  object  must  be  at  a  certain  distance  from  the  lens.  If  the 
object  is  too  near,  the  rays  as  they  strike  the  lens  are  too  divergent  and 
are  brought  to  a  focus  beyond  the  plane  F  H  D,  or  behind  the  retina ; 
and  as  a  consequence  the  image  is  confused.  In  optical  instruments 
the  adjustment  is  made  for  objects  at  different  distances  by  moving  the 
lens  itself.  In  the  eye,  however,  the  adjustment  is  effected  by  increas- 
ing or   diminishing  the  curvatures  of  the  lens,    so    that  the   rays   are 

A 


li 


Fig.  174.  —  Refractlo)i  by  convex  lenses. 


brought  to  a  focus  on  the  visual  surface  of  the  retina.  The  faculty  of 
thus  changing  the  curvatures  of  the  crystalline  lens  is  called  accommo- 
dation. This  power,  however,  is  restricted  within  certain  well-defined 
limits. 

In  some  individuals  the  antero-posterior  diameter  of  the  eye  is  too 
long,  and  the  rays,  for  most  objects,  come  to  a  focus  before  they  reach 
the  retina.  This  defect  may  be  remedied  by  placing  the  object  very 
near  the  eye  so  as  to  increase  the  divergence  of  the  rays  as  they  strike 
the  lens.  Such  persons  are  said  to  be  near-sighted  (myopic),  and  objects 
are  seen  distinctly  only  when  very  near  the  eye.  This  defect  may  be 
remedied  for  distant  objects,  by  placing  concave  lenses  before  the  eyes, 
by  which  the  rays  falling  upon  the  lens  are  diverged.  The  opposite 
condition,  in  which  the  antero-posterior  diameter  is  too  short  (hyperme- 
tropia),  is  such  that  the  rays  are  brought  to  a  focus  behind  the  retina. 
This  is  corrected  by  converging  the  rays  of  incidence  by  placing  convex 


6/2  SPECIAL    SENSES 

lenses  before  the  eyes.  In  old  age  the  crystalline  lens  becomes  flat- 
tened, its  elasticity  is  diminished  and  the  power  of  accommodation  is  les- 
sened ;  conditions  which  also  tend  to  bring  the  rays  to  a  focus  behind 
the  retina.  This  condition  is  called  presbyopia.  To  render  near  vision, 
as  in  reading,  distinct,  objects  are  placed  farther  from  the  eye  than 
under  normal  conditions.  The  defect  may  be  remedied,  as  in  hyperme- 
tropia,  by  placing  convex  lenses  before  the  eyes,  by  which  the  rays  are 
converged  before  they  fall  on  the  lens. 

SpJierical  Monochroviatic  Aberration.  —  In  a  convex  lens  in  which 
the  surfaces  are  segments  of  a  sphere,  the  rays  of  light  from  an  object 
are  not  converged  to  a  uniform  focus,  and  the  production  of  a  distinct 
image  is  impossible.  For  example,  if  the  lens  had  regular  curvatures, 
the  rays  refracted  by  its  peripheral  portion  would  be  brought  to  a  focus 
in  front  of  the  retina  ;  the  focus  of  the  rays  converged  by  the  lens  near 
its  centre  would  be  behind  the  retina ;  a  few,  only,  of  the  rays  would 
have  their  focus  at  the  retina  itself  ;  and  as  a  consequence,  the  image 
would  appear  confused.  This  is  illustrated  in  imperfectly-corrected 
lenses,  and  is  called  spherical  aberration.  It  is  also  called  monochro- 
matic aberration,  because  it  is  to  be  distinguished  from  an  aberration 
that  involves  decomposition  of  light  into  the  colors  of  the  spectrum.  If 
an  object  is  examined  under  the  microscope  with  an  imperfectly-corrected 
objective,  it  is  evident  that  the  field  of  view  is  not  uniform  and  that 
there  is  a  different  focal  adjustment  for  the  central  and  the  peripheral 
portions  of  the  lens.  In  the  construction  of  optical  instruments,  this 
error  may  be  in  part  corrected  if  the  rays  of  light  are  cut  off  from  the 
periphery  of  the  lens  by  a  diaphragm,  which  is  an  opaque  screen  with 
a  circular  perforation  allowing  the  rays  to  pass  to  a  restricted  portion 
of  the  lens,  near  its  centre.  The  iris  corresponds  to  the  diaphragm  of 
optical  instruments,  and  it  corrects  the  spherical  aberration  of  the  lens 
in  part,  by  eliminating  a  portion  of  the  rays  that  would  otherwise  fall 
upon  its  peripheral  portion.  This  correction,  however,  is  not  sufficient 
for  high  magnifying  powers ;  and  it  is  only  by  the  more  or  less  perfect 
correction  of  this  kind  of  aberration  by  other  means,  that  powerful  lenses 
have  been  rendered  available  in  optics. 

The  spherical  aberration  of  lenses  that  diverge  the  rays  of  light  is 
precisely  opposite  to  the  aberration  of  converging  lenses.  In  a  com- 
pound lens,  therefore,  it  is  possible  to  fulfil  the  conditions  necessary  to 
the  convergence  of  all  the  incident  rays  to  a  focus  on  a  uniform  plane, 
so  that  the  image  produced  behind  the  lens  is  not  distorted.  Given,  for 
example,  a  double-convex  lens,  by  which  the  rays  are  brought  to  innu- 
merable focal  points  situated  in  different  planes.  The  fact  that  but  few 
of  these  focal  points  are  in  the  plane  of  the  retina  renders  the  image 


REFRACTION    IN    THE    EYE  673 

indistinct.  If  a  concave  or  a  plano-concave  lens  is  placed  in  front  of 
this  convex  lens,  which  will  diverge  the  rays  more  or  less,  the  inequality 
of  the  divergence  by  different  portions  of  the  second  lens  will  have  the 
following  effect :  As  the  angle  of  divergence  gradually  increases  from 
the  centre  toward  the  periphery,  the  rays  near  the  periphery  —  which 
are  most  powerfully  converged  by  the  convex  lens  —  will  be  most  widely 
diverged  by  the  peripheral  portion  of  the  concave  lens  ;  so  that  if  the 
opposite  curvatures  are  accurately  adjusted,  the  aberrant  rays  may  be 
blended.  It  is  evident  that  if  all  the  rays  were  equally  converged  by 
the  convex  lens  and  equally  diverged  by  the  concave  lens,  the  action  of 
the  latter  would  be  simply  to  elongate  the  focal  distance  ;  and  it  is  equally 
evident  that  if  the  aberration  of  the  one  is  exactly  opposite  to  the  aberra- 
tion of  the  other,  there  will  be  perfect  correction.  Mechanical  art  has 
not  effected  correction  of  every  portion  of  powerful  convex  lenses  in 
this  way ;  but  by  a  combination  of  lenses  and  diaphragms  together, 
highly-magnified  images,  nearly  perfect,  have  been  produced.  Lenses 
in  which  spherical  aberration  has  been  corrected  are  called  aplanatic. 

It  is  evident  that  for  distinct  vision  at  different  distances,  the  lens 
must  be  nearly  free  from  spherical  aberration.  This  is  not  effected  by 
a  combination  of  lenses,  as  in  ordinary  optical  instruments,  but  by  the 
curvatures  of  the  lens  itself  and  by  certain  differences  in  the  consistence 
of  different  portions  of  the  lens,  which  will  be  fully  considered  hereafter. 

Chromatic  Aberration. — A  refracting  medium  does  not  act  equally 
on  the  different  colored  rays  into  which  white  light  may  be  decomposed  ; 
in  other  words,  as  the  white  ray  falling  on  the  inclined  surface  of  a  glass 
prism  is  bent,  it  is  decomposed  into  the  colors  of  the  spectrum.  As  a 
convex  lens  is  practically  composed  of  an  infinite  number  of  prisms,  the 
same  effect  would  be  expeqted.  Indeed,  a  simple  convex  lens,  even  if 
the  spherical  aberration  is  corrected,  always  produces  more  or  less  de- 
composition of  light.  The  image  formed  by  such  a  lens  consequently  is 
colored  at  its  borders  ;  and  this  defect  in  simple  lenses  is  called  chromatic 
aberration. 

In  prisms  the  chromatic  dispersion  may  be  corrected  by  allowing  the 
colored  rays  from  one  prism  to  fall  on  a  second  prism,  which  latter  is 
inverted,  so  that  the  colors  are  brought  together  and  produce  white  hght. 
Two  prisms  thus  applied  to  each  other  constitute,  in  fact,  a  fiat  plate  of 
glass,  and  the  rays  of  light  pass  without  deviation.  If  this  principle 
is  applied  to  lenses,  it  is  e\ddent  that  the  dispersive  power  of  a  convex 
lens  may  be  exactly  opposite  to  that  of  a  concave  lens.  By  the  convex 
lens  the  colored  rays  are  separated  by  convergence  and  cross  each  other ; 
and  in  the  concave  lens  the  colored  rays  are  diverged  in  the  opposite 
direction.     If,  then,  a  convex  is  combined  with  a  concave  lens,  the  white 


674  SPECIAL    SENSES 

light  decomposed  by  the  one  will  be  recomposed  by  the  other,  and  the 
chromatic  aberration  will  thus  be  corrected ;  but  in  using  a  convex  and 
a  concave  lens  composed  of  the  same  material,  the  convergence  by  the 
one  will  be  neutralized  by  the  divergence  of  the  other,  and  there  will  be 
no  amplification  of  the  object.  Newton  supposed  that  dispersion,  or 
decomposition  of  light,  by  lenses  was  always  in  exact  proportion  to  re- 
fraction, so  that  it  would  be  impossible  to  correct  chromatic  aberration 
and  retain  magnifying  power ;  but  it  has  been  ascertained  that  there  are 
great  differences  in  the  dispersive  power  of  different  kinds  of  glass, 
without  corresponding  differences  in  refraction.  This  discovery  ren- 
dered it  possible  to  construct  achromatic  lenses  (Dollond,  1757).  Ac- 
cording to  Ganot,  Hall  was  the  first  to  make  achromatic  lenses,  1753, 
but  his  discovery  was  not  published. 

In  the  construction  of  modern  optical  instruments,  chromatic  aberra- 
tion is  corrected,  with  a  certain  diminution  in  amplification,  by  cement- 
ing together  lenses  made  of  different  materials,  as  of  flint-glass  and 
crown-glass.  Flint-glass  has  a  much  greater  dispersive  power  than 
crown-glass.  If,  therefore,  a  convex  lens  of  crown-glass  is  combined 
jBowN  GLAS8_  wlth   cL  coucave  or  plano-concave  lens  of  flint- 

glass,  the  chromatic  aberration  of   the   convex 
lens  may  be  corrected  by  a  concave  lens  with  a 
curvature  that  will  reduce  the  magnifying  power 
ig- 175  —    c  foma /c  ens.     ^-^^^^^  ouc-half.      A    compouud    leus,  with    the 

spherical  aberration  of  the  convex  element  corrected  by  the  curvature 
of  a  concave  lens,  and  the  chromatic  aberration  corrected  in  part  by  the 
curvature  and  in  part  by  the  greater  refractive  power  of  flint-glass,  will 
produce  a  perfect  image. 

Although  the  eye  is  not  absolutely  achromatic,  the  dispersion  of  light 
is  not  sufficient  to  interfere  with  distinct  vision  ;  but  the  chromatic  aberra- 
tion is  practically  corrected  in  the  crystalline  lens,  probably  by  differences 
in  consistence  and  in  the  refractive  power  of  its  different  layers. 

Formation  of  Images  in  the  Eye 

It  is  necessary  only  to  call  to  mind  the  general  arrangement  of  the 
structures  in  the  eye  and  to  apply  the  simple  laws  of  refraction,  in  order 
to  comprehend  how  images  are  formed  on  the  retina. 

The  eye  corresponds  to  a  camera  obscura.  Its  interior  is  lined  with 
a  layer  of  dark  pigment-cells,  the  immediate  action  of  which  is  to 
prevent  the  confusion  of  images  by  internal  reflection.  The  rays  of 
light  are  admitted  through  a  circular  opening  (the  pupil),  the  size  of 
which  is  regulated  by  the  movements  of  the  iris.     The  pupil  is  con- 


FLINT  GLASS 


FORMATION    OF    IMAGES    IN    THE    EYE  6/5 

tracted  when  the  hght  striking  the  eye  is  intense  and  is  dilated  as  the 
quantity  of  hght  is  diminished.  In  accommodation  of  the  eye,  the 
pupil  is  dilated  for  distant  objects  and  contracted  for  near  objects;  for 
in  looking  at  near  objects,  the  aberrations  of  sphericity  and  achromatism 
in  the  lens  are  more  marked,  and  the  peripheral  portion  is  cut  off  by 
the  action  of  this  movable  diaphragm,  thus  aiding  correction.  The  rays 
of  light  from  an  object  pass  through  the  cornea,  the  aqueous  humor,  the 
crystalline  lens  and  the  vitreous  humor ;  and  they  are  refracted  with  so 
little  spherical  and  chromatic  aberration,  that  the  image  formed  upon 
the  retina  is  practically  perfect.  The  layer  of  rods  and  cones  of  the 
retina  is  the  only  part  in  the  eye  endowed  with  special  sensibility,  the 
impressions  of  light  being  conveyed  to  the  brain  by  the  optic  nerves. 
This  layer  is  situated  next  the  pigmentary  layer ;  but  the  other  layers 
of  the  retina,  through  which  the  light  passes  to  reach  the  rods  and 
cones,  are  transparent. 

It  has  been  shown  that  the  rods  and  cones  are  the  only  structures 
capable  of  directly  receiving  visual  impressions,  by  the  following  experi- 
ment, first  made  by  Purkinje  :  With  a  convex  lens  of  short  focus,  an 
intense  light  is  concentrated  on  the  sclerotic,  at  a  point  as  far  as  possi- 
ble removed  from  the  cornea.  This  passes  through  the  translucent 
coverings  of  the  eye  at  this  point,  and  the  image  of  the  light  reaches 
the  retina.  In  then  looking  at  a  dark  surface,  the  field  of  vision 
presents  a  reddish  yellow  illumination,  with  a  dark  arborescent  appear- 
ance produced  by  the  shadows  of  the  large  retinal  vessels ;  and  as  the 
lens  is  moved  slightly,  the  shadows  of  the  vessels  move  with  it.  With- 
out going  elaborately  into  the  mechanism  of  this  phenomenon,  it  is  suf- 
ficient to  state  that  Heinrich  Miiller  has  arrived  at  a  mathematical 
demonstration  that  the  shadows  of  the  vessels  are  formed  on  the  layer 
of  rods  and  cones,  and  that  this  layer  alone  is  capable  of  receiving 
impressions  of  light.  His  explanation  is  generally  accepted  and  is 
regarded  as  proof  of  the  peculiar  sensibility  of  this  portion  of  the  retina. 

Theoretically,  an  illuminated  object  placed  in  the  angle  of  vision 
would  form  upon  the  retina  an  image,  diminished  in  size  and  inverted. 
This  is  capable  of  demonstration  by  means  of  the  ophthalmoscope ;  as 
with  this  instrument  the  retina  and  the  images  formed  upon  it  may  be 
seen  during  hfe. 

All  parts  of  the  retina,  except  the  point  of  entrance  of  the  optic 
nerve,  are  sensitive  to  Hght ;  and  the  arrangement  of  the  cornea  and 
pupil  is  such  that  the  field  of  vision  is,  at  the  least  estimate,  equal 
to  the  half  of  a  sphere.  If  a  ray  of  hght  falls  on  the  border  of  the 
cornea  at  a  right  angle  to  the  axis  of  the  eye,  it  is  refracted  by  its  sur- 
face and  will  pass  through  the  pupil  to   the   opposite  border  of   the 


6/6  SPECIAL    SENSES 

retina.  Above  and  below,  the  circle  of  vision  is  cut  off  by  the  over- 
hanging arch  of  the  orbit  and  the  malar  prominence ;  but  externally 
the  field  is  free.  With  the  two  eyes,  therefore,  the  lateral  field  of  vision 
must  be  equal  to  at  least  one  hundred  and  eighty  degrees.  It  is  easy 
to  demonstrate,  however,  with  the  ophthalmoscope,  as  well  as  by  taking 
cognizance  of  the  impressions  made  by  objects  far  removed  from  the 
axis  of  distinct  vision,  that  images  formed  upon  the  lateral  and  periph- 
eral portions  of  the  retina  are  confused  and  imperfect.  One  has  a 
knowledge  of  the  presence  and  an  indefinite  idea  of  the  general  form 
of  large  objects  situated  outside  the  area  of  distinct  vision;  but  when  it 
is  desired  to  note  such  objects  exactly,  the  eyeball  is  turned  by  muscu- 
lar effort  so  as  to  bring  them  at  or  near  the  visual  axis.  This  fact,  with 
what  is  known  of  the  mechanism  of  refraction  by  the  cornea  and  lens, 
makes  it  evident  that  the  area  of  the  retina  on  which  images  are  formed 
with  perfect  distinctness  is  quite  restricted.  A  moment's  reflection  is 
sufificient  to  convince  one  that  in  order  to  see  an  object  distinctly,  it  is 
necessary  to  bring  the  visual  axis  to  bear  upon  it  directly. 

In  examining  the  fundus  of  the  eye  with  the  ophthalmoscope,  the 
yellow  spot,  with  the  fovea  centralis,  can  be  seen,  free  from  large 
bloodvessels  and  composed  chiefly  of  those  elements  of  the  retina  which 
are  sensitive  to  light.  If  at  the  same  time  an  image  for  which  the  eye 
is  perfectly  adjusted  is  observed,  it  will  be  seen  that  this  image  is  per- 
fect only  at  the  fovea  centralis  ;  and  if  the  object  is  removed  from  the 
visual  axis,  there  is  a  confused  image  upon  the  retina,  removed  from  the 
fovea,  at  the  same  time  that  the  subject  is  conscious  of  indistinct  vision. 

At  the  point  of  penetration  of  the  optic  nerve,  the  retina  is  insensi- 
ble to  luminous  impressions ;  or  at  least,  its  sensibility  is  here  so  obtuse 
as  to  be  inadequate  for  the  purposes  of  vision.  This  point  is  called  the 
punctum  caecum  ;  and  its  want  of  sensibility  was  demonstrated  many 
years  ago  (1668)  by  Mariotte. 

The  existence  of  this  spot  —  which  is  not  in  the  area  of  distinct 
vision  —  gives  no  inconvenience  for  the  reason  that  in  binocular  vision 
the  rays  from  an  object  do  not  fall  at  the  same  time  on  both  blind  spots. 
It  is  not  noticed  subjectively,  even  in  monocular  vision. 

The  relative  sensibility  of  different  portions  of  the  retina  has  been 
found  to  be,  in  an  inverse  ratio,  equal  to  about  the  square  of  the  dis- 
tance from  the  axis  of  most  perfect  vision  (Volkmann).  This  observer 
calculated  the  distance  between  the  sensitive  elements  of  the  retina  at 
which  he  supposed  that  two  parallel  lines  would  appear  as  one.  In  the 
axis  of  vision,  the  distance  was  0.00029  inch  (7.366  fi),  and  at  a  devia- 
tion inward  of  8°,  it  was  0.03186  inch  (809.244  /x),  a  diminution  in  acute- 
ness,  of  more  than  a  hundred  times. 


VISUAL   PURPLE  AND    VISUAL   YELLOW  Gj-J 

Visual  Pttrple  and  Visual  Yellow  and  Accommodation  of  the  Eye  for 
Different  Degrees  of  Illumination.  —  The  outer  segments  of  the  rods  of 
the  retina  sometimes  present  a  peculiar  red  or  purple  color  which  disap- 
pears after  ten  or  twelve  seconds  of  exposure  to  Hght.  This  was  first 
observed  by  Boll  (1876)  in  the  retinae  of  frogs  that  had  been  kept  for  a 
certain  time  in  the  dark.  From  his  preliminary  researches  Boll  con- 
cluded that  this  coloration  of  the  retina  exists  only  during  hfe  and  per- 
sists for  but  a  few  moments  after  death  ;  that  it  is  constantly  destroyed 
during  life  by  the  action  of  Hght  and  reappears  in  the  dark ;  and  finally 
that  it  plays  an  important  part  in  the  act  of  vision.  Kiihne  and  others 
have  since  confirmed  and  extended  the  original  observations  of  Boll ; 
and  the  visual  purple  (rhodopsin)  has  been  noted  in  the  mammalia  and 
in  man.  It  has  been  extracted  from  the  retinae  of  frogs  and  dissolved 
in  a  five-per-cent  solution  of  crystaUized  ox-gall,  still  presenting  in  solu- 
tion its  remarkable  sensitiveness  to  light.  Finally  it  has  been  found 
possible  to  fix  images  of  simple  objects,  such  as  strips  of  black  paper 
pasted  on  a  plate  of  ground  glass,  upon  the  retina,  by  a  process  very  like 
photography. 

The  visual  purple  is  produced  by  the  cells  of  the  pigmentary  layer 
of  the  retina  and  from  them  is  absorbed  by  the  outer  segments  of  the 
rods.  It  is  not  present  in  any  part  of  the  cones  and  does  not  exist, 
therefore,  in  the  area  of  distinct  vision,  at  the  fovea  centralis.  The 
rapid  disappearance  of  the  color  under  the  influence  of  actinic  rays  of 
light  renders  it  necessary  to  examine  the  retina  under  a  non-actinic 
(monochromatic)  sodium-flame.  When  thus  examined  and  gradually 
exposed  to  actinic  rays,  the  color  quickly  fades  into  a  yellow  and  finally 
disappears,  being  restored,  however,  in  the  dark.  If  the  choroid  and  the 
pigmentary  layer  of  the  retina  are  removed,  the  rods  are  bleached,  and 
the  color  is  restored  in  the  dark  when  the  choroid  is  replaced.  In  the 
eye  of  the  frog,  kept  in  the  dark,  the  hair-like  processes  that  extend 
from  the  pigmentary  layer  of  the  retina  downward  between  the  rods 
and  cones  are  retracted,  and  the  pigment  is  then  contained  chiefly  in 
the  cells  themselves.  After  prolonged  exposure  of  the  retina  to  light, 
these  processes,  loaded  with  pigment,  extend  between  the  cones  as  far 
as  the  limitary  membrane. 

The  fact  that  visual  purple  is  not  found  in  the  fovea  centralis  is 
opposed  to  the  theory  that  its  existence  is  directly  essential  to  distinct 
vision ;  nevertheless,  certain  phenomena  observed  in  passing  from  a 
bright  light  to  comparative  obscurity,  and  the  reverse,  show  that  the 
purple  has,  at  least,  an  important  indirect  action.  In  passing  from  the 
dark  to  a  bright  Hght,  the  eye  is  dazzled  and  distinct  vision  is  diflicult. 
It  may  be  assumed  that  this  is  due  to  unusual  general  sensitiveness  of 


dy^  SPECIAL   SENSES 

the  retina  to  light,  on  account  of  the  excessive  quantity  of  visual  purple 
which  has  accumulated  in  the  dark ;  and  that  distinct  vision  is  restored 
when  the  retina  is  bleached  to  a  yellow,  which  seems  to  be  the  most 
favorable  condition  for  the  exact  appreciation  of  visual  impressions 
under  full  illumination.  On  the  other  hand,  it  requires  time  for  the  eye 
to  become  accustomed  to  a  dim  light ;  and  during  this  time  the  yellow 
is  changing  to  purple.  Investigations  of  the  absorption-spectra  of  the 
purple  and  yellow  have  shown  that  the  purple  allows  the  actinic  rays  to 
pass  perfectly,  while  the  yellow  completely  absorbs  these  rays.  The 
existence  of  visual  purple  seems  to  be  most  favorable  to  the  imperfect 
and  shadowy  vision  which  occurs  under  dim  illumination,  when  the 
exact  appreciation  of  minute  details  is  impossible.  In  the  condition 
known  as  night-blindness,  it  is  probable  that  the  visual  purple  has  be- 
come exhausted  beyond  the  possibiUty  of  prompt  restoration  such  as  is 
normal ;  and  persons  so  affected  can  not  see  at  night,  although  minute 
vision  under  a  bright  light  may  not  be  affected.  In  certain  cases  of 
this  kind,  the  normal  conditions  may  be  restored  by  a  few  days'  seclu- 
sion in  the  dark.  What  is  called  functional  night-blindness  frequently 
occurs  in  sailors  during  long  tropical  voyages,  and  is  due  to  the  exces- 
sive action  of  diffused  light  on  the  retina. 

Change  of  visual  purple  to  yellow  is  readily  effected,  but  the  further 
change  to  white  is  slower  and  more  difficult.  Conversely,  change  from 
white  to  yellow  is  slow  and  change  from  yellow  to  purple  is  compara- 
tively prompt.  One  use  of  the  colors,  purple  and  yellow,  seems  to  be  to 
accommodate  the  retina  for  vision  under  different  degrees  of  illumina- 
tion. The  purple  adapts  the  eye  to  a  feeble  illumination,  and  the 
yellow,  to  a  full  illumination.  This  being  the  case,  it  is  manifestly 
proper  to  speak  of  a  visual  yellow  as  well  as  of  visual  purple. 

That  the  accommodation  of  the  eye  to  different  degrees  of  illumina- 
tion is  due  to  changes  in  the  colors  produced  by  the  pigmentary  layer 
of  the  retina  and  not  to  different  degrees  of  dilatation  of  the  pupil,  is 
shown  by  the  fact  that  a  person  does  not  see  better  in  the  dark  when 
the  pupil  has  been  dilated  by  atropin.  In  a  very  dim  light  there  is  no 
possibility  of  exact  accommodation  for  near  objects,  which,  when  small, 
can  not  be  seen  distinctly ;  and  the  contraction  of  the  pupil  that  attends 
accommodation  for  near  vision  does  not  occur.  It  is  possible  that  under 
dim  illumination,  parts  outside  of  the  fovea,  that  are  insensible  to  vision 
under  a  bright  light,  receive  visual  impressions.  Under  these  conditions 
the  pupil  is  dilated  and  rays  impinge  on  portions  of  the  retina  not  used 
in  direct  vision.  A  natural  extension  of  this  idea  would  confine  distinct 
vision  and  the  appreciation  of  minute  details  to  the  action  of  the  fovea 
centralis,  in  which  there  is  no  visual  purple,  other  parts  of  the  retina, 


MECHANISM    OF    REFRACTION    IN    THE    EYE  679 

under  full  illumination,  not  being  used.  To  express  this  in  a  few  words, 
the  fovea  centralis  is  used  by  day,  and  the  adjacent  parts  of  the  retina, 
by  night. 

Mechanism  of  Refraction  in  the  Eye 

An  object  that  is  seen  reflects  rays  from  all  points  of  its  surface  to 
the  cornea.  If  the  object  is  near,  the  rays  are  divergent  as  they  strike 
the  eye.  Rays  from  distant  objects  are  practically  parallel.  It  is  evident 
that  refraction  for  diverging  rays  must  be  greater  than  for  parallel  rays, 
as  a  necessity  for  distinct  vision  ;  in  other  words,  the  eye  must  be  ac- 
commodated for  vision  at  different  distances.  Leaving,  however,  the 
mechanism  of  accommodation  for  later  consideration,  it  may  be  stated 
simply  that  the  important  agents  in  refraction  in  the  eye  are  the  surfaces 
of  the  cornea  and  the  crystalline  lens.  Calculations  have  shown  that 
the  index  of  refraction  of  the  aqueous  humor  is  sensibly  the  same  as  that 
of  the  substance  of  the  cornea,  so  that  practically  the  refraction  is  the 
same  as  if  the  cornea  and  the  aqueous  humor  were  one  and  the  same 
substance.  The  index  of  refraction  of  the  vitreous  humor  is  practically 
the  same  as  that  of  the  aqueous  humor,  both  being  about  equal  to  the 
index  of  refraction  of  pure  water.^  Refraction  by  the  crystalline  lens, 
however,  is  more  complex  in  its  mechanism  ;  depending  first,  on  the 
curvatures  of  its  two  surfaces,  and  again,  on  differences  in  consistence 
of  different  portions  of  its  substance.  In  view  of  these  facts,  the  con- 
ditions of  refraction  in  the  eye  in  distinct  \'ision  may  be  simplified  by 
assuming  the  following  arrangement :  — 

The  cornea  presents  a  convex  surface  on  which  the  rays  of  light  are 
received.  At  a  certain  distance  behind  its  anterior  border,  is  the  crys- 
talline, a  double-convex  lens,  corrected  sufficiently  for  practical  purposes, 
both  for  spherical  and  chromatic  aberration.  This  lens  is  suspended  in 
a  liquid  with  an  index  of  refraction  equal  to  that  of  pure  water,  as 
both  the  aqueous  humor  in  front  and  the  vitreous  humor  behind  have  the 
same  refractive  index.  Behind  the  lens,  in  its  axis  and  exactly  in  the 
plane  upon  which  the  rays  of  light  are  brought  to  a  focus  by  the  action 
of  the  cornea  and  the  lens,  is  the  fovea  centralis,  in  which  is  the  centre 
for  distinct  vision.  The  anatomical  elements  of  the  fovea  are  capable  of 
receiving  visual  impressions,  which  are  conveyed  to  the  brain  by  the 
optic  nerves.  All  impressions  made  on  other  portions  of  the  retina  are 
comparatively  indistinct ;  and  the  point  of  entrance  of  the  optic  nerve 
is  insensible  to  light.     Inasmuch  as  the  punctum  caecum  is  situated  in 

1  The  index  of  refraction  is  the  ratio  between  the  sine  of  the  angle  of  incidence  and  the  sine 
of  the  angle  of  refraction.  This  is  practically  the  same  for  the  cornea,  the  crystalline  lens,  the 
aqueous  humor  and  the  vitreous  humor.  For  the  aqueous  and  vitreous  humors,  it  is  1.34  to 
1.36  ;   for  the  crystalline  lens,  it  is  1.40  to  1. 45,  a  little  higher. 


68o  SPECIAL    SENSES 

either  eye  upon  the  nasal  side  of  the  retina,  in  normal  vision,  rays  from 
the  same  object  can  not  fall  on  both  blind  points  at  the  same  time. 
Thus,  in  binocular  vision,  the  insensibility  of  the  punctum  caecum  does 
not  interfere  with  sight ;  and  the  movements  of  the  globe  prevent  any 
notable  interference  in  vision,  even  with  one  eye.  The  sclerotic  coat  is 
for  the  protection  of  its  contents  and  for  the  insertion  of  muscles.  The 
iris  has  an  action  similar  to  that  of  the  diaphragm  in  optical  instruments. 
The  suspensory  ligament  of  the  lens,  the  ciliary  body,  and  the  ciliary 
muscle  are  for  the  fixation  of  the  lens  and  its  accommodation  for  vision 
at  different  distances.  The  pigment-cells  are  for  the  absorption  of 
light,  preventing  confusion  of  vision  from  reflection  within  the  eye. 
They  also  produce  the  visual  purple. 

Refraction  by  the  cornea  is  effected  simply  by  its  external  surface. 
The  rays  of  light  from  a  distant  point  are  deviated  by  its  convexity  so 
that,  if  they  were  not  again  refracted  by  the  crystalline  lens,  they  would 
be  brought  to  a  focus  at  a  point  situated  about  j%  of  an  inch  (lo  milli- 
meters) behind  the  retina.  Without  the  crystalline  lens,  therefore,  dis- 
tinct unaided  vision  usually  is  impossible,  although  the  sensation  of  light 
is  appreciated.  In  cases  of  extraction  of  the  lens  for  cataract  (aphakia), 
the  place  of  the  crystalline  may  be  suppHed  by  a  convex  lens  placed 
before  the  eye. 

The  rays  of  light,  refracted  by  the  anterior  surface  of  the  cornea, 
are  received  upon  the  anterior  surface  of  the  crystalline  lens,  by  which 
they  are  still  further  refracted.  Passing  through  the  substance  of  the 
lens,  they  undergo  certain  modifications  in  refraction,  dependent  on  the 
differences  in  the  various  strata  of  the  lens.  These  modifications  have 
not  been  accurately  calculated  ;  but  it  is  sufficient  to  state  that  they 
contribute  to  the  accuracy  of  the  formation  of  a  retinal  image  practically 
free  from  chromatic  dispersion.  As  the  rays  pass  out  of  the  lens,  they 
are  again  refracted  by  its  posterior  curvature  and  are  brought  to  a  focus 
at  the  area  of  distinct  vision. 

The  rays  from  all  points  of  an  object  distinctly  seen  are  brought  to 
a  focus,  if  the  accommodation  of  the  lens  is  correct,  on  a  restricted  sur- 
face in  the  macula  lutea  ;  but  the  rays  from  different  points  cross  before 
they  reach  the  retina,  and  the  image  is  inverted. 

Calculating  the  curvatures  of  the  refracting  surfaces  in  the  eye  and 
the  indices  of  refraction  of  its  transparent  media,  it  has  been  pretty 
clearly  shown,  by  mathematical  formulae,  that  the  eye  —  viewed  simply 
as  an  optical  instrument,  and  not  practically,  as  the  organ  of  vision  — 
presents  a  certain  degree  of  spherical  and  chromatic  aberration ;  but 
these  calculations  are  not  important  in  a  purely  physiological  considera- 
tion of  the  sense  of  sight. 


ASTIGMATISM  68 1 

In  most  calculations  of  the  size  of  images,  the  positions  of  conjugate 
foci,  etc.,  in  normal  and  abnormal  eyes,  a  schematic  eye  reduced  by 
Bonders,  after  the  example  of  Listing,  is  regarded  as  sufficiently  exact 
for  all  practical  purposes.  This  simple  scheme  represents  the  eye  as 
reduced  to  a  single  refracting  surface,  the  cornea,  and  a  single  liquid 
assumed  to  have  an  index  of  refraction  equal  to  that  of  pure  water.  The 
distance  between  what  are  called  the  two  nodal  points  and  between  the 
two  principal  points  of  the  dioptric  system  of  the  eye  is  so  small,  amount- 
ing to  hardly  ^-^g  of  an  inch  (0.254  millimeter),  that  it  can  be  neglected. 
In  this  simple  eye,  there  is  assumed  to  be  a  radius  of  curvature  of  the 
cornea  of  about  ^  of  an  inch  (5  millimeters)  and  a  single  optical  centre 
situated  i  of  an  inch  (5  millimeters)  back  of  the  cornea,  the  "principal 
point  "  being  in  the  cornea,  in  the  visual  axis.  The  posterior  focal  dis- 
tance, that  is,  the  focus,  at  the  bottom  of  the  eye,  for  rays  parallel  in  the 
air,  is  about  |-  of  an  inch  (20  millimeters).  The  anterior  focal  distance, 
that  is,  for  rays  parallel  in  the  vitreous  humor,  is  about  -|  of  an  inch  (15 
millimeters).  The  measurements  in  this  simple  schematic  eye  can  easily 
be  remembered  and  used  in  calculations. 


Astigmatism  ■ 

In  the  normal  human  eye  the  visual  line  does  not  coincide  exactly 
with  the  mathematical  axis ;  but  there  is  still  another  normal  deviation 
from  mathematical  exactness  in  the  refraction  of  rays  by  the  cornea  and 
the  lens,  which  is  of  considerable  importance.  If  two  threads,  crossing 
each  other  at  right  angles  in  the  same  plane,  are  placed  before  the  eyes, 
one  of  these  threads  being  vertical,  and  the  other,  horizontal,  when  the 
optical  apparatus  is  adjusted  so  that  one  line  is  seen  with  distinctness, 
the  other  is  not  well  defined.  In  other  words,  when  the  eye  is  accommo- 
dated for  the  vertical  thread,  the  horizontal  thread  is  indistinct,  and  vice 
versa.  When  the  horizontal  line  is  seen  distinctly,  in  order  to  see  the 
vertical  line  without  modifying  the  accommodation,  it  must  be  removed 
to  a  greater  distance.  This  depends  chiefly  on  a  difference  in  the  ver- 
tical and  the  horizontal  curvatures  of  the  cornea,  so  that  the  horizontal 
meridian  has  a  focus  slightly  different  from  the  focus  of  the  vertical 
meridian.  A  condition  opposite  to  that  observed  in  the  cornea  usually 
exists  in  the  lens ;  that  is,  the  difference  which  exists  between  the 
curvatures  of  the  lens  in  the  vertical  and  the  horizontal  meridians  is 
such  that  the  deeper  curvature  in  the  lens  is  situated  in  the  meridian 
of  the  shallower  curvature  of  the  cornea.  In  this  way,  in  normal  eyes, 
the  aberration  of  the  lens  has  a  tendency  to  correct  the  aberration  in 
the  cornea;  but  this  correction  is  incomplete,  and  there  still  remains, 


682  SPECIAL   SENSES 

in  all  degrees  of  accommodation,  a  certain  difference  in  vision  as 
regards  vertical  and  horizontal  lines. 

The  condition  just  described  is  known  under  the  name  of  normal 
regular  astigmatism  ;  but  the  aberration  is  not  sufficient  to  interfere 
with  distinct  vision.  The  degree  of  regular  astigmatism  presents  normal 
variations  in  different  eyes.  In  some  eyes  there  is  no  astigmatism ; 
but  this  is  rare.  When  the  astigmatism  amounts  to  -^^  or  more,  it  is  to 
be  considered  abnormal ;  which  simply  means  that  beyond  this  point  the 
aberration  interferes  with  distinct  vision. 

From  the  simple  definition  of  regular  astigmatism,  it  is  evident  that 
this  condition  and  the  degree  in  which  it  exists  may  easily  be  determined 
by  noting  the  differences  in  the  foci  for  vertical  and  horizontal  lines, 
and  it  may  be  exactly  corrected  by  the  application  of  cylindrical  glasses 
of  proper  curvature.  Indeed,  the  curvature  of  a  cyHndrical  glass  that 
will  enable  a  person  to  distinguish  vertical  and  horizontal  lines  with 
perfect  distinctness  at  the  same  time,  is  an  exact  indication  of  the 
degree  of  aberration.  Regular  astigmatism,  such  as  just  described, 
may  be  so  exaggerated  as  to  interfere  seriously  with  vision,  when  it 
becomes  abnormal.  This  kind  of  aberration,  however,  which  usually  is 
dependent  on  an  abnormal  condition  of  the  cornea,  is  remediable  by  the 
use  of  properly-adjusted  cylindrical  glasses. 

Irregular  astigmatism,  excluding  cases  of  pathological  deformation, 
opaque  spots  etc.,  in  the  cornea,  depends  usually  on  irregularity  in  the 
different  sectors  of  the  crystalline  lens.  Instead  of  a  simple  and  regular 
aberration,  consisting  in  a  difference  between  the  depth  of  the  vertical 
and  the  horizontal  curvatures  of  the  cornea  and  lens,  there  are  irregular 
variations  in  the  curvatures  of  different  sectors  of  the  lens.  As  a  con- 
sequence of  this,  when  the  irregularities  are  very  great,  there  is  impair- 
ment of  the  sharpness  of  vision.  The  circles  of  diffusion,  which  are 
regular  in  normal  vision,  become  irregularly  radiated,  and  single  points 
appear  multiple,  an  irregularity  described  under  the  name  of  polyopia 
monocularis.  Accurate  observations  have  shown  that  this  condition 
exists  in  a  moderate  degree  in  normal  eyes ;  but  it  is  so  slight  as  not  to 
interfere  with  ordinary  vision.  In  what  is  called  normal  irregular  astig- 
matism, the  irregularity  depends  entirely  on  the  crystalline  lens.  If  a 
card  with  a  very  small  opening  is  placed  before  the  eye  and  is  moved  in 
front  of  the  lens,  so  that  the  pencil  of  light  falls  successively  on  different 
sectors,  it  can  be  shown  that  the  focal  distance  is  different  for  different 
portions.  The  radiating  lines  of  hght  observed  in  looking  at  remote 
luminous  points,  as  the  fixed  stars,  are  produced,  by  this  irregularity  in 
the  curvatures  of  the  different  sectors  of  the  lens. 

While  regular  astigmatism,  both  normal  and  abnormal,  may  be  per- 


MOVEMENTS    OF    THE    IRIS  683 

fectly  corrected  by  placing  cylindrical  glasses   before  the  eyes,   it   is 
impossible,  in   the   majority   of    cases,   to    construct    glasses  that   will 

correct  entirely  what  is  called  irregular  astigmatism. 


Movements  of  the  Iris 

There  are  two  physiological  conditions  under  which  the  size  of  the 
pupil  is  modified  :  The  first  of  these  depends  on  the  degree  of  illumina- 
tion to  which  the  eye  is  exposed.  When  the  illumination  is  dim,  the 
pupil  is  widely  dilated.  When  the  eye  is  exposed  to  a  bright  light,  the 
retina  is  protected  by  contraction  of  the  iris.  The  muscular  action  by 
which  the  iris  is  contracted  is  characteristic  of  the  smooth  muscular 
fibres,  as  can  be  readily  seen  by  exposing  an  eye,  in  which  the  pupil  is 
dilated,  to  a  bright  fight.  Contraction  does  not  take  place  instantly,  but 
an  appreciable  interval  elapses  after  the  exposure,  and  a  more  or  less 
gradual  diminution  in  the  size  of  the  pupil  is  obsen.-ed.  This  is  seen 
both  in  solar  and  in  artificial  light.  The  second  of  these  conditions 
depends  indirectly  on  the  voluntary  action  of  muscles.  The  effort  of 
converging  the  axes  of  the  eyes,  in  looking  at  a  very  near  object,  con- 
tracts the  pupils;  and  accommodation  of  the  eve  for  near  objects  pro- 
duces the  same  effect,  even  when  the  eyes  are  not  converged.  This 
action  will  be  fully  considered  under  the  head  of  accommodation. 

Direct  Actioji  of  Light  on  the  Iris.  — The  variations  in  the  size  of  the 
pupil  under  different  physiological  conditions  are  effected  almost  ex- 
clusively through  the  nen,-ous  system,  either  by  reflex  action  from 
variations  in  the  intensity  of  light,  or  by  a  direct  influence,  as  in  accom- 
modation for  distances ;  but  it  is  nevertheless  true  that  the  muscular 
tissue  of  the  iris  will  respond  directly  to  the  stimulus  of  fight.  Harless 
noted,  in  subjects  dead  of  various  diseases,  five  to  thirty  hours  after 
death,  that  the  iris  contracted  under  the  stimulus  of  light;  and  he 
regarded  this  as  probably  due  to  direct  action  on  its  muscular  tissue. 
The  experiments  of  Harless  were  made  on  the  two  eyes,  one  being 
exposed  to  the  fight,  while  the  other  was  closed.  The  contraction,  how- 
ever, took  place  slowly,  requiring  an  exposure  of  several  hours.  This 
mode  of  contraction  is  different  from  the  action  of  the  iris  during  life ; 
but  it  is  precisely  fike  the  contraction  observed  after  division  of  the 
motor  ocuh  communis,  which  is  slow  and  gradual  and  depends  on  the 
direct  action  of  fight  on  the  muscular  fibres. 

Action  of  the  Nervous  System  on  the  Iris. — This  subject,  so  far  as  it 
relates  to  the  third  pair,  has  been  considered  in  connection  with  the 
physiology  of   these  nerves ;    and   it  is  unnecessary  to  refer  again  in 


684  SPECIAL   SENSES 

detail  to  the  experiments  that  have  already  been  cited.  The  reflex 
phenomena  observed  are  sufficiently  distinct.  When  light  is  admitted 
to  the  retina,  the  pupil  contracts,  and  the  same  result  follows  mechanical 
irritation  of  the  optic  nerves.  When  the  third  pair  of  nerves  has  been 
divided,  no  such  reflex  phenomena  are  observed.  It  is  well  known,  also, 
that  division  of  the  third  nerves  in  the  lower  animals  or  their  paralysis 
in  the  human  subject  produces  permanent  dilatation  of  the  pupil,  the  iris 
responding,  only  in  the  slow  and  gradual  manner  already  indicated,  to 
the  direct  action  of  light. 

Taking  all  the  experimental  data  into  consideration,  it  is  certain  that 
the  third  nerve  has  an  important  influence  on  the  iris.  Filaments  from 
the  ophthalmic  ganglion  animate  the  circular  fibres,  or  sphincter,  and 
these  filaments  are  derived  from  the  third  cranial  nerve.  If  this  nerve 
is  divided,  the  iris  becomes  permanently  dilated  and  is  immovable,  ex- 
cept that  it  responds  slowly  to  the  direct  action  of  light.  The  reflex 
action  by  which  the  pupil  is  contracted  under  the  stimulus  of  light 
operates  through  the  third  nerve,  and  no  such  action  can  take  place 
after  this  nerve  has  been  divided.  In  view  of  these  facts,  there  can  be 
no  doubt  in  regard  to  the  nervous  action  on  the  sphincter  of  the  pupil, 
this  muscle  being  animated  exclusively  by  filaments  from  the  motor  oculi 
communis,  coming  through  the  ophthalmic  ganglion. 

Most  anatomists  admit  the  existence  of  radiating  muscular  fibres  in 
the  iris,  the  action  of  which  is  antagonistic  to  the  circular  fibres,  and 
which  dilate  the  pupil.  That  these  fibres  are  subjected  to  nervous 
influence,  is  rendered  certain  by  experiments  on  the  sympathetic  system. 
There  can  be  no  doubt  that  the  action  of  the  sympathetic  on  the  pupil 
is  directly  antagonistic  to  that  of  the  third  pair,  the  former  presiding 
over  the  radiating  muscular  fibres  ;  and  the  only  question  to  determine 
is  the  course  taken  by  the  sympathetic  filaments  to  the  iris.  Experi- 
ments on  the  influence  of  the  fifth  pair  on  the  pupil  have  been  somewhat 
contradictory  in  different  animals.  In  rabbits,  section  of  this  nerve  in 
the  cranial  cavity  produces  contraction  of  the  pupil;  but  in  dogs  and 
cats,  the  same  operation  produces  dilatation.  In  the  human  subject,  of 
course,  it  is  impossible  to  determine  this  point  by  direct  experiment ; 
and  the  varying  results  obtained  in  observations  on  different  animals 
probably  depend  upon  differences  in  the  anatomical  relations  of  the 
nerves.  It  is  probable,  however,  that  the  filaments  of  the  sympathetic 
that  animate  the  radiating  fibres  join  the  fifth  nerve  near  the  ganglion 
of  Gasser  and  from  this  nerve  pass  to  the  iris.  In  observations  on  the 
human  subject  it  has  been  noted  that  division  of  the  sympathetic  in  the 
neck  was  attended  with  contraction  of  the  pupil  on  the  side  of  the  in- 
jury (Mitchell).     Stimulation  of  the  cervical  sympathetic,  in  the  head  of 


MOVEMENTS    OF   THE    IRIS  685 

a  woman  eighteen  minutes  after  decapitation,  produced  dilatation  of  the 
pupil  (Wagner). 

There  seem  to  be  two  distinct  nerve-centres  corresponding  to  the  two 
sets  of  nerves  that  regulate  the  movements  of  the  iris.  One  of  these 
centres  presides  over  the  reflex  contractions  of  the  iris,  and  the  other  is 
the  centre  of  origin  of  the  nervous  influence  through  which  the  pupil 
is  dilated. 

The  mechanism  of  reflex  contraction  of  the  iris  under  the  stimulus 
of  light  is  sufficiently  simple.  An  impression  is  made  on  the  retina, 
which  is  conveyed  by  the  optic  nerves  to  the  centre,  and  in  obedience 
to  this  impression,  the  sphincter  of  the  iris  contracts.  If  the  optic  nerves 
are  divided,  so  that  the  impression  can  not  be  conveyed  to  the  centre, 
or  if  the  third  nerve  is  divided,  no  movements  of  the  iris  can  take  place. 
The  centres  which  preside  over  the  reflex  phenomena  of  contraction  of 
the  pupil  are  situated  in  the  bulb.  The  action  of  these  centres  is  crossed 
in  animals  in  which  the  decussation  of  the  optic  nerves  is  complete.  In 
man  the  axes  of  both  eyes  are  habitually  brought  to  bear  upon  objects, 
and  it  is  well  known  that  there  is  a  physiological  unity  in  the  action  of 
the  two  eyes  in  ordinary  vision.  It  has  been  observed  that  when  one 
eye  only  is  exposed  to  light,  the  pupil  becoming  contracted  under  this 
stimulus,  the  pupil  of  the  other  'eye  also  contracts.  There  is,  indeed,  a 
direct  contraction  and  dilatation  of  the  pupil  of  the  eye  which  is  exposed 
to  the  light,  and  an  indirect,  or  "consensual"  movement  of  the  iris  on 
the  opposite  side.  The  consensual  contraction  occurs  about  |  of  a  sec- 
ond later  than  the  direct  action,  and  the  consensual  dilatation,  about  ^  of 
a  second  later.  The  condition  of  the  pupillary  reflexes  often  gives  im- 
portant information  in  cases  of  cerebral  disease.  They  are  particularly 
important  in  the  early  stages  of  paresis. 

The  filaments  of  the  sympathetic  that  produce  dilatation  of  the 
pupil  take  their  origin  from  the  spinal  cord.  In  the  spinal  cord,  be- 
tween the  sixth  cervical  and  the  second  thoracic  nerves,  is  the  inferior 
cilio-spinal  centre.  When  the  cord  is  stimulated  in  this  situation,  both 
pupils  are  dilated.  If  the  cord  is  divided  longitudinally  and  the  two 
halves  are  separated  from  each  other  by  a  glass  plate,  stimulation  of  the 
right  half  produces  dilatation  of  the  right  pupil,  and  vice  veisd.  This 
does  not  occur  when  the  sympathetic  in  the  neck  has  been  divided.  In 
addition  to  the  inferior  cilio-spinal  centre,  there  is  a  superior  centre, 
which  is  in  communication  with  the  superior  cervical  ganglion  and  is 
situated  near  the  sublingual  nerve.  The  influence  of  this  centre  over 
the  pupil  can  not  be  demonstrated  by  direct  stimulation,  because  it  is 
too  near  the  origin  of  the  fifth,  irritation  of  which  affects  the  iris ;  but 
it  is  shown  by  division  of  its  filaments  of  communication  with  the  iris. 


686  SPECIAL    SENSES 

Accommodation   of   the  Eye  for  Vision  at  Different  Distances 

Supposing  the  eye  to  be  adapted  to  vision  at  an  infinite  distance,  in 
which  the  rays  from  an  object  as  they  strike  the  cornea  are  practically 
parallel,  it  is  evident  that  the  foci  of  the  rays,  as  they  form  a  distinct 
image  upon  the  retina,  are  all  situated  in  the  proper  plane.  Under 
these  conditions,  in  a  normal  eye,  the  image,  appreciated  by  the  in- 
dividual or  seen  by  means  of  the  ophthalmoscope,  is  clear  and  distinct. 
If  the  foci  are  situated  in  front  of  the  retina,  the  rays,  instead  of  com- 
ing to  a  focus  on  a  point  in  the  retina,  will  cross,  and,  from  their  diffu- 
sion or  dispersion,  will  produce  indistinct  vision.  Under  these  conditions 
a  distinct  point  is  not  perceived,  but  every  point  in  the  image  is  sur- 
rounded with  an  indistinct  circle.  These  are  called  "  circles  of  diffu- 
sion." If,  now,  the  eye,  adjusted  for  vision  at  an  infinite  distance,  is 
brought  to  bear  on  a  near  object,  the  rays  from  which  are  divergent  as 
they  strike  the  cornea,  the  image  will  no  longer  be  distinct  but  will  be 
obscured  by  circles  of  diffusion.  It  is  the  adjustment  by  which  these 
circles  of  diffusion  are  removed  that  constitutes  accommodation.  This 
fact  has  been  demonstrated  by  Helmholtz  by  means  of  the  ophthalmo- 
scope. "  If  the  eye  is  adjusted  to  the  observation  of  an  object  placed 
at  a  certain  distance,  it  is  found  that  the  image  of  a  flame,  placed  at  the 
same  distance,  is  produced  with  perfect  distinctness  upon  the  retina, 
and,  at  the  same  time,  upon  the  illuminated  plane  of  the  image,  the 
vessels  and  the  other  anatomical  details  of  the  retina  are  seen  with 
equal  distinctness.  But,  when  the  flame  is  brought  considerably  nearer, 
its  image  becomes  confused  while  the  details  of  the  structure  of  the 
retina  remain  perfectly  distinct." 

It  is  evident  that  there  is  a  certain  condition  of  the  eyes  adapted  to 
vision  at  an  infinite  distance ;  and  that  for  the  distinct  perception  of 
near  objects  the  transparent  media  must  be  so  altered  in  their  arrange- 
ment or  in  the  curvatures  of  their  surfaces  that  the  refraction  will  be 
greater ;  for  without  this,  the  rays  would  be  brought  to  a  focus  beyond 
the  retina. 

The  changes  in  the  eye  by  which  accommodation  is  effected  are  now 
known  to  consist  mainly  in  an  increased  convexity  of  the  lens  for  near 
objects ;  and  the  only  points  in  dispute  are  a  few  unimportant  details  in 
the  mechanism  of  this  action.  The  simple  facts  to  be  borne  in  mind  in 
studying  this  question  are  the  following :  — 

When  the  eye  is  accommodated  to  vision  at  an  infinite  distance  the 
parts  are  passive. 

In  the  adjustment  of  the  eye  for  near  objects  the  convexities  of  the 
lens  are  increased  by  muscular  action. 


ACCOMMODATION 


687 


In  accommodation  for  near  objects  the  pupil  is  contracted;  but  this 
action  is  accessory  and  is  not  essential. 

The  ordinary  range  of  accommodation  varies  between  a  distance  of 
about  five  inches  (12.7  centimeters)  and  infinity. 

Changes  in  the  Crystalline  Lens  in  Accominodatioji.  —  It  is  important 
to  determine  the  extent  and  nature  of  the  changes  of  the  lens  in  accom- 
modation ;  and  these  changes  have  been  accurately  measured  in  the 
living  subject.  It  has  been  ascertained  that  the  lens  becomes  increased 
in  thickness  in  accommodation  for  near  objects,  chiefly  by  an  increase 
in  its  anterior  curvature,  by  which  this  surface  of  the  lens  is  made  to 
project  toward  the  cornea.  As  the  iris  is  in  contact  with  the  anterior 
surface  of  the  lens,  this  membrane. is  made  to  project  in  the  act  of 
accommodation.  The  posterior  curvature  of  the  lens  is  also  increased, 
but  this  is  slight  as  compared  with  the  increase  of  the  curvature  of  its 
anterior  surface.  The  distance  between  the  posterior  surface  of  the 
lens  and  the  cornea  is  not  sensibly  altered.  It  is  unnecessary  to  de- 
scribe minutely  the  methods  employed  in  making  these  calculations,  and 
it  is  sufficient  to  state  that  it  is  done  by  accurately  measuring  the  com- 
parative size  of  images  formed  by  reflection  from  the  anterior  surface  of' 
the  lens.  The  results  obtained  by  Helmholtz,  in  observations  on  two 
persons,  are  the  following  :  — 


Persons 
Exam  LN  ED 

Radius  of  Curvature  of  the  Anterior  Surface  of 
THE  Lens 

Displacement  of  the  Pupil  in  Ac- 
commodation  for  Near  Objects 

Distant  Vision 

Near  Vision 

0.  H. 
B.  P. 

0.4641  in.  (11. 9  mm.) 
0.3432  in.  (8.8  mm.) 

0.3354  in.  (8.6  mm.) 
0.2701  in.  (5.9  mm.) 

0.0140  in.  (0.36  mm.) 
0.0172  in.  (0.44  mm.) 

The  mechanism  of  the  changes  in  the  thickness  and  in  the  curva- 
tures of  the  lens  in  accommodation  can  be  understood  only  by  keeping 
clearly  in  mind  the  physical  properties  of  the  lens  itself  and  its  anatomi- 
cal relations.  In  situ,  in  what  has  been  called  the  indolent  state  of  the 
eye,  the  lens  is  adjusted  for  vision  at  an  infinite  distance  and  is  flattened 
by  the  tension  of  its  suspensory  ligament.  After  death,  indeed,  it  is 
easy  to  produce  changes  in  its  form  by  applying  traction  to  the  zone  of 
Zinn.  Remembering  the  exact  relations  of  the  suspensory  ligament, 
the  ciliary  muscle  and  the  lens,  and  keeping  in  mind  the  tension  within 
the  globe,  it  is  evident  that  when  the  ciliar}'  muscle  is  at  rest,  the 
capsule  will  compress  the  lens,  increasing  its  diameter  and  diminishing 
its  convexity.     It  is  in  this  condition  that  the  eye  is  adapted  to  vision  at 


688 


SPECIAL    SENSES 


an  infinite  distance.  It  is  evident,  also,  that  slight  changes  in  the  con- 
vexity of  the  lens  are  sufficient  for  the  range  of  accommodation  re- 
quired. If  any  near  object  is  fixed  with  the  eye  there  is  a  conscious 
effort,  and  prolonged  examination  of  near  objects  produces  a  sense  of 
fatigue.  This  may  be  illustrated  by  the  very  familiar  experiment  of 
looking  at  a  distant  object  through  a  gauze.  When  the  object  is  seen 
distinctly,  the  gauze  is  scarcely  perceived ;  but  by  an  effort  the  eye  can 
be  brought  to  see  the  meshes  of  the  gauze  distinctly,  when  the  impres- 
sion of  the  distant  object  is  either  lost  or  becomes  indistinct. 

The  ciliary  muscle  arises  from  the  circular  line  of  junction  of  the 
cornea  and  sclerotic,  passes  backward,  and  is  lost  in  the  tissue  of  the 
choroid,  extending  as  far  as  the  anterior  border  of  the  retina.  Most  of 
the  fibres  pass  directly  backward  but  some  become  circular  or  spiral. 
When  this  muscle  contracts,  the  choroid  is  drawn  forward,  with  prob- 
ably a  slightly  spiral  motion  of  the  lens,  the  contents  of  the  globe,  situ- 


Fig.  176.  —  Sectio7i  of  the  lens,  etc.,  showing  the  mechanism  0/  acco7nmodation  (Fick). 

The  left  side  of  the  figure  {F)  shows  the  lens  adapted  to  vision  at  infinite  distances.  The  right  side 
of  the  figure  (A^)  shows  the  lens  adapted  to  the  vision  of  near  objects,  the  ciliary  muscle  being  con- 
tracted and  the  suspensory  ligament  of  the  lens  consequently  relaxed. 

ated  behind  the  lens,  are  compressed,  and  the  suspensory  ligament  is 
relaxed.  The  lens  itself,  the  compressing  and  flattening  action  of  the 
suspensory  ligament  being  diminished,  becomes  thicker  and  more  con- 
vex, by  virtue  of  its  own  elasticity,  in  the  same  way  that  it  becomes 
thicker  after  death,  when  the  tension  of  the  ligament  is  artificially 
diminished.  The  theory  of  Tscherning  that  the  ciliary  muscle  tightens 
the  suspensory  ligament,  compresses  the  lens  near  its  borders  and  pro- 
duces bulging  of  its  central  portion  is  not  tenable  in  view  of  demonstra- 
tions that  the  ligament  actually  is  relaxed  during  accommodation  for 
near  objects  (Hess). 

This  is  in  brief  the  mechanism  of  accommodation.  Near  objects 
are  seen  distinctly  by  a  voluntary  contraction  of  the  ciliary  muscle,  the 
action  of  which  is  perfectly  adapted  to  the  requirements  of  vision.  In 
early  life  the  lens  is  soft  and  elastic,  and  the  accommodating  power  is 
at  its  maximum ;  but  in  old  age  the  lens  becomes  flattened,  harder  and 
less  elastic,  and  the  power  of  accommodation  necessarily  is  diminished. 


ACCOALMODATION  689 

CJianges  in  the  Iris  in  Accommodation.  —  The  size  of  the  pupil  is 
sensibly  diminished  in  accommodation  of  the  eye  for  near  objects.  Al- 
though the  movements  of  the  iris  are  directly  associated  with  the 
muscular  effort  by  which  the  form  of  the  lens  is  modified,  the  contrac- 
tion of  the  pupil  is  not  one  of  the  essential  conditions  of  accommodation. 
Helmholtz  reported  a  case  in  which  the  iris  was  completely  paralyzed, 
the  power  of  accommodation  remaining  perfect ;  and  he  described  an- 
other case,  reported  by  Von  Graefe,  in  which  accommodation  was  not 
disturbed  after  loss  of  the  entire  iris. 

It  has  already  been  noted  that  the  pupil  contracts  when  the  eyes 
are  made  to  converge  by  the  action  of  the  muscles  animated  by  the  third 
pair  of  nerves;  and  it  is  evident  that  convergence  of  the  eyes  occurs  in 
looking  at  very  near  objects.  Increased  convergence  of  the  visual  lines 
without  change  of  accommodation  makes  the  pupil  contract,  as  is  easily 
proved  by  simple  experiments  with  prismatic  glasses.  When  accom- 
modation is  effected  without  converging  the  visual  axes,  "  each  stronger 
tension  is  combined  with  contraction  of  the  pupil"  (Bonders).  Con- 
traction of  the  pupil,  therefore,  occurs  both  in  convergence  of  the  visual 
axes  without  accommodation  and  in  accommodation  for  near  objects 
without  convergence  of  the  eyes. 

The  action  of  the  iris,  as  is  evident  from  the  facts  just  stated,  is  to 
a  certain  extent  under  the  control  of  the  will ;  but  it  can  not  be  disas- 
sociated, first,  from  the  voluntary  action  of  the  muscles  that  converge 
the  visual  axes,  and  second,  from  the  action  of  the  ciliary  muscle. 
Bonders,  by  alternating  the  accommodation  for  a  remote  and  a  near 
object,  was  able  to  contract  and  dilate  the  pupil  voluntarily  more  than 
thirty  times  in  a  minute.  Brown-Sequard,  in  discussing  the  voluntary 
movements  of  the  iris,  has  mentioned  a  case  in  which  "  the  pupil  could 
be  contracted  or  dilated  without  changing  the  position  of  the  eye  or 
making  an  effort  of  adaption  for  a  long  or  a  short  distance."  As 
further  evidence  of  the  connection  of  accommodation  with  muscular 
action,  cases  are  cited  in  works  on  ophthalmology  in  which  there  is 
paralysis  of  the  ciliary  muscle,  as  well  as  cases  in  which  the  act  of 
accommodation  is  painful. 

A  curious  phenomenon  connected  with  accommodation  may  be 
observed  in  looking  at  a  near  object  through  a  very  small  opening,  like 
a  pinhole.  The  shortest  distance  at  which  one  can  see  a  small  object 
distinctly  is  about  five  inches  (12.7  centimeters);  but  in  looking  at  the 
same  object  through  a  pinhole  in  a  card,  it  can  be  seen  distinctly  at  the 
distance  of  about  one  inch  (25.4  millimetres),  and  it  then  appears  con- 
siderably magnified.  In  this  experiment,  the  card  serves  as  a  diaphragm 
with  a  very  small  opening,  so  that  only  the  centre  of  the  lens  is  used ; 


690 


SPECIAL   SENSES 


and  the  apparent  increase  in  the  size  of  the  object  probably  is  due  to 
the  fact  that  its  distance  from  the  eye  is  many  times  less  than  the 
distance  at  which  distinct  vision  is  possible  under  ordinary  conditions. 
It  is  well  known  that  myopic  persons,  by  being  able  to  bring  the  eye 
nearer  to  objects  than  is  possible  in  ordinary  vision,  can  see  minute 
details  with  peculiar  distinctness. 

Erect  Impressions  produced  by  Images  inverted  tipon  the  Retina.  — 
The  images  that  make  visual  impressions  are  necessarily  inverted  on  the 
retina;  but  the  cerebral  visual  centre  takes  no  cognizance  of  this,  and 

objects  are  seen  in  their 
actual  position.  It  seems 
almost  absurd  to  enter 
into  a  serious  discussion 
of  this  "fact.  Quoting 
the  words  of  von  Helm- 
holtz,  "our  natural  con- 
sciousness is  completely 
ignorant  even  of  the  ex- 
istence of  the  retina  and 
of  the  formation  of  im- 
ages: how  should  it  know 
anything  of  the  posi- 
tion of  images  formed 
upon  it .''  " 

Field  of  Indirect  Vis- 
ion. —  If  the  eye  is  kept 
fixed  on  a  certain  point, 
and  an  object  is  moved 
from  this  point  as  a 
centre  in  lines  radiating 
in  different  directions 
until  it  passes  from  the  field  of  view,  the  limits  of  indirect  vision  are 
indicated.  Eight  or  ten  such  points  of  limit,  connected  by  a  curved  line, 
give  a  map  of  the  visual  field.  This  may  be  done  roughly  on  a  flat 
surface,  such  as  a  blackboard,  placed  at  a  distance  of  twelve  to  eighteen 
inches  (3  to  4.5  centimeters)  from  the  eye,  or  a  chart  may  be  made  with 
an  instrument  called  the  perimeter,  by  which  the  field  is  marked  on  the 
inner  surface  of  a  hemisphere.  The  field  of  vision  thus  delineated  is 
an  irregular  oval,  extending  from  the  fixed  point  farther  to  the  temporal 
side  than  to  either  the  nasal  side  or  above  and  below.  The  extent  from 
the  fixed  point  is  about  90°  on  the  temporal  side,  and  about  70°  to  the 
nasal  side  and  above  and  below.     The  field  for  white  light  is  larger  than 


Fig.  177.  —  Field  of  vision  of  the  right  eye,  as  projected  by  the 
patient  on  the  inner  surface  of  a  hemisphere,  the  pole  of  which 
forms  the  object  of  regard  —  semidiagrammatic  (Landolt). 

T,  temporal  side ;  A'^,  nasal  side;  H'' boundary  for  white  ;  B, 
boundary  for  blue  ;  R,  boundary  for  red  ;    G,  boundary  for  green. 


BINOCULAR   VISION  69 1 

for  colors,  especially  on  the  nasal  side,  as  is  seen  in  Fig.  177.  The  field 
is  smallest  for  green,  a  little  larger  for  red,  and  is  still  larger  for  blue. 
Investigation  of  the  field  of  indirect  vision  with  the  perimeter  is  useful 
in  ophthalmology ;  but  the  chief  physiological  interest,  as  regards  the 
sensibility  of  the  retina,  is  connected  with  direct  vision. 

Binocular  Vision 

Thus  far  the  mechanism  of  the  eye  and  its  action  as  an  optical 
instrument  have  been  described  for  monocular  vision  only ;  but  it  is 
evident  that  both  eyes  are  habitually  used,  and  that  their  axes  are  prac- 
tically parallel  in  looking  at  distant  objects  and  are  converged  when 
objects  are  approached  to  the  nearest  point  at  which  there  is  distinct 
vision.  In  fact  an  image  is  formed  simultaneously  on  the  retina  of  either 
eye,  but  it  is  nevertheless  appreciated  as  a  unit.  If  the  axis  of  one  eye 
is  slightly  deviated  by  pressure  on  the  globe,  so  that  the  images  are  not 
formed  upon  corresponding  points  in  the  retina  of  either  eye,  vision  is 
more  or  less  indistinct  and  is  double.  In  strabismus,  when  this  condition 
is  recent,  temporary  or  periodical,  as  in  recent  cases  of  paralysis  of  the 
external  rectus  muscle,  when  both  eyes  are  normal,  there  is  double 
vision.  When  the  strabismus  is  permanent  and  has  existed  for  a  long 
time,  double  vision  may  not  be  observed,  unless  the  subject  directs  the 
attention  strongly  to  this  point.  As  but  one  eye  is  capable  of  fixing 
objects  accurately,  images  are  formed  on  the  fovea  of  this  eye  only. 
Images  formed  upon  the  retina  of  the  other  eye  are  indistinct,  and  in 
many  instances  are  habitually  disregarded  ;  so  that  practically  the  sub- 
ject uses  but  one  eye,  and  presents  the  errors  of  appreciation  that  attend 
monocular  vision,  such  as  a  want  of  exact  estimation  of  the  solidity  and 
distance  of  objects.  It  is  stated  as  the  rule  that  when  strabismus  of  long 
standing  is  remedied,  so  far  as  the  axes  of  the  eyes  are  concerned,  by 
an  operation,  binocular  vision  is  not  restored.  This  is  explained  on  the 
supposition  that  the  perceptive  power  of  the  retina  of  the  affected  eye 
has  been  gradually  lost  from  disuse.  In  normal  binocular  vision  the 
images  are  formed  on  the  fovea  centralis  of  either  eye ;  that  is,  on  cor- 
responding points,  which  are,  for  each  eye,  the  centres  of  distinct 
vision.  The  concurrence  of  both  eyes  is  necessary  to  the  exact  appre- 
ciation of  distance  and  form ;  and  when  the  two  images  are  formed  on 
corresponding  points,  the  visual  centre  receives  a  correct  impression  of 
a  single  object.  When  vision  is  perfect,  the  sensation  of  the  situation 
of  any  single  object  is  referred  to  one  and  the  same  point;  and  the 
impression  of  a  double  image  can  not  be  received  unless  the  conditions 
of  vision  are  abnormal. 


692  SPECIAL    SENSES 

Corresponding  Points.  — While  it  is  evident,  after  the  statements  just 
made,  that  images  must  be  formed  on  the  fovea  of  each  eye  in  order 
to  produce  the  effect  of  a  single  object,  it  becomes  important  to  ascer- 
tain how  far  it  is  necessary  that  the  correspondence  of  points  should 
be  carried  out  in  the  retina.  It  is  almost  certain  that  for  absolutely 
perfect  single  vision  with  the  two  eyes,  the  impressions  must  be  made 
on  exactly  corresponding  points,  even  to  the  ultimate  sensitive  elements 
of  the  retina.  It  may  be  assumed,  indeed,  that  each  rod  and  each 
cone  of  one  eye  has  its  corresponding  rod  and  cone  in  the  other,  situated 
at  exactly  the  same  distance  and  in  corresponding  directions  from  the 
visual  axis.  When  the  two  images  of  an  object  are  formed  on  these 
corresponding  points,  they  appear  as  one  ;  but  when  the  images  do  not 
correspond,  the  impression  is  as  though  the  images  were  formed  on 
different  points  in  one  retina,  and  of  necessity  they  appear  double. 

The  effect  of  a  sUght  deviation  from  the  corresponding  points  may 
be  illustrated  by  the  following  experiment :  If  a  small  object,  like  a 
lead-pencil,  held  at  a  distance  of  a  few  inches,  is  fixed  with  the  eyes,  it  is 
seen  distinctly  as  a  single  object.  Holding  another  small  object  in  the 
same  line,  a  few  inches  farther  removed,  when  the  first  is  seen  distinctly, 
the  second  appears  double.  If  the  second  object  is  fixed  with  the  eyes, 
the  first  appears  double.  It  is  evident  here,  that  when  the  axes  of  the 
eyes  bear  on  one  of  these  objects,  the  images  of  the  other  must  be 
formed  at  a  certain  distance  from  the  corresponding  retinal  points. 

The  Horopter.  —  The  above-mentioned  experiment  affords  an  expla- 
nation of  the  horopter.  If  both  eyes  are  fixed  on  a  point  directly  in 
front  and  are  kept  in  this  position,  an  object  moved  to  one  side  or  the 
other,  within  a  certain  area,  may  be  seen  without  any  change  in  the 
direction  of  the  axis  of  vision  ;  but  the  distance  from  the  eye  at  which 
there  is  single  vision  of  this  object  is  fixed,  and  at  any  other  distance 
the  object  appears  double.  The  explanation  of  this  is  that  at  a  certain 
distance  from  the  eye,  the  images  are  formed  on  corresponding  points 
in  the  retina ;  but  at  a  shorter  or  longer  distance,  this  can  not  occur. 
This  illustrates  the  fact  that  there  are  corresponding  points  in  a  large 
part  of  the  sensitive  layer  of  the  retina  as  well  as  in  the  fovea  centralis. 
By  these  experiments  the  following  facts  have  been  ascertained  :  With 
both  eyes  fixed  on  an  object,  another  object  moved  to  one  side  or  the 
other  can  be  seen  distinctly  only  when  it  is  carried  in  a  certain  curved 
line.  On  either  side  of  this  line,  the  object  appears  double.  This  line, 
or  area  —  for  the  line  may  have  any  direction  —  is  called  the  horopter. 
It  was  supposed  at  one  time  to  be  a  regular  cur\'e,  or  a  portion  of  a 
circle  drawn  through  the  fixed  point  and  the  points  of  intersection  of 
the  ravs  of  light  in  each  eve.     Although  it  has  been  ascertained  that 


BINOCULAR   VISION 


693 


the  line  varies  somewhat  from  a  regular  curve,  and  also  varies  in 
different  meridians,  this  is  due  to  differences  in  refraction,  etc.,  and 
the  principle  is  not  altered. 

If  the  visual  areas  of  the  two  retinae  are  superimposed,  the  fixation- 
points  coinciding,  it  becomes  evident  that  a  portion  only  of  the  two  fields 
can  have  corresponding  points.  This  is  the  light  portion  shown  in  Fig. 
178,  which  may  be  called  the  binocular  field  of  vision.  Binocular  vision 
must  be  impossible  in  the  temporal  portion  of  each  visual  area. 

It  is  undoubtedly  true  that  education  and  habit  have  much  to  do  with 
the  correction  of  visual  impressions  and  the  just  appreciation  of  the  size, 
form  and  distance  of  objects.  In  the  remarkable  case  of  Kaspar  Hauser, 
who  is  said  to  have  been  kept  in  total  darkness  and  seclusion  from  the 
age  of  five  months  until  he  was  nearly  seventeen  years  old,  the  appre- 
ciation of  size,  form  and  distance  were  acquired  by  correcting  and 
supplementing  the  sense  of 
sight  by  experience.  This 
boy  at  first  had  no  idea  of 
the  form  of  objects  or  of 
distance,  until  he  had  learned 
by  touch,  by  walking  etc., 
that  certain  objects  were 
round  and  others  were  square, 
and  had  actually  traversed  the 
distance  from  one  object  to 
another.  At  first  all  objects 
appeared  as  if  painted  upon 
a   screen.        Such    points    as 

these  it  would  be  impossible  to  observe  accurately  in  infants  ;  but  young 
children  often  grasp  at  distant  objects,  apparently  under  the  impression 
that  they  are  within  reach.  It  must  be  admitted,  however,  that  the 
account  of  the  case  of  Kaspar  Hauser  is  rather  indefinite ;  but  it  is 
certain  that  even  in  the  adult,  education  and  habit  greatly  improve  the 
faculty  of  estimating  distances. 

Careful  observations  leave  no  doubt  of  the  fact  that  monocular  vision 
is  incomplete  and  inaccurate,  and  that  it  is  only  when  two  images  are 
formed,  one  upon  either  retina,  that  vision  is  perfect.  The  sum  of 
actual  knowledge  on  this  important  point  is  expressed  in  the  follow- 
ing quotation  from  Giraud-Teulon  :  — 

"  Monocular  vision  only  indicates  to  us  immediately,  visual  direction, 
and  not  precise  locality.  At  whatever  distance  a  luminous  point  may  be 
situated  in  the  line  of  direction,  it  forms  its  image  upon  the  same  point 
in  the  retina. 


Fig.  178.  —  Binocular  field  of  vision  (Forster). 
F,  fixation-point;  B,  B,  blind  spots. 


694  SPECIAL    SENSES 

"  In  the  physiological  action  of  a  single  eye,  in  order  to  arrive  at  an 
idea  of  the  distance  of  a  point  in  a  definite  direction,  we  have  only  the 
following  elements :  — 

"  I.    The  consciousness  of  an  effort  of  accommodation. 

"  2.    Our  own  movement  in  its  relations  to  the  point  observed. 

"  3.  Facts  brought  to  bear  from  recollection,  education,  our  acquired 
knowledge  with  regard  to  the  form  and  size  of  objects :  in  a  word,  ex- 
perience. 

"4.    The  geometric  perspective  of  form  and  position. 

"  5.    Aerial  perspective. 

"All  these  are  elements  wanting  in  precision  and  leaving  the  prob- 
lem without  a  decisive  solution. 

"  And,  indeed  :  — 

"  We  place  before  one  of  our  eyes,  the  other  being  closed,  the  exca- 
vated mould  of  a  medallion  :  we  do  not  hesitate,  after  a  few  seconds,  to 
mistake  it  for  the  relief  of  the  medallion.  This  illusion  ceases  at  the 
instant  that  both  eyes  are  opened. 

"  Or  again  :  — • 

"A  miniature,  a  photograph,  a  picture,  produces  for  a  single  eye  a 
perfect  illusion ;  but  if  both  eyes  are  open,  the  picture  becomes  flat,  the 
prominences  and  the  depressions  are  effaced. 

"  We  may  repeat  the  following  experiment  described  by  Malebranche : 
'  Suspend  by  a  thread  a  ring,  the  opening  of  which  is  not  directed  toward 
us  ;  step  back  two  or  three  paces  ;  take  in  the  hand  a  stick  curved  at  the 
end ;  then,  closing  one  eye  with  the  hand,  endeavor  to  insert  the  curved 
end  of  the  stick  within  the  ring,  and  we  shall  be  surprised  at  being  unable 
to  do  in  a  hundred  trials  what  we  should  believe  to  be  very  easy.  If, 
indeed,  we  abandon  the  stick  and  endeavor  to  pass  one  of  the  fingers 
through  the  ring,  we  shall  experience  a  certain  degree  of  difficulty, 
although  it  is  very  near.  This  difficulty  ceases  at  the  instant  that  both 
eyes  are  opened. 

"  As  regards  precision,  exactitude  of  information  concerning  the 
relative  distance  of  objects,  that  is  to  say,  the  idea  of  the  third  dimen- 
sion, or  of  depth,  there  is  then  a  notable  difference  between  binocular 
vision  and  that  which  is  obtained  by  means  of  one  eye  alone." 

It  is  evident  that  an  accurate  idea  of  the  distance  of  near 
objects  can  not  be  obtained  except  by  the  use  of  both  eyes,  and  this 
fact  will  partly  explain  the  errors  of  monocular  vision  in  looking  with 
one  eye  at  objects  in  relief  ;  for  under  these  conditions  it  is  impossible  to 
determine  with  accuracy  whether  the  points  in  relief  are  nearer  or  farther 
from  the  eye  than  the  plane  surface.  This  will  not  fully  explain,  how- 
ever, the  idea  of  solidity  of  objects,  which  is  obtained  by  the  use  of  both 


DURATION    OF    LUMINOUS    IMPRESSIONS  695 

eyes;  for  the  estimation  of  distance  is  obtained  by  bringing  the  axes  of 
both  eyes  to  bear  on  a  single  object,  be  it  near  or  remote.  The  fact  is  — 
as  was  distinctly  stated  by  Galen  in  the  second  century  —  that  in  look- 
ing at  any  solid  object  not  so  far  removed  as  to  render  the  visual  axes 
practically  parallel,  a  portion  of  the  surface  seen  with  the  right  eye  is 
not  seen  with  the  left  eye,  and  vice  veisd.  The  two  impressions,  there- 
fore, are  not  identical  for  each  retina  ;  the  image  on  the  left  retina  includ- 
ing a  portion  of  the  left  side  of  the  object,  not  seen  with  the  right  eye,  the 
right  image  in  the  same  way  including  a  portion  of  the  right  surface,  not 
seen  with  the  left  eye.  These  slightly  dissimilar  impressions  are  fused  and 
produce  the  impression  of  a  single  image,  when  vision  is  normal ;  and 
this  gives  the  idea  of  relief  or  solidity  and  an  exact  appreciation  of  the 
form  of  objects,  when  they  are  not  too  remote. 

Although  an  opposite  opinion  is  held  by  some  experimenters,  Helm- 
holtz,  with  many  others,  has  stated  that  when  one  color  is  seen  with  one 
eye  and  another  color,  with  the  other  eye,  in  the  stereoscope,  the  im- 
pression is  not  of  a  single  color  resulting  from  the  combination  of  the 
two.  It  is  true  that  there  is  an  imperfect  mingling  of  the  two  colors, 
but  this  is  different  from  the  resulting  color  produced  by  the  actual 
fusion,  of  the  two.  There  is,  in  other  words,  a  sort  of  confusion  of 
colors,  without  the  complete  combination  observed  in  ordinary  experi- 
ments. One  additional  point  of  importance,  however,  is  that  the  binoc- 
ular fusion  of  two  pictures,  unequally  illuminated  or  of  different  colors, 
produces  a  single  image  of  a  peculiar  lustre,  even  when  both  surfaces 
are  dull.  This  may  be  shown  by  making  a  stereoscopic  combination  of 
images  of  crystals,  one  with  black  lines  on  a  white  ground,  and  the  other 
with  white  lines  on  a  black  ground.  The  resulting  image  has  then  the 
appearance  of  dark  brilliant  crystals,  like  graphite. 

Duration  of  Liunijioics  hnpressions  {^After-Images\  —  The  time  re- 
quired for  a  single  visual  stimulation  of  the  retina  is  short.  The  letters 
on  a  printed  page  are  distinctly  seen  when  illuminated  by  an  electric 
spark,  the  duration  of  which  is  not  more  than  forty-billionths  of  a  second 
(Rood).  An  impression  made  on  the  retina,  however,  endures  for  a 
length  of  time  that  bears  a  certain  relation  to  the  intensity  of  the  lumi- 
nous excitation.  If  the  eyes  are  closed  after  looking  steadily  at  a  bright 
object,  the  object  is  more  or  less  distinctly  seen  after  the  rays  have 
ceased  to  pass  to  the  eye  and  the  image  fades  away  gradually.  When 
there  is  a  rapid  succession  of  images,  they  may  be  fused  into  one,  as 
the  spokes  of  a  rapidly  revolving  wheel  are  indistinct  and  produce  a 
single  impression.  This  is  due  to  the  persistence  of  the  successive 
retinal  impressions  ;  for  if  a  revolving  wheel  or  even  a  falling  body  is 
illuminated  for  the  brief  duration  of  an  electric  spark,  it  appears  to  be 


696  SPECIAL    SENSES 

stationary,  as  the  period  of  time  necessary  for  distinct  vision  and  the 
duration  of  the  illumination  are  so  short  that  there  is  no  time  for  any 
appreciable  movement  of  the  object.  The  familiar  experiments  made 
with  revolving  disks  illustrate  these  points.  In  a  disk  marked  with 
alternate  radiating  lines  of  black  and  white,  the  rays  become  indistin- 
guishable during  rapid  revolution,  and  the  disk  appears  of  a  uniform 
color,  such  as  would  be  produced  by  a  combination  of  the  black  and 
white.  The  effects  of  an  artificial  combination  of  colors  may  be  pro- 
duced in  this  way,  the  resultant  color  appearing  as  if  the  individual 
colors  had  been  ground  together.  The  duration  of  retinal  impressions 
varies  considerably  for  the  different  colors.  According  to  Emsmann, 
the  duration  for  yellow  is  0.25  of  a  second ;  for  white,  0.25  of  a  second; 
for  red,  0.22  of  a  second ;  and  for  blue,  0.2 1  of  a  second. 

The  impressions  that  remain  on  the  retina  after  an  object  has  been 
looked  at  steadily  are  called  after-images.  When  these  are  bright  and 
of  the  same  character  as  the  object,  they  are  called  positive  after-images. 
When  the  stimulation  of  the  retina  has  been  powerful  and  prolonged, 
the  after-image  frequently  is  dark.  Such  images  are  called  negative 
after-images. 

It  is  unnecessary  to  describe  further  in  detail  the  well-known  phe- 
nomena which  illustrate  the  point  under  consideration.  The  circle  of 
light  produced  by  rapidly  revolving  a  burning  coal,  the  track  of  a  meteor 
and  other  illustrations,  are  sufficiently  familiar,  as  well  as  many  scien- 
tific toys  producing  optical  illusions  of  various  kinds. 

Ir-radiation.  —  It  has  been  observed  that  luminous  impressions  are 
not  always  confined  to  the  elements  of  the  retina  directly  involved,  but 
are  sometimes  propagated  to  those  immediately  adjacent.  This  gives 
to  objects  a  certain  degree  of  amplification,  which  usually  is  in  propor- 
tion to  their  brightness.  An  illustration  of  this  is  afforded  by  the 
simple  experiment  of  looking  at  two  circles,  one  black  on  a  white 
ground,  and  the  other  white  on  a  black  ground.  Although  the  di- 
mensions of  the  two  circles  are  identical,  the  irradiation  of  rays  from 
the  white  circle  makes  this  appear  the  larger.  In  a  circle  with  one 
half  black  and  the  other  white,  the  white  portion  will  appear  larger,  for 
the  same  reason.  These  phenomena  are  due  to  what  has  been  called 
irradiation ;  and  their  explanation  is  very  simple.  It  is  probable  that 
luminous  impressions  are  never  confined  absolutely  to  those  parts  of  the 
retina  on  which  the  rays  of  light  directly  impinge,  but  that  the  sensitive 
elements  immediately  contiguous  are  always  more  or  less  involved.  In 
looking  at  powerfully-illuminated  objects,  the  irradiation  is  considerable, 
as  compared  with  objects  which  send  fewer  luminous  rays  to  the  eye. 

In  experiments  analogous  to  those  just  described,  made  with  strongly 


IRRADIATION  697 

colored  objects,  it  has  been  observed  that  the  border  of  irradiation  takes 
a  color  complementary  to  that  of  the  object  itself.  This  is  particularly 
well  marked  when  the  objects  are  steadily  looked  at  for  some  time. 
Illustrations  of  this  point  also  are  very  simple.  In  looking  steadily  at 
a  red  spot  or  figure  on  a  white  ground,  a  faint  areola  of  a  pale  green 
soon  appears  surrounding  the  red  object ;  or  if  the  image  is  yellow,  the 
areola  will  appear  pale  blue.  These  appearances  are  called  accidental 
areolae. 


CHAPTER   XXVIII 

MOVEMENTS      OF     THE     EYEBALL  — PARTS     FOR      PROTECTION     OF 

THE    EYE 

Action  of  the  recti  muscles  —  Action  of  the  oblique  muscles — Associated  action  of  the  muscles 
of  the  eyeball  —  Centres  for  vision  —  Perception  of  colors  —  Parts  for  the  protection  of  the 
eyeball  —  Muscles  that  open  and  close  the  eyelids  —  Conjunctival  mucous  membrane  — 
The  lachr)-mal  apparatus — The  tears. 

The  eyeball  nearly  fills  the  cavity  of  the  orbit,  resting  by  its  poste- 
rior portion  upon  a  bed  of  adipose  tissue,  which  is  never  absent,  even  in 
extreme  emaciation.  External  to  the  sclerotic,  is  a  fibrous  membrane, 
the  tunica  vaginalis  oculi,  or  capsule  of  Tenon,  which  is  useful  in  main- 
taining the  equilibrium  of  the  globe.  This  membrane  surrounds  the 
posterior  two-thirds  of  the  globe  and  is  loosely  attached  to  the  sclerotic. 
It  is  perforated  by  the  optic  nen'e  posteriorly,  and  by  the  tendons  of 
the  recti  and  oblique  muscles  of  the  eyeball  in  front,  being  reflected 
over  these  muscles.  It  also  is  continuous  with  the  palpebral  ligaments 
and  is  attached,  by  two  tendinous  bands,  to  the  border  of  the  orbit  at- 
the  internal  and  the  external  angles  of  the  hds. 

The  muscles  that  move  the  globe  are  six  in  number  for  either  eye. 
These  are  the  external  and  internal  recti,  the  superior  and  inferior  recti 
and  the  two  oblique  muscles.  The  four  recti  and  the  superior  oblique 
arise  posteriorly  from  the  apex  of  the  orbit.  The  recti  pass  directly 
forward  by  the  sides  of  the  globe  and  are  inserted  by  short  tendinous 
bands  into  the  sclerotic,  at  a  distance  of  one-fourth  to  one-third  of  an 
inch  (6.4  to  8.5  millimeters)  from  the  margin  of  the  cornea.  The  supe- 
rior oblique,  or  trochlearis  muscle  passes  along  the  upper  and  inner  wall 
of  the  orbit  to  a  point  near  the  inner  angle.  It  here  presents  a  rounded 
tendon,  which  passes  through  a  ring,  or  pulley,  of  fibro-cartilage ;  and 
it  is  from  this  point  that  its  action  is  exerted  on  the  globe.  From  the 
pulley,  or  trochlea,  the  tendon  becomes  flattened,  passes  outward  and 
backward  beneath  the  superior  rectus,  and  is  inserted  into  the  sclerotic 
about  midway  between  the  superior  and  the  external  rectus  and  just 
behind  the  equator  of  the  globe.  The  inferior  oblique  muscle  arises 
just  within  the  anterior  margin  of  the  orbit  near  the  inner  angle  of  the 
eye  and  passes  around  the  anterior  portion  of  the  globe  beneath  the 
inferior  rectus  and  between  the  external  rectus  and  the  eveball,  taking  a 
direction  outward  and  slightly  backward.     Its  tendon  is  inserted  into 

69S 


MOVEMENTS    OF   THE    EYEBALL 


699 


the  sclerotic  a  little  below  the  insertion  of  the  superior  oblique.     The 
general  arrangement  of  these  muscles  is  shown  in  Fig.  179. 

The  movements  of  the  eyeball  are  easily  understood  from  a  study  of 
the  associated  movements  of  the  muscles  just  enumerated,  at  least  so 
far  as  is  necessary  to  the  comprehension  of  the  mechanism  by  which 
the  eyes  are  directed  toward  any  particular  object.  The  centre  of 
distinct  vision  is  in  the  fovea;  and  it  is  evident  that  in  order  to  see  any 
object  distinctly,  it  is  necessary  to  bring  it  within  the  axes  of  vision  of 
both  eyes.  As  the  globe  is  so  balanced  in  the  orbit  as  to  be  capable 
of  rotation,  within  certain  Hmits,  in  every  direction,  it  is  necessary  only  to 


Fig.  179.  —  Muscles  of  the  eyeball  (Sappey). 

I,  attachment  of  the  tendon  connected  with  the  inferior  rectus,  internal  rectus  and  external  rectus ; 

2,  external  rectus,  divided  and  turned  downward,  to  expose  the  inferior  rectus;  3,  internal  rectus ; 
4,  inferior  rectus  ;  5,  superior  rectus  ;  6,  superior  oblique  ;  7,  pulley  and  reflected  portion  of  the  superior 
oblique ;  8,  inferior  oblique ;  9,  levator  palpebri  superioris ;  10,  10,  middle  portion  of  the  levator 
palpebri  superioris;   11,  optic  nerve. 

note  the  exact  mode  of  action  of  each  of  the  muscles,  in  order  to  com- 
prehend how  the  different  movements  are  accomplished ;  and  it  is 
sufficient  for  practical  purposes  to  admit  that  approximately  there  is  a 
common  axis  of  rotation  for  each  pair  of  muscles. 

Under  ordinar)^  conditions  in  the  human  subject,  the  action  of  the 
six  ocular  muscles  is  confined  to  movements  of  rotation  and  torsion  of 
the  globe.  It  is  said  that  in  the  human  subject  there  is  no  such  thing 
as  protrusion  of  the  eye  from  general  relaxation  of  these  muscles,  and 
that  it  is  impossible,  by  a  combined  action  of  the  four  recti  muscles,  to 
retract  the  globe  in  the  orbit ;  but  those  who  have  operated  on  the  eyes 
assert   that    this  statement  is  erroneous,  and  that  the  globe  is  almost 


70O  SPECIAL   SENSES 

always  suddenly  and  powerfully  drawn  within  the  orbit  when  a  painful 
impression  is  made  on  the  cornea.  This  is  a  matter  of  common  obser- 
vation by  ophthalmic  surgeons. 

The  extent  to  which  the  line  of  vision  may  be  turned  by  a  voluntary 
effort  varies  in  different  individuals,  even  when  the  eyes  are  normal. 
In  myopic  eyes,  the  centre  of  rotation  is  deeper  in  the  orbit  than  normal 
and  the  extent  of  the  possible  deviation  of  the  visual  line  is  correspond- 
ingly diminished.  Helmholtz  stated  that  in  his  own  person,  with  the 
greatest  effort  that  he  was  capable  of  making,  he  could  move  the  line  of 
vision  in  the  horizontal  plane  to  the  extent  of  about  fifty  degrees,  and 
in  the  vertical  plane,  about  forty-five  degrees ;  but  he  added  that  these 
extreme  rotations  were  very  forced,  and  that  they  could  not  be  sustained 
for  any  considerable  length  of  time.  It  is  probable  that  the  eyeball  is 
seldom  moved  in  an  angle  of  forty-five  degrees,  the  direction  of  the 
visual  line  being  more  easily  accomplished  by  movements  of  the  head. 

Action  of  the  Recti  Muscles.  —  The  internal  and  external  recti  rotate 
the  globe  on  a  vertical  axis  that  is  perpendicular  to  the  axis  of  the  eye. 
The  isolated  action  of  these  muscles,  particularly  of  the  external  rectus, 
is  often  illustrated  in  certain  forms  of  paralysis,  which  have  been  alluded 
to  in  connection  with  the  history  of  the  cranial  nerves. 

The  superior  and  inferior  recti  rotate  the  globe  on  a  horizontal  axis, 
which  is  not  at  right  angles  with  the  axis  of  the  eye  but  is  incHned  from 
the  nasal  side  slightly  backward.  The  line  that  serves  as  the  axis  of 
rotation  for  these  muscles  forms  an  angle  of  about  seventy  degrees  with 
the  axis  of  the  globe  ;  and  as  a  consequence,  their  action  is  not  so  simple 
as  that  of  the  internal  and  external  recti.  The  insertion  of  the  superior 
rectrus  is  such,  that  when  it  contracts,  the  pupil  is  directed  upward  and 
inward,  the  inferior  rectus  directing  the  pupil  downward  and  inward. 

The  above  represents  the  isolated  action  of  each  pair  of  recti 
muscles ;  but  it  is  easy  to  see  how,  without  necessarily  involving  the 
action  of  the  oblique  muscles,  the  globe  may  be  made  to  perform  a  great 
variety  of  rotations  and  the  line  of  vision  may  be  turned  in  nearly  every 
direction  by  the  action  of  the  recti  muscles  alone. 

Action  of  the  Oblique  Muscles.  — It  is  sufficient  for  all  practical  pur- 
poses to  assume  that  the  superior  and  the  inferior  oblique  muscles  act 
as  direct  antagonists  to  each  other.  The  most  exact  measurements 
show  that  the  axis  of  rotation  for  these  muscles  is  horizontal  and  has 
an  oblique  direction  from  before  backward  and  from  without  inward. 
The  angle  formed  by  the  axis  of  rotation  of  the  oblique  muscles  with 
the  axis  of  the  globe  is  thirty-five  degrees ;  and  the  angle  between  the 
axis  of  the  oblique  muscles  and  the  axis  of  the  superior  and  inferior 
recti  muscles  is  seventy-five  degrees. 


MOVE.AIENTS    OF    THE    EYEBALL 


701 


Given  the  direction  of  the  axis  of  rotation  and  the  direction  of  the 
superior  oblique  muscle,  it  is  easy  to  understand  the  effects  of  its  con- 
traction. As  this  muscle,  passing  obUquely  backward  and  forward  over 
the  globe,  acts  from  the  pulley  near  the  inner  angle  of  the  eye  to  its  in- 
sertion just  behind  the  anterior  half  of  the  globe  on  its  external  and 
superior  surface  (7,  Fig.  179  J,  it  must  rotate  the  globe  so  as  to  direct 
the  pupil  downward  and  outward. 

The  inferior  oblique,  passing 
outward  and  slightly  backward 
under  the  globe,  acts  from  its  origin 
at  the  margin  of  the  orbit  near  the 
inner  angle  of  the  eye  to  its  inser- 
tion, which  is  just  below  the  inser- 
tion of  the  superior  oblique.  This 
muscle  rotates  the  globe  so  as  to 
direct  the  pupil  upward  and  out- 
ward. 

The  action  of  the  oblique  mus- 
cles is  specially  connected  with  the 
movements  of  torsion  of  the  globe. 
It  is  necessarv  to  distinct  single  vis- 
ion  with  both  eyes,  that  the  images 
should  be  formed  on  corresponding 
points  on  the  retina,  and  that  they 
should  bear,  for  the  two  eyes,  cor- 
responding relations  to  the  perpen- 
dicular. Thus  it  is  that  when  the 
head  is  inchned  to  one  side,  the  eyes 
are   twisted   on   an    oblique    antero- 


rior  and  the  inferior  recti  and  the  axes  of  the 
oblique  muscles. 


Fig.  180.  —  Diagram  illustrating'  the  action  of 
the  muscles  of  the  eyeball  (Fick). 

The  heavy  lines  represent  the  muscles  of  the 
posterior     axis;      as     can     be     readily    eyeball,  and  the  fine  hnes,  the  axes  of  the  supe- 

seen  by  obsen'ing  little  spots  on  the 
iris  during  these  movements. 

The  superior  oblique  muscle  is  supplied  by  a  single  ner\'e,  the 
patheticus.  When  this  muscle  is  paralyzed,  the  inferior  obHque  acts 
without  its  antagonist,  and  the  eyeball  is  immovable  so  far  as  the 
twisting  of  the  globe  is  concerned.  When  the  head  is  moved  toward 
the  shoulder,  the  globe  can  not  rotate  to  maintain  a  position  correspond- 
ing to  that  of  the  other  eye  and  there  is  double  vision. 

Associated  Action  of  the  Muscles  of  the  Eyeball.  —  It  is  almost  un- 
necessary to  add,  after  the  description  just  given  of  the  actions  of  the 
individual  muscles  of  the  globe,  that  their  contractions  may  be  asso- 
ciated so   as   to  produce   a  great  variety  of  movements.     There  is  no 


702  SPECIAL    SENSES 

consciousness,  under  ordinary  conditions,  of  the  muscular  action  by 
which  the  globe  is  rotated  and  twisted  in  various  directions,  except 
that  by  an  effort  of  the  will  the  line  of  vision  is  directed  toward  differ- 
ent objects.  By  a  strong  effort  the  axes  of  the  eyes  may  be  converged 
by  contracting  both  internal  recti,  and  some  persons  can  produce 
extreme  divergence  by  using  both  external  recti ;  but  this  is  abnormal. 

In  looking  at  distant  objects  the  axes  of  vision  are  practically  paral- 
lel. In  looking  at  near  objects  the  effort  of  accommodation  is  attended 
with  the  degree  of  convergence  necessary  to  bring  the  visual  axes  to 
bear  on  identical  points.  In  looking  around  at  different  objects  the 
head  is  moved  more  or  less  and  the  globes  are  rotated  in  various  direc- 
tions. In  the  movements  of  the  globes  vertically  the  axes  are  kept 
parallel,  or  at  the  proper  angle,  by  the  internal  and  external  recti,  and 
the  superior  and  inferior  recti  on  the  two  sides  act  together.  In  rotat- 
ing the  globe  from  one  side  to  the  other  on  a  vertical  axis,  the  external 
rectus  on  one  side  acts  with  the  internal  rectus  on  the  other.  In  the 
movements  of  torsion  on  an  antero-posterior  axis,  there  must  be  an 
associated  action  of  the  oblique  muscles  and  the  recti. 

An  important  point,  not  to  be  lost  sight  of  in  the  study  of  the  asso- 
ciated action  of  the  muscles  of  the  globe,  relates  to  the  associated  move- 
ments of  the  two  eyes.  Perfect  binocular  vision  is  possible  only  when 
impressions  are  made  on  corresponding  points  in  the  retina  of  each  eye. 
If  one  eye  is  deviated  in  the  horizontal  plane,  the  points  no  longer  cor- 
respond and  there  is  double  vision,  the  same  as  if  two  impressions  were 
made  on  one  retina;  for  when  the  impressions  exactly  correspond,  the 
two  retinae  act  practically  as  a  single  organ.  The  same  is  true  in  devia- 
tion of  the  globe  in  the  vertical  plane.  If  it  be  supposed,  for  the  sake  of 
argument,  that  the  retina  is  square,  it  is  evident  that  a  torsion  or  twist- 
ing of  one  globe  on  an  antero-posterior  axis  must  be  attended  with  an 
analogous  movement  of  the  other  globe  in  order  to  bring  the  visual  rays 
to  bear  on  the  corresponding  points ;  in  other  words,  the  obliquity  of 
the  assumed  square  of  the  retina  must  be  exactly  the  same  for  the  two 
eyes  or  the  coincidence  of  the  corresponding  points  would  be  disturbed 
and  there  would  be  double  vision.  Deviation  of  one  eye  in  the  horizon- 
tal or  the  vertical  plane  disturbs  the  relation  of  the  corresponding 
points,  and  a  deviation  from  exact  coincidence  of  action  in  torsion  of 
the  globes,  twists,  as  it  were,  the  corresponding  points,  so  that  their  rela- 
tion is  also  disturbed.  It  is  evident,  therefore,  that  the  varied  move- 
ments of  the  globes,  by  the  combined  action  of  the  recti  and  oblique 
muscles,  must  correspond  for  either  eye,  in  the  movements  of  torsion  on 
an  antero-posterior  axis  as  well  as  in  movements  of  rotation  on  the 
horizontal  or  the  vertical  axis. 


CENTRES    FOR   VISION  703 

Centres  for  Vision 

Experiments  have  been  made  on  the  lower  animals  by  Ferrier, 
Munk,  Exner  and  many  others,  with  the  object  of  locating  in  the 
cerebrum  a  centre  for  vision.  It  is  important,  however,  to  compare 
the  results  of  such  experiments  with  cases  of  cerebral  lesions  in  the 
human  subject.  As  the  general  result  of  experiments,  both  on  dogs 
and  monkeys,  and  of  pathological  observations,  the  present  opinion  is 
that  the  centres  for  vision  are  in  the  occipital  lobes.  The  convolutions 
immediately  above  and  below  the  calcarine  fissure,  on  the  mesial  surface 
of  the  cerebrum  (Figs.  134  and  140,  pages  566  and  570),  seem  to  be  the 
cerebral  terminations  of  fibres  that  are  continuous  with  the  optic  tracts. 
These  fibres  are  not  crossed  in  the  cerebrum,  but  the  conductors  decus- 
sate at  the  optic  chiasm  as  they  pass  to  the  eyes.  Cases  have  been 
observed  in  the  human  subject  in  which  lesion  of  these  parts  on  one 
side  has  been  followed  by  loss  of  vision  in  one  lateral  half  of  the  retina 
in  either  eye.  This  condition  is  called  hemianopsia.  In  these  instances 
the  blindness  is  confined  to  the  temporal  side  of  the  retina  correspond- 
ing to  the  lesion  and  the  nasal  side  of  the  retina  of  the  opposite  eye. 
This  is  called  lateral  homonymous  hemianopsia,  and  this  is  the  form 
that  occurs  in  unilateral  cerebral  lesion.  In  dogs  and  in  monkeys,  de- 
struction of  both  occipital  lobes  and  both  angular  convolutions  produces 
total  and  permanent  blindness  of  both  eyes. 

The  complete  and  perfect  perception  of  visual  impressions  involves 
intellectual  action  connected  with  the  simple  visual  sense.  An  individ- 
ual may  see  objects  and  yet  not  be  able  to  appreciate  their  significance. 
In  the  condition  known  as  word-blindness,  words  are  seen,  but  they  con- 
vey no  idea.  A  dog  with  part  of  the  occipital  lobes  removed  may  see 
objects  such  as  food,  but  does  not  recognize  their  character.  There  are, 
indeed,  psychical  centres,  which  elaborate  the  impressions  received  by 
the  simple  visual  centres. 

What  seems  at  present  to  be  the  most  rational  view  to  take  in  regard 
to  the  location  and  action  of  the  visual  centres  is  the  following :  — 

1.  The  centre  for  simple  visual  impressions  is  on  the  inner  surface 
of  the  cerebrum,  on  either  side  of  the  calcarine  fissure,  between  the 
cuneus  and  the  lobulus  lingualis.  This  part  is  connected  with  homony- 
mous halves  of  the  retina  of  either  eye  —  the  temporal  half  of  the  retina 
of  the  same  side  and  the  nasal  half  of  the  retina  of  the  opposite  side. 
The  part  above  the  calcarine  fissure  is  connected  with  the  upper  portion 
of  the  retina,  and  the  part  below,  with  the  lower  portion  of  the  retina. 

2.  The  action  of  the  cortex  of  the  convex  surface  of  the  temporal 
lobe — ^perhaps  only  on  the  left  side  —  is  necessary  for  full  visual  per- 


704  SPECIAL    SENSES 

ception  and  recognition  and  for  the  production  of  visual  memories. 
This  may  be  called  the  psychical  visual  centre.  Psychical  blindness 
may  exist,  indeed,  without  loss  of  visual  sensation. 

3.  The  angular  convolution  is  not  a  visual  centre,  as  was  claimed  by 
Ferrier.  It  is  related  to  visual  perception  only  in  so  far  as  it  affects 
"  the  memories  of  the  appearance  of  written  or  printed  words  "  (Hun). 
In  cases  of  word-blindness  lesions  have  been  found  in  this  situation. 

Perception  of  Colors.  —  By  far  the  most  obscure  question  connected 
with  vision  relates  to  the  perception  of  colors.  In  treatises  on  physi- 
ology, the  difficulty  of  this  subject  is  well  illustrated  in  the  indefinite 
manner  in  which  it  is  discussed  ;  and  I  am  tempted  to  dismiss  the 
question  with  the  remark  —  which  appeared  in  earlier  writings  on 
vision — that  "nothing  is  known  of  the  mechanism  of  color-percep- 
tion." It  is  well  known,  however,  that  white  light  may  be  decomposed 
into  the  colors  of  the  spectrum  and  that  different  colors  have  different 
—  often  widely  different  —  wave-lengths.  If  a  beam  of  white  light, 
with  a  certain  wave-length,  impinges  on  the  retina,  it  produces  a  certain 
impression  that  is  appreciated  by  the  visual  centres.  If,  now,  beams  of 
light,  different  in  color  and  with  different  wave-lengths,  reach  the  retina, 
they  must  produce  different  impressions  and  a  different  impression  for 
each  color  and  combination  of  colors.  When  these  impressions  have 
been  frequently  repeated  and  the  visual  centres  have,  so  to  speak, 
become  educated,  different  colors  are  recognized.  It  seems  a  ques- 
tion, indeed,  if  there  be  anything  more  than  this  in  color-perception. 
Certain  it  is,  that  if  the  waves  that  make  the  impression  on  the  retina 
which  gives  the  sensation  of  light  and  color  are  perceived  in  a  certain 
way,  differences  in  wave-lengths  must  involve  differences  in  the  nature 
of  the  impressions,  corresponding  with  necessary  differences  in  the  na- 
ture of  the  stimuli.  It  almost  seems  better  to  take  this  view,  however 
unsatisfactory  it  may  appear,  than  to  enter  into  a  discussion  that  is  not 
likely  to  lead  to  positive  conclusions.  In  olfaction,  of  course  different 
odorous  impressions  are  made  by  different  substances  composed  of  dif- 
ferent numbers  of  molecules.  It  has  been  found  that  the  odor  of  ethyl 
mercaptan  is  recognizable  in  a  dilution  of  one  part  in  fifty  billions  of  air. 
If  such  infinitesimally  small  particles  can  make  a  decided  and  peculiar 
impression  on  the  nerves  of  smell,  it  is  not  unreasonable  to  suppose  that 
the  parts  concerned  in  vision  may  appreciate  the  difference  between  red 
and  violet,  with  392,000,000,000,000  and  757,000,000,000,000  vibrations 
in  a  second  respectively.  There  are,  indeed,  quite  as  wide  differences, 
as  regards  number  of  molecules,  between  red  and  violet  as  there  is 
between  ethyl  mercaptan  (CgHgSH)  and  benzene  sulphide  (C6H5)2  and 
between  many  other  distinctively  odorous  substances. 


PERCEPTION    OE    COLORS  705 

Color-blindness  is  an  abnormal  condition  in  which  the  power  of  dis- 
crimination between  different  colors  is  impaired  or  lost.  Some  persons 
are  insensible  to  all  colors  and  others  to  certain  colors  only.  Red-green 
bUndness  is  the  most  common  form.  Cases  of  disease  of  the  brain,  in 
which  ordinary  visual  perception  remains  while  the  sense  of  color  is 
absent,  seem  to  show  that  parts  of  the  visual  centres  are  specially  con- 
cerned in  the  appreciation  of  colors.  That  this  defect,  however,  may 
depend  on  the  retina,  is  shown  in  cases  in  which  one  eye  is  color-blind 
while  the  other  is  normal.  There  are  cases,  also,  in  which  these  defects 
seem  to  be  due  exclusively  to  atrophy  of  the  disk  and  contraction  of 
the  visual  field,  the  acuteness  of  vision  not  being  much  impaired ;  but 
unfortunately  even  these  striking  pathological  conditions  throw  little 
light  on  the  physiology  of  normal  color-perception. 

Parts  for  the  Protection  of  the  Eyeball 

The  orbit,  formed  by  the  union  of  certain  of  the  bones  of  the  face, 
receives  the  eyeball,  the  ocular  muscles,  the  muscle  of  the  upper  lid, 
bloodvessels,  nerves  and  a  part  of  the  lachrymal  apparatus.  It  con- 
tains, also,  a  certain  quantity  of  adipose  tissue,  which  latter  never  dis- 
appears, even  in  extreme  marasmus.  The  bony  walls  of  this  ca\'ity 
protect  the  globe  and  lodge  the  parts  enumerated  above.  The  internal, 
or  nasal  wall  of  the  orbit  projects  considerably  beyond  the  external 
wall,  so  that  the  extent  of  vision  is  greater  in  an  outward  than  in  an  in- 
ward direction.  As  the  globe  is  more  exposed  to  accidental  injury  from 
an  outward  direction,  the  external  wall  of  the  orbit  is  strong,  while  the 
bones  that  form  its  internal  wall  are  comparatively  fragile.  The  upper 
border  of  the  orbit  (the  superciHary  ridge)  is  proxided  with  short  stiff 
hairs  (the  eyebrows)  which  serve  to  shade  the  eye  from  excessive  light 
and  to  protect  the  eyelids  from  perspiration  from  the  forehead. 

The  eyelids  are  covered  with  a  thin  integument  and  are  lined  with 
the  conjunctival  mucous  membrane.  The  subcutaneous  connective  tissue 
is  thin  and  loose  and  is  free  from  fat.  The  skin  presents  a  large  number 
of  short  papillae  and  small  sudoriparous  glands.  At  the  borders  of  the 
lids,  are  short,  stiff,  curved  hairs  arranged  in  two  or  more  rows,  called 
the  eyelashes,  or  cilia.  Those  of  the  upper  lid  are  in  greater  number 
and  longer  than  the  lower  cilia.  The  curve  of  the  lashes  is  from  the 
eyeball.  They  serve  to  protect  the  globe  from  dust,  and  to  a  certain 
extent  to  shade  the  eye. 

The  tarsal  cartilages  are  small,  elongated,  semilunar  plates,  extend- 
ing from  the  edges  of  the  lids  toward  the  margin  of  the  orbit,  between 
the  skin  and  the  mucous  mxembrane.     Their   leng-th  is  about  an  inch 


706  SPECIAL    SENSES 

(25.4  millimeters).  The  central  portion  of  the  upper  cartilage  is  about 
one-third  of  an  inch  (8.5  millimeters)  broad,  and  the  corresponding  part 
of  the  lower  cartilage  measures  about  one-sixth  of  an  inch  (4.2  milli- 
meters). At  the  inner  canthus,  or  angle  of  the  eye,  is  a  small  delicate 
ligament,  or  tendon,  the  tendo  palpebrarum,  which  is  attached  to  the 
lachrymal  groove  internally,  passes  outward  and  divides  into  two  lamellae 
that  are  attached  to  the  two  tarsal  cartilages.  At  the  outer  canthus 
the  cartilages  are  attached  to  the  malar  bone  by  the  external  tarsal 
ligament.  The  tarsal  cartilages  receive  additional  support  from  the 
palpej^ral  ligament,  a  fibrous  membrane  attached  to  the  margin  of 
the  orbit  and  the  convex  border  of  the  cartilages  and  lying  beneath 
the  orbicularis  muscle.  This  membrane  is  strongest  near  the  outer 
angle  of  the  eye. 

On  the  posterior  surface  of  the  tarsal  cartilages,  partly  embedded  in 
them  and  lying  just  beneath  the  conjunctiva,  are  the  Meibomian  glands. 
The  structure  and  uses  of  these  glands  have  already  been  described  in 
connection  with  the  physiology  of  secretion.  They  produce  an  oily 
liquid,  which  smears  the  edges  of  the  eyelids  and  prevents  the  overflow 
of  tears. 

Muscles  that  open  and  close  the  Eyelids.  —  The  corrugator  supercilii 
draws  the  skin  of  the  forehead  downward  and  inward  ;  the  orbicularis 
palpebrarum  closes'  the  lids ;  and  the  levator  palpebrae  superioris  raises 
the  upper  lid.  The  tensor  tarsi,  called  the  muscle  of  Horner,  is  a  very 
thin  delicate  muscle,  which  is  regarded  by  some  anatomists  as  a  deep 
portion  of  the  orbicularis.  Considering  this  as  a  distinct  muscle,  it 
consists  of  two  delicate  slips,  which  pass  from  either  eyelid  behind  the 
lachrymal  sac,  uniting  here  to  go  to  its  attachment  at  the  posterior  por- 
tion of  the  lachrymal  bone.  When  this  acts  with  the  orbicularis,  it 
compresses  the  lachrymal  sac. 

The  orbicularis  palpebrarum  is  a  broad  thin  muscle,  closely  attached 
to  the  skin,  surrounding  the  free  margin  of  the  lids  and  extending  a 
short  distance  over  the  bones  beyond  the  margin  of  the  orbit.  This 
muscle  may  be  described  as  arising  from  the  tendo  palpebrarum,  the 
surface  of  the  nasal  process  of  the  superior  maxillary  bone  and  the  in- 
ternal angular  process  of  the  os  frontis.  From  this  origin  at  the  inner 
angle  of  the  eye,  its  fibres  pass  elliptically  around  the  fissure  of  the  lids, 
as  indicated  above.  Its  action  is  to  close  the  lids.  In  the  ordinary 
moderate  contraction  of  this  muscle,  only  the  upper  lid  is  moved;  but 
in  forcible  contraction,  the  lower  lid  moves  slightly  and  the  lids  are 
drawn  toward  the  nose. 

The  levator  palpebrae  superioris  is  situated  within  the  orbit.  It  arises 
from  a  point  a  little  above  and  in  front  of  the  optic  foramen  at  the  apex 


PARTS  FOR  THE  PROTECTION  OF  THE  EYEBALL      707 

of  the  orbit,  passes  forward  above  the  eyeball  and  spreads  into  a  thin 
tendon,  which  is  inserted  into  the  anterior  surface  of  the  superior  tarsal 
cartilage.  Its  action  is  to  raise  the  upper  lid.  This  muscle  and  its 
relations  are  shown  in  Fig.  179(9,  ^O-  io)>  pa-ge  699. 

In  the  act  of  opening  the  eyes  the  levator  muscles  alone  are  brought 
into  play.  Closing  the  lids  is  accomplished  by  the  orbicular  muscles. 
Both  these  sets  of  muscles  act  to  a  great  extent  without  the  interven- 
tion of  the  will.  The  eyes  are  kept  open  almost  involuntarily,  except 
in  extreme  fatigue ;  although  when  the  will  ceases  to  act  the  lids  are 
closed.  Nevertheless  there  is  hardly  a  conscious  effort  usually  in  keep- 
ing the  eyes  open,  and  an  effort  is  required  to  close  the  eyes.  During 
sleep  the  eyes  are  closed  and  the  globes  are  turned  upward.  The  con- 
tractions of  the  orbicular  muscles  which  take  place  in  winking  usually 
are  involuntary.  This  act  occurs  at  short  intervals,  and  it  is  useful  in 
spreading  the  lachrymal  secretion  over  the  exposed  portions  of  the 
globes.  The  action  of  both  sets  of  muscles  ordinarily  is  simultaneous, 
although  they  may  be  educated  so  as  to  close  one  eye  while  the  other  is 
open.  The  action  of  the  orbicularis  is  so  far  removed  from  the  control 
of  the  will,  that  when  the  surface  of  the  globe  is  touched  or  irritated  or 
when  the  impression  of  light  produces  intense  pain,  it  is  almost  impos- 
sible to  keep  the  eye  open. 

Cojijunctii'al  Miicous  Membrane.  —  The  entire  inner  surface  of  the 
upper  and  lower  eyelids  is  lined  with  a  mucous  membrane  which  is  re- 
flected forward  from  the  inner  periphery  of  the  lids  over  the  eyeball. 
The  membrane  lining  the  lids  is  called  the  palpebral  conjunctiva,  and 
that  covering  the  eyeball,  the  ocular  conjunctiva.  The  latter  presents  a 
sclerotic  and  a  corneal  portion.  The  conjunctiva  presents  a  superior 
and  an  inferior  fold,  where  it  is  reflected  over  the  globe.  In  the  supe- 
rior conjunctival  fold,  are  glandular  follicles,  or  accessory  lachrymal 
glands,  which  secrete  a  certain  portion  of  the  liquid  that  moistens  the 
surface  of  the  eyeball.  These  usually  are  described  as  forming  a  part 
of  the  lachrymal  gland.  At  the  inner  canthus  there  is  a  vertical  fold, 
the  plica  semilunaris,  with  a  reddish  spongy  elevation  at  its  inner  por- 
tion, called  the  caruncula  lacrymalis.  The  caruncula  presents  a  collec- 
tion of  follicular  glands,  with  a  few  delicate  hairs  on  its  surface.  The 
conjunctiva  is  continuous  with  the  membrane  of  the  lachrymal  ducts,  of 
the  puncta  lacrymalia  and  of  the  Meibomian  glands.  Beneath  the  con- 
junctiva, except  in  the  corneal  portion,  is  a  loose  connective  tissue. 

The  palpebral  conjunctiva  is  reddish,  thicker  than  the  ocular  portion, 
furrowed,  and  presents  small  isolated  papillae  near  the  borders  of  the 
lids,  which  increase  in  number  and  size  toward  the  folds.  This  portion 
of  the  membrane  presents  large  capillary  bloodvessels  and  lymphatics 


7o8 


SPECIAL    SENSES 


and  is  covered  with  a  layer  of  cells  of  flattened  epithelium.  The  scle- 
rotic portion  is  thinner,  less  vascular  and  has  no  papillae.  It  is  covered 
with  conical  and  rounded  epithelial  cells  in  two  to  four  layers.  Over 
the  cornea  the  epithelium  of  the  sclerotic  portion  is  continued  in  deli- 
cate transparent  layers,  without  a  distinct  basement-membrane. 

TJie  LacJijy vial  Apparatus.  —  The  eyeball  is  constantly  bathed  in  a 
watery  liquid,  which  is  secreted  by  the  lachrymal  gland,  is  spread  over 
the  globe  by  the  movements  of  the  lids  and  of  the  eyeball  and  is  pre- 
vented, under  ordinary  conditions,  from  overflowing  upon  the  cheek  by 
the  Meibomian  secretion.  The  excess  of  this  secretion  is  collected  into 
the  lachrymal  sac,  and  is  carried  into  the  nose  by  the  nasal  duct.     The 

lachrymal  gland,  the 
lachrymal  canals,  duct 
and  sac,  and  the  nasal 
duct  constitute  the 
lachrymal  apparatus. 

The  lachrymal  gland 
is  an  ovoid  flattened 
gland  of  the  racemose 
variety,  resembling  the 
salivary  glands  in  its 
general  structure.  It 
is  about  the  size  of  a 
small  almond  and  is 
lodged  in  a  shallow 
depression  in  the  bones 
of  the  orbit  at  its  upper 
and  outer  portion.  It 
is  closely  attached  to 
the  periosteum  by  its 
upper  surface  and  is  moulded  below  to  the  convexity  of  the  globe.  Its 
anterior  portion  is  separated  from  the  rest  by  a  well-marked  groove,  is 
comparatively  thin  and  adheres  to  the  upper  lid.  It  presents  six  to 
eight  (usually  seven)  ducts,  which  form  a  row  of  openings  into  the  con- 
junctival fold.  Five  or  six  of  these  openings  are  situated  above  the 
outer  canthus,  and  two  or  three  open  below.  In  its  minute  structure 
this  gland  presents  no  points  of  special  physiological  importance  as  dis- 
tinguished from  the  ordinary  racemose  glands.  It  receives  nervous 
filaments  from  the  fifth  cranial  and  the  sympathetic. 

The  channels  by  which  the  excess  of  tears  is  conducted  into  the 
nose  begin  by  two  little  points  situated  on  the  margin  of  the  upper 
and    the  lower    lid   near   the  inner  canthus,  called    the   puncta   lacry- 


Fig.  i8i.  —  Lachrymal  and  Meibomian  glands  (Sappey). 

I,  1,  internal  wall  of  the  orbit ;  2,  2,  internal  portion  of  the  orbicu- 
laris palpebrarum ;  3,  3,  attachment  of  this  muscle  to  the  orbit ;  4, 
orifice  for  the  passage  of  the   nasal   artery;  5,  muscle  of  Horner ; 

6,  6,  posterior  surface  of  the  eyelids,  with   the   Meibomian  glands  ; 

7,  7.  8,8,  9,  9,  10,  lachrymal  gland  and   ducts;   11,  openings  of  the 
lachrymal  ducts. 


THE  LACHRYMAL  APPARATUS 


709 


malia,  which  present  each  a  minute  opening.  These  open  respec- 
tively into  the  upper  and  the  lower  lachrymal  canals,  which  together 
surround  the  caruncula  lacrymalis.  At  the  inner  angle  just  beyond  the 
caruncula,  the  two  canals  join  to  empty  into  the  lachrymal  sac,  which 
is  the  dilated  upper  extremity  of  the  nasal  duct.  The  duct  is  about 
half  an  inch  (12.7  millimeters)  in  length  and  empties  into  the  inferior 
meatus  of  the  nose,  taking  a  direction  nearly  vertical  and  incHned 
slightly  outward  and  backward.  This  portion  of  the  lachrymal  appara- 
tus is  fibrous  and  is  lined  by  a  reddish  mucous  membrane  that  presents 
several  well-marked  folds.  Near  the  puncta  are  two  folds,  one  for 
each  lachrymal  canal.  Another  pair  of  folds  ex- 
ists near  the  horizontal  portions  of  the  canals. 
At  the  opening  of  the  duct  into  the  nose,  is  an 
overhanging  fold  of  the  nasal  mucous  membrane. 
These  folds  are  supposed  to  prevent  the  reflux  of 
liquid  from  the  lachrymal  canals  and  the  entrance 
of  air  from  the  nose.  The  mucous  membrane  of 
the  lachrymal  canals  is  covered  with  flattened 
epithelium  like  that  of  the  conjunctiva.  The 
lachrymal  sac  and  duct  are  lined  with  a  continua- 
tion of  the  ciliated  epithehum  of  the  nose.  The 
disposition  of  the  apparatus  just  described  is  shown 
in  Fig.  182. 


Fig.  182.  —  Lachrymal 
canals,  lachrymal  sac  and 
nasal  catial,  opened   by  their 

The   Tears. — The  secretion  of  the  lachrymal    anterior  portion  {^^^^^ay). 
gland    is    constant,    although    its    flow    may    be        i,  walls  of  the  lachrymal 

passages,  smooth  and  adhe- 


rent ;  2,  2,  walls  of  the  lach- 
rymal sac,  presenting  delicate 
folds  of  the  mucous  mem- 
brane; 3,  a  similar  fold  be- 
longing to  the  nasal  mucous 
membrane. 

That  this  drainage  of 


may 
increased  under  various  conditions.  The  actual 
quantity  of  the  secretion  has  never  been  estimated. 
During  sleep  it  is  much  diminished  ;  and  when  the 
eyes  are  open,  the  quantity  is  sufficient  to  moisten 
the  eyeball,  the  excess  being  carried  into  the  nose 
so  gradually  that  this  process  is  not  appreciated, 
the  excess  of  tears  takes  place,  is  shown  by  cases  of  obstruction  of  the 
nasal  duct,  when  the  liquid  constantly  overflows  upon  the  cheeks,  pro- 
ducing considerable  inconvenience. 

It  is  probable  that  the  openings  at  the  puncta  lacrymalia  take  up 
the  lachrymal  secretion,  like  little  pipettes;  this  action  being  aided  by  the 
movements  in  winking,  by  which,  when  the  lids  are  closed,  the  points 
are  compressed  and  turned  backward,  opening  and  drawing  in  the  tears 
when  the  lids  are  opened.  It  is  possible  that  the  lachrymal  sac  is 
compressed  in  the  act  of  winking,  by  the  contractions  of  the  muscle  of 
Horner ;  and  that  this,  while  it  empties  the  sac,  may  in  the  subsequent 
relaxation  assist  in  the  introduction  of  liquid  from  the  orbit. 


710  SPECIAL    SENSES 

Little  is  known  in  regard  to  the  chemical  composition  of  tears 
beyond  an  analysis  made  many  years  ago  by  Frerichs.  According  to 
this  observer,  the  following  is  the  composition  of  the  lachrymal  secre- 
tion :  — 

COMPOSITION   OF  THE  TEARS 

Water 990.60     to     987.00 

Epithelium 1.40     to         3.20 

Albumin 0.80     to         i.oo 

Sodium  chloride         1 
Alkaline  phosphates  I 

Earthy  phosphates     \ 7.20     to         8.80 

Mucus 
Fat 


The  specific  gravity  of  the  tears  has  not  been  ascertained.  The 
liquid  is  clear,  colorless,  of  a  saltish  taste  and  a  feebly  alkaline  reaction. 
The  albumin  given  in  the  table  is  called  by  some  authors,  lachrymin, 
thraenin  or  dacryolin.  This  substance,  whatever  it  may  be  called, 
resembles  mucus  in  many  regards  and  probably  is  secreted  by  the 
conjunctiva  and  not  by  the  lachrymal  glands.  Unlike  ordinary  mucus 
it  is  coagulated  by  water.      It  is  supposed  to  be  a  globulin  (Halliburton). 

The  secretion  of  tears  is  readily  influenced  through  the  nervous 
system.  Aside  from  the  increased  flow  of  this  secretion  from  emotional 
causes,  which  probably  operate  through  the  sympathetic,  a  hypersecre- 
tion almost  immediately  follows  irritation  of  the  mucous  membrane  of 
the  conjunctiva  or  of  the  nose.  The  same  result  follows  violent  mus- 
cular effort,  laughing,  coughing,  sneezing  etc.  The  secretion  of  tears 
following:  stimulation  of  the  mucous  membrane  is  reflex. 


CHAPTER   XXIX 

AUDITION 

Auditory  (eighth  nerve)  — General  properties  of  the  auditory  nerves — Topographical  anatomy  of 
the  parts  essential  to  the  appreciation  of  sound — ^The  external  ear  —  General  arrangement 
of  parts  composing  the  middle  ear  —  General  arrangement  of  the  bony  labyrinth — Physics 
of  sound  —  Pitch  of  musical  sounds — Musical  scale  —  Quality  of  musical  sounds  —  Har- 
monics, or  overtones  ^  Harmony  —  Discords  and  dissonance — Tones  by  influence  — 
Uses  of  different  parts  of  the  middle  ear  —  Structure  of  the  membrana  tympani  —  Uses  of 
the  membrana  tympani  —  Mechanism  of  the  ossicles  of  the  ear — Physiological  anatomy  of 
the  internal  ear  —  General  arrangement  of  the  membranous  labyrinth  —  Liquids  of  the 
labyrinth  —  Distribution  of  the  nerves  in  the  labyrinth —  Organ  of  Corti  — Uses  of  different 
parts  of  the  internal  ear — Uses  of  the  semicircular  canals — Uses  of  the  parts  contained  in 
the  cochlea  —  Centres  for  audition. 

Impressions  of  sound  are  conveyed  to  the  brain  by  special  nerves ; 
but  in  order  that  these  impressions  shall  reach  these  nerves  so  as  to 
be  properly  appreciated,  a  complex  accessory  apparatus  is  required,  the 
integrity  of  which  is  essential  to  normal  audition.  The  study  of  the 
arrangement  and  action  of  these  accessory  parts  is  even  more  important 
and  is  far  more  intricate  than  the  physiology  of  the  auditory  nerves. 
The  auditory  nerves  conduct  impressions  of  sound,  as  the  optic  nerves 
conduct  impressions  of  light ;  but  there  is  an  elaborate  arrangement  of 
parts  by  which  the  waves  are  collected,  conveyed  to  a  membrane 
capable  of  vibration,  and  finally  carried  to  the  nerves  by  which  the 
intensity  and  the  varied  qualities  of  sound  are  appreciated. 


Auditory   (Eighth    Nerve) 

The  origin  of  the  auditory  nerve  can  easily  be  traced  to  the  floor 
of  the  fourth  ventricle,  where  it  presents  two  roots.  The  external,  or 
superficial  root,  sometimes  called  the  posterior  root,  can  be  seen  usually 
without  preparation.  It  consists  of  five  to  seven  grayish  filaments, 
which  decussate  in  the  median  line  and  pass  outward,  winding  from  the 
fourth  ventricle  around  the  restiform  body.  The  deep  root  consists  of 
a  number  of  distinct  filaments  arising  from  the  gray  matter  of  the  fourth 
ventricle,  two  or  three  of  which  pass  to  the  median  line  to  decussate 
with  corresponding  filaments  from  the  opposite  side.  Filaments  from 
this  root  have  been  traced  to  a  gray  nucleus  in  the  inferior  peduncle  of 
the    cerebellum  and  thence  to  the  white  substance  of  the  cerebellum 

711 


712  SPECIAL    SENSES 

itself.  The  deep  root  passes  around  the  restiform  body  inward,  so  that 
this  portion  of  the  bulb  is  encircled  by  the  two  roots.  Passing  from  the 
superior  and  lateral  portion  of  the  bulb,  the  trunk  of  the  nerve  is  applied 
to  the  superior  and  anterior  surface  of  the  facial.  It  then  passes  around 
the  middle  peduncle  of  the  cerebellum  and  receives  a  process  from  the 
arachnoid  membrane,  which  envelops  it  in  a  common  sheath  with  the 
facial.  It  finally  penetrates  the  internal  auditory  meatus.  In  its  course 
it  receives  filaments  from  the  restiform  body  and  probably  from  the  pons 
Varolii.  Within  the  meatus  the  nerve  divides  into  an  anterior  and  a 
posterior  branch,  the  anterior  being  distributed  to  the  cochlea,  and  the 
posterior,  to  the  vestibule  and  semicircular  canals.  The  distribution  of 
these  branches  will  be  described  in  connection  with  the  anatomy  of  the 
internal  ear. 

The  auditory  nerves  are  grayish  in  color  and  their  consistence  is 
soft,  thus  differing  from  the  ordinary  cerebro-spinal  nerves  and  resem- 
bling in  a  certain  degree  the  other  nerves  of  special  sense.  On  the 
external,  or  superficial  root,  is  a  small  ganglioform  enlargement,  contain- 
ing fusiform  nerve-cells.  The  filaments  of  the  trunk  of  the  nerve  con- 
sist of  very  large  axis-cylinders,  surrounded  with  a  medullary  sheath  but 
having  no  tubular  membrane.  In  the  course  of  these  fibres,  are  found 
small,  nucleated,  ganglionic  enlargements. 

General  Properties  of  tlie  Auditory  Nerves.  —  There  can  be  no  doubt, 
as  regards  the  eighth,  that  it  is  the  only  nerve  capable  of  receiving  and 
conveying  to  the  brain  the  special  impressions  produced  by  waves  of 
sound  ;  but  it  is  an  important  question  to  determine  whether  this  nerve 
be  endowed  also  with  general  sensibility.  Analogy  with  most  of  the 
other  nerves  of  special  sense  would  indicate  that  the  auditory  nerves  are 
insensible  to  ordinary  impressions ;  and  this  view  has  been  sustained  by 
direct  experiments.  In  experiments  made  by  passing  electric  currents 
through  the  ears,  some  physiologists  have  thought  that  auditory  sensa- 
tions were  produced ;  but  it  is  probable  that  the  sensations  observed 
were  due  to  clonic  spasm  of  the  stapedius  muscle  and  not  to  impressions 
of  sound  produced  by  the  action  of  the  stimulus  on  the  auditory  nerves. 
In  cases  of  complete  facial  paralysis  from  otitis,  in  which  paralysis  of 
the  auditory  nerve  could  be  excluded,  it  has  not  been  possible  to  produce 
subjective  auditory  sensations,  even  by  powerful  faradization  by  means 
of  a  catheter  passed  through  the  Eustachian  tube  into  the  tympanic 
cavity  or  by  the  external  meatus.  In  addition  there  are  well-established 
clinical  observations  which  sustain  the  theory  of  muscular  contraction 
and  are  opposed  to  the  idea  of  impressions  of  sound  produced  by  direct 
stimulation  of  the  auditory  nerves.  The  results,  then,  as  regards  stimu- 
lation of  the  auditory  nerves,  have  been  negative.     Were  it  practicable  to 


THE    EXTERNAL    EAR 


713 


subject  the  nerves  to  mechanical  or  electric  stimulation  in  the  human 
subject  without  involving  other  parts,  it  might  be  possible  to  arrive  at  a 
definite  conclusion  ;  but  the  difficulties  in  the  way  of  such  an  experiment 
have  thus  far  proved  insurmountable. 


Topographical  Anatomy  of   the    Parts   essential  to  the  Appre- 
ciation OF  Sound 

Perfect  audition  involves  the  anatomical  integrity  of  a  complex 
apparatus,  which,  for  convenience  of  anatomical  description,  may  be 
divided  into  the  external,  middle  and  internal 
ear. 

1.  The  external  ear  includes  the  pinna  and 
the  external  auditory  meatus  and  is  bounded 
internally  by  the  membrana  tympani. 

2.  The  middle  ear  includes  the  cavity  of 
the  tympanum,  or  drum,  with  its  boundaries. 
The  parts  here  to  be  described  are  the  mem- 
brana tympani,  the  form  of  the  tympanic 
cavity,  its  openings,  its  lining  membrane,  and 
the  small  bones  of  the  ear,  or  ossicles,  with 
their  ligaments,  muscles  and  nerves.  The 
cavity  of  the  tympanum  communicates  by  the 
Eustachian  tube  with  the  pharynx  and  it  also 
presents  openings  into  the  mastoid  cells.  Fig.  183.—  The  p'mna  (Sappey). 

3.  The  internal  ear  contains  the  terminal        i,  i,  helix;  2,  2,  fossa  of  the 

m,  r    ,1  -i.,  T.I.    •       1      1  helix;  3,  3,  antihelix;  4,  fossa  of 

aments  of  the  auditory  nerve.      It  mcludes   the  antihelix;  5,  concha;  6,  tra- 

the  vestibule,  the  three  semicircular  canals  and   g^s;  7,  antitragus;   8,  external 

,  11  ,   .    ,  .  r  1        1    1         •      1        auditory  meatus;  g,  lobule. 

the  cochlea,  which  together  form  the  labyrinth. 

The  pinna  and  the  external  meatus  simply  conduct  the  waves  of 
sound  to  the  tympanum.  The  parts  entering  into  the  structure  of  the 
middle  ear  are  accessory  and  are  analogous  in  their  uses  to  the  refract- 
ing media  of  the  eye.  Structures  contained  in  the  labyrinth  constitute 
the  true  sensory  organ. 

TJie  External  Ear.  —  The  pinna,  auricle,  or  pavilion  is  that  portion 
projecting  from  the  head,  which  first  receives  the  waves  of  sound.  The 
outer  ridge  of  the  pinna  is  called  the  helix.  Just  within  this  is  a  groove 
called  the  fossa  of  the  helix.  This  fossa  is  bounded  anteriorly  by  a 
prominent  but  shorter  ridge,  bifurcating  above  and  anteriorly,  called 
the  antihelix ;  and  above  the  concha,  between  the  bifurcating  arms  of 
the  antihelix  and  the  anterior  portion  of  the  helix,  is  a  shallow  fossa, 
called  the  fossa  of  the    antihelix.      The   deep  fossa  immediately  sur- 


714 


SPECIAL   SENSES 


rounding  the  opening  of  the  meatus  is  called  the  concha.  A  small 
lobe  projects  posteriorly,  covering  the  anterior  portion  of  the  concha, 
which  is  called  the  tragus ;  and  the  projection  at  the  lower  extremity  of 
the  antihehx  is  called  the  antitragus.  The  fleshy  dependent  portion  of 
the  pinna  is  called  the  lobule. 

The  form  of  the  pinna  and  its  consistence  depend  on  the  presence 
of  elastic  cartilage,  which  occupies  the  entire  external  ear  except  the 
lobule.  The  structure  of  this  kind  of  cartilage  has  already  been  de- 
scribed (see  Plate  X,  Fig.  4). 

The  integument  covering  the  ear  does  not  vary  much  from  the 
integument  of  the  general  surface.  It  is  thin,  closely  attached  to  the 
subjacent  parts,  and  possesses  small  rudimentary  hairs,  with  sudoripa- 
rous and  sebaceous  glands. 

The  muscles  of  the  external  ear 
are  not  important  in  the  human  sub- 
ject; and  excluding  a  few  exceptional 
cases,  they  are  not  under  the  control 
of  the  will.  The  extrinsic  muscles  are 
the  superior,  or  attollens,  the  anterior, 
or  attrahens,  and  the  posterior,  or 
retrahens  aurem.  In  addition  there 
are  the  six  small  intrinsic  muscles, 
situated  between  the  ridges  upon  the 
cartilaginous  surface.  The  pinna  is 
attached  to  the  sides  of  the  head  by 
two  distinct  ligaments  and  a  few  deli- 
cate Hgamentous  fibres. 
The  external  auditory  meatus  is  about  an  inch  and  a  quarter  (31.8 
millimeters)  in  length  and  extends  from  the  concha  to  the  membrana 
tympani.  Its  course  is  somewhat  tortuous.  Passing  from  without 
inward,  its  direction  is  at  first  somewhat  upward,  turning  abruptly  over 
a  bony  prominence  near  the  middle,  from  which  it  has  a  slightly  down- 
ward direction  to  the  membrana  tympani.  Its  general  course  is  from 
without  inward  and  slightly  forward.  The  inner  termination  of  the 
canal  is  the  membrana  tympani,  which  is  quite  oblique,  the  upper  por- 
tion being  inclined  outward,  so  that  the  inferior  wall  of  the  meatus  is 
considerably  longer  than  the  superior. 

The  walls  of  the  external  meatus  are  partly  cartilaginous  and  fibrous, 
and  partly  bony.  The  cartilaginous  and  fibrous  portion  occupies  a 
little  less  than  one-half  of  the  entire  length  and  consists  of  a  continua- 
tion of  the  cartilage  of  the  pinna,  with  fibrous  tissue.  The  lower  two- 
thirds  of  this  portion  of  the  canal  is  cartilaginous  and  the  upper  third 


Fig.  184.  —  Posterior  view  of  a  mould 
in  ivax  of  the  cavity  of  the  concha  and  the 
external  auditory  meatus  (Sappey). 


THE    MIDDLE    EAR  715 

is  fibrous.  The  rest  of  the  tube  is  osseous  and  is  a  little  longer  and 
narrower  than  the  cartilaginous  portion.  Around  the  inner  extremity 
of  the  canal,  except  at  its  superior  portion,  is  a  narrow  groove  which 
receives  the  greater  portion  of  the  margin  of  the  membrana  tympani. 

The  skin  of  the  external  meatus  is  continuous  with  the  integument 
covering  the  pinna.  It  is  very  delicate,  becoming  thinner  from  without 
inward.  In  the  osseous  portion  it  adheres  closely  to  the  periosteum, 
and  at  the  bottom  of  the  canal  it  is  reflected  over  the  membrana  tym- 
pani, forming  its  outer  layer.  In  the  cartilaginous  and  fibrous  portion 
are  short  stiff  hairs,  with  sebaceous  glands  attached  to  their  follicles,  and 
the  coiled  tubes  known  as  the  ceruminous  glands.  The  structure  of 
these  glands  and  the  properties  and  composition  of  the  cerumen  have 
already  been  described  in  connection  with  the  physiology  of  the  glands 
of  the  skin. 

General  Arrangement  of  the  Parts  composing  the  Middle  Ear.  — 
A  minute  and  purely  anatomical  description  of  the  middle  ear  would  be 
out  of  place  in  this  work,  where  it  is  desired  to  give  only  such  an 
account  of  the  anatomy  as  will  enable  the  student  to  comprehend  the 
physiology  of  the  ear,  reserving  for  special  description  certain  of  the 
most  important  structures.  It  will  be  useful,  however,  to  give  a  general 
outline  of  the  different  parts,  with  their  names. 

The  middle  ear  presents  a  narrow  cavity  of  irregular  shape, 
situated  between  the  external  ear  and  the  labyrinth,  in  the  petrous  por- 
tion of  the  temporal  bone.  The  general  arrangement  of  its  parts  is 
shown  in  Fig.  185.  The  outer  wall  of  the  tympanic  cavity  is  formed 
by  the  membrana  tympani  (6,  Fig.  185).  This  membrane  is  concave,  its 
concavity  looking  outward,  and  oblique,  inclining  usually  at  an  angle  of 
forty-five  degrees  with  the  perpendicular.  This  angle,  however,  varies 
considerably  in  different  individuals.  The  roof  is  formed  by  a  thin  plate 
of  bone.  The  floor  is  bony  and  is  much  narrower  than  the  roof.  The 
inner  wall,  separating  the  tympanic  cavity  from  the  labyrinth,  is  irregu- 
lar, presenting  several  small  elevations  and  foramina.  The  fenestra 
ovalis,  an  ovoid  opening  near  its  upper  portion,  leads  to  the  cavity  of 
the  vestibule.  This  is  closed  in  the  natural  state  by  the  base  of  the 
stapes  and  its  annular  ligament.  Below  is  a  smaller  opening,  the  fenes- 
tra rotunda,  which  leads  to  the  cochlea.  This  is  closed  in  the  natural 
state  by  a  membrane  called  the  secondary  membrana  tympani.  The 
principal  portion  of  the  tympanic  cavity  is  sometimes  called  the  atrium, 
although  this  name  is  applied  to  other  parts  not  connected  with  the  ear. 
From  the  general  tympanic  cavity  is  a  prolongation,  extending  upward 
and  backward,  in  which  are  lodged  the  head  of  the  malleus  and  a  great 
part  of  the  incus.     This  is  called  the  epitympanic  recess,  or  attic.      It 


p,l5  SPECIAL    SENSES 

communicates  with  the  mastoid  antrum,  into  which  open  little  canals 
leading  to  the  mastoid  cells.  The  tympanum  also  presents  an  opening 
leading  to  the  Eustachian  tube  and  a  small  foramen  that  gives  passage 
to  the  tendon  of  the  stapedius  muscle.  The  Eustachian  tube  extends, 
from  the  upper  part  of  the  pharynx  to  the  tympanum. 

The  small  bones  of 
the  ear   are  three  in 

ll^K^'''''''Sii^^i  number  —  the      mal- 

leus, the  incus  and  the 
k\  ^^SC'  stapes,. —  forming     a 

chain  and  connected 
together  by  ligaments 
(Fig.  1 86).  These 
bones  are  situated  in 
the  upper  part  of  the 
tympanum.  The  han- 
dle of  the  malleus 
(II,  3,  Fig.  1 86)  is 
closely  attached  to 
the    membrana    tym- 


Fig.  185.—  General  vieiD  of  the  ofgaii  of  hearing  (Sappey). 


I,  pinna;  2,  cavity  of  the  concha,  011  the  walls  of  which  are  seen 
the  orifices  of  a  great  number  of  sebaceous  glands;  3,  external  audi- 
tory meatus ;  4,  angular  projection  formed  by  the  union  of  the  an- 
terior portion  of  the  concha  with  the  posterior  wall  of  the  auditory 
canal ;  5,  openings  of  the  ceruminous  glands,  the  most  internal  of 
which  form  a  curved  line  which  corresponds  with  the  beginning  of 
the  osseous  portion  of  the  external  meatus ;  6,  membrana  tympani 
and  the  elastic  fibrous  membrane  which  forms  its  border;  7,  anterior 
portion  of  the  incus;  8,  malleus;  9,  handle  of  the  malleus,  applied  to 
the  internal  surface  of  the  membrana  tympani,  which  it  draws  in- 
ward toward  the  projection  of  the  promontory;  10,  tensor-tympani 
muscle,  the  tendon  of  which  is  reflected  at  a  right  angle,  to  become 
attached  to  the  superior  portion  of  the  handle  of  the  malleus;  11, 
tympanic  cavity;  12,  Eustachian  tube,  the  internal  or  pharyngeal  ex- 
tremity of  which  has  been  removed  by  a  section  perpendicular  to  its  j^g^j.  ^^Q  openings  of 
curve;    13,  superior  semicircular  canal;    14,  posterior  semicircular  J^  ° 

canal;    15,  external    semicircular   canal;    16,   cochlea;    17,   internal     the  maStoid  Cclls.       It 
auditory  canal;   18,  facial  nerve;   19,  large  petrosal  branch,  given  off 
from  the  ganglioform  enlargement  of  the  facial  and  passing  below 
the  cochlea,  to  go  to  its  distribution ;    20,  vestibular  branch  of  the 
auditory  nerve ;  21,  cochlear  branch  of  the  auditory  nerve. 


pani,  and  the  long 
process  (II,  2,  Fig. 
186)  is  attached  to 
the  Glasserian  fissure 
of  the  temporal  bone. 
The  malleus  is  articu- 
lated with  the  in- 
cus. The  incus  (I,  2, 
Fig.  186)  is  connected 
with  the  posterior  wall 
of     the     tympanum. 


is  articulated  with  the 
malleus,  and  by  the 
extremity  of  its  long 
process,  with  the  stapes.  The  stapes  (I,  3,  Fig-  186)  is  the  most  internal 
bone  of  the  middle  ear.  It  is  articulated  by  its  smaller  extremity  with 
the  long  process  of  the  incus.  Its  base  is  oval  and,  with  its  annular 
ligament,  is  applied  to  the  fenestra  ovalis.  The  direction  of  the  stapes 
is  nearly  at  a  right  angle  with  the  long  process  of  the  incus,  in  the 
natural  state.     Some  anatomists  describe  a  fourth  bone  as  existing  be- 


THE    MIDDLE   EAR  /I/ 

tween  the  long  process  of  the  incus  and  the  stapes ;  but  this  is  seldom 
distinct,  usually  being  united  either  with  the  incus  or  with  the  stapes. 

There  are  two  well-defined  muscles  connected  with  the  ossicles  of 
the  middle  ear.  One  of  these  is  attached  to  the  malleus,  and  the  other, 
to  the  stapes.  The  so-called  laxator  tympani  probably  is  not  composed 
■of  muscular  fibres  and  should  not  be  enumerated  with  the  muscles  of 
the  tympanum. 

The  larger  of  the  two  muscles  is  the  tensor  tympani.  Its  fibres 
arise  from  the  cartilaginous  portion  of  the  Eustachian  tube,  the  spinous 
process  of  the  sphenoid  bone  and  the  adjacent  portion  of  the  temporal. 
From  this  origin  it  passes  backward,  almost  horizontally,  to  the  tym- 
panic cavity.     In  front  of  the  fenestra  ovalis  it  turns  at  nearly  a  right 


Fig.  i86. —  Ossicles  of  the  tympanum,  X  4  (modified  from  Riidinger). 

I,  ossicles  of  the  left  ear;   i,  malleus;  2,  incus;  3,  stapes.     II,  ossicles  of  the  right  ear;  i,  malleus; 
2,  long  process;  3,  handle;  4,  long  process  of  the  incus;  5,  short  process  of  the  incus;  6,  stapes. 

angle  over  a  bony  process,  and  its  tendon  is  inserted  into  the  handle  of 
the  malleus  at  its  inner  surface  near  the  root.  The  tendon  is  very  deli- 
cate, and  the  muscular  portion  is  about  half  an  inch  (12.7  milhmeters) 
in  length  (10,  Fig.  185).  The  muscle  and  its  tendon  are  enclosed  in 
a  distinct  fibrous  sheath.  The  action  of  this  muscle  is  to  draw  the 
handle  of  the  malleus  inward,  pressing  the  base  of  the  stapes  against 
the  membrane  of  the  fenestra  ovalis  and  producing  tension  of  the 
membrana  tympani.  The  fibres  of  this,  and  of  all  the  muscles  of  the 
middle  ear,  are  of  the  striated  variety.  The  tensor  tympani  is  supplied 
with  motor  filaments  from  the  otic  ganglion,  which  probably  are  derived 
from  the  facial  nerve. 

The' stapedius  muscle  is  situated  in  the  descending  portion  of  the 
acqugeductus  Fallopii  and  in  the  cavity  of  the  pyramid  on  the  posterior 
wall  of  the  tympanic  cavity.     Its  tendon  emerges  from  a  foramen  at 


7i8 


SPECIAL    SENSES 


the  summit  of  the  pyramid.  In  the  canal  in  which  this  muscle  is 
lodged,  its  direction  is  vertical.  At  the  summit  of  the  pyramid  it  turns 
at  nearly  a  right  angle,  its  tendon  passing  horizontally  forward  to  be 
attached  to  the  head  of  the  stapes.  Like  the  other  muscles  of  the  ear, 
this  is  enveloped  in  a  fibrous  sheath.  Its  action  is  to  draw  the  head  of 
the  stapes  backward,  relaxing  the  membrana  tympani.  This  muscle 
receives  filaments  from  the  facial  nerve,  by  a  distinct  branch,  the 
tympanic. 

The  posterior  wall  of  the  tympanic  cavity  presents  foramina  that 
open   directly   into   a   number   of    irregularly-shaped   cavities  (mastoid 

cells)  communicating  freely 
with  each  other  in  the  mastoid 
process  of  the  temporal  bone. 
These  are  lined  with  a  contin- 
uation of  the  mucous  mem- 
brane of  the  tympanum. 
There  is,  under  certain  con- 
ditions, a  free  circulation  of 
air  between  the  pharynx  and 
the  cavity  of  the  tympanum 
through  the  Eustachian  tube 
and  from  the  tympanum  to 
the  mastoid  cells. 

The  Eustachian  tube  (12, 
Fig.  185)  is  partly  bony  and 
party  cartilaginous.  Following 
its  direction  from  the  tym- 
panic cavity,  it  passes  forward, 
inward  and  slightly  downward. 
Its  entire  length  is  about  an 
inch  and  a  half  (38.1  milli- 
meters). Its  calibre  gradually 
contracts  from  the  tympanum 
to  the  spine  of  the  sphenoid, 
and  from  this  constricted  portion  it  gradually  dilates  to  its  opening  into 
the  pharynx,  the  entire  canal  presenting  the  appearance  of  two  cones. 
The  osseous  portion  extends  from  the  tympanum  to  the  spine  of  the 
sphenoid  bone.  The  cartilaginous  portion  is  an  irregularly-triangular 
cartilage,  bent  on  itself  above,  forming  a  furrow,  with  its  concavity  pre- 
senting downward  and  outward.  The  fibrous  portion  occupies  about 
one-half  of  the  tube,  beyond  the  osseous  portion,  and  completes  the 
canal,  forming  its  inferior  and  external  portion.      In  its  structure  the 


Fig.  187.  —  The  right  temporal  bone,  the  petrous  por- 
tion removed,  showing  the  ossicles  seen  from  within- — re- 
duced about  one-half  .     From  a  photograph  (Riidinger). 

4,  the  incus,  the  short  process  of  which  is  directed 
nearly  in  a  horizontal  direction  backward;  5,  the  long 
process  of  the  incus,  free  in  the  tympanic  cavity,  articu- 
lated with  the  stapes ;  6,  the  malleus,  articulated  with  the 
incus;  7,  the  long  process  of  the  malleus,  in  the  Giasse- 
rian  fissure ;  8,  the  stapes,  articulated  with  the  incus. 
This  is  drawn  somewhat  outward ;  otherwise  the  base  of 
the  stapes  alone  would  be  visible.  This  figure  shows  the 
handle  of  the  malleus  attached  to  the  membrana  tym- 
pani. 


THE    MIDDLE    EAR  719 

cartilage  of  the  Eustachian  tube  is  intermediate  between  hyahne  and 
elastic  cartilage. 

The  circumflexus,  or  tensor  palati  muscle,  which  has  already  been 
described  in  connection  with  deglutition,  is  attached  to  the  anterior 
margin,  or  the  hook  of  the  cartilage.  The  attachments  of  this  muscle 
have  been  accurately  described  by  Rudinger,  who  called  it  the  dilator 
of  the  tube. 

The  action  of  certain  of  the  muscles  of  deglutition  dilates  the  pharyn- 
geal opening  of  the  Eustachian  tube.  If  the  mouth  and  nostrils  are 
closed  and  several  repeated  acts  of  deglutition  are  made,  air  is  drawn 
from  the  tympanic  cavity,  and  the  atmospheric  pressure  renders  the 
membrane  of  the  tympanum  tense,  increasing  its  concavity.  By  one  or 
two  lateral  movements  of  the  jaws,  the  tube  is  opened,  the  pressure  of 
air  is  equalized  and  the  ear  returns  to  its  former  condition.  The  nerves 
animating  the  dilator  tubaecome  from  the  pneumogastric  and  are  derived 
originally  from  the  spinal  accessory. 

A  smooth  mucous  membrane  forms  a  continuous  lining  for  the 
Eustachian  tube,  the  cavity  of  the  tympanum  and  the  mastoid  cells. 
In  all  parts  it  is  closely  adherent  to  the  subjacent  tissues,  and  in  the 
cavity  of  the  tympanum  it  is  very  thin.  In  the  cartilaginous  portion 
of  the  Eustachian  tube  there  are  mucous  glands,  which  are  most  abun- 
dant near  the  pharyngeal  orifice,  and  gradually  diminish  in  number 
toward  the  osseous  portion,  in  which  there  are  no  glands.  Throughout 
the  tube  the  surface  of  the  mucous  membrane  is  covered  with  conoidal 
cells  of  ciliated  epithelium.  The  mucous  membrane  of  the  tympanic 
cavity  is  very  thin,  consisting  of  little  more  than  epithelium  and  a  layer 
of  connective  tissue.  It  lines  the  walls  of  the  cavity  and  the  inner  sur- 
face of  the  membrana  tympani,  is  prolonged  into  the  mastoid  cells  and 
covers  the  ossicles  and  those  portions  of  the  muscles  and  tendons  which 
pass  through  the  tympanum.  On  the  floor  of  the  tympanic  cavity  and 
on  its  anterior,  inner  and  posterior  walls,  the  epithelium  is  of  the  co- 
noidal ciliated  variety.  On  the  promontory,  roof,  ossicles  and  muscles, 
the  cells  are  of  the  pavement-variety  and  not  ciliated,  the  transition  from 
one  form  to  the  other  being  gradual.  The  entire  mucous  membrane 
contains  lymphatics,  a  plexus  of  nerve-fibres  and  nerve-cells,  with  some 
peculiar  cells,  the  physiology  of  which  is  not  understood. 

The  above  is  merely  a  general  sketch  of  the  physiological  anatomy 
of  the  middle  ear,  and  it  will  not  be  necessary  to  treat  more  fully  of  the 
cavity  of  the  tympanum,  the  mastoid  cells  or  the  Eustachian  tube,  except 
as  regards  certain  points  in  their  physiology.  The  minute  anatomy  of 
the  membrana  tympani  and  the  articulations  of  the  ossicles  can  be  more 
conveniently  considered  in  connection  with  the  physiology  of  these  parts. 


720 


SPECIAL    SENSES 


General  Arrangevicnt  of  the  Bony  LabyrintJi.  —  The  internal  portion 
of  the  auditory  apparatus  is  contained  in  the  petrous  portion  of  the  tem- 
poral bone.  It  consists  of  an  irregular  cavity,  called  the  vestibule, 
the  three  semicircular  canals  (13,  14,  15,  Fig.  185)  and  the  cochlea 
(16,  Fig.  185).  The  general  arrangement  of  these  parts  in  situ  and 
their  relations  to  the  adjacent  structures  are  shown  in  Fig.  185.  Fig- 
ure 188,  showing  the  bony  labyrinth  isolated,  is  from  a  photograph  in 

Riidinger's  atlas. 

The  vestibule  is  the 
central  chamber  of  the 
labyrinth,  communicat- 
ing with  the  tympanic 
cavity  by  the  fenestra 
ovalis,  which  is  closed 
in  the  natural  state  by 
the  base  of  the  stapes. 
This  is  the  central 
ovoid  opening  shown  in 
Fig.  188.  The  inner 
wall  of  the  vestibule 
presents  a  round  de- 
pression, called  the 
fovea  hemispherica,  per- 
forated by  a  number  of 
small  foramina  through 
which  pass  nervous  fila- 
ments from  the  internal 
auditory  meatus.  Be- 
hind this  depression -is 
the  opening  of  the 
aqueduct  of  the  vesti- 
bule. In  the  posterior 
wall  of  the  vestibule  are  five  small  round  openings  leading  to  the  semi- 
circular canals,  with  a  larger  opening  below  leading  to  the  cochlea. 

The  general  arrangement  of  the  semicircular  canals  is  shown  in 
Fig.  188  (6,  7,  8,  9,  10,  II,  12). 

The  arrangement  of  the  cochlea  —  the  anterior  division  of  the  laby- 
rinth—  is  shown  in  Fig.  188  (i,  3,  4).  This  is  a  spiral  canal,  about  an 
inch  and  a  half  (38.1  millimeters)  long,  and  one-tenth  of  an  inch 
(2.5  millimeters)  wide  at  its  beginning,  gradually  tapering  to  the  apex, 
and  making,  in  its  course,  two  and  a  half  turns.  Its  interior  presents  a 
central  pillar  around  which  winds  a  spiral  lamina  of  bone.    The  fenestra 


Fig.  188.  —  The  left  bony  labyrinth  of  a  newborn  child,  for- 
ward and  outward  view,  X  4.  From  a  photograph,  and  slightly 
reduced  (Riidinger). 

I,  the  wide  canal,  the  beginning  of  the  spiral  canal  of  the 
cochlea;  2,  the  fenestra  rotunda;  3,  the  second  turn  of  the  coch- 
lea; 4,  the  final  half-turn  of  the  cochlea ;  5,  the  border  of  the  bony 
wall  of  the  vestibule,  situated  between  the  cochlea  and  the  semi- 
circular canals;  6,  the  superior,  or  sagittal  semicircular  canal; 
7,  the  portion  of  the  semicircular  canal  bent  outward;  8,  the  pos- 
terior, or  transverse  semicircular  canal ;  9,  the  portion  of  the 
posterior  connected  with  the  superior  semicircular  cana! ;  10,  point 
of  junction  of  the  superior  and  the  posterior  semicircular  canals  ; 
II,  the  ampulla  ossea  externa;  12,  the  horizontal,  or  external  semi- 
circular canal.  The  explanation  of  this  figure  has  been  modified 
and  condensed  from  Riidinger. 


PHYSICS    OF    SOUND  72 1 

rotunda  (2,  Fig.  188),  closed  in  the  natural  state  by  a  membrane,  —  the 
secondary  membrana  tympani,  —  lies  between  the  lower  portion  of  the 
cochlea  and  the  cavity  of  the  tympanum. 

What  is  called  the  membranous  labyrinth  is  contained  within  the 
bony  parts  just  described.  Some  of  the  anatomical  points  connected 
with  its  structure  and  the  distribution  and  connections  of  the  auditory 
nerve  have  direct  and  important  relations  to  the  physiology  of  hearing, 
while  many  are  of  purely  anatomical  interest.  Such  facts  as  bear 
directly  on  physiology  will  be  considered  in  connection  with  the  uses 
of  the  internal  ear. 

Physics  of  Sound 

Most  of  the  points  in  acoustics  that  are  essential  to  the  comprehen- 
sion of  the  physiology  of  audition  are  definitely  settled.  The  theories 
of  the  propagation  of  sound  involve  wave-action,  concerning  which  there 
is  no  question.  For  the  conduction  of  sound  a  ponderable  medium  is 
essential ;  and  it  is  not  necessary,  as  in  the  case  of  the  undulatory 
theory  of  light,  to  assume  the  existence  of  an  imponderable  ether.  The 
human  ear,  though  perhaps  not  so  acute  as  the  auditory  apparatus  of 
some  of  the  inferior  animals,  not  only  appreciates  irregular  waves,  such 
as  produce  noise  as  distinguished  from  sounds  called  musical,  but  is 
capable  of  distinguishing  regular  waves,  as  in  simple  musical  sounds 
and  harmonious  combinations. 

In  music  certain  successions  of  regular  sounds  are  agreeable  to  the 
ear  and  constitute  what  is  called  melody.  Again,  there  is  appreciation, 
not  only  of  the  intensity  of  sounds,  both  noisy  and  musical,  but  of  pitch 
and  different  qualities,  particularly  in  music.  Still  further,  musical  notes 
may  be  resolved  into  certain  invariable  component  parts,  such  as  the 
octave,  the  third,  fifth  etc.  These  components  of  what  were  formerly 
supposed  to  be  simple  sounds  —  which  may  be  isolated  by  artificial 
means,  to  be  described  farther  on  —  are  called  tones;  while  the  sounds 
themselves,  produced  by  the  union  of  the  different  tones,  are  called 
notes,  which  may  themselves  be  combined  to  form  chords. 

The  quality  of  musical  sounds  may  be  modified  by  the  simultaneous 
production  of  others  which  correspond  to  certain  of  the  components  of 
the  predominating  note.  For  example,  if  there  is  added  to  a  single 
note,  the  third,  fifth  and  octave,  the  result  is  a  major  chord,  the  sound 
of  which  is  different  from  that  of  a  single  note  or  of  a  note  with  its 
octave.  If  the  third  is  diminished  by  a  semitone,  there  is  a  different 
quality,  which  is  peculiar  to  minor  chords.  In  this  way  a  great  variety 
of  musical  sounds  may  be  made  on  a  single  instrument,  as  the  piano ; 
and  by  the  harmonious  combinations  of  the  notes  of  different  instru- 


722 


SPECIAL    SENSES 


ments  and  of  different  registers  of  the  human  voice,  as  in  choral  and 
orchestral  compositions,  shades  of  effect,  almost  innumerable,  may  be 
produced.  The  modification  of  sounds  in  this  way  constitutes  harmony  ; 
and  an  educated  ear  not  only  experiences  pleasure  from  these  musical 
combinations,  but  can  distinguish  their  different  component  parts. 

A  chord  may  convey  to  the  ear  the  sensation  of  completeness  in 
itself  or  it  mav  lead  to  a  succession  of  notes  before  this  sense  of  com- 
pleteness is  attained.  Different  chords  in  the  same  key  may  be  made 
to  follow  each  other,  or  by  transition-notes,  may  pass  to  the  chords  of 
other  keys.  Each  key  has  its  fundamental  note  ;  and  the  transition  from 
one  key  to  another,  in  order  to  be  agreeable  to  the  ear,  must  be  made 
in  certain  ways.  These  regular  transitions  constitute  modulation.  The 
ear  becomes  fatigued  by  long  successions  of  notes  or  chords  always  in 
one  key,  and  modulation  is  essential  to  the  enjoyment  of  elaborate 
musical  compositions;  otherwise  the  notes  would  not  only  become 
monotonous,  but  their  correct  appreciation  would  be  impaired,  as  the 
appreciation  of  colors  becomes  less  distinct  after  looking  for  a  long 
time  at  an  object  presenting  a  single  vivid  tint. 

Lazi.'s  of  Sonorous  Vibrations.  —  Sound  is  produced  by  vibrations  in 
a  ponderable  medium  ;  and  the  sounds  ordinarily  heard  are  transmitted 
to  the  ear  by  means  of  vibrations  of  the  atmosphere.  A  simple  and 
very  common  illustration  of  this  fact  is  afforded  by  the  experiment  of 
striking  a  bell  carefully  arranged  /;/  vacuo.  Although  the  stroke  and 
the  vibration  can  readily  be  seen,  there  is  no  sound;  and  if  air  is  grad- 
ually introduced,  the  sound  will  become  appreciable  and  progressively 
more  intense  as  the  surrounding  medium  is  increased  in  density.  The 
oscillations  of  sound  are  to  and  fro  in  the  direction  of  the  line  of  con- 
duction and  are  said  to  be  longitudinal.  In  the  undulatory  theory  of 
light,  the  vibrations  are  supposed  to  be  at  right  angles  to  the  line  of 
propagation,  or  transverse.  A  complete  oscillation  to  and  fro  is  called 
a  sound-wave. 

It  is  evident  that  vibrating  bodies  may  be  made  to  perform  and  im- 
part to  the  atmosphere  oscillations  of  greater  or  less  amplitude.  The 
intensity  of  sound  is  in  proportion  to  the  amplitude  of  the  vibrations. 
In  a  vibrating  body  capable  of  producing  a  definite  number  of  waves  of 
sound  in  a  second,  it  is  evident  that  the  greater  the  amplitude  of  the 
wave,  the  greater  is  the  velocity  of  the  particles  thrown  into  vibration. 
It  has  been  ascertained  that  there  is  an  invariable  mathematical  relation 
between  the  intensity  of  sound,  the  velocity  of  the  conducting  particles 
and  the  amplitude  of  the  waves ;  and  this  is  expressed  by  the  formula, 
that  the  intensity  is  proportional  to  the  square  of  the  amplitude.  It  is 
evident,  also,  that   the  intensity  of  sound   is   diminished  by  distance. 


PHYSICS    OF    SOUND  723 

The  sound,  as  the  waves  recede  from  the  sonorous  body,  becomes  dis- 
tributed over  an  increased  area.  The  propagation  of  sound  has  been 
reduced  also  to  the  formula,  that  the  intensity  diminishes  in  proportion 
to  the  square  of  the  distance. 

Sonorous  vibrations  are  subject  to  many  of  the  laws  of  reflection  of 
light.  Sound  may  be  absorbed  by  soft  and  non-vibrating  surfaces  in  the 
same  way  that  certain  surfaces  absorb  the  rays  of  light.  By  carefully 
arranged  convex  surfaces,  the  waves  of  sound  may  readily  be  collected 
to  a  focus.  These  laws  of  the  reflection  of  sonorous  waves  explain  echoes 
and  the  conduction  of  sound  by  confined  strata  of  air,  as  in  tubes.  To 
extend  the  parallel  between  sonorous  and  luminous  transmission,  it  has 
been  ascertained  that  the  waves  of  sound  may  be  refracted  to  a  focus  by 
being  made  to  pass  through  an  acoustic  lens,  as  a  balloon  filled  with  car- 
bon dioxide.  The  waves  of  sound  also  may  be  deflected  around  solid 
bodies,  when  they  produce  what  have  been  called  shadows  of  sound. 

Observing  the  sound  produced  by  the  blow  of  an  axe,  it  is  seen  that 
sound  is  transmitted  with  much  less  rapidity  than  light.  At  a  short  dis- 
tance the  view  of  the  blow  is  practically  instantaneous ;  but  there  is  a 
considerable  interval  between  this  and  the  sound.  This  interval  rep- 
resents the  velocity  of  sonorous  conduction.  This  fact  is  also  illus- 
trated by  the  interval  between  a  flash  of  lightning  and  the  sound  of 
thunder.  The  velocity  of  sound  depends  on  the  density  and  elasticity 
of  the  conducting  medium.  The  rate  of  conduction  of  sound  by  atmos- 
pheric air  at  the  freezing-point  of  water  is  about  1118  feet  (340  meters) 
per  second.  This  rate  presents  comparatively  slight  variations  for  the 
different  gases,  but  it  is  much  more  rapid  in  liquids  and  in  solids. 

Noise  and  Musical  Sounds.  —  There  is  a  well-defined  physical  as  well 
as  an  aesthetic  distinction  between  noise  and  music.  Taking  as  examples, 
single  sounds,  a  sound  becomes  noise  when  the  air  is  thrown  into  con- 
fused and  irregular  vibrations.  A  noise  may  be  composed  of  musical 
sounds  when  these  are  not  in  accord  with  each  other,  and  sounds  called 
musical  are  not  always  free  from  discordant  vibrations.  A  noise  pos- 
sesses intensity,  varying  with  the  amplitude  of  the  vibrations,  and  it  may 
have  different  qualities  depending  on  the  form  of  its  vibrations.  A  noise 
may  be  dull,  sharp,  ringing,  metallic,  hollow  etc.,  these  terms  express- 
ing qualities  that  are  readily  understood.  A  noise  also  may  be  called 
sharp  or  low  in  pitch,  as  the  rapid  or  slow  vibrations  predominate,  with- 
out answering  the  requirements  of  musical  sounds. 

A  musical  sound  consists  of  vibrations  following  each  other  at  regular 
intervals,  provided  that  the  succession  of  waves  be  not  too  slow  or  too 
rapid.  When  the  vibrations  are  too  slow,  there  is  an  appreciable  suc- 
cession of  impulses  and  the  sound  is  not  musical.     When  they  are  too 


724 


SPECIAL   SENSES 


rapid,  the  sound  is  excessively  sharp,  but  it  is  painfully  acute  and  has  no 
pitch  that  can  be  accurately  determined  by  the  auditory  apparatus.  Such 
sounds  may  be  occasionally  employed  in  musical  compositions,  but  in 
themselves  they  are  not  strictly  musical. 

Musical  sounds  have  the  characters  of  duration,  intensity,  pitch  and 
quality.  Duration  depends  on  the  length  of  time  during  which  the 
vibrating  body  continues  in  action.  Intensity  depends  on  the  ampli- 
tude of  the  vibrations  and  has  no  relation  to  pitch.  Pitch  depends  on 
the  rapidity  of  the  regular  vibrations.  Quality  depends  on  combinations 
of  different  notes  in  harmony,  the  character  of  the  harmonics  of  funda- 
mental tones  and  the  form  of  the  vibrations. 

PitcJi  of  Mjisical  Sounds.  —  Pitch  depends  on  the  number  of  vibra- 
tions. A  musical  sound  may  be  of  greater  or  less  intensity ;  it  may  at 
first  be  quite  loud  and  gradually  die  away  ;  but  the  number  of  vibrations 
in  a  definite  note  is  invariable,  be  it  weak  or  powerful.  The  rapidity  of  the 
conduction  of  sound  does  not  vary  with  its  intensity  or  pitch  ;  and  in  the 
harmonious  combination  of  the  sounds  of  different  instruments,  be  they 
high  or  low  in  pitch,  intense  or  feeble,  it  is  always  the  same  in  the  same 
conducting  medium.  Distinct  musical  notes  may  present  a  great  variety 
of  qualities,  but  all  notes  of  the  same  pitch  have  equal  rates  of  vibration. 
Notes  equal  in  pitch  are  said  to  be  in  unison.  An  educated  ear  can  dis- 
tinguish slight  differences  in  pitch  in  ordinary  musical  notes  ;  but  this 
power  of  appreciation  of  pitch  is  restricted  within  well-defined  limits 
that  vary  slightly  in  different  individuals.  According  to  Helmholtz,  the 
range  of  sounds  that  may  be  legitimately  employed  in  music  is  between 
40  and  4000  vibrations  in  a  second,  embracing  about  seven  octaves. 
In  an  orchestra  the  double  bass  gives  the  lowest  note,  which  has 
40.25  vibrations  in  a  second,  and  the  highest  note,  given  by  the  small 
flute,  has  4752  vibrations.  In  grand  organs  there  is  a  pipe  that  gives 
a  note  of  16.5  vibrations,  and  the  deepest  note  of  modern  pianos  has 
27.5  vibrations;  but  delicate  shades  of  pitch  in  these  low  notes  are  not 
appreciable  to  most  persons.  Sounds  above  the  limits  just  indicated  are 
audible  but  are  painfully  sharp,  and  their  pitch  can  not  be  exactly  appre- 
ciated by  the  ear. 

The  limits  of  appreciation  of  musical  sounds  do  not  apply  to  ordi- 
nary audition  ;  and  the  extreme  range  of  hearing  is  much  greater,  being 
about  eleven  octaves.  Shrill  sounds,  that  can  not  be  recognized  as  musi- 
cal, still  are  audible  and  the  number  of  their  vibrations  may  be  measured 
mechanically.  "  Galton's  whistle  "  produces  sounds  that  have  between 
30,000  and  40,000  vibrations  in  a  second ;  but  beyond  these  limits  the 
vibrations  are  inaudible.  It  is  possible,  however,  that  vibrations  inau- 
dible to  the  human  subject  may  be  heard  by  some  of  the  lower  animals. 


PHYSICS    OF    SOUND 


/^3 


Musical  Scale.  —  A  knowledge  of  the  relations  of  different  notes  to 
each  other  lies  at  the  foundation  of  the  science  of  music ;  and  without  a 
clear  idea  of  certain  of  the  fundamental  laws  of  music,  it  is  impossible  to 
comprehend  thoroughly  the  mechanism  of  audition. 

It  requires  but  little  cultivation  of  the  ear  to  enable  one  to  compre- 
hend the  fact  that  the  successions  and  combinations  of  notes  must  obey 
certain  laws;  and  long  before  these  laws  were  subjects  of  mathematical 
demonstration,  the  relations  of  the  different  notes  of  the  scale  were  estab- 
lished, merely  because  certain  successions  and  combinations  were  agree- 
able to  the  ear,  while  others  were  discordant  and  apparently  unnatural. 

The  most  convenient  sounds  for  study  are  those  produced  by  vibrat- 
ing strings,  and  the  phenomena  here  observed  are  essentially  the  same 
for  all  musical  sounds  ;  for  it  is  by  means  of  vibrations  communicated  to 
the  air  that  the  waves  of  sound  find  their  way  to  the  auditory  apparatus. 
Take,  to  begin  with,  a  string  vibrating  48  times  in  a  second.  If  this 
string  is  di\'ided  into  two  equal  parts,  each  part  will  vibrate  96  times  in 
a  second.  The  note  thus  produced  is  the  octave,  or  the  8th  of  the  pri- 
mary note,  called  the  8th,  because  the  natural  scale  contains  eight  notes, 
of  which  the  first  is  the  lowest,  and  the  last,  the  highest.  The  half  may 
be  divided  again,  producing  a  second  octave,  and  so  on,  within  the  limits 
of  appreciation  of  musical  sounds.  If  the  string  is  divided  so  that  -|  of 
its  length  will  vibrate,  there  are  72  vibrations  in  a  second,  and  this  note 
is  the  5th  in  the  scale.  If  the  string  is  divided  again,  so  as  to  leave  4  of 
its  length,  there  are  60  vibrations,  which  give  the  3d  note  in  the  scale. 
These  are  the  most  prominent  subdivisions  of  the  note;  and  the  ist,  3d, 
5th  and  8th,  when  sounded  together,  make  what  is  known  as  the  common 
major  chord.  Three-fourths  of  the  length  of  the  original  string  make 
64  vibrations,  and  give  the  4th  note  in  the  scale.  With  f  of  the  string, 
there  are  54  vibrations,  and  the  note  is  the  2d  in  the  scale.  With  |  of 
the  string,  there  are  80  vibrations,  or  the  6th  note  in  the  scale.  With  -^-^ 
of  the  string,  there  are  90  vibrations,  or  the  7th  note  in  the  scale.  The 
original  note,  which  may  be  called  C,  is  the  key-note,  or  the  tonic.  In 
this  scale,  which  is  called  the  natural,  or  diatonic,  there  is  a  regular  mathe- 
matical progression  from  the  ist  to  the  8th.  This  is  called  the  major 
key.  Melody  consists  in  an  agreeable  succession  of  notes,  which  may 
be  assumed,  for  the  sake  of  simplicity,  to  be  pure.  In  a  simple  melody 
every  note  must  be  one  of  those  in  the  scale.  When  a  different  note  is 
sounded,  the  melody  passes  into  a  key  that  has  a  different  fundamental 
note,  or  tonic,  with  a  different  succession  of  3ds,  5ths  etc.  Every  key, 
therefore,  has  its  ist,  3d,  5th  and  8th,  as  well  as  the  intermediate  notes. 
If  a  note  formed  by  a  string  |  the  length  of  the  tonic  instead  of  4^,  is  sub- 
stituted for  the  major  3d,  the  key  is  converted  into  the  minor.     The  minor 


726  SPECIAL    SENSES 

chord,  consisting  of  the  ist,  the  minor  3d,  the  5th  and  the  8th,  is  harmo- 
nious, but  it  has  a  quality  quite  different  from  that  of  the  major  chord. 
The  notes  of  a  melody  may  progress  in  the  minor  key  as  well  as  in  the 
major.  Taking  the  small  numbers  of  vibrations  merely  for  convenience, 
the  following  is  the  mode  of  progression  in  the  natural  scale,  which  may 
be  assumed  to  be  the  scale  of  C  major :  — 


1st 

2d 

3d 

4th 

5th 

6th 

7th 

8th 

c 

D 

E 

F 

G 

A 

B 

C 

J 

R 

4 

3 

9 

3 

8 

1 

? 

4 

3 

1  0 

2 

48 

54 

6^ 

64 

72 

80 

90 

96 

Note 

Lengths  of  the  strings 
Number  of  vibrations 

The  intervals  between  the  notes  of  the  scale,  it  is  seen,  are  not  equal. 
The  smallest,  between  the  3d  and  4th  and  the  7th  and  8th,  are  called 
semitones.  The  other  intervals  are  either  full  perfect  tones  or  small 
perfect  tones.  Although  there  are  semitones,  not  belonging  to  the  key 
of  C,  between  C  and  D,  D  and  E,  F  and  G,  G  and  A,  and  A  and  B, 
these  intervals  are  not  all  composed  of  exactly  the  same  number  of 
vibrations ;  so  that,  taking  the  notes  on  a  piano,  with  D  as  the  tonic, 
the  5th  would  be  A.  It  is  assumed  that  D  has  54  vibrations,  and  A, 
80,  giving  a  difference  of  26.  With  C  as  the  tonic  and  G  as  the  fifth, 
there  is  a  difference  of  24.  It  is  on  account  of  these  differences  in  the 
intervals,  that  each  key  in  music  has  a  more  or  less  peculiar  and  dis- 
tinctive character. 

Even  in  melody,  and  still  more  in  harmony,  in  long  compositions, 
the  ear  becomes  fatigued  by  a  single  key,  and  it  is  necessary  in  order  to 
produce  the  most  pleasing  effects  to  change  the  tonic,  by  what  is  called 
modulation,  returning  afterward  to  the  original  key. 

Quality  of  Musical  Sounds.  —  Nearly  all  musical  sounds,  which 
seem  at  first  to  be  simple,  can  be  resolved  into  certain  well-defined  con- 
stituents ;  but  with  the  exception  of  the  notes  of  great  stopped  pipes  in 
the  organ,  there  are  few  absolutely  simple  sounds  used  in  music.  Thesi 
simple  sounds  are  pure,  but  are  of  unsatisfactory  quality  and  wanting 
in  richness.  Almost  all  other  musical  sounds  have  a  fundamental  tone 
which  is  at  once  recognized  ;  but  this  tone  is  accompanied  by  harmonics 
caused  by  secondary  vibrations  of  subdivisions  of  the  sonorous  body. 
The  number,  pitch  and  intensity  of  these  harmonic,  or  aliquot  vibra- 
tions affect  what  is  called  the  quality,  or  timbre  of  musical  notes,  by 
modifying  the  form  of  the  sonorous  waves.  A  string  vibrating  a  certain 
number  of  times  in  a  second,  if  the  vibrations  were  absolutely  simple, 
would  produce,  according  to  the  laws  of  vibrating  bodies,  a  simple  musi- 
cal tone ;  but  as  the  string  subdivides  itself  into  different  portions,  one 
of  which  gives  the  3d,  another,  the  5th,  and  so  on,  of  the  fundamental, 
it  is  evident  that  the  form  of  the  vibrations  must  be  considerably  modi- 


PHYSICS    OF    SOUND  727 

fied,  and  with  these  modifications  in  form,  the  quality,  or  timbre  of  the 
note  is  changed. 

From  what  has  just  been  stated,  it  follows  that  nearly  all  musical 
notes  consist,  not  only  of  a  fundamental  sound,  but  of  harmonic  vibra- 
tions subordinate  to  the  fundamental  and  qualifying  it  in  a  particular 
way.  These  harmonics  may  be  feeble  or  intense  ;  certain  of  them  mav 
predominate  over  others  ;  some  that  usually  are  present  may  be  elimi- 
nated ;  and,  in  short,  there  may  be  a  great  diversity  in  their  arrangement, 
and  thus  the  timbre  may  present  an  infinite  variety.  This  is  one  of  the 
elements  entering  into  the  composition  of  notes,  and  it  affords  a  partial 
explanation  of  quality. 

Another  element  in  the  quality  of  notes  depends  on  their  reenforce- 
ment  by  resonance.  The  vibrations  of  a  stretched  string  not  connected 
with  a  resonant  body  are  almost  inaudible.  In  musical  instruments  the 
sound  is  taken  up  by  some  mechanical  arrangement,  as  the  sound- 
board of  the  organ,  piano,  violin,  harp  or  guitar.  In  the  violin,  for 
example,  the  sweetness  of  the  notes  depends  mainly  on  the  construction 
of  the  resonant  part  of  the  instrument  and  but  little  on  the  strings  them- 
selves, which  latter  are  frequently  changed ;  and  the  same  is  in  a 
measure  true  of  the  human  voice. 

In  addition  to  the  harmonic  tones  of  sonorous  bodies,  various  discord- 
ant sounds  usually  are  present,  which  modify  the  timbre,  producing  a 
certain  roughness,  such  as  the  grating  of  a  violin-bow,  the  friction  of 
the  columns  of  air  against  the  angles  in  wind-instruments,  etc.  All 
these  conditions  have  their  effect  on  the  quality  of  tones ;  and  these  dis- 
cordant sounds  may  exist  in  infinite  number  and  variety.  These  sounds 
are  composed  of  irregular  vibrations  and  consequently  are  inharmonious. 
Nearly  all  notes  that  are  spoken  of  in  general  terms  as  musical  are  com- 
posed of  musical,  or  harmonic  aliquot  tones,  with  the  discordant  ele- 
ments to  which  allusion  has  just  been  made. 

Aside  from  the  relations  of  the  various  component  parts  of  musical 
notes,  the  quality  depends  largely  on  the  form  of  the  vibrations.  To 
quote  the  words  of  Helmholtz,  "the  more  uniformly  rounded  the  form 
of  the  wave,  the  softer  and  milder  is  the  qualitv  of  the  sound.  The 
more  jerking  and  angular  the  wave-form,  the  more  piercing  the  quality. 
Tuning-forks,  with  their  rounded  form  of  waves,  have  a  remarkably  soft 
quality  ;  and  the  qualities  of  sound  produced  by  the  zither  and  violin 
resemble  in  harshness  the  angularity  of  their  wave-forms." 

Harmonics,  or  Overtoiics.  —  As  before  stated,  nearly  all  sounds  are 
composite  ;  but  some  contain  many  more  aliquot,  or  secondary  vibrations 
than  others.  The  notes  of  vibrating  strings  are  peculiarly  rich  in  har- 
monics; and  these  may  be  used  for  illustration,  remembering  that  the 


728  SPECIAL   SENSES 

phenomena  here  observed  have  their  analogies  in  nearly  all  varieties  of 
musical  sounds.  If  a  stretched  string  is  made  to  vibrate,  the  secondary 
tones,  which  qualify  the  fundamental,  are  called  harmonics,  or  overtones. 
While  it  is  difficult  at  all  times  to  distinguish  by  the  ear  the  individ- 
ual overtones  of  vibrating  strings,  their  existence  can  be  demonstrated 
by  certain  simple  experiments.  Take,  for  example,  a  string,  the  funda- 
mental tone  of  which  is  C.  If  this  string  is  damped  with  a  feather  at 
one-fourth  of  its  length  and  a  violin-bow  is  drawn  across  the  shorter 
section,  not  only  the  fourth  part  of  the  string  across  which  the  bow  is 
drawn  is  made  to  vibrate,  but  the  remaining  three-fourths  ;  and  if  little 
riders  of  paper  are  placed  on  the  longer  section  at  distances  equal  to 
one-fourth  of  the  entire  string,  they  will  remain  undisturbed,  while  riders 
placed  at  any  other  points  on  the  string  will  be  thrown  off.  This  ex- 
periment shows  that  the  three-fourths  of  the  string  have  been  divided. 
This  may  be  illustrated  by  connecting  one  end  of  the  string  with  a  tun- 
ing-fork. When  this  is  done  and  the  string  is  brought  to  the  proper 
degree  of  tension,  it  will  first  vibrate  as  a  whole,  then,  when  a  little 
tighter,  will  spontaneously  divide  into  two  equal  parts,  and  under  in- 
creased tension,  into  three,  four  and  so  on.  By  damping  a  string  with 
the  light  touch  of  a  feather,  it  is  possible  to  suppress  the  fundamental 
tone  and  bring  out  the  overtones,  which  exist  in  all  vibrating  strings  but 
usually  are  overpowered  by  the  fundamental.  The  points  that  mark 
the  subdivisions  of  the  string  into  segments  of  secondary  vibrations  are 
called  nodes.  When  the  string  is  damped  at  its  centre,  the  fundamental 
tone  is  quenched  and  there  are  overtones  an  octave  above ;  damping  it 
at  a  distance  of  one-fourth,  there  is  the  second  octave  above,  and  so  on. 
When  the  string  is  damped  at  a  distance  of  one-fifth  from  the  end,  the 
four-fifths  sound  the  3d  of  the  fundamental,  with  the  second  octave  of 
the  3d.  If  it  is  damped  at  a  distance  of  two-thirds,  there  is  the  5th  of 
the  fundamental,  with  the  octave  of  the  5th.  Every  vibrating  string 
thus  possesses  a  fundamental  tone  and  overtones.  Qualifying  the 
fundamental,  there  is  first,  as  the  most  simple,  a  series  of  octaves;  next, 
a  series  of  5ths  of  the  fundamental  and  their  octaves ;  and  next,  a  series 
of  3ds.  These  are  the  most  powerful  overtones,  and  they  form  the 
common  chord  of  the  fundamental ;  but  they  are  so  far  concealed  by 
the  greater  intensity  of  the  fundamental  that  they  can  not  easily  be 
distinguished  by  the  unaided  ear,  unless  the  fundamental  has  been 
quenched  in  some  way.  In  the  same  way  the  harmonic  5ths  and  3ds 
overpower  other  overtones ;  for  the  string  is  subdivided  again  and  again 
into  overtones,  which  are  not  harmonious  like  the  notes  of  the  common 
chord  of  the  fundamental. 

The  presence  of   overtones,  resultant   tones  and    additional   tones, 


PHYSICS   OF   SOUND 


729 


which  latter  will  be  described  hereafter,  can  be  demonstrated,  without 
damping  the  strings,  by  resonators.  It  is  well  known  that  if  a  glass 
tube,  closed  at  one  end,  which  contains  a  column  of  air  of  a  certain 
length,  is  brought  near  a  resounding  body  emitting  a  note  identical  with 
that  produced  by  the  vibrations  of  the  column  of  air,  the  air  in  the  tube 
will  resound  in  consonance  with  the  note,  while  no  other  note  will  have 
this  effect.  The  resonators  of  Helmholtz  are  constructed  on  this  prin- 
ciple. A  glass  globe  or  tube  (Fig.  189)  is  constructed  so  as  to  produce 
a  certain  note.  This  has  a  larger  opening  (a)  and  a  smaller  opening  (b), 
which  latter  is  fitted  in  the  ear  with  warm  sealing-wax,  the  other  ear 
being  closed.  When  the  proper  note  is  sounded,  it  is  reenforced  by  the 
resonator  and  is  greatly  increased  in  intensity,  while  all  other  notes  are 
heard  very  faintly.  By  using  resonators  graduated  to  the  musical  scale, 
it  is  easy  to  analyze  a  note 
and  distinguish  its  over- 
tones. The  resonators  of 
Helmholtz  that  are  open 
at  the  larger  extremity  are 
more  delicate  than  those 
in  which  this  is  closed  with 
a  membrane. 

A  striking  and  instruc- 
tive point  in  the  present 
discussion  is  the  follow- 
ing :  All  the  overtones  are  ' 
produced  by  vibrations  of 
divisions  of  the  string  in- 
cluded between  the  comparatively  still  points,  called  nodes ;  and  if 
a  string  is  thrown  into  vibration  by  plucking  or  striking  it  at  one  of 
these  nodal  points,  the  overtones  which  vibrate  from  this  node  at  a 
fixed  point  are  abolished.  It  is  readily  understood  that  when  a  string 
is  plucked  at  any  point,  it  will  vibrate  so  vigorously  at  this  point  that  no 
node  can  be  formed.  This  fact  has  long  been  recognized  by  practical 
musicians,  although  many  probably  are  unacquainted  with  its  explana- 
tion. Performers  on  stringed  instruments  habitually  attack  the  strings 
near  one  of  their  extremities.  In  the  piano,  where  the  strings  may  be 
struck  at  almost  any  point,  the  hammers  are  placed  at  a  distance  of  ^ 
to  ^  of  the  length  of  the  strings  from  their  extremities  ;  and  it  has  been 
ascertained  by  experience  that  this  gives  the  richest  notes.  The  nodes 
formed  at  these  points  would  produce  the  /ths  and  9ths  as  overtones, 
which  do  not  belong  to  the  perfect  major  chord,  while  the  nodes  for  the 
harmonious    overtones    are    undisturbed.      The  reason,  then,  why  the 


Fig.  189.  —  Resonators  of  Helmholtz. 


730 


SPECIAL    SExNSES 


notes  are  richer  when  the  strings  are  attacked  at  this  point,  is  that 
the  harmonious  overtones  are  full  and  perfect,  and  certain  of  the  dis- 
cordant overtones  are  suppressed. 

When  two  harmonious  notes  are  produced  under  favorable  condi- 
tions, one  can  hear,  in  addition  to  the  two  sounds,  a  sound  differing 
from  both  and  much  lower  than  the  lower  of  the  two.  This  sound  is 
too  low  for  an  harmonic,  and  it  has  been  called  a  resultant  tone.  The 
formation  of  a  new  sound  by  combining  two  sounds  of  different  pitch 
is  analogous  to  the  blending  of  colors  in  optics,  except  that  the  primary- 
sounds  are  not  lost.  The  laws  of  the  production  of  these  resultant 
sounds  are  very  simple.  When  two  notes  in  harmony  are  sounded,  the 
resultant  tone  is  equal  to  the  difference  between  the  two  primaries. 
For  example,  C,  with  48  vibrations,  and  its  5th,  with  72  vibrations  in  a 
second,  give  a  resultant  tone  equal  to  the  difference,  which  is  24  vibra- 
tions, and  it  is  consequently  the  octave  below  C.  These  resultant  tones 
are  feeble  as  compared  with  the  primary  tones,  and  they  can  be  heard 
under  only  the  most  favorable  experimental  conditions.  In  addition  to 
these  sounds,  Helmholtz  has  discovered  sounds,  even  more  feeble,  which 
he  calls  additional,  or  summation-tones.  The  value  of  these  is  equal  to 
the  sum  of  vibrations  of  the  primary  tones.  For  example,  C  (48)  and 
its  5th  (72)  would  give  a  summation-tone  of  120  vibrations,  or  the  octave 
of  the  3d  ;  and  C  (48)  with  its  3d  (60)  would  give  108  vibrations,  the 
octave  of  the  2d.  These  tones  can  be  distinguished  by  means  of 
resonators. 

It  is  thus  seen  that  musical  sounds  are  complex.  With  single 
notes  there  are  many  different  harmonics,  or  overtones,  and  in  chords 
there  are  series  of  resultants,  that  are  lower  than  the  primary  notes,  and 
series  of  additional,  or  summation-tones,  that  are  higher ;  but  both  the 
resultant  and  the  summation-tones  bear  exact  mathematical  relations  to 
the  primary  notes. 

Harmony.  —  Overtones,  resultant  tones  and  summation-tones  of 
strings  have  been  discussed  rather  fully,  for  the  reason  that  in  studying 
the  physiology  of  audition,  it  will  be  seen  that  the  ear  is  capable  of 
recognizing  single  sounds  or  successions  of  single  sounds  ;  but  at  the 
same  time  certain  combinations  of  sounds  are  appreciated  and  are  even 
more  agreeable  than  those  which  apparently  are  produced  by  simple 
vibrations.  Combinations  of  notes  which  thus  produce  an  agreeable 
impression  are  called  harmonious.  They  seem  to  become  blended  with 
each  other  into  a  complete  sound  of  peculiar  quality,  all  the  different 
vibrations  entering  into  their  composition  being  simultaneously  appre- 
ciated by  the  ear.  The  blending  of  notes  which  bear  to  each  other 
certain  mathematical  relations   is   called  harmony ;    but  two    or   more 


HARMONY   AND    DISCORDS  73 1 

notes,  though  each  one  be  musical,  are  not  necessarily  harmonious. 
The  most  prominent  overtone,  except  the  octave,  is  the  5th,  with  its 
octaves,  and  this  is  called  the  dominant.  The  next  is  the  3d,  with  its 
octaves.  The  other  overtones  are  comparatively  feeble.  Reasoning, 
now,  from  a  knowledge  of  the  relations  of  overtones,  it  might  be  in- 
ferred that  the  reenforcement  of  the  5th  and  3d  by  other  notes  bearing 
similar  relations  to  the  tonic  would  be  agreeable.  This  is  the  fact ;  and 
it  was  ascertained  empirically  long  before  the  pleasing  impression  pro- 
duced by  such  combinations  was  explained  mathematically. 

It  is  a  law  in  music  that  the  simpler  the  ratio  between  the  number 
of  vibrations  in  two  sounds,  the  better  the  harmony.  The  simplest 
relation,  of  course,  is  i  :  i,  when  the  two  sounds  are  said  to  be  in  unison. 
The  next  in  order  is  1:2.  In  sounding  C  and  its  8th,  for  example, 
there  are  48  vibrations  of  one  to  96  of  the  other.  These  sounds  can 
produce  no  discord,  because  the  waves  never  interfere  with  each  other, 
and  the  two  sounds  can  be  prolonged  indefinitely,  always  maintaining 
the  same  relations.  The  combined  impression,  therefore,  is  continuous. 
The  next  in  order  are  the  ist  and  5th,  their  relations  being  2:3.  In 
other  words,  with  the  ist  and  5th,  for  two  waves  of  the  ist  there  are 
three  waves  of  the  5th.  The  two  sounds  may  thus  progress  indefi- 
nitely, for  the  waves  coincide  for  every  second  wave  of  the  ist  and 
every  third  wave  of  the  5th.  The  next  in  order  is  the  3d.  The  3d 
of  C  has  the  8th  of  C  for  its  5th,  and  the  5th  of  C  for  its  minor  3d. 
The  1st,  3d,  5th  and  8th  form  the  common  major  chord  ;  and  the  waves 
of  each  note  blend  with  each  other  at  such  short  intervals  of  time  that 
the  ear  experiences  a  continuous  impression,  and  no  discord  is  heard. 
This  explanation  of  the  common  major  chord  illustrates  the  law  that 
the  smaller  the  ratio  of  vibration  between  different  tones,  the  better  is 
their  harmony.  Sounded  with  the  ist,  the  4th  is  more  harmonious 
than  the  3d ;  but  its  want  of  harmony  with  the  5th  excludes  it  from  the 
common  chord.  The  1st,  4th  and  8th  are  harmonious,  but  to  make  a 
complete  chord  the  6th  must  be  added. 

Discords  and  Dissonance.  —  A  knowledge  of  the  mechanism  of  sim- 
ple accords  leads  naturally  to  a  comprehension  of  the  rationale  of  dis- 
cords and  dissonance.  Two  inharmonious  notes  that  can  not  be  resolved 
into  harmony  by  the  addition  of  another  note  or  other  notes  produce 
discord.  When  the  inharmonious  sound  is  resolved  into  a  harmony, 
the  notes  first  sounded  produce  what  is  called  dissonance.  The  fact 
that  certain  combinations  of  musical  notes  produce  a  disagreeable  im- 
pression was  first  ascertained  empirically,  with  no  knowledge  of  the 
exact  cause ;  but  the  mechanism  of  discord  is  now  regarded  by  most 
physicists  as  settled. 


732 


SPECIAL    SENSES 


The  sounds  produced  by  two  tuning-forks  giving  precisely  the  same 
number  of  vibrations  in  a  second  are  in  unison.  If  one  of  the  forks  is 
loaded  with  a  bit  of  wax,  so  that  its  vibrations  are  sHghtly  reduced,  and 
if  both  are  put  in  vibration  at  the  same  instant,  there  is  discord.  Taking 
the  illustration  given  by  Tyndall,  it  may  be  assumed  that  one  fork  has 
256,  and  the  other,  255  vibrations  in  a  second.  While  these  two  forks 
are  vibrating,  one  is  gradually  gaining  on  the  other ;  but  at  the  end  of 
half  a  second,  one  will  have  made  128  vibrations,  while  the  other  wall 
have  made  127.^.  At  this  point  the  two  waves  are  moving  in  exactly 
opposite  directions ;  and  as  a  consequence,  the  sounds  neutralize  each 
other  and  there  is  an  instant  of  silence.  The  perfect  sounds,  as  the 
two  forks  continue  to  vibrate,  are  thus  alternately  reenforced  and  dimin- 
ished, and  this  produces  what  is  known  in  music  as  beats.  As  the 
difference  in  the  number  of  vibrations  in  a  second  is  one,  the  instants 
of  silence  occur  once  in  a  second  ;  and  in  this  illustration  the  beats 
occur  once  a  second.  Unison  takes  place  when  two  sounds  can  follow 
each  other  indefinitely,  their  waves  blending  perfectly ;  and  discord  or 
dissonance  is  marked  by  successive  beats,  or  pulses.  If  the  forks  are 
loaded  so  that  one  will  vibrate  240  times  in  a  second,  and  the  other  234, 
there  will  be  six  instants  in  a  second  when  the  interference  will  be  mani- 
fest ;  or  in  other  words  in  |  of  a  second,  one  fork  will  make  40  vibra- 
tions, while  the  other  is  making  39.  This  will  give  6  beats  in  a  second. 
From  these  experiments  the  law  may  be  deduced  that  the  number  of 
beats  produced  by  two  tones  not  in  harmony  is  equal  to  the  difference 
between  the  two  rates  of  vibration.  An  analogous  interference  of 
undulations  is  observed  in  optics,  when  waves  of  light  are  made  to 
interfere  and  produce  darkness. 

It  is  evident  that  the  number  of  beats  will  increase  as  two  discord- 
ant notes  are  produced  higher  and  higher  in  the  scale.  According  to 
Helmholtz,  beats  can  be  recognized  up  to  132  in  a  second.  Beyond 
that  point  they  become  confused  and  there  is  only  a  general  sensation 
of  discord.  Beats,  then,  are  due  to  interference  of  sound-waves.  There 
is  no  interference  of  the  waves  of  notes  in  unison,  provided  waves  start 
at  the  same  instant ;  the  intensity  of  the  sound  being  increased  by 
reenforcement.  The  differences  between  the  ist  and  8th,  the  ist  and 
5th,  the  1st  and  3d,  and  other  harmonious  combinations,  is  so  great  that 
there  are  no  beats  and  no  discord,  the  more  rapid  waves  reenforcing 
the  harmonics  of  the  primary  sound.  It  is  important  to  remember,  in 
this  connection,  that  resultant  tones  are  equal  to  the  difference  in  the 
rates  of  vibration  of  two  harmonious  notes.  Taking  a  note  of  240 
vibrations,  and  its  5th,  with  360  vibrations,  these  two  have  a  difference 
of  120,  which  is  the  lower  octave  of  the  ist  and  is  an  harmonious  tone. 


TONES    BY    INFLUENCE  733 

The  laws  just  stated  are  applicable  to  overtones,  resultant  tones  and 
additional  tones,  which,  like  the  primary  notes,  have  their  beats  and 
discords. 

To7ies  by  Influence.  —  After  what  has  been  stated  in  regard  to  the 
laws  of  musical  vibrations,  it  will  be  easy  to  comprehend  the  production 
of  sounds  by  influence.  If  a  key  of  the  piano  is  hghtly  touched  so  as 
to  raise  the  damper  but  not  to  sound  the  string,  and  then  a  note  is 
sung  in  unison,  the  string  will  return  the  sound,  by  the  "influence"  of 
the  sound-waves  of  the  voice.  The  sound  thus  produced  by  the  string 
will  have  its  fundamental  tone  and  overtones ;  but  the  series  of  over- 
tones will  be  complete ;  for  none  of  the  nod'es  are  abolished,  as  in 
striking  or  plucking  a  string  at  any  particular  point.  If,  instead  of  a 
note  in  unison,  any  of  the  octaves  are  sounded,  the  string  will  return 
the  exact  note  sung  ;  and  the  same  is  true  of  the  3d,  5th  etc.  If  a 
chord  in  harmony  with  the  undamped  string  is  struck,  this  chord  will 
be  exactly  returned  by  influence.  In  other  words,  a  string  may  be 
made  to  sound  by  influence,  its  fundamental  tone,  its  harmonics  and 
harmonious  combinations.  To  carry  the  observation  still  farther,  the 
string  will  return,  not  only  a  note  of  its  exact  pitch  and  its  harmonics, 
but  notes  of  the  peculiar  quality  of  the  primary  note.  This  is  an  im- 
portant point  in  its  applications  to  the  physiology  of  hearing  and  can  be 
readily  illustrated.  Taking  identical  notes  in  succession,  produced  by 
the  voice,  trumpet,  violin,  clarinet  or  any  other  musical  instrument,  it 
can  easily  be  noted  that  the  quality  of  the  sound,  as  well  as  the  pitch,  is 
rendered  by  a  resounding  string ;  and  the  same  is  true  of  combinations 
of  notes.  The  laws  of  tones  by  influence  have  been  illustrated  by 
strings  merely  for  the  sake  of  simplicity  ;  but  they  are  applicable  more 
or  less  to  all  bodies  capable  of  producing  musical  sounds,  except  that 
some  are  thrown  into  vibration  with  more  difficulty  than  others. 

A  thin  membrane,  like  a  piece  of  bladder  or  thin  rubber,  stretched 
over  a  circular  orifice,  such  as  the  mouth  of  a  wide  bottle,  may  readily 
be  tuned  to  a  certain  note.  When  arranged  in  this  way,  the  membrane 
can  be  made  to  sound  its  fundamental  tone  by  influence.  In  addition, 
the  membrane,  like  a  string,  will  divide  itself  so  as  to  sound  the  har- 
monics of  the  fundamental,  and  it  will  likewise  be  thrown  into  vibration 
by  the  5th,  3d  etc.,  of  its  fundamental,  thus  obeying  the  laws  of  vibra- 
tions of  strings,  although  the  harmonic  sounds  are  produced  with  greater 
difficulty.^ 

1  The  account  just  given  of  some  of  the  laws  of  sonorous  vibrations  and  their  relations  to 
musical  effects  and  combinations,  although  by  no  means  complete,  may  seem  rather  extended 
for  a  work  on  physiology;  but  it  should  be  borne  in  mind  that  the  mechanism  of  the  apprecia- 
tion of  musical  sounds  includes  the  entire  physiology  of  audition.     This  subject   can   not    be 


734 


SPECIAL    SENSES 


Uses  of  Different  Parts  of  the  Middle  Ear 


The  uses  of  the  pavilion  and  of  the  external  auditory  meatus  are 
sufficiently  plain.  The  pavilion  serves  to  collect  the  waves  of  sound, 
and  probably  it  inclines  them  toward  the  external  meatus  as  they  come 
from  various  directions.  Although  this  action  is  simple,  it  has  some 
importance,  and  the  various  curves  of  the  concavity  of  the  pavilion  tend 
more  or  less  to  concentrate  sonorous  vibrations.  Such  has  long  been 
the  opinion  of  physiologists,  and  this  seems  to  be  carried  out  by  experi- 
ments in  which  the  concavities  of  the  external  ear  have  been  obliterated 
by  wax.  There  probably  is  no  resonance  or  vibration  of  much  impor- 
tance until  the  waves  of  sound  strike  the  membrana  tympani.  The  same 
remarks  may  be  made  in  regard  to  the  external  auditory  meatus.  It  is 
not  known  precisely  how  the  obliquity  and  the  curves  of  this  canal 
affect  the  waves  of  sound,  but  it  is  probable  that  the  deviation  from  a 
straight  course  protects,  to  a  certain  extent,  the  tympanic  membrane 
from  impressions  that  might  otherwise  be  too  violent. 

Structure  of  the  Membrana  Tympani.  —  The  general  arrangement  of 
the  membrana  tympani  has  already  been  described  in  connection  with 
the  topographical  anatomy  of  the  auditory  apparatus.  The  membrane 
is  elastic,  about  the  thickness  of  ordinary  gold-beater's  skin,  and  is 
subject  to  various  degrees  of  tension  by  the  action  of  the  muscles  of  the 
middle  ear  and  under  different  conditions  of  atmospheric  pressure  within 
and  without  the  tympanic  cavity.  Its  form  is  nearly  circular ;  and  it  has  a 
diameter  in  the  adult,  according  to  Sappey,  of  a  little  more  than  |-  of  an 
inch  (lo  to  II  millimeters)  vertically  and  about  \  of  an  inch  (lo  milli- 
meters) antero-posteriorly.  The  excess  of  the  vertical  over  the  hori- 
zontal diameter  is  about  ^^q  of  an  inch  (0.5  millimeter). 

The  periphery  of  the  tympanic  membrane  is  received  into  a  little 
ring  of  bone,  which  may  be  separated  by  maceration  in  early  life  but  is 
consolidated  with  the  adjacent  bony  structures  in  the  adult.  This  bony 
ring  is  incomplete  at  its  superior  portion,  but  aside  from  this,  it  resem- 
bles the  groove  which  receives  the  crystal  of  a  watch.  At  the  periphery 
of  the  membrane,  is  a  ring  of  condensed  fibrous  tissue  which  is  received 
into  the  bony  ring.  This  ring  also  presents  a  break  at  its  superior 
portion. 

The  concavity  of  the  membrana  tympani  presents  outward,  and  it 

comprehended  without  a  general  knowledge  of  the  physics  of  sound  and  of  some  of  the  laws  of 
harmony  ;  for  not  only  is  there  a  perception  of  single  notes  by  the  auditory  apparatus,  but  the 
most  elaborate  combinations  of  sounds  in  harmony  are  appreciated  together  and  at  one  and  the 
•  same  instant,  as  will  be  seen  in  studying  the  action  and  uses  of  different  parts  concerned  in  audi- 
tion. Many  of  the  laws  of  musical  combinations  are  directly  applicable  to  the  physiology  of 
hearing. 


THE   MEMBRANA    TYMPANI 


735 


may  be  increased  or  diminished  by  the  action  of  the  muscles  of  the 
middle  ear.  The  point  of  greatest  concavity,  where  the  extremity  of 
the  handle  of  the  malleus  is  attached,  is  called  the  umbo.  On  the  inner 
surface  of  the  membrane  are  two  pouches,  or  pockets.  One  is  formed 
by  a  small,  irregular,  triangular  fold,  situated  at  the  upper  part  of  its 
posterior  half  and  consisting 
of  a  process  of  the  fibrous 
layer.  This,  which  is  called 
the  posterior  pocket,  is  open 
below  and  extends  from  the 
posterior  upper  border  of 
the  membrane  to  the  handle 
of  the  malleus,  which  it  as- 
sists in  holding  in  position. 
"  After  it  has  been  divided, 
the  bone  is  much  more 
movable  than  before" 
(Troltsch).  The  anterior 
pocket  is  lower  and  shorter 
than  the  posterior.  It  is 
formed  by  a  small  bony 
process  turned  toward  the 
neck  of  the  malleus,  by 
the  mucous  membrane,  by 
the  bony  process  of  the  mal- 
leus, by  its  anterior  liga- 
ment, the  chorda  tympani 
and  the  anterior  tympanic 
artery.  The  handle  of  the 
malleus  is  inserted  between 
the  two  layers  of  the  fibrous 
structure  of  the  membrana 
tympani  and  occupies  the 
upper  half  of  its  vertical  di- 
ameter, extending  from  the 
periphery  to  the  umbo. 

The  membrana  tympani,  though  thin  and  translucent,  presents  three 
distinct  layers.  Its  outer  layer  is  a  very  thin  extension  of  the  integu- 
ment lining  the  external  meatus,  presenting,  however,  neither  papillae 
nor  glands.  The  inner  layer  is  a  delicate  continuation  of  the  mucous 
membrane  lining  the  tympanic  cavity  and  is  covered  with  tessellated 
epithelial  cells.     The  fibrous  portion,  or  lamina  propria,  is  formed  of 


Fig.  190.  —  Right  met?ibra>7a  tympani,  seen  from  within,  X  6. 
Reduced  about  one-fifth  from  a  photograph  (Riidinger). 

I,  head  of  the  malleus,  divided;  2,  neck  of  the  malleus; 
3,  handle  of  the  malleus,  with  the  tendon  of  the  tensor-tym- 
pani  muscle;  4,  divided  tendon  of  the  tensor  tympani;  5,  6, 
portion  of  the  malleus  between  the  layers  of  the  membrana 
tympani;  7,  outer  (radiating)  and  inner  (circular)  fibres  of 
the  membrana  tympani;  8,  fibrous  ring  of  the  membrana 
tympani ;  9,  14,  15,  dentated  fibres,  discovered  by  Gruber ; 
10,  posterior  pocket ;  ii,  connection  of  the  posterior  pocket 
with  the  malleus;  12,  anterior  pocket ;  13,  chorda-tympani 
nerve. 


736  SPECIAL    SENSES 

two  layers.  The  outer  layer  consists  of  fibres  radiating  from  the  handle 
of  the  malleus  to  the  periphery.  These  are  best  seen  near  the  centre. 
The  inner  layer  is  composed  of  circular  fibres,  which  are  most  abundant 
near  the  periphery  and  diminish  in  number  toward  the  centre. 

The  color  of  the  membrana  tympani,  when  it  is  examined  with  an 
aural  speculum  by  daylight,  is  peculiar,  and  it  is  rather  difficult  to 
describe,  as  it  varies  in  the  normal  ear  in  different  individuals.  Politzer 
described  the  membrane,  examined  in  this  way,  as  translucent,  and  of  a 
color  which  "  most  nearly  approaches  a  neutral  gray,  mingled  with  a 
weaker  tint  of  violet  and  light  yellowish  brown."  This  color  is  modified, 
in  certain  portions  of  the  membrane,  by  the  chorda  tympani  and  the 
bones  of  the  ear,  which  produce  some  opacity.  The  entire  membrane 
in  health  has  a  soft  lustre.  In  addition  there  is  seen,  with  proper  illu- 
mination, a  well-marked  triangular  cone  of  light,  with  its  apex  at  the 
end  of  the  handle  of  the  malleus,  spreading  out  in  a  downward  and  for- 
ward direction,  and  ^^  to  j^  of  an  inch  (1.6  to  2.1  millimeters)  broad  at 
its  base.  This  appearance  is  regarded  by  physiologists  as  indicating  a 
normal  condition  of  the  membrane.  It  is  undoubtedly  due  to  reflection 
of  light  and  not  to  a  peculiar  structure  of  that  portion  of  the  membrane 
on  which  it  is  seen. 

[/ses  of  the  Membrana  Tympani.  —  It  is  unquestionable  that  the 
membrana  tympani  is  very  important  in  audition.  In  cases  of  disease 
in  which  the  membrane  is  thickened,  perforated  or  destroyed,  the  acute- 
ness  of  hearing  is  more  or  less  affected.  That  this  is  in  great  part  due 
to  the  absence  of  a  vibrating  surface  for  the  reception  of  waves  of  sound, 
is  shown  by  the  relief  experienced  by  patients  who  can  tolerate  the 
presence  of  an  artificial  membrane  of  rubber.  As  regards  the  mere 
acuteness  of  hearing,  aside  from  the  pitch  of  sounds,  the  explanation  of 
the  action  of  the  membrane  is  very  simple.  Sonorous  vibrations  are 
not  readily  transmitted  through  the  atmosphere  to  solid  bodies,  like  the 
bones  of  the  ear;  and  when  they  are  thus  transmitted  they  lose  consid- 
erably in  intensity.  When,  however,  the  aerial  vibrations  are  received  by 
a  membrane,  under  the  conditions  of  the  membrana  tympani,  they  are 
transmitted  with  little  loss  of  intensity  ;  and  if  this  membrane  is  con- 
nected with  solid  bodies,  like  the  bones  of  the  middle  ear,  the  vibrations 
are  readily  conveyed  to  the  sensory  portions  of  the  auditory  apparatus. 
The  parts  composing  the  middle  ear  are  well  adapted  to  the  transmis- 
sion of  sonorous  waves  to  the  auditory  nerves.  The  membrane  of  the 
tympanum  is  delicate  in  structure,  stretched  to  the  proper  degree  of 
tension,  and  vibrates  under  the  influence  of  the  waves  of  sound. 
Attached  to  this  membrane,  is  the  angular  chain  of  bones,  which  con- 
ducts its  vibrations,  hke  the  bridge  of  a  violin,  to  the    liquid   of    the 


THE    MEMBRANA   TYMPANI  737 

labyrinth.  The  membrane  is  fixed  at  its  periphery  and  has  air  on  both 
sides,  so  that  it  is  under  conditions  favorable  for  vibration. 

A  study  of  the  mechanism  of  the  ossicles  and  muscles  of  the  middle 
ear  shows  that  the  membrana  tympani  is  subject  to  certain  physiological 
variations  in  tension,  due  to  the  contraction  of  the  tensor  tympani.  It  is 
also  evident  that  this  membrane  may  be  drawn  in  and  rendered  tense  by 
exhausting  or  rarefying  the  air  in  the  drum.  If  the  mouth  and  nose  are 
closed  and  an  attempt  is  made  to  breathe  forcibly  by  expanding  the  chest, 
the  external  pressure  tightens  the  membrane.  In  this  condition  the  ear 
is  rendered  insensible  to  grave  sounds,  but  high-pitched  sounds  appear 
to  be  more  intense.  If  the  tension  is  removed,  as  may  be  done  by  an 
act  of  swallowing,  the  grave  sounds  are  heard  with  normal  distinctness. 
This  experiment,  tried  at  a  concert,  produces  the  curious  effect  of  abol- 
ishing a  great  number  of  the  lowest  tones,  while  the  shrill  sounds  are 
heard  very  acutely.  The  same  phenomena  are  observed  when  the 
external  pressure  is  increased  by  descent  in  a  diving  bell. 

Undoubted  cases  of  voluntary  contraction  of  the  tensor  tympani 
have  been  observed  by  otologists ;  and  in  these,  by  bringing  this  mus- 
cle into  action,  the  limit  of  perception  of  high  tones  may  be  greatly  in- 
creased. In  two  instances  of  this  kind,  recorded  by  Blake,  the  ordinary 
limit  of  perception  was  found  to  be  three  thousand  single  vibrations,  and 
by  contraction  of  the  muscle,  this  was  increased  to  five  thousand. 

The  concave  form  of  the  membrana  tympani  and  the  presence  of  a 
bony  process  between  its  layers,  which  is  part  of  the  chain  of  bones  of 
the  middle  ear,  are  conditions  under  which  it  is  impossible  that  it  should 
have  a  single  fundamental  tone.  This  has  been  shown  by  experiments 
with  stretched  membranes  depressed  in  their  central  portion  by  means 
of  a  solid  rod.  No  membrane  can  have  a  single  fundamental  tone 
unless  it  be  in  a  condition  of  uniform  tension,  like  a  string,  and  this  is 
impossible  in  the  membrana  tympani.  Nevertheless,  the  membrana 
tympani  repeats  sounds  by  influence  and  is  capable  of  repeating  in  this 
way  a  much  greater  variety  of  sounds  than  if  it  had  itself  a  fundamental 
tone  and  were  capable  of  a  uniform  degree  of  tension.  This  has  been 
shown  by  experiments  with  stretched  elastic  membranes  made  to  assume 
a  concave  form.  If  the  membrana  tympani  had  a  single  fundamental 
tone,  it  would  vibrate  by  influence  only  with  certain  tones  in  unison  with 
it  and  the  overtones  would  be  eliminated.  It  would  then  act  like  a 
resonator  closed  with  a  membrane  ;  and  the  tone  with  which  it  hap- 
pened to  be  in  unison  would  overpower  all  others.  The  fact  is  that  all 
tones,  the  vibrations  of  which  reach  the  membrane,  are  appreciated 
at  their  proper  value  as  regards  intensity.  Again,  if  the  membrana 
tympani  had  its  own  fundamental  tone,  it  would  have  overtones  of  the 


738  SPECIAL   SENSES 

fundamental,  which  would  produce  errors  and  confusion  in  auditory 
appreciation.  The  chain  of  bones,  also,  attached  to  the  membrane  acts  as 
a  damper  and  prevents  the  persistence  of  vibrations  after  the  waves  of 
sound  cease  in  the  air.  This  provision  enables  rapid  successions  of 
sounds  to  be  distinctly  and  accurately  repeated. 

The  arrangement  of  the  muscles  and  bones  of  the  middle  ear  is  such 
that  the  tension  of  the  membrana  tympani  may  be  regulated  and  gradu- 
ated with  great  nicety.  It  does  not  seem  to  be  necessary  to  perfect 
audition  that  this  should  be  done  for  every  single  note  or  combination  of 
notes,  but  the  membrane  probably  is  brought  by  voluntary  effort  to  a 
definite  degree  of  tension  for  notes  within  a  certain  range  as  regards 
pitch  or  for  successions  and  progressions  of  sounds  in  a  particular  key. 
So  far  as  the  consciousness  of  this  muscular  action  is  concerned,  it  may 
be  revealed  only  by  the  fact  of  the  correct  appreciation  of  certain  musi- 
cal sounds.  Some  persons  can  educate  the  ear  so  as  to  acquire  what  is 
called  the  faculty  of  absolute  pitch ;  that  is,  without  the  aid  of  a  tuning- 
fork  or  any  musical  instrument,  they  are  able  to  recognize  the  exact 
musical  value  of  any  given  note.  A  possible  explanation  of  this  is  that 
such  persons  may  have  educated  the  muscles  of  the  ear  so  as  to  put  the 
tympanic  membrane  in  such  a  condition  of  tension  as  to  respond  to  a 
given  note  and  to  recognize  the  position  of  this  note  in  the  musical 
scale.  Finally,  an  accomplished  musician,  in  conducting  an  orchestra, 
can  by  a  voluntary  effort  direct  his  attention  to  certain  instruments  and 
hear  their  notes  distinctly,  separating  them  from  the  general  volume  of 
sound,  can  distinguish  discords  and  designate  a  single  instrument  making 
a  false  note. 

Destruction  of  both  tympanic  membranes  does  not  necessarily  pro- 
duce total  deafness,  although  this  condition  involves  considerable  im- 
pairment of  hearing.  So  long  as  there  is  simple  destruction  of  these 
membranes,  the  bones  of  the  middle  ear  and  the  other  parts  of  the  auditory 
apparatus  being  intact,  the  waves  of  sound  are  conducted  to  the  auditory 
nerves,  although  this  is  done  imperfectly.  In  a  case  reported  by  Astley 
Cooper,  one  membrana  tympani  was  entirely  destroyed,  and  the  other  was 
nearly  gone,  there  being  some  parts  of  its  periphery  remaining.  In  this 
person  the  hearing  was  somewhat  impaired,  although  he  could  distin- 
guish ordinary  conversation  without  much  difficulty.  Fortunately,  he 
had  considerable  musical  taste,  and  it  was  ascertained  that  his  musical 
ear  was  not  seriously  impaired  ;  "  for  he  played  well  on  the  flute  and 
had  frequently  borne  a  part  in  a  concert.  I  speak  this,  not  from  his 
authority  only,  but  also  from  that  of  his  father,  who  is  an  excellent  judge 
of  music,  and  plays  well  on  the  violin  :  he  told  me  that  his  son,  besides 
playing  on  the  flute,  sang  with  much  taste,  and  perfectly  in  tune." 


THE    MEMBRANA   TYMPANI  739 

There  is  an  important  consideration  that  must  be  kept  in  view  in 
studying  the  uses  of  any  distinct  portion  of  the  auditory  apparatus,  like 
the  membrana  tympani.  This  membrane,  like  all  other  parts  of  the 
apparatus,  except  the  auditory  nerves  themselves,  has  simply  an  acces- 
sory action.  If  the  regular  waves  of  a  musical  sound  are  conveyed  to 
the  terminal  filaments  of  the  auditory  nerves,  these  waves  make  their 
impression  and  the  sound  is  correctly  appreciated.  It  makes  no  differ- 
ence, except  as  regards  intensity,  how  these  waves  are  conducted  ;  the 
sound  is  appreciated  by  the  impression  made  on  the  nerves,  and  on  the 
nerves  only.  The  waves  of  sound  are  not  like  the  waves  of  light, 
refracted,  decomposed,  perhaps,  and  necessarily  brought  to  a  focus  as 
they  impinge  on  the  retina ;  but  so  far  as  the  action  of  the  accessory 
parts  of  the  ear  are  concerned,  the  waves  of  sound  are  unaltered  ;  that 
is,  the  rate  of  their  succession  remains  the  same,  though  they  are  reflected 
by  the  concavities  of  the  concha  and  repeated  by  the  tympanic  membrane. 
Even  if  it  be  assumed  that  the  membrane  under  normal  conditions  repeats 
musical  sounds  by  vibrations  produced  by  influence,  and  that  sounds  are 
exactly  repeated,  the  position  of  these  sounds  in  the  musical  scale  is  not 
and  can  not  be  altered  by  the  action  of  any  of  the  accessory  organs  of 
hearing.  The  fact  that  a  person  may  retain  his  musical  ear  with  both 
membranes  destroyed  is  not  an  argument  against  the  view  that  the  mem- 
brane repeats  sounds  by  influence  ;  for  if  musical  sounds  or  irregular 
vibrations  are  conducted  to  the  auditory  nerves,  the  impression  produced 
must  of  necessity  be  dependent  exclusively  on  the  character,  regularity 
and  number  of  the  sonorous  vibrations.  And  again,  the  physical  laws  of 
sound  teach  that  a  membrane  like  the  membrana  tympani  must  repro- 
duce sounds  with  which  it  is  more  or  less  closely  in  unison  much  better 
than  discordant  or  irregular  vibrations.  In  a  loud  confusion  of  sounds, 
one  can  readily  distinguish  melody  or  harmony,  even  when  the  vibrations 
of  the  latter  are  comparatively  feeble. 

It  has  been  shown  that  the  appreciation  of  the  pitch  of  sounds  bears 
a  certain  relation  to  the  degree  of  tension  of  the  tympanic  membrane. 
When  the  membrane  is  rendered  tense,  there  is  insensibility  to  low 
notes.  When  the  membrane  is  brought  to  the  highest  degree  of  tension 
by  voluntary  contraction  of  the  tensor  tympani,  the  limit  of  appreciation 
of  high  notes  may  be  raised  from  three  thousand  to  five  thousand  vibra- 
tions. It  is  a  fact  in  the  physics  of  the  membrana  tympani  that  the 
vibrations  are  more  intense  the  nearer  the  membrane  approaches  to  a 
vertical  position  ;  and  it  has  been  observed  that  the  membrane  has  a 
position  more  nearly  vertical  in  musicians  than  in  persons  with  an 
imperfect  musical  ear  (Trdltsch). 

Experiments  have  shown  that  the  tympanic  membrane  vibrates  more 


740 


SPECIAL    SENSES 


forcibly  when  relaxed  than  when  it  is  tense.  In  certain  cases  of  facial 
palsv,  in  which  it  is  probable  that  the  branch  of  the  facial  going  to  the 
tensor  tympani  was  affected,  the  ear  has  been  found  painfully  sensitive 
to  powerful  impressions  of  sound.  This  probably  has  no  relation  to 
pitch,  and  most  sounds  that  are  painfully  loud  are  comparatively  grave. 
Artillerists  are  in  danger  of  rupture  of  the  membrana  tympani  from 
sudden  concussions.  To  guard  against  this  injury,  it  is  recommended 
to  stop  the  ear,  draw  the  shoulder  up  against  the  ear  most  in  danger, 
and  particularly  to  inflate  the  middle  ear  after  Valsalva's  method. 
"  This  method  consists  in  making  a  powerful  expiration,  with  the  mouth 
and  nostrils  closed"  (Troltsch). 

Mechanism  of  the  Ossicles  of  the  Ear.  —  The  ossicles  of  the  middle 
ear,  in  connection  with  the  muscles,  have  a  twofold  office :  First,  by  the 
action  of  the  muscles  the  membrana  tympani  may  be  brought  to  differ- 
ent degrees  of  tension.  Second,  the  angular  chain  of  bones  serves  to 
conduct  sonorous  vibrations  to  the  labyrinth.  It  must  be  remembered 
that  the  handle  of  the  malleus  is  closely  attached  to  the  membrana 
tympani,  especially  near  its  lower  end.  Near  the  short  processes  — 
which  is  a  conical  projection  at  the  root  of  the  handle  —  the  attachment 
is  looser  and  there  is  even  an  incomplete  joint-space.  The  long  process 
is  attached  closely  to  the  Glasserian  fissure  of  the  temporal  bone. 

The  malleus  is  articulated  with  the  incus  by  a  peculiar  joint.  This 
is  so  arranged,  presenting  a  sort  of  cog,  that  the  handle  can  rotate  only 
outward ;  and  when  a  force  is  applied  that  would  have  a  tendency  to 
produce  a  rotation  inward,  the  malleus  must  carry  the  incus  with  it. 
This  mechanism  has  been  compared  to  that  of  a  watch-key  with  cogs 
that  are  fitted  together  and  allow  the  key  to  turn  in  one  direction,  but 
are  separated  so  that  only  the  upper  portion  turns  when  the  force  is 
applied  in  the  opposite  direction  (Helmholtz).  In  the  articulation 
between  the  malleus  and  the  incus,  the  only  difference  is  that  there  is 
but  one  cog  ;  but  this  is  suflficient  to  prevent  an  independent  rotation  of 
the  malleus  inward. 

The  body  of  the  incus  is  attached  to  the  posterior  bony  wall  of  the 
tympanum.  Its  articulation  with  the  malleus  has  just  been  indicated. 
By  the  extremity  of  its  long  process,  it  also  is  articulated  with  the  stapes, 
which  completes  the  chain.  In  situ,  the  stapes  forms  nearly  a  right 
angle  with  the  long  process  of  the  incus. 

The  stapes  is  articulated  with  the  incus,  as  indicated  above,  and  its 
oval  base  is  applied  to  the  fenestra  ovaHs.  Surrounding  the  base  of  the 
stapes  is  a  ring  of  fibro-cartilage  that  is  closely  united  to  the  bony  wall 
of  the  labyrinth  by  an  extension  of  the  periosteum. 

The  articulations  between  the  malleus  and  the  incus  and  between 


OSSICLES    OF   THE    EAR  74I 

the  incus  and  the  stapes  are  so  arranged  that  when  the  membrana 
tympani  is  forced  outward  —  as  it  may  be  by  inflation  of  the  tympanic 
cavity  —  there  is  no  danger  of  tearing  the  stapes  from  its  attachment  to 
the  fenestra  ovalis ;  for  when  the  handle  of  the  malleus  is  drawn  out- 
ward, the  cog-joint  between  the  malleus  and  the  incus  is  loosened  and 
no  considerable  traction  can  be  exerted  on  the  stapes. 

The  tensor  tympani  is  by  far  the  more  important  of  the  two  muscles 
of  the  middle  ear.  Its  action  is  to  tighten  the  cog-like  joint  between 
the  malleus  and  the  incus,  to  tighten,  also,  all  the  ligaments  of  the 
incus,  to  draw  the  long  process  of  the  malleus  inward,  thereby  increas- 
ing the  tension  of  the  membrana  tympani,  and  to  press  the  base  of  the 
stapes  against  the  fenestra  ovalis.  By  the  action  of  this  muscle  the 
chain  of  ossicles  becomes  practically  a  solid  and  continuous  angular 
rod. 

Although  experiments  have  demonstrated  the  mechanism  of  the 
ossicles  and  the  action  of  the  tensor  tympani,  both  as  regards  the  chain 
of  bones  and  the  membrana  tympani,  direct  observations  are  wanting 
to  show  the  exact  relations  of  these  different  conditions  of  the  ossicles 
and  of  the  membrane  to  the  physiology  of  audition.  One  very  impor- 
tant physical  point,  however,  which  has  been  the  subject  of  much  dis- 
cussion, is  settled.  The  chain  of  bones  acts  as  a  single  solid  body  in 
conducting  vibrations  to  the  labyrinth.  It  is  a  matter  of  physical 
demonstration  that  vibrations  of  the  bones  themselves  would  be  incon- 
ceivably rapid  as  compared  with  the  highest  tones  that  can  be  appre- 
ciated by  the  ear,  if  it  were  possible  to  induce  in  these  bones  regular 
vibrations.  Practically,  then,  the  ossicles  have  no  independent  vibra- 
tions that  can  be  appreciated.  This  being  the  fact,  the  ossicles  simply 
conduct  to  the  labyrinth  vibrations  induced  in  the  membrana  tympani  by 
sound-waves ;  and  their  arrangement  is  such  that  these  vibrations  lose 
but  little  in  intensity.  While  it  has  been  shown  experimentally  that 
the  amplitude  of  vibration  in  the  membrana  tympani  and  the  ossicles 
diminishes  as  the  tension  of  the  membrane  is  increased,  it  would  seem 
that  when  the  tensor  tympani  contracts,  it  must  render  the  conduction 
of  sound-waves  to  the  labyrinth  more  delicate  than  when  the  auditory 
apparatus  is  in  a  relaxed  condition,  which  may  be  compared  with  the 
"  indolent "  condition  of  accommodation  of  the  eye.  When  the  mem- 
brana tympani  is  relaxed  and  the  cog-like  articulation  between  the 
malleus  and  the  incus  is  loosened,  the  vibrations  of  the  membrane  and 
of  the  malleus  may  have  a  greater  amplitude ;  but  when  the  malleo- 
incudal  joint  is  tightened  and  the  stapes  is  pressed  against  the  fenestra 
ovalis,  the  loss  of  intensity  of  vibration,  in  conduction  through  the  bones 
to  the  labyrinth,  must  be  reduced  to  the  minimum.     With   this  view. 


742  SPECIAL    SENSES 

the  tensor-tympani  muscle,  while  it  contracts  to  secure  for  the  mem- 
brana  tympani  the  degree  of  tension  most  favorable  for  vibration  under 
the  influence  of  certain  sounds,  puts  the  chain  of  bones  in  the  condition 
best  adapted  to  the  conduction  of  the  vibrations  of  the  membrane  to  the 
labyrinth,  with  the  smallest  loss  of  intensity. 

Physiological  Anatomy  of  the  Internal  Ear 

The  internal  ear  consists  of  the  labyrinth,  which  is  divided  into  the 
vestibule,  semicircular  canals  and  cochlea.  The  general  arrangement 
of  these  parts  has  already  been  described ;  and  it  remains  only  to  study 
the  structures  contained  within  the  bony  labyrinth,  in  so  far  as  their 
anatomy  bears  directly  on  the  physiology  of  audition.  Passing  inward 
from  the  tympanum,  the  first  division  of  the  internal  ear  is  the  vestibule. 
This  cavity  communicates  with  the  tympanum  by  the  fenestra  ovalis, 
which  is  closed  in  the  natural  state  by  the  base  of  the  stapes.  It  com- 
municates, also,  with  the  semicircular  canals  and  with  the  cochlea. 

General  Arrangement  of  the  Membranous  LabyrintJi.  —  The  bony  laby- 
rinth is  lined  with  a  moderately-thick  periosteum,  consisting  of  connective 
tissue,  a  few  delicate  elastic  fibres,  nuclei  and  bloodvessels  and  spots  of  cal- 
careous concretions.  This  membrane  adheres  closely  to  the  bone  and  ex- 
tends over  the  fenestra  ovalis  and  the  fenestra  rotunda.  Its  inner  surface 
is  smooth  and  is  covered  with  a  single  layer  of  cells  of  endothelium,  which 
in  some  parts  is  segmented  and  in  others  forms  a  continuous  nucleated 
sheet.  In  certain  portions  of  the  vestibule  and  semicircular  canals,  the 
periosteum  is  united  to  the  membranous  labyrinth  more  or  less  closely 
by  fibrous  bands,  which  have  been  called  Hgaments  of  the  labyrinth. 
The  fenestra  rotunda,  which  lies  between  the  cavity  of  the  tympanum 
and  the  cochlea,  is  closed  with  a  membrane  formed  by  an  extension  of 
the  periosteum  lining  the  cochlea,  on  one  side,  and  the  mucous  mem- 
brane lining  the  tympanic  cavity,  on  the  other. 

In  the  bony  vestibule,  occupying  about  two-thirds  of  its  cavity,  are 
two  distinct  sacs :  a  large  ovoid  sac,  the  utricle,  situated  in  the  upper 
and  posterior  portion  of  the  cavity,  and  a  smaller  rounded  sac,  the  saccule, 
situated  in  its  lower  and  anterior  portion.  These  two  sacs  communicate 
with  each  other  through  a  small  canal  in  the  form  of  the  letter  Y,  which 
is  represented  in  the  upper  diagram  in  Fig.  191.  The  utricle  communi- 
cates with  the  three  semicircular  canals,  and  the  saccule  is  connected 
with  the  true  membranous  cochlea  by  the  canalis  reuniens.  At  a  point 
in  the  utricle  corresponding  to  the  entrance  of  a  branch  of  the  auditory 
nerve,  is  a  round  whitish  spot,  called  the  acoustic  spot  (macula  acustica), 
containing  otoliths,  or  otoconia,  which  are  attached  to  the  inner  surface 


THE    INTERNAL    EAR 


743 


in    man,    mam- 
birds    and   rep- 


of  the  membrane.  A  similar  spot  containing  otoliths  exists  in  the  saccule 
at  the  point  of  entrance  of  its  nerve.  Otoliths  are  also  found  in  the 
ampullae  of  the  semicircular  canals.  These  calcareous  masses  are  com- 
posed of  crystals  of  calcium  carbonate,  which  are  hexagonal  and  pointed 
at  their  extremities.  Nothing  definite  is  known  of  the  uses  of  these  cal- 
careous bodies,  which 
exist 
mals, 
tiles. 

The  membranous 
semicircular  canals  oc- 
cupy about  one-third 
of  the  cavity  of  the 
bony  canals.  They 
present  small  ovoid 
dilatations,  called  am- 
pullae, corresponding 
to  the  ampullate  en- 
largements of  the 
bony  canals.  They 
are  held  in  place  by  a 
large  number  of  little 
fibrous  bands  extend- 
ing to  the  bony  laby- 
rinth. 

The  membranes  of 
the  cochlea  include 
the  periosteum  lin- 
ing the  bony  canal, 
and  the  true  membra- 
nous cochlea.  Viewed 
externally,  the  true 
membranous  cochlea 
appears  as  a  single 
tube  following  the 
turns  of  the  bony  cochlea,  beginning  below  by  a  blind  extremity  and  ter- 
minating in  a  blind  extremity  at  the  summit  of  the  cochlea.  If  a  section 
of  the  cochlea  is  made  in  a  direction  vertical  to  the  spiral,  it  will  be  seen 
that  the  bony  canal  is  divided,  partly  by  bone  and  partly  by  membrane, 
into  an  inferior  portion,  a  superior  portion,  and  a  triangular  canal,  lying 
between  the  two,  which  is  external.  The  bony  septum  is  in  the  form  of 
a  spiral  plate  extending  from  the  central  column  (the  modiolus)  into  the 


Fig.  zgi.  —  Diagram  of  the  labyrinth.     From   a  photograph,  and 
slightly  reduced  (Riidinger). 

Upper  figure:  i,  utricle;  2,  saccule;  3,  5,  membranous  cochlea; 
4,  canalis  reuniens ;  6,  semicircular  canals. 

Lower  figure:  i,  utricle;  2,  saccule;  3,4,6,  ampullag;  5,7,8,9, 
semicircular  canals;  10,  auditory  nerve  (partly  diagrammatic); 
II,  12,  13,  14,  15,  distribution  ot  the  branches  of  the  nerve  to  the 
vestibule  and  the  semicircular  canals. 


744 


SPECIAL    SENSES 


cochlea,  about  halfway  to  its  external  wall,  and  terminating  above  in  a 
hook-shaped  extremity  called  the  hamulus.  The  free  edge  of  this  bony 
lamina  is  thin  and  dense.  Near  the  modiolus  it  divides  into  two  plates, 
with  an  intermediate  spongy  structure,  in  which  are  lodged  vessels  and 
nerves.  The  surface  of  the  bony  lamina  looking  toward  the  base  of  the 
cochlea  is  marked  by  a  number  of  regular  transverse  ridges. 

Attached  to  the  free  margin  of  the  bony  lamina  is  a  membrane,  the 
membrana  basilaris,  which  extends  to  the  outer  wall  of  the  cochlea.     In 

this  way  the  bony  coch- 
lea is  divided  into  two 
portions,  one  above  and 
the  other  below  the 
septum.  The  portion 
below  begins  at  the 
fenestra  rotunda  and  is 
called  the  scala  tympani. 
The  portion  above,  ex- 
clusive of  the  triangular 
canal  of  the  cochlea, 
communicates  with  the 
vestibule  and  is  called 
the  scala  vestibuli. 

Above  the  membrana 
basilaris  is  a  membrane, 
the  limbus  laminae  spi- 
ralis, the  external  con- 
tinuation of  which  is 
called  the  membrana 
tectoria,  or  the  mem- 
brane of  Corti.  Between  the  membrana  tectoria  and  the  membrana 
basilaris  is  the  quadrilateral  canal,  which  contains  the  organ  of  Corti. 
The  membrane  of  Reissner  extends  from  the  inner  portion  of  the  limbus 
upward  and  outward  to  the  outer  wall  of  the  cochlea.  This  divides  the 
portion  of  the  cochlea  situated  above  the  scala  tympani  into  two  por- 
tions :  an  internal  portion,  the  scala  vestibuli,  and  an  external  triangular 
canal,  called  the  canalis  cochleae,  or  the  true  membranous  cochlea. 

In  the  anatomical  description  of  the  contents  of  the  bony  cochlea, 
the  scalae  and  membranous  parts  may  be  designated  as  follows :  The 
canalis  cochleae  is  divided,  as  just  indicated,  by  the  membrana  tectoria. 
The  portion  between  the  membrana  tectoria  and  the  membrane  of 
Reissner  is  called  the  scala  media.  This  communicates  with  the  sac- 
cule by  the  canalis  reuniens. 


Fig.  192.  —  Otoliths  front  various  animals  (Rlidinger). 

I,  from  the  goat ;  2,  from  the  herring ;  3,  from  the  devil-fish  ; 
4,  from  the  mackerel ;  5,  from  the  flying-fish;  6,  from  the  pike; 
7,  from  the  carp ;  8,  from  the  ray;  9,  from  the  shark;  10,  from 
the  grouse. 


THE    INTERNAL    EAR 


745 


1.  The  portion  below  the  bony  and  membranous  septum,  called  the 
scala  tympani.  This  is  bounded  by  the  periosteum  lining  the  corre- 
sponding portion  of  the  bony  cochlea  and  the  under  surface  of  the  bony 
lamina  and  by  the 
membrana  basilaris. 

2.  The  scala  vesti- 
buli.  This  is  bounded 
by  the  periosteum  lin- 
ing the  corresponding 
portion  of  the  bony 
cochlea  and  the  upper 
surface  of  the  bony 
septum  and  by  the 
membrane  of  Reissner. 

3.  The  true  mem- 
branous cochlea.  This 
is  the  spiral,  trian- 
gular canal,  bounded 
externally  by  the  peri- 
osteum of  the  corre- 
sponding portion  of 
the  wall  of  the  coch- 
lea, internally,  by  the 
membrane  of  Reissner, 
and  on  the  other  side, 
by  the  membrana  ba- 
silaris. What  is  thus 
called  the  membra- 
nous cochlea  is  divided 
by  the  limbus  laminae 
spiralis  and  the  mem- 
brana tectoria  into 
two  portions ;  a  tri- 
angular canal  above 
(scala  media),  which 
is  the  larger,  and  the 
quadrilateral  canal  be- 
low, between  the  lim- 
bus and  membrana  tectoria  and  the  membrana  basilaris.  The  quadri- 
lateral canal  contains  the  organ  of  Corti  and  various  complex  anatomical 
structures.  The  relations  of  these  parts  are  shown  in  Fig.  193,  but  the 
numbers  in  the  figure  are  made  out  with  s'ome  difficultv. 


Fig.  193.  —  Section  of  the  first  turn  of  the  spiral  canal  of  a  cat 
newly  born.  —  Section  of  the  cochlea  of  a  human  fcetus  at  the  fourth 
month.     From  a  photograph,  and  slightly  reduced  (RiidingerJ  . 

Upper  figure  :  i,  2,  6,  lamina  spiralis;  2,  lower  plate;  3,  4,  5,  5, 
nervus  cochlearis ;  7,  membrane  of  Reissner ;  8,  membrana  tecto- 
ria; 9,  epithelium;  10,  11,  pillars  of  Corti;  12,  inner  hair-cells; 
13,  outer  hair-cells;  14,  16,  membrana  basilaris;  15,  epithelium  in 
the  sulcus  spiralis  ;  17,  18,  19,  ligamentum  spirale  ;  20,  spiral  canal, 
below  the  membrana  basilaris. 

Lower  figure,  ST,  S  T,  5,  5,  7,  7,  8,  8,  scala  tympani ;  S  V,  S  V, 
9,  9,  scala  vestibuli ;  i,  base  of  the  cochlea;  2,  apex;  3,  4,  central 
column  ;  10,  10,  10,  10,  ductus  cochlearis  ;  11,  branches  of  the  nervTis 
cochlearis ;  12,  12,  12,  spiral  ganglion ;  13,  14,  limbus  laminae 
spiralis;  15,  membrane  of  Reissner ;  16,  epithelium  ;  17,  outer  hair- 
cells  ;  18,  epithelium  of  the  membrana  basilaris;  19,  nervous  fila- 
ments; 20,  union  of  the  membrana  basilaris  with  the  ligamentum 
spirale ;  21,  epithelium  of  the  peripheral  wall  of  the  ductus  cochlea- 
ris ;  22,  23,  membrana  tectoria ;  24,  spiral  canal,  below  the  mem- 
brana basilaris. 


746  SPECIAL   SENSES 

The  membranous  cochlea,  as  just  described,  includes  the  scala 
media  and  the  quadrilateral  canal,  follows  the  spiral  course  of  the  coch- 
lea, terminates  superiorly  in  a  pointed  blind  extremity  at  the  cupola, 
beyond  the  hamulus,  and  is  connected  below  with  the  saccule  of  the 
vestibule,  by  the  canalis  reuniens.  The  relations  of  the  different  por- 
tions of  the  membranous  cochlea  to  each  other  and  to  the  scalae  of  the 
cochlea  also  are  shown  in  Fig.  193. 

Liquids  of  the  Labyrinth.  —  The  labyrinth  contains  a  certain  quan- 
tity of  a  clear  watery  liquid,  called  the  humor  of  Cotugno  or  of  Valsalva. 
A  portion  of  this  liquid  surrounds  the  utricle  and  saccule,  the  semicircu- 
lar canals  and  the  true  membranous  cochlea ;  and  this  is  known  as  the 
perilymph  of  Breschet.  Another  portion  of  the  liquid  fills  the  true 
membranous  labyrinth  and  is  sometimes  called  the  humor  of  Scarpa; 
but  it  is  known  more  commonly  as  the  endolymph  of  Breschet.  The 
perilymph  occupies  about  one-third  of  the  cavity  of  the  bony  vestibule 
and  semicircular  canals  and  both  scalae  of  the  cochlea.  Both  this  liquid 
and  the  endolymph  are  clear  and  watery,  becoming  somewhat  opales- 
cent on  the  addition  of  alcohol.  The  spaces  in  the  labyrinth  are  directly 
connected  with  the  lymphatic  system.  The  space  occupied  by  the  peri- 
lymph communicates  with  lymphatics  chiefly  through  the  aqueduct  of 
the  cochlea,  but  there  also  is  a  communication  through  the  internal 
auditory  meatus  with  the  space  beneath  the  dura  mater.  The  endo- 
lymph passes  to  the  subarachnoid  space  beneath  the  arachnoid  covering 
of  the  auditory  nerve.  So  far  as  is  known,  the  uses  of  the  liquid  of  the 
internal  ear  are  to  sustain  the  delicate  structures  contained  in  this  por- 
tion of  the  auditory  apparatus  and  to  conduct  sonorous  vibrations  to  the 
terminal  filaments  of  the  auditory  nerves  and  the  parts  with  which  they 
are  connected. 

Distribution  of  the  Nerves  in  the  Labyrijith.  — As  the  auditory  nerves 
enter  the  internal  auditory  meatus,  they  divide  into  an  anterior,  or  coch- 
lear, and  a  posterior,  or  vestibular  branch.  The  vestibular  branch  di- 
vides into  three  smaller  branches,  a  superior  and  anterior,  a  middle,  and 
a  posterior  branch.  The  superior  and  anterior  branch,  the  largest  of 
the  three,  is  distributed  to  the  utricle,  the  superior  semicircular  canal 
and  the  external  semicircular  canal.  The  middle  branch  is  distributed 
to  the  saccule.  The  posterior  branch  passes  to  the  posterior  semicircu- 
lar canal.  The  nerves  distributed  to  the  utricle  and  saccule  penetrate 
at  the  points  occupied  by  the  otoliths,  and  the  nerves  going  to  the  semi- 
circular canals  pass  to  the  ampullae,  which  also  contain  otoliths  (see 
Fig.  191).  In  each  ampulla,  at  the  point  where  the  nerv^e  enters,  is  a 
transverse  fold  projecting  into  the  canal  and  occupying  about  one-third 
of  its  circumference,  called  the  septum  transversum. 


THE    INTERNAL   EAR 


747 


The  nerves  terminate  in  essentially  the  same  way  in  the  sacs  of  the 
vestibule  and  the  ampullae  of  the  semicircular  canals.  At  the  points 
where  the  nerves  enter,  in  addition  to  the  otoliths,  are  cylindrical  cells 
of  various  forms,  which  pass  gradually  into  the  general  endothelium  of 
the  cavities.  In  addition  to  these  cells,  are  fusiform  nucleated  bodies, 
the  free  ends  of  which  are  provided  with  hair-like  processes,  called  fila 
acustica.  These  are  about  g^Q  of  an  inch  (31  /x)  in  length  and  are  dis- 
tributed in  quite  a  regular  manner  around  the  otoliths.  The  nerves  form 
an  anastomosing  plexus  beneath  the  endothelium  and  terminate  proba- 
bly in  the  fusiform  bodies  just  described  as  presenting  the  fila  acustica 
at  their  free  extremities.  In  the  sacs  of  the  vestibule  and  in  the 
semicircular  canals,  nerves 
exist  only  in  the  maculae 
acusticae  and  the  ampullae. 

The  cochlear  division 
of  the  auditory  nerve 
breaks  up  into  a  number 
of  small  branches  which 
pass  through  the  foramina 
at  the  base  of  the  cochlea 
in  what  is  called  the  tractus 
spiralis  foraminulentus. 
These  follow  the  axis  of 
the  cochlea  and  pass  in 
their  course  toward  the 
apex,  between  the  plates 
of  the  bony  spiral  lamina. 
Between  these  plates  of 
bone,  the  dark-bordered 
nerve-fibres  pass  each  one 
through  a  bipolar  cell,  these  cells  together  forming  a  spiral  ganglion 
known  as  the  ganglion  of  Corti.  Beyond  this  ganglion  the  nerves  form 
an  anastomosing  plexus  and  finally  enter  the  quadrilateral  canal,  or  the 
canal  of  Corti.  As  they  pass  into  this  canal  they  suddenly  become  pale 
and  exceedingly  fine.  They  probably  are  connected  finally  with  the 
organ  of  Corti,  although  their  exact  mode  of  termination  has  not  yet 
been  determined.  The  course  of  the  nerve-fibres  to  their  distribution 
in  the  cochlea  is  shown  in  Fig.  194. 

Organ  of  Corti.  —  In  the  quadrilateral  canal,  bathed  in  the  endolymph 
throughout  its  spiral  course,  is  an  arrangement  of  pillars,  or  rods, 
which  are  regular,  like  the  strings  of  a  harp  in  miniature.  These  are 
the  pillars  of  Corti.     These  pillars  are  external  and  internal,  with  their 


Fig.  194.  —  Distribution  of  the  cochlear  nerve  in  the  spiral 
laniina.  The  cochlea  is  from  the  right  side  and  is  seeti  from  its 
antero-i?iferior  part  (Sappey). 

I,  trunk  of  the  cochlear  nerve;  2,  2,  2,  membranous  zone 
of  the  spiral  lamina  ;  3,  3,  3,  terminal  expansion  of  the  cochlear 
nerve,  exposed  in  its  whole  extent  by  the  removal  of  the  supe- 
rior plate  of  the  lamina  spiralis;  4,  orifice  of  communication 
of  the  scala  tympani  with  the  scala  vestibuli. 


748  SPECIAL    SENSES 

bases  attached  to  the  basilar  membrane  and  their  summits  articulated 
above,  so  as  to  form  a  regular  spiral  arcade  enclosing  a  triangular  space 
that  is  bounded  below  by  the  basilar  membrane.  The  number  of  the 
elements  of  the  organ  of  Corti  is  estimated  at  about  4500,  for  the  outer, 
and  6500,  for  the  inner  rods  (Pritchard).  The  relations  of  these  struc- 
tures to  the  membranous  labyrinth  are  seen  in  Fig.  193.  The  external 
pillars  are  longer,  more  delicate,  and  more  rounded  than  the  internal 
pillars.  The  form  of  the  pillars  is  more  exactly  shown  in  Figs.  195 
and  196,  the  latter  figure,  however,  exhibiting  other  structures  which 
enter  into  the  constitution  of  the  organ  of  Corti.  It  will  be  remarked 
that  a  small  nucleated  body  is  attached  to  the  base  of  either  pillar.  At 
the   summit,  where   the    internal   and   the  external   pillars  are   joined 


Fig.  195.  —  The  two  pillars  of  the  organ  of  Corti  (Sappey). 

A,  external  pillar  of  the  organ  of  Corti :  I,  body,  or  middle  portion  ;  2,  posterior  e.vtremity,  or  base ; 
3,  cell  on  its  internal  side ;  4,  anterior  extremity ;  5,  convex  surface,  by  which  it  is  joined  to  the  inter- 
nal pillar;  6,  prolongation  of  this  extremity. 

B,  internal  pillar  of  the  organ  of  Corti:  i,  body,  or  middle  portion;  2,  posterior  extremity;  3,  cell 
on  its  external  side;  4,  anterior  extremity;  5,  concave  surface,  by  which  it  is  joined  to  the  external 
pillar;  6,  prolongation,  lying  above  the  corresponding  prolongation  of  the  external  pillar. 

C,  the  two  pillars  of  the  organ  of  Corti,  united  by  their  anterior  extremity,  and  forming  an  arcade, 
the  concavity  of  which  presents  outward;  i,  i,  body,  or  middle  portion  of  the  pillars;  2,  2,  posterior 
extremities;  3,3,  cells  attached  to  the  posterior  extremities;  4,  4,  anterior  extremities  joined  together; 
5,  terminal  prolongation  of  this  extremity. 

together,  is  a  delicate  prolongation,  directed  outward,  which  is  attached 
to  the  covering  of  the  quadrilateral  canal. 

The  above  description  comprises  about  all  that  is  definitely  known, 
of  the  arrangement  of  the  pillars  or  rods  of  Corti.  They  are  nearly 
homogeneous,  except  when  treated  with  reagents,  and  are  said  to  be  of 
about  the  consistence  of  cartilage.  They  are  closely  set  together,  with 
narrow  spaces  between  them,  and  it  is  difficult  to  see  how  they  can  be 
stretched  to  any  considerable  degree  of  tension.  The  arch  is  longer  at 
the  summit  than  at  the  base  of  the  cochlea,  the  longest  rods,  at  the 
summit,  measuring,  according  to  Pritchard,  about  -cy^j^  of  an  inch  (125  /*), 
and  the  shortest,  at  the  base,  about  -^^q-  of  an  inch  (50  /i).  At  the  base 
of  the  cochlea  the  two  sets  of  rods  are  about  equal  in  length.  From  the 
base  to  the  apex,  both  sets,  outer  and  inner,  progressively  increase  in 


THE    INTERNAL    EAR 


749 


length,  and  the  outer  rods  become  the  longer,  so  that  near  the  apex  they 
are  nearly  twice  as  long  as  the  inner.  The  anatomical  relations  between 
the  pillars  and  the  terminal  filaments  of  the  auditory  nerves  are  not 
definitely  settled. 

In  addition  to  the  pillars  just  described,  various  cellular  elements 
enter  into  the  structure  of  the  organ  of  Corti.  The  most  important  of 
these  are  the  inner  and  the  outer  hair-cells.  These  are  16,400  to  20,000 
in  number  (Hensen,  Waldeyer).  The  inner  hair-cells  are  arranged  in  a 
single  row,  and  the  outer  hair-cells,  in  four  rows.  Nothing  definite  is 
known  of  the  uses  of  these  cells.  The  relations  of  these  parts  are 
shown  in  Fig.  196.     It  is  supposed  by  some  anatomists  that  the  fila- 


Fig.  196. —  Vertical  section  of  the  organ  of  Corti  of  the  dog  (Waldeyer). 

a-^,  homogeneous  layer  of  the  basilar  membrane;  v,  tympanic  layer,  with  nuclei,  granular  cell- 
protoplasm  and  connective  tissue ;  a^,  tympanic  lip  of  the  crista  spiralis ;  c,  thickened  portion  of  the 
basilar  membrane;  d,  spiral  vessel;  e,  bloodvessel;  f  h,  bundle  of  nerves;  g,  epithelium;  i,  inner 
hair-cell,  with  its  basilar  process,,^;  /,  head-plate  of  the  inner  pillar;  »z,  union  of  the  two  pillars; 
n,  base  of  the  inner  pillar ;  o,  base  of  the  outer  pillar ;  /,  q,  r,  outer  hair-cells,  with  traces  of  the  cilia ; 
t,  bases  of  two  other  hair-cells;  2,  Hensen's  prop-cell;  /-Z^,  lamina  reticularis;  w,  nerve-fibre  passing 
to  the  first  hair-cell,/. 

ments  of  the  auditory  nerves  terminate  in  the  cells  above  described; 
but  this  point  is  not  definitely  settled. 


Uses  of  Different  Parts  of  the  Internal  Ear 

The  precise  uses  of  the  different  parts  found  in  the  internal  ear  are 
somewhat  obscure,  notwithstanding  the  careful  researches  that  have 
been  made  into  the  anatomy  and  the  physiology  of  the  labyrinth. 
There  are  several  points,  however,  bearing  on  the  physiology  of  this 
portion  of  the  auditory  apparatus,  concerning  which  there  can  be  no 
doubt : — 

First,  it  is   certain  that  impressions  of   sound  are  received  by  the 


750  SPECIAL    SENSES 

terminal  filaments  of  the  auditory  nerves  and  by  these  nerves  are  con- 
veyed to  the  brain. 

Second,  the  uses  of  the  parts  composing  the  external  and  the  middle 
ear  are  chiefly  accessory.  The  sonorous  waves  are  collected  by  the 
pinna  and  are  conveyed  by  the  external  meatus  to  the  middle  ear  ;  the 
membrana  tympani  vibrates  under  their  influence  ;  and  they  are  thus 
collected,  repeated  and  transmitted  to  the  internal  ear. 

Uses  of  t lie  Semicircular  Canals.  —  In  the  experiments  of  Flourens, 
on  pigeons  and  rabbits  (1824),  it  was  shown  that  destruction  of  the 
semicircular  canals  had  apparently  no  effect  on  the  sense  of  hearing, 
while  destruction  of  the  cochlea  on  both  sides  produced  total  deaf- 
ness. In  addition  it  was  observed  that  destruction  of  the  -semicircular 
canals  on  both  sides  was  followed  by  remarkable  disturbances  in  equi- 
libration. The  animals  could  maintain  the  standing  position,  but  so 
soon  as  they  made  any  movements,  "  the  head  began  to  be  agitated ; 
and  this  agitation  increasing  with  the  movements  of  the  body,  walking 
and  all  regular  movements  finally  became  impossible,  in  nearly  the  same 
way  as  when  equilibrium  and  stability  of  movements  are  lost  after  turn- 
ing several  times  or  violently  shaking  the  head."  These  observations 
of  Flourens,  at  least  so  far  as  regards  the  influence  of  the  semicircular 
canals  on  equilibration,  have  been  confirmed  by  Goltz  and  are  sus- 
tained by  observations  on  the  human  subject,  in  the  condition  known  as 
Meniere's  disease.  So  far  as  can  be  determined  from  experimental 
data,  it  does  not  seem  probable  that  the  nerves  directly  concerned  in 
audition  are  distributed  to  any  considerable  extent  in  the  semicircular 
canals.  Indeed,  the  uses  of  these  parts  is  obscure ;  for  it  can  hardly  be 
admitted,  on  purely  anatomical  grounds,  that  they  are  concerned  in 
the  discrimination  of  the  direction  of  sonorous  vibrations,  an  idea  that 
has  been  advanced  by  some  physiologists.^ 

Uses  of  the  Parts  contained  in  the  Cochlea.  — There  can  be  no  doubt 
in  regard  to  the  capital  point  in  the  physiology  of  the  cochlea ;  namely, 
that  those  branches  of  the  auditory  nerve  which  are  essential  to  the 
sense  of  hearing  and  which  receive  the  impressions  of  sound  are  dis- 
tributed in  the  cochlea.  An  analysis  of  sonorous  impressions  shows 
that  they  possess  various  attributes,  such  as  intensity,  quality  and  pitch. 
So  far  as  the  terminal  filaments  of  the  auditory  nerve  are  concerned,  it 
is  evident  that  the  intensity  of  sound  is  appreciated  in  proportion  to  the 
force  of  the  impression  made  on  these  nerves.     In  regard  to  quality  of 

^  Although  the  physiological  literature  of  the  semicircular  canals  is  of  immense  volume, 
little  of  a  convincing  and  definite  character  has  been  learned  concerning  their  function  since 
the  observations  of  Flourens;  and  their  further  discussion  would  be  out  of  place  in  this  work. 
The  directions  of  the  canals  may  be  studied  in  Fig.  iSS,  page  720, 


THE    INTERNAL   EAR  75 1 

sound,  it  has  been  seen  that  this  is  due  to  the  form  of  sonorous  vibra- 
tions ;  and  that  musical  sounds  usually  are  compound,  their  quality  de- 
pending largely  on  the  relative  loudness  of  the  harmonics,  partial  tones 
etc.  It  has  also  been  seen  that  resonant  bodies  may  repeat  by  influence, 
not  only  the  actual  pitch  of  tones,  but  their  quality.  If  there  is  in  the 
cochlea  an  anatomical  arrangement  of  rods  or  fibres  by  which  the 
sonorous  vibrations  conveyed  to  the  ear  are  repeated,  there  is  reason  to 
believe  that  the  quality  as  well  as  the  pitch  is  reproduced. 

The  arrangement  of  the  rods  entering  into  the  structure  of  the  organ 
of  Corti  and  of  the  fibres  of  the  membrana  basilaris  has  afforded  a  theo- 
retical explanation  of  the  final  mechanism  of  the  appreciation  of  pitch. 
With  the  exception  of  the  internal  ear,  the  action  of  different  portions 
of  the  auditory  apparatus  is  simply  to  conduct  and  repeat  sonorous 
vibrations ;  and  the  sole  use  of  these  accessory  parts,  aside  from  the 
protection  of  the  organs,  is  to  convey  the  vibrations  to  the  terminal 
nervous  filaments.  Whatever  may  be  the  uses  of  the  membrana  tympani 
in  repeating  sounds  by  influence,  it  is  certain  that  this  membrane  pos- 
sesses no  true  auditory  nerves,  and  that  the  auditory  nerves  only  are 
capable  of  receiving  impressions  of  sound.  Thus,  hearing,  and  even  the 
appreciation  of  pitch,  is  not  necessarily  lost  after  destruction  of  the 
membrana  tympani ;  and  if  sonorous  vibrations  reach  the  auditory  nerves, 
they  will  be  appreciated  and  appreciated  correctly. 

In  view  of  the  arrangement  of  the  organ  of  Corti,  with  its  eleven 
thousand  or  more  rods  of  different  lengths  arranged  with  a  certain 
degree  of  regularity,  a  number  more  than  sufficient  to  represent  all  the 
notes  of  the  musical  scale,  it  is  not  surprising  that  they  should  be  re- 
garded as  capable  of  repeating  all  the  notes  heard  in  music.  Helmholtz 
formulated  this  idea  in  the  theory  that  sounds  conveyed  to  the  cochlea 
throw  into  vibration  only  those  elements  of  the  organ  of  Corti  which  are 
tuned,  so  to  speak,  in  unison  with  them.  According  to  this  hypothesis, 
the  rods  of  Corti  constitute  a  harp  of  several  thousand  strings,  played 
on,  as  it  were,  by  the  sonorous  vibrations.  Theories  analogous  to  that 
proposed  by  Helmholtz,  but  of  course  lacking  the  basis  of  exact  anatom- 
ical and  physical  details  developed  by  modern  researches  and  experi- 
m.ents,  were  advanced  by  Du  Verney  (1683)  and  by  Le  Cat  (1767). 

Viewing  the  question  anatomically,  it  is  by  no  means  certain  that  the 
rods  of  Corti  are  so  attached  and  stretched  that  they  are  capable  of 
separate  and  individual  vibrations.  It  has  not  been  demonstrated  that 
certain  of  these  rods  vibrate  under  the  influence  of  certain  notes  or  that 
they  are  tuned  in  accord  with  certain  notes.  Hensen  and  others  have 
rejected  the  theory  of  Helmholtz,  basing  their  opinions  mainly  on  the 
anatomical  arrangement  of  the  organ  of  Corti.     Hensen  assumed  it  to  be 


752  SPECIAL    SENSES 

a  physical  impossibility  for  the  different  rods  to  vibrate  individually,  and 
he  regarded  it  as  improbable  that  the  rods  are  tuned  in  accord  with 
different  musical  notes.  The  present  idea  is  that  strands  of  the  mem- 
brana  basilaris,  stretched  between  the  lower  extremities  of  the  pillars  of 
Corti,  being  of  different  lengths,  vibrate  in  obedience  to  the  waves  of 
sound  conveyed  to  them  through  the  -auditory  nerves  ;  but  even  this  does 
not  afford  an  entirely  satisfactory  explanation  of  the  mechanism  of  the 
final  appreciation  of  pitch.  It  is  the  fact,  however,  that  disease  of  the 
lower  part  of  cochlea  is  attended  with  deafness  to  high  tones,  and 
disease  affecting  the  summit  produces  deafness  to  low  tones. 

It  is  not  necessary  that  sonorous  vibrations  should  pass  to  the 
cochlea  through  the  external  ear  and  parts  in  the  middle  ear.  Sounds 
may  be  conducted  to  the  auditory  nerves  through  the  bones  of  the  head 
or  through  the  Eustachian  tubes,  as  is  shown  by  the  simple  and  familiar 
experiment  of  placing  a  tuning-folk  in  contact  with  the  head  or  between 
the  teeth,  the  ears  being  closed. 

The  action  of  the  two  ears  does  not  seem  to  be  essential  to  the  correct 
appreciation  of  auditory  impressions  ;  but  variations  in  the  force  of  such 
impressions  made  on  either  ear  aid  in  determining  the  direction  of  sounds, 
although  errors  in  regard  to  this  often  occur. 

The  estimate  of  the  distance  of  sounds  is  made  by  judging  of  their 
intensity,  in  connection  with  information  obtained  through  other  senses, 
especially  the  sense  of  sight.  The  power  of  estimating  distance  is 
largely  influenced  by  experience  and  education. 

Centi'es  foi'  Audition.  —  The  centres  for  audition  in  dogs  and  monkeys 
are  in  the  superior  temporo-sphenoidal  convolution  (Ferrier,  Munk).  In 
man  these  centres  are  in  the  first  and  second  temporal  convolutions  of 
the  temporo-sphenoidal  lobe,  parts  supplied  by  the  fourth  branch  of  the 
middle  cerebral  artery.  This  has  been  ascertained  by  pathological  ob- 
servations as  well  as  by  experiments  on  the  lower  animals.  In  man  the 
action  of  these  centres  is  not  completely  crossed,  and  destruction  of  the 
centre  upon  one  side  does  not  cause  total  deafness  in  either  ear.  Com- 
plete destruction  of  the  centres  on  both  sides,  however,  produces  deaf- 
ness in  both  ears.  Injury  of  the  first  temporal  convolution  often  is 
followed  by  the  condition  known  as  word-deafness,  in  which  the  subject 
hears  the  sound  of  words,  but  these  sounds  convey  no  idea.  This  is  the 
psychical  auditory  centre  and  is  confined  to  the  first  temporal  convolu- 
tion on  the  left  side  (Wernicke).  Word-deafness  is  analogous  to  the 
condition  already  described  under  the  name  of  word-blindness,  and  the 
centre  usually  is  confined  to  the  left  side  of  the  cerebrum.  It  has  been 
suggested  by  Westphal  that  this  centre  may  be  on  the  right  side  of  the 
cerebrum  in  left-handed  persons. 


CHAPTER   XXX 

EMBRYOLOGY 

Female  organs  of  generation  —  The  ovaries  —  Graafian  follicles — The  parovarium  —  The 
uterus — The  Fallopian  tubes  —  Structure  of  the  ovum  —  Discharge  of  the  ovum  —  Passage 
of  ova  into  the  Fallopian  tubes  —  Puberty  and  menstruation  —  Changes  in  the  Graafian 
follicles  after  their  rupture  (corpus  luteum)  — Corpus  luteum  of  pregnancy  —  Male  organs 
of  generation —  Interstitial  gland  of  the  testis  —  Vas  deferens  —  Vesiculse  seminales —  Pros- 
tate—  Glands  of  the  urethra  —  Male  element  of  generation  —  Spermatozoids. 

Generation  is  one  of  the  most  important  of  the  animal  functions  and 
as  such  usually  is  treated  of  quite  fully  in  works  on  physiology  ;  but  a 
more  or  less  extended  account  is  also  to  be  found  in  every  complete 
treatise  on  anatomy  and  in  most  works  on  obstetrics.  The  physiologi- 
cal history  of  the  human  organism,  however,  would  not  be  complete 
without  an  account  of  generation  and  development;  although  this  will 
involve,  to  some  extent,  a  repetition  of  what  usually  is  found  in  works 
on  other  subjects. 

In  what  is  known  as  sexual  generation,  the  two  anatomical  elements 
—  spermatozoid  and  ovum — ^are  developed  in  separate  beings,  male 
and  female,  and  are  brought  together,  in  man  and  in  the  higher  animals, 
by  sexual  connection,  or  copulation.  In  this  way,  the  life  of  animals  is 
prolonged  and  individual  forms  are  preserved  in  future  beings.  This 
can  not  be  secured  without  the  acquisition  by  the  ovum  of  a  new  ele- 
ment. The  animal  cell  may  and  does  multiply  by  the  process  already 
described  under  the  name  of  karyokinesis ;  but  this  can  not  continue  in- 
definitely. After  a  cell  has  undergone  this  process  about  one  hundred 
and  fifty  times,  the  reproductive  power  of  the  protoplasm,  having  gradu- 
ally become  enfeebled,  is  finally  lost.  It  has  been  estimated  that  the  cell 
increases  in  mass  by  the  appropriation  of  nutritive  matters,  as  the  cube 
of  its  diameter,  while  the  absorbing  surface  increases  as  the  square  of 
the  diameter  (Herbert  Spencer).  If  this  view  is  accepted,  it  is  evident 
that  a  time  will  inevitably  come  in  its  life-history  when  the  cell  can  no 
longer  absorb  enough  material  for  growth  ;  but  with  every  division,  there 
is  a  relative  increase  in  surface  ;  and  thus  it  becomes  possible  for  growth 
to  continue.  The  process  of  growth,  indeed,  might  continue  indefinitely 
were  it  not  that  the  cytoplasm  gradually  loses  its  power  of  appropriating 
new  matter.  By  the  introduction  of  a  new  element,  however,  in  the 
3c  753 


754 


EMBRYOLOGY 


union  of  male  with  female  cells,  the  power  of  the  resulting  cell  to  per- 
petuate itself  is  secured. 

Female  Organs  of  Generation 

A  knowledge  of  certain  points  in  the  anatomy  of  the  female  organs 
of  generation  is  essential  to  a  comprehension  of  the  most  important  of 
the  processes  of  reproduction.  Following  a  fruitful  intercourse,  the 
function  of  reproduction,  as  regards  the  male,  ceases  with  the  compara- 
tively simple  process  of  penetration  of  the  male  element  through  the 
protective  covering  of  the  ovum  and  its  fusion  with  the  female  element. 
The  fertilized  ovum  then  passes  through  certain  changes,  forms 
attachments  to  the  body  of  the  mother,  continues  its  development  and 
is  nourished  and  grows,  until  the  foetus  at  term  is  brought  into  the 
world. 

The  female  organs  of  generation  are  divided  anatomically  into  inter- 
nal and  external.  The  external  organs  are  the  vulva,  the  adjacent  parts 
and  the  vagina.  The  internal  organs  are  the  uterus,  Fallopian  tubes 
and  the  ovaries.  The  ovaries  are  the  true  female  organs,  in  which  alone 
the  female  element  can  be  produced.  The  Fallopian  tubes  and  the 
uterus  are  accessory  in  their  uses,  the  female  element,  the  ovum,  pass- 
ing through  the  tubes  to  the  uterus,  where  it  forms  the  attachments  to 
the  body  of  the  mother  that  are  essential  to  its  nourishment  and  full 
development. 

The  vagina  has  a  direction,  sUghtly  curved  anteriorly,  that  is  nearly 
coincident  with  the  axis  of  the  outlet,  or  the  inferior  strait  of  the  pelvis. 
Projecting  into  the  vagina,  at  its  upper  extremity,  is  the  lower  part  of 
the  neck  of  the  uterus.  The  uterus  extends  from  the  vagina  nearly  to 
the  brim  of  the  pelvis.  It  is  situated  between  the  bladder  and  the  rec- 
tum, and  has  an  antero-posterior  inclination  when  the  bladder  is  moder- 
ately distended,  which  brings  its  axis  nearly  coincident  with  that  of  the 
superior  strait  of  the  pelvis.  With  the  body  erect,  the  angle  of  the 
uterus  with  the  perpendicular  is  about  forty-five  degrees. 

The  uterus  is  held  in  place  by  ligaments,  certain  of  which  are  formed 
of  folds  of  the  peritoneum.  The  anterior  ligament  is  reflected  from  the 
anterior  surface  to  the  bladder ;  the  posterior  ligament  extends  from  the 
posterior  surface  to  the  rectum  ;  the  round  ligaments  extend  from 
the  upper  angle  of  the  uterus,  on  either  side,  between  the  folds  of  the 
broad  ligament  and  through  the  inguinal  canal,  to  the  symphysis  pubis; 
the  broad  ligaments  extend  from  the  sides  of  the  uterus  to  the  walls  of 
the  pelvis. 

The  uterus  and  the  broad  ligaments  partially  divide  the  pelvis  into 
two  portions ;  and  these  ligaments,  which  consist  of  a  double  fold  of 


FEMALE  ORGANS  OF  GENERATION 


755 


peritoneum,  present  a  superior,  or  posterior  surface,  and  an  inferior,  or 
anterior  surface.  The  superior,  or  anterior  border  of  this  fold  is  occupied 
by  the  Fallopian  tubes,  the  peritoneum  constituting  their  outer  coat. 
Laterally,  at  the  free  extremities  of  the  tubes,  the  peritoneum  ceases, 
and  there  is  an  actual  opening  of  each  Fallopian  tube  into  the  peritoneal 
cavity.  Attached  to  the  broad  ligament  and  projecting  on  its  posterior 
surface,  is  the  ovary,  which  is  connected  with  the  fibrous  tissue  between 
the  two  layers  of  the  ligament.  At  the  hilum  of  the  ovary,  as  will  be 
seen  farther  on,  the  structure  of  the  peritoneum  undergoes  a  marked 
change. 

_jfO  T^^^l  9 


Fig.  197. —  Uterus,  Fallopian  tubes  and  ovaries — posterior  view  (Sappey). 

I,  ovaries;  2,  2,  Fallopian  tubes;  3,  3,  fimbriated  extremity  of  the  left  Fallopian  tube,  seen  from  its 
concavity;  4,  opening  of  the  left  tube;  5,  fimbriated  extremity  of  the  right  tube,  posterior  view;  6,  6, 
fimbriae  which  attach  the  extremity  of  each  tube  to  the  ovary;  7,  7,  ligaments  of  the  ovary;  8,  8,  9,  9, 
broad  ligaments;   10,  uterus;   11,  cervix  uteri;   12,  os  uteri;   13,  13,  14,  vagina. 


The  Ovaries.  —  The  ovaries,  attached  to  the  broad  ligament  and  pro- 
jecting on  its  posterior  surface,  lie  nearly  horizontally  in  the  pelvic 
cavity,  on  either  side  of  the  uterus.  They  are  of  a  whitish  color,  and 
their  form  is  ovoid  and  flattened,  with  the  anterior  border,  sometimes 
called  the  base,  attached  to  the  broad  ligament.  By  closely  examining 
their  mode  of  connection  with  the  broad  ligament,  it  is  seen  that  at  the 
margin  of  the  attached  surface  of  the  ovary,  the  posterior  layer  of  the 
ligament  ceases,  and  that  the  fibrous  stroma  of  the  medullary  portion  of 
the  ovary  is  continuous  with  the  fibrous  tissue  lying  between  the  two 
layers. 

The  ovary  is  about  an  inch  and  a  half  (38.1  millimeters)  in  length, 
half  an  inch  (12.7  millimeters)  in  thickness,  and  three-quarters  of  an 
inch   (19. 1    millimeters)   in   width   at   its    widest    portion.      The    outer 


756  EMBRYOLOGY 

extremity  is  somewhat  rounded  and  is  attached  to  one  of  the  fimbriae 
of  the  Fallopian  tube.  The  inner  extremity  is  more  pointed  and  is 
attached  to  the  side  of  the  uterus  by  means  of  the  ligament  of  the  ovary. 
This  ligament  is  shown  in  Fig.  197  (7,  7).  It  is  a  rounded  cord,  com- 
posed of  non-striated  muscular  fibres  spread  out  on  the  attached  extrem- 
ity of  the  ovary  and  the  posterior  surface  of  the  uterus,  and  is  covered 
by  peritoneum.  The  weight  of  the  ovary  is  sixty  to  one  hundred  grains 
(3.9  to  6.5  grams),  and  it  is  largest  in  the  adult  virgin.  Its  attached 
border  is  called  the  hilum ;  and  at  this  portion  the  vessels  and  nerves 
penetrate.  The  surface  presents  rounded  translucent  elevations,  pro- 
duced by  distended  Graafian  follicles,  with  little  cicatrices  indicating  the 
situation  of  ruptured  follicles.  There  may  also  be  seen,  between  the 
distended  follicles,  corpora  lutea  in  different  stages  of  atrophy. 

After  the  peritoneum  has  reached  the  ovary,  its  fibrous  layer  be- 
comes indistinct  and  fuses  with  the  fibrous  stroma  of  the  ovary  itself. 
The  peritoneal  endothelium  here  undergoes  a  change,  and  the  cells  on 
the  surface  of  the  ovary  are  cuboidal  and  in  a  single  layer.  This 
change  in  the  structure  of  the  peritoneum  is  abrupt  and  is  indicated  by 
a  distinct  line  surrounding  the  hilum  of  the  ovary. 

On  making  a  section  of  the  ovary,  it  is  readily  seen  with  the  naked 
eye  that  the  organ  is  composed  of  two  distinct  structures ;  a  cortical 
substance,  sometimes  called  the  tunica  albuginea,  which  is  about  2V  ^^ 
an  inch  (i  millimeter)  in  thickness,  and  a  medullary  substance  contain- 
ing a  large  number  of  bloodvessels.  The  cortical  substance  alone  con- 
tains the  Graafian  follicles.  The  external  layer  of  this  is  denser  than 
the  deeper  portion,  but  there  is  no  distinct  fibrous  membrane  such  as  is 
sometimes  described  under  the  name  of  tunica  albuginea. 

The  cortical  substance  of  the  ovary  consists  of  connective  tissue  in 
several  layers,  the  fibres  of  which  are  continuous  with  the  looser  fibres 
of  the  medullary  portion.  In  the  substance  of  this  layer,  are  embedded 
the  ova,  enclosed  in  the  sacs  called  Graafian  follicles.  This  layer  con- 
tains a  few  bloodvessels  coming  from  the  medullary  portion,  which 
surround  the  follicles.    - 

The  medullary  portion  of  the  ovary  is  very  vascular  and  is  composed 
of  small  bands,  or  trabeculae  of  connective  tissue,  with  non-striated 
muscular  fibres.  The  bloodvessels,  which  penetrate  at  the  hilum,  are 
large  and  convoluted,  especially  at  the  hilum  itself,  where  there  is  a 
mass  of  convoluted  veins,  forming  a  sort  of  vascular  bulb.  In  the 
medullary  portion,  which  is  sometimes  called  the  vascular  zone,  the 
muscular  fibres    follow  the  vessels,  in  the  form  of    muscular  sheaths. 

In  addition  to  the  bloodvessels,  the  ovary  receives  nerves  from  the 
spermatic  plexus  of  the  sympathetic,  the  exact  mode  of  termination  of 


FEMALE  ORGANS  OF  GENERATION  757 

which  has  not  been  ascertained.  Lymphatics  have  also  been  demon- 
strated at  the  hilum. 

Graafian  Follicles.  —  These  vesicles,  or  follicles,  were  described  and 
figured  by  DeGraaf  in  1672,  and  are  known  by  his  name.  They  con- 
tain the  ova,  undergo  a  series  of  peculiar  changes,  enlarge,  approach  the 
surface  of  the  ovary,  and  finally  are  ruptured,  discharging  their  contents 
into  the  fimbriated  extremity  of  the  Fallopian  tube.  The  Graafian 
follicles  are  developed  exclusively  in  the  cortical  substance.  If  the 
ovary  is  examined  at  any  period  of  life,  no  follicles  are  found  in  the 
medullary  substance ;  but  a  few  of  the  larger  may  project  downward,  so 
as  to  encroach  somewhat  upon  it,  being  actually  of  a  diameter  greater 
than  the  thickness  of  the  cortex.  The  entire  number  of  follicles  of  all 
sizes  in  either  ovary  is  about  36,000  (Henle).  According  to  the  table  of 
measurements  given  by  Waldeyer,  the  primordial  follicles  in  the  human 
embryo,  at  the  seventh  month,  measure  g^Q-  to  jAq-  of  an  inch  (30  to 
100  /ti)  in  diameter,  and  the  primordial  ova,  y-g^-Q  to  yo^oo  of  an  inch 
(15  to  25  /z). 

The  ovary  appears  early  in  embryonic  life,  in  the  form  of  a  cellular 
outgrowth  from  the  Wolffian  body.  Most  of  its  cells  are  small,  but  as 
early  as  the  fourth  or  fifth  day,  in  the  chick,  some  of  them  are  to  be 
distinguished  by  their  large  size,  their  rounded  form  and  the  presence 
of  a  large  nucleus.  These  cells  are  supposed  to  be  primordial  ova.  In 
the  process  of  development,  some  of  the  peripheral  cells  penetrate  in 
the  form  of  tubes  (the  so-called  ovarian  tubes) ;  and  at  the  same  time, 
delicate  processes,  formed  of  connective  tissue  and  bloodvessels,  extend 
from  the  fibrous  stroma  underlying  the  epithelium  and  enclose  collec- 
tions of  cells.  It  is  probable  that  there  are  two  modes  of  formation  of 
follicles;  one,  by  the  penetration  of  epithelial  tubes  from  the  surface, 
which  become  constricted  and  divided  off  into  closed  cavities,  and  the 
other,  by  the  extension  of  fibrous  processes  from  below,  which  enclose 
little  collections  of  cells.  By  both  these  processes,  little  cavities  are 
formed,  which  contain  a  number  of  cells.  In  each  of  these  cavities, 
there  is  a  single,  large,  rounded  cell,  with  a  large  nucleus,  this  cell  be- 
ing a  primordial  ovum  ;  and  in  addition,  in  the  same  cavity,  there  are 
other  cells,  which  are  the  cells  of  the  Graafian  follicle.  The  exact 
nature  of  the  processes  just  described  has  been  studied  in  the  chick ; 
but  it  is  probable  that  the  same  kind  of  development  occurs  in  mam- 
malia and  in  the  human  subject. 

From  birth  until  just  before  puberty,  the  cortical  substance  of  the 
ovary  contains  several  thousands  of  what  are  termed  primordial  follicles 
enclosing  the  primordial  ova ;  and  it  is  probable  that  after  the  ovaries 
are  fully  developed  at  birth,  no  additional  ova  or  Graafian  follicles  make 


758 


EMBRYOLOGY 


their  appearance.  The  prevailing  idea  is,  indeed,  that  the  great  major- 
ity of  these  never  arrive  at  maturity  and  that  they  undergo  atrophy  at 
various  stages  of  their  development.  In  the  adult,  according  to  Wal- 
deyer,  the  smallest  Graafian  follicles  measure  g-J^  to  g J-g-  of  an  inch 
(30  to  40  /jl),  and  the  smallest  ova,  a  little  more  than  y6oo  °^  ^"  ^^^^^ 
(26  fx).  The  primordial  ova  have  the  form  of  rounded  cells,  each  with  a 
large  clear  nucleus  and  a  nucleolus.  Other  structures  are  developed  in 
and  surrounding  these  cells  as  the  ova  arrive  at  their  full  development. 


Fig.  198.  —  Ovum  0/ the  cat,  loithin  the  ovary,  directly  reproduced Jrom  a  photograph  of  a 
preparation  by  Dahlgren,  x  235  (Wilson). 

The  ovum  lies  in  the  discus  proligerus  within  the  Graafian  follicle. 


The  most  important  stage  in  the  development  of  the  ova  and 
Graafian  follicles  is  observed  at  about  the  beginning  of  puberty.  At 
this  time  a  number  of  follicles  (twelve,  twenty,  thirty  or  even  more) 
enlarge,  so  that  all  sizes  are  observed,  between  the  smallest  primordial 
follicles,  g^Q  of  an  inch  (30  /a),  and  the  largest,  nearly  \  an  inch 
(12  millimeters)  in  diameter.  In  follicles  that  have  attained  any  consid- 
erable size,  there  are  the  fully-developed  ova,  one  in  each  follicle  — 
except  in  rare  instances,  when  there  are  two ;  and  these  ova  have  a 
diameter  of  about  y^g  of  an  inch  (200  }x).  In  the  process  which  cul- 
minates in  the  discharge  of  the  ovum  into  the  fimbriated  extremity  of 


FEMALE  ORGANS  OF  GENERATION 


759 


the  Fallopian  tube,  the  Graafian  follicle  gradually  enlarges,  becomes 
distended  with  liquid  which  finally  breaks  through,  and  the  follicle  rup- 
tures on  the  surface  of  the  ovary. 

At  or  near  the  period  of  their  maturity  the  Graafian  follicles  present 
several  coats  and  are  filled  with  an  albuminous  liquid.  The  mature  folli- 
cles project  just  beneath  the  surface  and  form  little  rounded  translucent 
elevations.  The  smallest  follicles  are  near  the  surface,  and  as  they 
enlarge,  at  first  they  become  deeper,  becoming  superficial  only  as  they 
approach  the  condition  of  fullest  distention. 

Taking  one  of  the  largest  follicles  as  an  example,  two  fibrous  layers 
can  be  distinguished ;  an  outer  layer,  of  ordinary  connective  tissue,  and 
an  inner  layer,  the  tunica  propria,  formed  of  the  same  kind  of  tissue, 
with  the  difference  that  as  the  follicle  enlarges  the  inner  layer  becomes 
vascular.  The  vascular  tunica  propria  is  lined  with  cells  of  epithelium, 
forming  the  so-called  membrana  granulosa.  At  a  certain  point  in  this 
membrane,  is  a  mass  of  cells,  called  the  discus  or  cumulus  proligerus,  in 
which  the  ovum  is  embedded.  The  situation  of  the  discus  proligerus  is 
not  invariable ;  sometimes  it  is  at  the  most  superficial,  and  sometimes 
it  is  at  the  deepest  part  of  the  Graafian  follicle. 

The  liquid  of  the  Graafian  follicle  is  alkaline,  shghtly  yellowish  and 
not  viscid.  It  contains  a  small  quantity  of  albuminous  matter  coagu- 
lable  by  heat,  alcohol  and  acids.  This  liquid  is  supposed  to  be  secreted 
by  the  cells  lining  the  inner  membrane  of  the  follicle. 

The  Parovarium. — The  parovarium,  or  organ  of  Rosenmiiller,  is 
simply  the  remains  of  the  Wolffian  body,  lying  in  the  folds  of  the  broad 
hgament,  between  the  ovary  and  the  Fallopian  tube.  It  consists  of 
twelve  to  fifteen  tubes  of  fibrous  tissue,  lined  with  ciliated  epithelium. 
It  has  no  physiological  importance. 

The  Uterus. — The  form,  situation  and  relations  of  the  uterus  and 
Fallopian  tubes  have  already  been  indicated  and  are  shown  in  Fig.  197. 
It  is  a  pear-shaped  body,  somewhat  flattened  antero-posteriorly,  present- 
ing a  fundus,  a  body  and  a  neck.  At  its  lower  extrerriity,  is  an  opening 
into  the  vagina,  called  the  os  externum.  At  the  upper  portion  of  the 
neck,  is  a  constriction,  which  indicates  the  situation  of  the  os  internum. 
The  form  of  the  uterus  is  shown  in  Fig.  199  (A).  It  usually  is  about 
three  inches  (76.2  miUimeters)  in  length,  two  inches  (50.8  millimeters) 
in  breadth  at  its  widest  portion,  and  one  inch  (25.4  millimeters)  in 
thickness.  Its  weight  is  one  and  a  half  to  two  and  a  half  ounces 
(42.5  to  71  grams).  It  is  somewhat  loosely  held  in  place  by  the  broad 
and  round  Hgaments  and  by  the  folds  of  the  peritoneum  in  front  and 
behind.  The  delicate  layer  of  peritoneum  that  forms  its  external  cover- 
ing extends  behind  as  far  down  as  the  vagina,  where  it  is  reflected  back 


76o 


E.MBRVOLOGY 


upon  the  rectum,  and  anteriorly,  a  little  below  the  upper  extremity  of 
the  neck  (os  internum),  where  it  is  reflected  upon  the  urinary  bladder. 
At  the  sides  of  the  uterus,  the  peritoneal  covering,  a  little  below  the 
entrance  of  the  Fallopian  tubes,  becomes  loosely  attached  and  leaves 
a  line  for  the  penetration  of  the  vessels  and  nerves.  Fig.  199  (C), 
giving  a  view  of  the  interior  of  the  uterus,  shows  a  triangular  cavity, 
with  two  cornua  corresponding  to  the  openings  of  the  Fallopian  tubes, 
and  very  thick  walls,  the  greatest  part  of  which  is  composed  of  layers 
and  bands  of  non-striated  muscular  fibres. 

The  muscular  walls  of  the  uterus  are  composed  of  non-striated  fibres 
arranged  in  several  layers.     These  fibres  are  spindle-shaped  and  always 

A  B  3       G 


Fig.  199.  —  Virgin  uterus  (  fro?n  a  woman  haetity-tioo  years  old) . 


8 

A.  —  anterior  view.     B.  —  median 


longitudinal  section.     C.  —  transverse  longitudinal  section  (Sappey). 

A.  I,  body;  2,  2,  angles;  3,  cervix;  4,  site  of  the  os  internum  ;  5,  vaginal  portion  of  the  cervix;  6,  ex- 
ternal OS  ;  7,  7,  vagina. 

B.  I,  I,  profile  of  the  anterior  surface;  2,  vesico-uterine  cul-de-sac ;  3,  3,  profile  of  the  posterior  sur- 
face; 4,  body;  5,  neck;  6,  isthmus;  7,  cavity  of  the  body;  8,  cavity  of  the  cervix;  9,  os  internum; 
10,  anterior  lip  of  the  os  externum  ;    11,  posterior  lip;    12,  12,  vagina. 

C.  I,  cavity  of  the  body;  2,  lateral  wall;  3,  superior  wall;  4,  4,  cornua;  5,  os  internum;  6,  cavity 
of  the  cervix;  7,  arbor  vita;  of  the  cervix;  8,  os  externum;  9,  9,  vagina. 

nucleated,  the  nucleus  presenting  one  or  two  large  granules  that  have 
been  taken  for  nucleoli.  Thev  are  closely  bound  together,  so  that  they 
are  isolated  with  great  difficulty.  In  addition  to  an  amorphous  adhesive 
substance  between  the  muscular  fibres,  there  are  many  rounded  and 
spindle-shaped  cells  of  connective  tissue,  and  a  few  elastic  fibres.  The 
muscular  fibres  of  the  uterus  enlarge  immensely  during  gestation,  becom- 
ing at  that  time  ten  or  fifteen  times  as  long  and  five  or  six  times  as  broad 
as  they  are  in  the  unimpregnated  state.  They  are  united  into  bundles,  or 
fasciculi,  which  in  certain  of  the  layers  interlace  with  each  other  in  every 
direction.    The  fibres  are  divided  into  external,  middle  and  internal  layers. 


FEMALE  ORGANS  OF  GENERATION 


761 


The  external  muscular  layer,  which  is  very  thin  but  distinct,  is 
closely  attached  to  the  peritoneum.  When  the  uterus  is  somewhat 
enlarged  after  impregnation,  there  are  observed  oblique  and  transverse 
superficial  fibres  passing  over  the  fundus  and  the  anterior  and  posterior 
surfaces  to  the  sides.  Here  they  are  prolonged  upon  the  Fallopian 
tubes,  the  round  ligament  and  the  ligament  of  the  ovary,  and  they  also 
extend  between  the  layers  of  the  broad  ligament.  This  external  layer 
is  so  thin  that  it  can  not  be  very  efihcient  in  the  expulsive  contractions 
of  the  uterus ;  but  from  its  connections  with  the  Fallopian  tubes  and 
the  ligaments,  it  is  useful  in  holding  the  uterus  in  place.  It  does  not 
extend  entirely  over  the  sides  of  the  uterus. 

A  -R  G 


/ 

Fig.  200.  —  Muscular  fibres  of  the  uterus  (Sappey). 

A,  fibres  of  the  uterus  of  the  foetus  at  term ;  j5,  of  a  woman  twenty  years  of  age ;    C,  of  a  woman 
just  delivered. 

The  middle  muscular  layer  is  the  one  most  efficient  in  the  parturient 
contractions  of  the  uterus.  It  is  composed  of  a  thick  and  intricate 
network  of  fasciculi  interlacing  with  each  other  in  every  direction. 

The  inner  muscular  layer  is  arranged  in  the  form  of  broad  rings, 
which  surround  the  Fallopian  tubes,  become  larger  as  they  extend 
over  the  body  of  the  uterus  and  meet  at  the  centre  of  the  organ,  near 
the  neck. 

The  mucous  membrane  of  the  uterus  is  of  a  pale  reddish  color ; 
and  that  portion  lining  the  body  is  smooth  and  is  so  closely  attached  to 
the  subjacent  structures  that  it  can  not  be  separated  to  any  great  extent 
by  dissection.     There  is,  indeed,  no  proper  submucous  areolar  tissue. 


762 


EMBRYOLOGY 


the  membrane  being  applied  directly  to  the  uterine  walls.  It  is  cov- 
ered by  a  single  layer  of  cylindrical  epithelial  cells,  with  delicate  cilia, 
the  movements  of  which  are  from  without  inward,  toward  the  openings 
of  the  Fallopian  tubes.  Examination  of  the  surface  of  the  membrane 
with  a  low  magnifying  power  shows  the  openings  of  a  great  number  of 
tubular  glands.  These  glands  usually  are  simple,  sometimes  branched, 
dividing,  about  midway  between  the  opening  and  the  lower  extremity, 
into  two  and  very  rarely  into  three  secondary  tubules.  Their  course 
usually  is  tortuous,  so  that  their  length  frequently  exceeds  the  thick- 
ness of  the  mucous  membrane.     The  openings  of  these  tubes  are  about 

gJo^  of  an  inch  (72  fx)  in 
diameter.  Their  secre- 
tion, which  forms  a  thin 
layer  of  mucus  on  the 
surface  of  the  membrane 
in  health,  is  grayish,  vis- 
cid and  feebly  alkaline. 
The  tubes  themselves 
have  very  thin  structure- 
less walls  and  are  lined 
with  cylindrical  ciliated 
epithelial  cells. 

The  changes  which 
the  mucous  membrane  of 
the  body  of  the  uterus 
undergoes  during  men- 
struation are  remarkable. 
Under  ordinary  condi- 
tions its  thickness  is   2^5 


Fig.  201. 


■Superficial  muscular  fibres  of  the  anterior  surface  of 
the  uterus  (Liegeois). 


a,  a,  round  ligaments;  i,  i,  Fallopian  tubes;   c,  c,  c 
verse  fibres;  d,f  longitudinal  fibres. 


e,  trans- 


to  Yj  of  an  inch  (i  to 
1.8  millimeters);  but  it 
measures  during  the  menstrual  period  \  to  \  of  an  inch  (4.2  to  6.4  milli- 
meters). 

In  the  cervix  the  membrane  is  paler,  firmer  and  thicker  than  the 
membrane  of  the  body  of  the  uterus,  and  between  these  two  mucous 
surfaces  there  is  a  distinct  line  of  demarcation.  It  is  more  loosely 
attached  to  the  subjacent  tissue  in  the  cervix,  and  the  anterior  and  pos- 
terior surfaces  of  the  neck  present  an  appearance  of  folds  radiating 
from  the  median  line,  forming  what  has  been  called  the  arbor  vitae 
uteri,  or  plicae  palmatae.  Throughout  the  cervical  membrane,  are 
mucous  glands,  and  in  addition,  in  the  lower  portion,  are  a  few  rounded, 
semitransparent,  closed  follicles,  called  the  ovules  of  Naboth,  which  are 


FEMALE  ORGANS  OF  GENERATION 


763 


cystic  enlargements  of  obstructed  follicles.  The  upper  half  of  the  cer- 
vical membrane  is  smooth  but  the  lower  half  presents  a  large  number  of 
villi.  The  epithelium  of  the  cervix  presents  great  variations  in  its  char- 
acter in  different  individuals.  Before  puberty  the  entire  membrane  of 
the  cervix  is  covered  with  ciliated  epithelium.  After  puberty,  however, 
the  epithelium  of  the  lower  portion  changes  its  character,  and  there  are 
cylindrical  cells  above,  with  squamous  cells  in  the  inferior  portion. 
The  latter  extend  upward  in  the  neck  for  a  variable   distance. 

The  bloodvessels  of  the  uterus  are  very  large  and  present  certain 
important  peculiarities  in  their  arrangement.  The  uterine  arteries  pass 
between  the  layers  of  the  broad 
ligament,  to  the  neck,  and  then 
ascend  by  the  sides  of  the  uterus, 
presenting  a  rich  plexus  of  ves- 
sels, anastomosing  above  with 
branches  from  the  ovarian  arte- 
ries, sending  branches  over  the 
body  of  the  uterus,  and  finally 
penetrating  the  organ,  to  be  dis- 
tributed mainly  in  the  middle 
layer  of  muscular  fibres.  In  their 
course  these  vessels  present  a 
convoluted  arrangement  and 
form  a  sort  of  mould  of  the  body 
of  the  uterus.  Rouget  has  called 
this  the  erectile  tissue  of  the 
internal  generative  organs.  It 
lacks,  however,  certain  of  the 
characters  of  true  erectile  tissue. 
By  placing  the  pelvis  in  a  bath 
of  warm  water  and  injecting 
what  he  called  the  spongy  bodies  of  the  ovaries  and  uterus  by  the 
ovarian  veins,  he  produced  a  distention  of  the  vessels  and  a  sort  of 
erection,  the  uterus  executing  a  movement  upward. 

In  the  muscular  walls  of  the  uterus,  are  large  veins,  the  walls  of 
which  are  closely  adherent  to  the  uterine  tissue.  During  gestation 
these  vessels  become  enlarged,  forming  the  so-called  uterine  sinuses. 

Lymphatics  are  not  very  abundant  in  the  unimpregnated  uterus,  but 
they  become  largely  developed  during  utero-gestation.  They  exist  in 
a  superficial  and  a  deep  layer,  the  deeper  vessels  being  connected  with 
lymph-spaces  in  the  muscular  walls  and  in  the  mucous  membrane. 

The  uterine  nerves  are  derived  from  the  inferior  hypogastric   and 


Fig.  202.- 


Inner  layer  of  muscular  fibres  of  the  uterus 
(Liegeois). 

a,  a,  rings  around  the  openings  of  the  Fallopian  tubes  ; 
b,  b,  circular  fibres  of  the  cervix. 


764 


EMBRYOLOGY 


the  spermatic  plexuses  and  the  third  and  fourth  sacral.  In  the  sub- 
stance of  the  uterus  they  present  in  their  course  small  collections  of 
ganglionic  cells,  and  it  is  said  that  the  nerves  pass  finally  to  the  nucleoli 
of  the  muscular  fibres  (Frankenhaeuser). 

8 


Fig    203.  —  Uterine  and  utero-ovarLan  veins  (SappeyJ . 

I,  Anterior  face  of  the  uterus,  the  right  side  covered  with  peritoneum  —  on  the  left  side  the  utero- 
ovarian  plexus  is  exposed;  2,  2,  3,  3,  Fallopian  tubes;  5,  5,  round  ligaments;  6,  utero-ovarian  veins 
covered  with  peritoneum;  7,  same  vessels  exposed;  8,  8,  8,  veins  in  the  broad  ligament;  9,  plexus  at 
the  hilum  of  the  ovary;  10,  uterine  vein;  11,  uterine  artery;  12,  venous  plexus  covering  the  uterus; 
13,  anastomoses  of  the  uterine  with  the  utero-ovarian  veins. 

T/ie  Fallopian  Tubes. — The  Fallopian  tubes,  or  oviducts,  lead  from 
the  ovaries  to  the  uterus.  They  are  three  to  four  inches  {^.6  to  lo.  i 
centimeters)  long,  but  their  length  is  not  always  equal  on  the  two  sides. 
They  lie  between  the  folds  of  the  broad  ligament  at  its  upper  border. 
Opening  into  the  uterus  on  either  side  at  the  cornua,  they  present  each  a 


Fig.  204.  —  Section  through  the  left  Fallopian  tube  (Williams,  after  Sappey). 

small  orifice,  about  .,V  of  an  inch  (i  millimeter)  in  diameter.  From  the 
cornua  they  take  a  somewhat  undulatory  course  outward,  gradually 
increasing  in  size,  so  that  they  are  rather  trumpet-shaped.  Near  the 
ovary  they  turn  downward  and  backward.  The  extremity  next  the 
ovary  is  marked  by  ten  to  fifteen  fimbriae,  or  fringes,  which  have  given 
this  the   name  of    the    fimbriated    extremity,  or    morsus    diaboli.     All 


FEMALE  ORGANS  OF  GENERATION 


765 


these  fringe-like  processes  are  free  except  one ;  and  this  one,  which  is 
longer  than  the  others,  is  attached  to  the  outer  angle  of  the  ovary  and 
presents  a  little  gutter,  or  furrow,  extending  from  the  ovary  to  the  open- 
ing of  the  tube.  At  this  extremity,  is  the  abdominal  opening  of  the 
tube,  which  is  two  or  three  times  larger  than  the  uterine  opening. 
Passing  from  the  uterus,  the  calibre  of  the  tube  gradually  increases  as 
the  tube  itself  enlarges,  and  there  is  an  abrupt  constriction  at  the 
abdominal  opening. 

Beneath  the  peritoneal  coat,  which  is  formed  by  the  layers  of  the 
broad  ligament,  is  a  layer  of  connective  tissue,  containing  a  rich  plexus 

A 


Fig.  205.  —  External  erectile  organs  of  the  female  (Liegeois) . 

A,  pubis;  B,  B,  ischium;  C,  clitoris;  A  gland  of  the  clitoris;  £,  bulb;  F,  constrictor  muscle 
of  the  vulva ;  G,  left  pillar  of  the  clitoris  ;  H,  dorsal  vein  of  the  clitoris ;  /,  intermediary  plexus  ;  /,  vein 
of  communication  with  the  obturator  vein ;   K,  obturator  vein  ;  M,  labia  minora. 

of  bloodvessels.  This  constitutes  the  proper  fibrous  coat  of  the  Fallo- 
pian tubes. 

The  muscular  layer  is  composed  mainly  of  circular  fibres  of  the  non- 
striated  variety,  with  a  few  longitudinal  fibres  prolonged  over  the  tube 
from  the  external  muscular  layer  of  the  uterus.  This  coat  is  quite  thick 
and  sends  bands  between  the  layers  of  the  broad  hgament  to  the  ovary. 

The  mucous  membrane  of  the  tube  is  thrown  into  folds,  which  are 
longitudinal  and  transverse  near  the  uterus  and  are  more  complicated 
at  the  dilated  portion.  In  this  portion,  next  the  ovary,  embracing  about 
the  outer  two-thirds,  the  folds  project  far  into  the  calibre  of  the  tube. 
These  are  sometimes  simple,  but  more  frequently  they  present  secondary 
folds,  often  meeting  as  they  project  from  opposite  sides.  This  arrange- 
ment gives  an  arborescent  appearance  to  the  membrane  on  transverse 


^66  EMBRYOLOGY 

section  of  the  tube.  The  mucous  membrane  is  covered  with  cylindrical 
ciliated  epithelium,  the  movement  of  the  cilia  being  from  the  ovary 
toward  the  uterus.  The  membrane  of  the  tubes  has  no  mucous  glands 
(see  Plate  X,  Fig.  5). 

It  is  not  necessary  to  give  a  minute  description  of  the  external 
organs  of  the  female.  Opening  by  the  vulva  externally,  and  termina- 
ting at  the  neck  of  the  uterus,  is  a  membranous  tube,  the  vagina.  This 
lies  between  the  bladder  and  the  rectum.  It  has  a  curved  direction, 
being  3|  to  3.3  inches  (8  to  9  centimeters)  long  in  front,  and  3^  to  4 
inches  (9  to  10  centimeters)  long  posteriorly.  At  the  constricted  por- 
tion of  the  outer  opening,  there  is  a  muscle,  called  the  sphincter  vaginas, 
and  the  tube  is  somewhat  narrowed  at  its  upper  end,  where  it  embraces 
the  cervix  uteri.  The  inner  surface  presents  a  mucous  membrane, 
marked  by  transverse  rugae,  with  papillae  and  mucous  glands.  Its  sur- 
face is  covered  with  stratified  epithelium  in  several  layers.  The  vagina 
is  quite  extensible,  as  it  must  be  during  parturition  to  allow  the  passage 
of  the  child.  It  presents  a  proper  coat  of  dense  fibrous  tissue,  with 
longitudinal  and  circular  muscular  fibres  of  the  non-striated  variety. 
Surrounding  it,  is  a  rather  loose  so-called  erectile  tissue,  which  is  most 
prominent  at  its  lower  portion. 

The  parts  composing  the  external  organs  are  abundantly  supplied 
with  vessels  and  nerves.  In  the  clitoris,  which  corresponds  to  the  penis 
of  the  male,  and  on  either  side  of  the  vestibule,  there  is  a  true  erectile 
tissue. 

Structure  of  tJie  Ovum. — The  ovum  lies  in  the  Graafian  follicle,  em- 
bedded in  the  mass  of  granular  cells  which  forms  the  discus  proligerus. 
Surrounding  the  ovum  are  cells  similar  to  those  found  in  other  parts  of 
the  membrana  granulosa,  and  two  or  three  layers  of  columnar  cells,  the 
latter  lying  next  the  zona  pellucida.  These  columnar  cells  constitute 
the  corona  radiata.  The  ovum  itself  presents  the  following  structures : 
(i)  Zona  pellucida;  (2)  perivitelline  space;  (3)  a  clear  outer  zone  of 
the  vitellus ;  (4)  protoplasmic  zone  (formative  yolk);  (5)  deutoplasmic 
zone  (nutritive  yolk);  (6)  germinal  vesicle  (Purkinje);  germinal  spot 
(Wagner).  The  thin  membrane  within  the  zona  pellucida  and  immedi- 
ately surrounding  the  vitellus,  described  under  the  name  of  vitelline 
membrane  by  some  anatomists,  was  not  observed  by  Nagel  in  the 
human  ovum. 

The  ovum  is  globular,  with  a  diameter  of  about  ■^\-^  of  an  inch  (165 
to  170  /i)  measured  from  the  outer  border  of  the  zona  pellucida. 

The  zona  pellucida  (zona  radiata,  or  vitelline  membrane)  is  yoVo  ^^ 
ToVo  ^^  ^'^  \nz\i  (20  to  24  \x)  in  thickness.  It  is  a  strong  membrane,  ap- 
pearing in  the  form  of  a  clear  zone  in  the  mass  of  surrounding  cells. 


THE    OVUM 


767 


It  is  marked  by  striae,  which  are  thought  by  some  anatomists  to  indicate 
the  presence  of  small  pores  ;  but  the  large  single  opening  called  a  mi- 
cropyle,  which  is  found  in  many  of  the  osseous  fishes  and  in  mollusks, 
has  not  been  demonstrated  in  the  human  ovum. 

Between  the  zona  pellucida  and  the  vitellus,  is  a  narrow  space,  about 
-oQ^QQ  of  an  inch  ("1.3  /j.)  in  diameter.  This  is  called  the  perivitelline 
space. 

The  vitellus  is  contained  within  the  zona  pellucida.  It  presents  a  clear 
outer  zone  goVo  ^°  40V0  °^  ^^  ^^"-^  ^4  ^°  ^  f^)  ^^  diameter.  This  can  not 
be  distinguished  from  the  protoplasmic  zone,  except  in  perfectly  fresh 


Zona  pelluciaa 


Protoplasmic  . 
Zone 


"^, 


"^^ 


Per  vt  I  'ne  Space 


ells  of  the  discus 
proligerus 

'^^^^&~^J§j-       'x,C<^        -  Corona  radiata 


_  Gerr/iinal  Vesicle, 
with  two  germinal 
-  Spots 


t33<g'^ 


Fig.  206.  —  Deutoplasm-formitig  ovum  from  a   Graafian  follicle  of  a  woman  twenty-seven  years 

old,  X  160  (Xagel). 

This  ovum  was  taken  from  a  fresh  ovarj'  removed  from  the  li%-ing  subject. 


ova.  It  is  composed  of  clear  protoplasm  without  granules  and  repre- 
sents that  portion  of  the  protoplasm  of  the  vitellus  which  is  not  at  any 
time  converted  into  deutoplasm.  \\'ithin  the  clear  zone,  is  the  proto- 
plasmic zone  fformative  yolk).  This  presents  very  fine  granules,  and 
the  zone  is  osVir  ^"^  i^Vio  °f  ^^  '\nz\s-  (10  to  21  /x)  in  thickness.  Occupy- 
ing the  central  portion  of  the  vitellus,  is  the  deutoplasm  (nutritive  yolk), 
forming  a  mass  about  g-i^  of  an  inch  (82  to  87  }j.)  in  diameter.  The 
deutoplasm  presents  granules  of  different  sizes  and  different  refractive 
power.  Treated  with  eosin,  the  protoplasm  becomes  rose-colored,  but 
the  deutoplasm  is  unaffected.  As  the  ovum  reaches  its  final  stage  of 
development,  the  protoplasmic  zone,  as  far  as  that  portion  which  forms 
the  so-called    outer   zone,  is    gradually  changed  into    deutoplasm.     In 


yez 


EMBRYOLOGY 


Fig.  206,  a  human  ovum  is  represented  in  which  this  change  of  proto- 
plasm into  deutoplasm  is  in  progress. 

The  germinal  vesicle  lies  always  in  the  protoplasmic  zone,  just  out- 
side  of   the   deutoplasm.     As    the    mass    of   deutoplasm   extends,    the 


Corona  radial  a 
\ 


Protoplasmic  Zone 

i 


.^■aC';^,.-  , ,r:r^\  Zona  pellucida 


Deutoplasmic  Zone 


"'^'^  '  \  *^ 


t'] 


^>.^.rfs 


fe 


%' 


■s 


Germinal  Vesicle, 
with  an  ameboid 
germinal  Spot 


/ 

Perivitelline  Space 

Clear  Outer  Zone 

Fig.  207.  —  Ovum  from  a  Graajian  follicle  of  a  zvoman  thirty  years  old,  X  375  (Nagel). 

This  ovum  was  taken  from  a  fresh  ovary  removed  from  the  Uving  subject. 

germinal  vesicle  is  pushed  toward  the  periphery  of  the  vitellus.  The 
vesicle  measures  about  yoVo  ^^  ^"  ^^^h  (25  to  27  /a)  in  diameter.  It  is 
globular,  with  a  double  contour.  In  hardened  preparations  it  presents 
a  frame-work  of  fine  anastomosing  fibres.  In  the  fully-developed  human 
ovum,  no  ameboid  movements  have  as  yet  been  observed  in  the  ger- 
minal vesicle.  In  Fig.  207,  the  germinal  vesicle  is  seen  lying  upon  and 
not  within  the  deutoplasmic  zone.  The  mature  ovum  presents  but  one 
germinal  vesicle.  Two  germinal  vesicles,  however,  are  sometimes  found 
in  primordial  ova  (see  Fig.  208). 


THE    OVUM  769 

The  germinal  spot  (Wagner)  is  contained  in  the  germinal  vesicle. 
Some  vesicles  present  two  germinal  spots.  In  perfectly  fresh  ova  the 
germinal  spots  have  been  observed  to  undergo  ameboid  movements. 

Discharge  of  the  Ovum.  —  A  ripe  Graafian  follicle  measures  -|  to  |-  of 
an  inch  (10  to  12  millimeters)  in  diameter,  and  presents  a  rounded 
elevation,  containing  a  plexus  of  bloodvessels,  on  the  surface  of  the 
ovary.  At  its  most  prominent  portion,  is  an  ovoid  spot  in  which  the 
membranes  are  entirely  free  from  bloodvessels.  At  this  spot,  which  is 
called  the  macula  folliculi,  or  stigma,  the  coverings  finally  give  way  and 
the  contents  of  the  follicle  are  discharged.  For  a  short  time  anterior  to 
the  rupture  of  the  folhcle  important  changes  have  been  going  on  in  its 
structure.  In  the  first  place,  the  portion  situated  at  the  very  surface  of 
the  ovary  undergoes  degeneration,  by  which  this  part  of  the  wall  gradu- 
ally becomes  weakened.  At  the  same  time,  at  the  other  portions  of  the 
follicle,  there  is  a  proliferation  of  cells  which  project  into 
the  interior,  and  an  extension  into  the  interior  of  blood- 
vessels in  the  form  of  loops.  These  changes,  with  an 
increase  in  the  pressure  of  liquid  and  the  degeneration 
at  the  macula,  cause  the  follicle  to  burst ;  and  with  the 
liquid,  the  discus  proligerus  and  the  ovum  are  expelled.       ^^^^  ^°^-  ~  ^^.l' 

'■         '  10  i  inoraial    ovum    with 

The  formation  of  a  cell-growth  in  the  interior   of  the  two  germinal  vesicles 

r    ^^•    ^      •      .^        ^         •        •  r^i  1^  ii.1-       and  follicular  epithe- 

follicle  IS  the  begmnmg  of  the  corpus  luteum  ;  and  this  uum_from  the  ovary 
occurs  some  time  before  the  discharge   of    the    ovum  of  a  fiewbom  chUd 

.11  (Nagel). 

takes  place. 

The  time  at  which  the  follicle  ruptures,  particularly  with  reference 
to  the  menstrual  period,  is  not  definite  ;  but  it  is  certain  that  while  sex- 
ual excitement  probably  hastens  the  discharge  of  an  ovum  by  producing 
a  greater  or  less  tendency  to  congestion  of  the  internal  organs,  ovulation 
takes  place  independently  of  coition.  The  opportunities  for  determin- 
ing this  fact  in  the  human  female  are  not  frequent ;  but  it  has  been 
fully  demonstrated  by  observations  on  the  inferior  animals,  and  there 
is  now  no  doubt  in  regard  to  the  identity  of  the  phenomena  of  rut  and 
of  menstruation.  At  stated  periods  marked  by  the  phenomena  of  men- 
struation, one  Graafian  follicle  —  and  sometimes  more  than  one^ — 
becomes  distended  and  usually  ruptures  and  discharges  its  contents  into 
the  Fallopian  tubes.  This  discharge  of  an  ovum  or  ova  may  occur  at 
the  beginning,  at  the  end,  or  at  any  time  during  the  continuance  of  the 
menstrual  flow.  On  this  point  the  observations  of  Coste  seem  entirely 
conclusive.  In  a  woman  who  died  on  the  first  day  of  menstruation,  he 
found  a  recently-ruptured  follicle  ;  in  other  instances,  at  a  more  ad- 
vanced period  and  toward  the  decline  of  the  menstrual  flow,  he  found 
evidences  that  the  rupture  had  occurred  later ;  in  the  case  of  a  female 

3D 


770  EMBRYOLOGY 

who  drowned  herself  four  or  five  days  after  the  cessation  of  the  menses, 
a  follicle  was  found  in  the  right  ovary,  so  distended  that  it  was  ruptured 
by  very  slight  pressure  ;  and  other  instances  were  observed  in  which 
follicles  were  not  ruptured  during  the  menstrual  period. 


Passage  of  Ova  into  the  Fallopian  Tubes 

The  fact  that  the  ova  in  the  great  majority  of  instances  pass  into  the 
Fallopian  tubes  is  sufficiently  evident.  The  fact,  also,  that  ova  may  fall 
into  the  cavity  of  the  peritoneum  is  illustrated  by  the  occasional  occur- 
rence of  extra-uterine  pregnancy,  a  rare  accident,  which  shows  that  in  all 
probability  the  failure  of  unimpregnated  ova  to  enter  the  tubes  is  excep- 
tional. As  regards  the  mechanism  of  the  passage  of  the  ova  into  the 
tubes,  however,  the  explanation  is  difficult.  At  the  present  time  there 
are  two  theories  in  regard  to  this  process  ;  one,  in  which  it  is  supposed 
that  the  fimbriated  extremities  of  the  Fallopian  tubes,  at  the  time  of 
rupture  of  the  Graafian  follicles,  become  adapted  to  the  surface  of  the 
ovaries,  and  the  other,  that  the  ova  are  carried  to  the  openings  of  the 
tubes,  by  ciliary  currents.  Neither  of  these  theories,  however,  is  sus- 
ceptible of  actual  demonstration  ;  and  their  value  is  to  be  judged  from 
anatomical  facts.  It  is  not  difficult  to  understand,  taking  into  account 
the  situation  of  the  ovaries  and  the  relations  of  the  Fallopian  tubes,  how 
an  ovum  may  pass  into  the  tube,  without  invoking  the  aid  of  muscular 
action.  It  may  be  supposed,  for  example,  that  a  Graafian  follicle  is 
ruptured  when  the  fimbriated  extremity  of  the  tube  is  not  applied  to  the 
surface  of  the  ovary.  One  of  the  fimbriae,  longer  than  the  others,  is 
attached  to  the  outer  angle  of  the  ovary  and  presents  a  little  furrow,  or 
gutter,  leading  to  the  opening  of  the  tube.  This  furrow  is  lined  with 
ciHated  epithelium,  as,  indeed,  is  the  mucous  membrane  of  all  the  fim- 
briae, the  movements  of  which  produce  a  current  in  the  direction  of  the 
opening,  which  would  apparently  be  sufficient  to  carry  the  ovum  into  the 
tube.  At  the  same  time  there  probably  is  a  constant  flow  of  liquid  over 
the  ovarian  surface,  directed  by  the  ciliary  current  toward  the  tube ;  and 
when  the  liquid  of  the  ruptured  follicle  is  discharged  this,  with  the  ovum, 
takes  the  same  course.  This  probably  is  the  mechanism  of  the  passage 
of  ova  into  the  Fallopian  tubes  ;  and  it  is  possible  that  the  fimbri- 
ated extremity  may  be  drawn  toward  the  ovarian  surface,  although  it  is 
difficult  to  understand  how  it  can  be  closely  applied  to  the  ovary  and 
exert  any  considerable  pressure  on  the  distended  follicle.  It  is  proper 
to  note,  also,  that  the  conditions  dependent  on  the  currents  of  liquid 
directed  by  the  movements  of  cilia  are  constant  and  could  influence  the 
passage  of  an  ovum  at  whatever  time  it  might  be  discharged,  while  a 


PUBERTY  AND  MENSTRUATION  771 

muscular  action  would  be  more  or  less  intermittent.  The  time  occupied 
in  the  passage  of  an  ovum  from  the  ovary  to  the  uterus  has  been  esti- 
mated affour  to  eight  days. 

Puberty  and  Menstruation.  —  At  a  certain  period  of  life,  usually 
between  the  ages  of  thirteen  and  fifteen,  the  human  female  undergoes 
a  remarkable  change  and  arrives  at  what  is  termed  the  age  of  puberty. 
At  this  time  there  is  a  marked  increase  in  the  general  development  of 
the  body ;  the  limbs  become  fuller  and  more  rounded ;  a  growth  of  hair 
makes  its  appearance  upon  the  mons  Veneris ;  the  mammary  glands 
increase  in  size  and  take  on  a  new  stage  of  development ;  Graafian  fol- 
licles enlarge,  and  one  or  more  approach  the  condition  favorable  to 
rupture  and  the  discharge  of  ova.  The  female  becomes  capable  of  impreg- 
nation, and  continues  so,  in  the  absence  of  pathological  conditions,  until 
the  cessation  of  the  menses. 

The  age  of  puberty  is  earlier  in  warm  than  in  cold  climates ;  and 
many  instances  are  on  record  in  which  the  menses  have  appeared 
exceptionally  much  before  the  usual  period.  Usually,  at  the  age  of 
forty  or  forty-five,  the  menstrual  flow  becomes  irregular,  occasionally 
losing  its  sanguineous  character,  and  it  ceases  at  about  the  age  of 
fifty  years.  The  time  of  cessation  of  the  menses  is  called  the  meno- 
pause, climacteric,  or  change  of  life.  Ova  then  are  no  longer  developed 
and  discharged,  and  impregnation  does  not  follow  intercourse.  It  is  said, 
however,  that  sometimes  the  menses  return,  with  a  second  period  of  fecun- 
dity, although  this  is  rare.  According  to  most  writers,  while  climate  has 
a  certain  influence  over  the  time  of  cessation  as  well  as  the  first  appear- 
ance of  the  menses,  this  is  not  very  marked.  When  the  menses  appear 
early  in  life,  they  usually  cease  at  a  correspondingly  early  period ;  but 
this  is  by  no  means  constant.  There  are,  also,  many  exceptions  to  the 
ordinary  limits  to  the  period  of  fecundity.  An  instance  of  childbirth 
at  the  age  of  sixty-three  years,  with  menstruation  following  at  the  usual 
time,  has  been  reported  by  Kennedy. 

In  the  human  female,  near  the  time  .of  puberty,  there  sometimes  is  a 
periodical  sero-mucous  discharge  from  the  genital  organs,  preceding,  for 
a  few  months,  the  regular  establishment  of  the  menstrual  flow.  Some- 
times, also,  after  the  first  discharge  of  blood,  the  female  passes  several 
months  without  another  period,  when  the  second  flow  takes  place  and 
the  menses  become  regular.  In  a  condition  of  health  the  periods  recur 
every  month  until  they  cease  at  the  climacteric.  In  the  majority  of  cases 
the  flow  recurs  on  the  twenty-seventh  or  the  twenty-eighth  day ;  but 
sometimes  the  interval  is  thirty  days.  As  a  rule,  also,  utero-gestation, 
lactation,  and  severe  diseases,  acute  and  chronic,  suspend  the  periods ; 
but  this  has  exceptions,  as  some  females  menstruate  regularly  during 


772 


EMBRYOLOGY 


pregnancy,  and  it  is  not  very  uncommon  for  the  menses  to  appear  during 
lactation. 

When  a  cow  gives  birth  to  twins,  one  a  male  and  the  other  apparently 
a  female,  the  latter  is  called  a  free-martin  and  has  no  ovaries.  John 
Hunter,  in  his  paper  on  the  free-martin,  gave  a  full  description  of  this 
anomalous  animal  and  stated  that  it  does  not  breed  or  show  any  inclina- 
tion for  the  bull.  In  an  examination  of  a  free-martin,  raised  and  killed 
by  the  late  Professor  James  R.  Wood,  in  1868,  the  uterus  was  found  rudi- 
mentary and  there  were  no  ovaries  (Flint). 

A  menstrual  period  presents  three  stages  :  first,  invasion ;  second,  a 
sanguineous  discharge  ;  third,  cessation. 

The  stage  of  invasion  is  variable  in  different  females.  There  is 
usually,  anterior  to  the  establishment  of  the  flow,  more  or  less  of  a  feeling 
of  general  malaise  and  a  sense  of  fulness  and  weight  in  the  pelvic  organs, 
accompanied  with  an  increase  in  the  quantity  of  vaginal  mucus,  which  be- 
comes brownish  or  rusty  in  color  and  has  a  peculiar  odor.  At  this  time, 
also,  the  breasts  become  slightly  enlarged.  This  stage  may  continue  for 
one  or  two  days,  although  in  many  instances  the  first  evidence  of  the 
access  of  a  period  is  a  discharge  of  blood. 

When  the  symptoms  above  indicated  occur,  the  general  sense  of  un- 
easiness usually  is  relieved  by  the  discharge  of  blood.  During  this,  the 
second  stage,  blood  flows  from  the  vagina  in  variable  quantity,  and  the 
discharge  continues  for  three  to  five  days.  In  regard  to  the  duration  of 
the  flow,  there  are  great  variations  in  different  individuals.  Some  women 
have  a  flow  of  blood  for  one  or  two  days  only ;  while  in  others  the  flow 
continues  for  five  to  eight  days,  within  the  limits  of  health.  A  fair  aver- 
age, perhaps,  is  four  days.  It  is  difficult  to  arrive  at  even  an  approxi- 
mation of  the  total  quantity  of  the  menstrual  flow ;  but  it  has  been 
estimated  at  five  to  six  ounces  (150  to  175  grams). 

Supposing  the  menstrual  discharge  to  continue  for  four  days,  on  the 
first  day  the  quantity  is  comparatively  small ;  on  the  second  and  third 
the  flow  is  at  its  height ;  and  the  quantity  is  diminished  on  the  fourth 
day.  During  this,  the  second  stage,  the  flow  has  the  appearance  of  pure 
arterial  blood,  not  coagulated,  and  mixed  with  epithehum  from  the  vagina, 
cylindrical  cells  from  the  uterus,  leucocytes  and  a  certain  quantity  of 
sero-mucous  secretion.  Chemical  examinations  of  the  liquid  have  not 
shown  any  marked  peculiarities,  except  that  the  quantity  of  fibrin  is 
either  not  estimated  or  is  given  as  much  less  than  in  ordinary  blood. 

The  mechanism  of  the  hemorrhage  probably  is  the  same  as  in  epis- 
taxis.  There  is  a  rupture  of  small  bloodvessels,  probably  capillaries,  and 
blood  is  thus  exuded  from  the  entire  surface  of  the  membrane  lining  the 
uterus,  and  sometimes,  but  rarely,  from  the  membrane  of  the  Fallopian 


CORPUS    LUTEU.M  773 

tubes.  The  blood  is  then  discharged  into  the  vagina  and  is  kept  liquid 
by  the  vaginal  mucus.  The  mucus  of  the  body  of  the  uterus  is  viscid 
and  alkaline ;  the  mucus  secreted  at  the  neck  is  gelatinous,  viscid  and 
tenacious,  and  also  is  alkaline :  the  vaginal  mucus  is  decidedly  acid, 
creamy  and  not  viscid,  containing  epithelium  and  leucocytes. 

The  third  stage  is  that  of  cessation  of  the  menses.  During  the  latter 
part  of  the  second  stage,  the  flow  of  blood  gradually  diminishes.  The 
discharge  becomes  rusty,  then  lighter  in  color,  and  in  the  course  of 
about  twenty-four  hours,  it  assumes  the  characters  observed  in  the  inter- 
menstrual period. 

When  the  menstrual  flow  has  become  fully  established,  there  is  no 
marked  general  disturbance,  except  a  sense  of  lassitude,  which  may  be- 
come exaggerated  if  the  discharge  be  unusually  abundant. 

If  the  mucous  membrane  of  the  uterus  is  examined  during  the  men- 
strual flow,  it  is  found  smeared  with  blood,  which  sometimes  extends  into 
the  Fallopian  tubes.  It  is  then  much  thicker  and  softer  than  during 
the  intermenstrual  period.  Instead  of  measuring  about  ^^  of  an  inch 
(1.8  millimeters)  in  thickness,  as  it  does  under  ordinary  conditions,  its 
thickness  is  ^  to  |  of  an  inch  (4.2  to  6.4  millimeters).  It  becomes  more 
loosely  attached  to  the  subjacent  parts,  is  somewhat  rugous  and  the 
glands  are  enlarged.  At  the  same  time  there  are  developed,  in  the 
substance  of  the  membrane,  large  numbers  of  spherical  and  fusiform 
cells.  This  condition  probably  precedes  the  discharge  of  blood  by  sev- 
eral days,  during  which  time  the  membrane  is  gradually  preparing  for 
the  reception  of  the  ovum.  There  also  is  a  degeneration  of  the  different 
elements  entering  into  the  structure  of  the  mucous  membrane,  including 
the  bloodvessels,  this  change  being  most  marked  at  the  surface ;  and  it 
is  on  account  of  the  weakened  condition  of  the  vascular  walls  that  the 
hemorrhage  takes  place.  A  short  time  after  the  flow  has  ceased,  the 
mucous  membrane  returns  to  its  ordinary  condition.  There  is  a  con- 
siderable desquamation  of  epithelium  from  the  uterus,  with  the  flow  of 
blood,  during  the  menstrual  period.  Sometimes,  in  normal  menstrua- 
tion, the  epithelium  thrown  off  is  in  the  form  of  patches. 

Changes  in  the  Graafian  Follicles  after  their Rnptnre  (Corpus  Lnteum). 
—  After  the  discharge  of  an  ovum,  its  Graafian  follicle  undergoes  cer- 
tain retrograde  changes,  involving  the  formation  of  what  is  called  the 
corpus  luteurn.  Even  when  the 'discharged  ovum  has  not  been  fer- 
tilized, the  corpus  luteum  persists  for  several  weeks,  so  that,  ovulation 
occurring  every  month,  several  of  these  bodies,  in  different  stages  of 
retrogression,  may  sometimes  be  seen  in  the  ovaries. 

For  a  certain  time  anterior  to  the  discharge  of  the  o\aim,  there  is  a 
cell-proliferation  from  the  proper  coat  of  the  Graafian  follicle,  and  prob- 


774 


EMBRYOLOGY 


ably  from  the  membrana  granulosa,  with  a  projection  of  looped  blood- 
vessels into  the  interior  of  the  folUcle.  This  is  the  iirst  formation  of  the 
corpus  luteum.  At  the  time  of  rupture  of  the  follicle,  the  ovum,  with  a 
great  part  of  the  membrana  granulosa,  is  discharged.  Usually,  at  the 
time  of  rupture  of  the  follicle,  there  is  a  discharge  of  blood  into  its  inte- 
rior; but  this  is  not  invariable,  although  there  is  always  a  gelatinous 
exudation  more  or  less  colored  with  blood.  At  the  same  time  the  fol- 
licular wall  undergoes  hypertrophy,  and  it  becomes  convoluted  or  folded, 
and  highly  vascular.  This  convoluted  wall,  formed  by  the  proper  coat  of 
the  follicle,  is  surrounded  with  the  fibrous  tunic,  and  its  thickening  is 
most  marked  at  the  deepest  portion  of  the  follicle.  At  the  end  of  about 
three  weeks,  the  body  —  which  is  now  called  the  corpus  luteum,  on  ac- 
count of  its  yellowish  or  reddish  yellow  color  —  has  arrived  at  its  maxi- 
mum of  development  and  measures  about  half  an  inch  (12.7  millimeters) 
in  depth,  by  about  three-quarters  of  an  inch  (19.1  millimeters)  in  length, 
its  form  being  ovoid.  The  convoluted  wall  then  contains  a  layer  of  large, 
pale,  finely-granular  cells,  which  are  internal  and  are  supposed  to  be  the 
remains  of  the  epithelium  of  the  follicle.  The  great  mass  of  this  wall, 
however,  is  composed  of  large  nucleated  cells  (leutein  cells),  contain- 
ing fatty  globules  and  granules  of  reddish  or  yellowish  pigmentary  matter. 
The  thickness  of  the  wall  is  about  one-eighth  of  an  inch  (3.2  miUimeters) 
at  its  deepest  portion. 

After  about  the  third  week  the  corpus  luteum  begins  to  contract ;  its 
central  portion  and  the  convoluted  wall  become  paler ;  and  at  the  end  of 
seven  or  eight  weeks,  a  small  cicatrix  marks  the  point  of  rupture  of  the 
follicle. 

The  above  are  the  changes  which  occur  in  the  Graafian  follicles  after 
their  rupture  and  the  discharge  of  ova,  when  the  ova  have  not  been 
fertilized ;  and  the  bodies  thus  produced  are  called  false  corpora 
lutea,  as  distinguished  from  corpora  lutea  formed  after  conception, 
which  latter  are  called  true  corpora  lutea. 

Corpus  Liiteinn  of  Pregnancy.  — When  a  discharged  ovum  has  been 
fertilized,  the  corpus  luteum  passes  through  its  various  stages  of  devel- 
opment and  retrogression  more  slowly  than  the  ordinary  corpus  luteum 
of  menstruation.  The  retrogression  begins  toward  the  end  of  the  third 
month.  "  During  the  fourth  month,  the  corpus  luteum  diminishes  by 
nearly  a  third,  and  toward  the  end  oi  the  fifth,  it  ordinarily  is  reduced 
one-half.  It  still  forms,  however,  during  the  first  days  after  parturition, 
and  in  the  greatest  number  of  cases,  a  tubercle  which  has  a  diameter  of 
not  less  than  |  to  \  of  an  inch  (7.3  to  8.5  millimeters).  The  tubercle 
afterward  diminishes  quite  rapidly ;  but  it  is  nearly  a  month  before  it  is 
reduced  to  the  condition  of  a  little,  hardened  nucleus,  which  persists 


MALE    ORGANS    OF   GENERATION 


775 


more  or  less  as  the  last  vestige  of  a  process  so  slow  in  arriving  at  its 
final  term.  Nevertheless,  there  is  nothing  absolute  in  the  retrograde 
progress  of  this  phenomenon.  I  have  seen  women,  dead  at  the  sixth 
and  even  the  eighth  month  of  pregnancy,  present  corpora  lutea  as  volu- 
minous as  others  at  the  fourth  month  "  (Coste,  1849). 


C.E  - 


^lA-R 


Fig.  209. — Portion  of  an  ovary,  showing  a  corpus  luteum  of  pregnancy  (Williams). 
B,  C,  blood-clot ;    C,  F,  C,  F,  corpus  petrosum ;  F,  F,  F,  Graafian  follicles ;  L,  C,  folds  of  corpus 


luteum. 


Male  Organs  of  Generation 

The  chief  physiological  interest  attached  to  the  anatomy  of  the  male 
organs  of  generation  relates  to  the  testicles,  which  are  the  organs  in 
which  the  male  element  of  generation  is  developed.  As  regards  the 
penis,  it  will  be  necessary  to  do  little  more  than  describe  the  mechanism 
of  erection  and  of  the  ejaculation  of  semen. 

The  Testicles.  —  The  testicles  are  two  symmetrical  organs,  situated, 
during  a  certain  period  of  intra-uterine  life,  in  the  abdominal  cavity,  but 
finally  descending  into  the  scrotum.  Immediately  beneath  the  skin  of 
the  scrotum,  is  a  loose,  reddish,  contractile  tissue,  called  the  dartos, 
which  forms  two  distinct  sacs,  one  enveloping  either  testicle,  the  inner 
portion  of  these  sacs  fusing  in  the  median  line,  to  form  a  septum. 
Within  these  two  sacs  the  coverings  of  each  testicle  are  distinct.  These 
organs  are  suspended  in  the  scrotum  by  the  spermatic  cords,  the  left 


j-je  EMBRYOLOGY 

usually  hanging  a  little  lower  than  the  right.  The  coverings  for  each 
testicle,  in  addition  to  those  just  mentioned,  are  the  intercolumnar  fascia, 
the  cremaster  muscle,  the  infundibuliform  fascia,  the  tunica  vaginalis  and 
the  proper  fibrous  coat. 

The  tunica  vaginalis  is  a  closed  sac  of  serous  membrane,  covering 
the  testicle  and  epididymis  and  reflected  from  the  posterior  border  of  the 
testicle  to  the  wall  of  the  scrotum,  lining  the  cavity  occupied  by  the 
testicle  on  either  side  and  also  extending  over  the  spermatic  cord. 
This  tunic  is  a  process  of  peritoneum  that  has  been  shut  off  from 
the  general  lining  of  the  abdominal  cavity.  The  spermatic  cord  is 
composed  of  the  vas  deferens,,  bloodvessels,  lymphatics  and  nerves, 
with  the  coverings  already  described,  which  expand  and  surround  the 
testicle. 

Beneath  the  tunica  vaginalis  are  the  testicles,  with  their  proper 
fibrous  coat.  These  organs  are  ovoid  and  flattened  laterally  and 
posteriorly.  "They  are  an  inch  and  a  half  to  two  inches  (38.1  to  50.8 
millimeters)  long,  about  an  inch  and  a  quarter  (31.8  millimeters)  from 
the  anterior  to  the  posterior  border,  and  nearly  an  inch  (25.4  millimeters) 
from  side  to  side.  The  weight  of  each  varies  from  three-quarters  of  an 
ounce  to  an  ounce  (21.2  to  28.3  grams),  and  the  left  is  often  a  little  the 
larger  of  the  two"  (Quain).  The  proper  fibrous  coat  is  everywhere 
covered  with  the  closely-adherent  tunica  vaginalis,  except  at  the  posterior 
border,  where  the  vessels  enter  and  the  duct  passes  out.  At  the  outer 
edge  of  this  border,  is  the  epididymis,  formed  of  convoluted  tubes,  pre- 
senting a  superior  enlargement,  called  the  globus  major,  a  long  mass 
running  the  length  of  the  testicle,  called  the  body,  and  a  smaller,  in- 
ferior enlargement,  called  the  globus  minor.  This  too  is  covered  with 
the  tunica  vaginalis.  Between  the  membrane  covering  the  testicle  and 
epididymis  and  the  layer  lining  the  scrotal  cavity,  is  a  small  quantity  of 
serum,  just  enough  to  moisten  the  serous  surfaces.  At  the  superior 
portion  of  the  testicle  are  one  or  more  small  ovoid  bodies,  called  the 
hydatids  of  Morgagni,  each  attached  to  the  testicle  by  short  constricted 
processes.  These  have  no  physiological  importance  and  are  supposed 
to  be  the  remains  of  foetal  structures. 

The  proper  fibrous  coat  of  the  testicle  is  called  the  tunica  albuginea. 
It  is  white,  dense,  inelastic,  measures  about  2V  of  ^^  \n<z\\  (i  millimeter) 
in  thickness,  and  is  simply  for  the  protection  of  the  contained  structures. 
Sections  of  the  testicle,  made  in  various  directions,  show  an  incomplete 
vertical  process  of  the  tunica  albuginea,  called  the  corpus  Highmor- 
ianum,  or  the  mediastinum  testis.  This  is  wedge-shaped,  about  \  of  an 
inch  (4.2  millimeters)  wide  at  its  superior  and  thickest  portion,  is  pierced 
by  a  number  of  openings  and  lodges  bloodvessels  and  the  seminiferous 


MALE    ORGANS    OF   GENERATION 


777 


tubes.  From  the  mediastinum,  delicate  radiating  processes  of  connec- 
tive tissue  pass  to  the  inner  surface  of  the  tunica  albuginea,  dividing  the 
substance  of  the  testicle  into  imperfect  lobules  which  lodge  the  seminif- 
erous tubes.  The  number  of  these  lobules  has  been  estimated  at  two 
hundred  and  fifty  to  four  hundred.  Their  shape  is  pyramidal,  the  larger 
extremities  presenting  toward  the  surface,  with  the  pointed  extremities 
situated  at  the  mediastinum. 

Lining  the  tunica  albuginea  and  following  the  mediastinum  and  the 
processes  which  penetrate  the  testicle,  is  a  tunic,  composed  of  blood- 


Fig.  210.  —  Lobes  of  the  testicle  and  epididymis  (Sappey) . 

^,  ^,  I,  I,  I,  lobes  of  the  testicle;  2,  rate  testis;  3,  3,  vasa  efferentia;  4,  4,  4,  epididymis ;  5,  vas 
aberrans ;  6,  opening  of  the  vas  aberrans  into  the  epididymis ;  7,  7,  convoluted  beginning  of  the  vas 
deferens;  8,  vas  deferens.  B,  B,  i,  beginning  of  one  of  the  vasa  efferentia;  2,  3,  3,  convoluted  por- 
tion ;  4,  opening  into  the  epididymis  ;  5,  5,  beginning  of  the  epididymis. 

vessels  and  delicate  connective  tissue,  called  the  tunica  vasculosa,  or  pia 
mater  testis. 

Lodged  in  the  cavities  formed  by  the  trabeculas  of  connective  tissue, 
are  the  seminiferous  tubes,  in  which  the  male  elements  of  generation  are 
developed  (see  Plate  XV,  Fig.  2).  These  tubes  exist  to  the  number 
of  about  eight  hundred  and  forty  in  either  testicle  and  constitute  almost 
the  entire  substance  of  the  lobules.  The  larger  lobules  may  contain  five 
or  six  tubes,  the  lobules  of  median  size,  three  or  four,  and  the  smallest 
enclose  sometimes  but  a  single  tube.  Each  tube  presents  a  convoluted 
mass,  which  can  be  disentangled  under  water,  particularly  if  the  testicle 
is  macerated  for  several  months  in  water  with  a  little  nitric  acid.  The 
entire  length  of  the  tube  when  thus  unravelled  is  about  thirty  inches 


y-j^  EMBRYOLOGY 

(7.6  decimeters),  and  its  diameter  is  0-^0  to  y|-Q  of  an  inch  (125  to  166  /i). 
It  begins  by  two  to  seven  short  blind  extremities  and  sometimes  by 
anastomosing  loops.  The  caecal  diverticula  usually  are  found  in  the 
external  half  of  the  tube,  and  their- length  is  ^.^  to  \  of  an  inch  (2.1  to 
3.2  millimeters).  The  anastomoses  are  sometimes  between  the  tubes  of 
different  lobules,  sometimes  between  tubes  in  the  same  lobule  and  some- 
times between  different  points  in  the  same  tube.  As  the  tubes  pass 
toward  the  posterior  part  of  the  testicle,  they  unite  into  twenty  to  thirty 
straight  canals,  called  the  vasa  recta,  about  -^^  of  an  inch  (0.5  milli- 
meter) in  diameter,  which  penetrate  the  mediastinum  testis.  In  the 
mediastinum  the  tubes  form  a  close  network,  called  the  rete  testis ;  and 
at  the  upper  part  of  the  posterior  border  they  pass  out  of  the  testicle, 
by  twelve  to  fifteen  or  twenty  ducts,  called  vasa  efferentia. 

Having  passed  out  of  the  testicle,  the  vasa  efferentia  form  a  series 
of  small  conical  masses,  which  together  constitute  the  globus  major,  or 
head  of  the  epididymis.  Each  of  these  tubes  when  unravelled  is  six  to 
eight  inches  ( 1 5  to  20  centimeters)  long,  gradually  increasing  in  diameter, 
until  they  all  unite  into  a  single  convoluted  tube,  which  forms  the  body 
and  the  globus  minor  of  the  epididymis.  This  single  tube  of  the 
epididymis,  when  unravelled,  is  about  twenty  feet  (6  meters)  in  length. 

The  walls  of  the  seminiferous  tubes  in  the  testicle  itself  are  com- 
posed of  connective  tissue  and  of  peculiar  structures  that  will  be  fully 
described  in  connection  with  spermatogenesis.  In  the  rete  testis  it  is 
uncertain  whether  the  tubes  have  a  special  fibrous  coat  or  are  simple 
channels  in  the  fibrous  structure.  They  are  here  lined  with  squamous 
epithelium.  In  the  vasa  efferentia  and  the  epididymis,  there  is  a  fibrous 
membrane,  with  longitudinal  and  circular  fibres  of  non-striated  muscular 
tissue  and  a  lining  of  ciliated  epithelium.  The  movements  of  the  cilia 
are  toward  the  vas  deferens.  In  the  lower  portion  of  the  epididymis  the 
cilia  are  absent.  The  tubular  structures  of  the  testicle,  the  epididymis 
and  the  beginning  of  the  vas  deferens  are  shown  in  Fig.  210. 

At  the  lower  part  of  the  epididymis,  communicating  with  the  canal, 
there  usually  is  found  a  small  mass,  formed  of  a  convoluted  tube  of 
variable  length,  called  the  vas  aberrans  of  Haller  (5,^,  A,  Fig.  210). 
This  sometimes  is  wanting. 

Interstitial  Gland  of  the  Testis.  —  Lying  between  the  seminiferous 
tubes  and  apparently  giving  support  to  them,  are  collections  of  delicate 
fibres  of  areolar  tissue  with  abundant  bloodvessels,  large  cytoplasmic 
cells  and  sometimes  fatty  and  pigmentary  globules  and  granules.  These 
structures  are  said  by  some  anatomists  to  constitute  an  interstitial  gland 
that  influences  the  development  of  spermatozoids  and  may  be  the  seat  of 
an  "  internal  secretion." 


MALE  ORGANS  OF  GENERATION  779 

Vas  Deferens.  —  The  excretory  duct  of  the  testicle  extends  from  the 
epididymis  to  the  prostatic  portion  of  the  urethra  and  is  a  continuation  of 
the  single  tube  that  forms  the  body  and  globus  minor  of  the  epididymis. 
It  is  somewhat  tortuous  near  its  origin,  and  it  becomes  larger  at  the 
base  of  the  bladder,  just  before  it  is  joined  by  the  duct  of  the  seminal 
vesicle.  Near  its  point  of  junction  with  this  duct  it  becomes  narrower. 
Its  entire  length  is  nearly  two  feet  (about  6  decimeters). 

The  course  of  the  vas  deferens  is  in  the  spermatic  cord  to  the  exter- 
nal abdominal  ring,  and  through  the  inguinal  canal  to  the  internal  ring, 


3  V"T^- 


Fig.  211.  —  Section  of  the  testicle  of  a  full-grown  rabbit — Interstitial  gland  (Bouin  and  Ancel). 

This  figure  shows  the  seminiferous  tubes  in  three  of  which  there  is  spermatogenesis.     The  darker 
cells  between  the  tubes  are  cells  of  the  interstitial  gland. 

■where  it  leaves  the  bloodvessels,  passes  beneath  the  peritoneum  to  the 
side  of  the  bladder,  then  along  the  base  of  the  bladder  by  the  inner  side 
of  the  seminal  vesicle,  finally  joining  the  duct  of  the  seminal  vesicle, 
the  common  tube  forming  the  ejaculatory  duct,  which  opens  into  the 
prostatic  portion  of  the  urethra. 

The  walls  of  the  vas  deferens  are  thick,  abundantly  supplied  with 
vessels  and  nerves,  and  provided  with  an  external  fibrous,  a  middle 
muscular,  and  an  internal  mucous  coat.  The  greater  part  of  that  por- 
tion of  the  tube  which  is  connected  with  the  bladder  is  dilated  and 
sacculated.     The  fibrous  coat  is  composed  of  strong  connective  tissue. 


78o 


EMBRYOLOGY 


The  muscular  coat  presents  three  layers  ;  an  external,  rather  thick  layer 
of  longitudinal  fibres,  a  thin  middle  layer  of  circular  fibres,  and  a  thin 
layer  of  longitudinal  fibres,  all  of  the  non-striated  variety.  By  the  action 
of  these  fibres  the  vessel  may  be  made  to  undergo  energetic  peristaltic 
movements,  and  this  has  followed  stimulation  of  that  portion  of  the 
spinal  cord    corresponding   to    the   fourth    lumbar   vertebra,    which    is 

described    by    Budge    as   the 
genito-spinal  centre. 

The  mucous  membrane  of 
the  vas  deferens  is  pale, 
thrown  into  longitudinal  folds 
in  the  greatest  part  of  the 
canal,  and  presents  a  number 
of  additional  rugae  in  the  sac- 
culated portion,  these  rugaa 
enclosing  little  irregularly- 
polygonal  spaces.  The  mem- 
brane is  covered  with  co- 
lumnar epithelium  which  is 
not  ciliated.  In  the  saccu- 
lated portion  are  large  num- 
bers of  mucous  glands. 

Attached  to  the  vas  de- 
ferens, near  the  head  of  the 
epididymis,  is  a  little  mass 
of  convoluted  and  sacculated 
tubes,  called  the  organ  of 
Giraldes,  or  the  corpus  innom- 
inatum.  The  body  is  ^  to  ^ 
of  an  inch  (4.2  to  8.5  milli- 
meters) long  and  -^.2  ^^  ^^  i^^^ 
(2.1  millimeters)  broad.  Its 
tubes  are  lined  with  cells  of 
squamous  epithelium,  which  often  are  filled  with  fatty  granules.  Usually 
the  tubes  present  only  blind  extremities,  but  some  of  them  occasionally 
communicate  with  the  tubes  of  the  epididymis.  This  part  has  no  physio- 
logical importance.  It  was  regarded  by  Giraldes  as  the  remnant  of 
the  Wolffian  body,  analogous  to  the  parovarium. 

Vesic7ilcs  Scviijialcs.  —  Attached  to  the  base  of  the  bladder  and  situ- 
ated externally  to  the  vasa  deferentia,  are  the  two  vesiculas  seminales. 
These  bodies  are  each  composed  of  a  coiled  and  sacculated  tube,  four  to 
six  inches  (10  to  15  centimeters)  in  length  when  unravelled,  and  some- 


Fig.  212.  —  VesiculcB  seminales,  vasa  deferentia  and  ejacii- 
latory  ducts  (Sappey) . 

y4, /4,  vesiculag  seminales ;  i,  i,  2,  vasa  deferentia;  3,3, 
right  seminal  vesicle  ;  4,  junction  of  the  vas  deferens  with 
the  duct  of  the  seminal  vesicle;  5,  6,  ejaculatory  ducts ; 
7,  left  lobe  of  the  prostate ;  8,  median  groove ;  9,  membra- 
nous urethra. 


MALE  ORGANS  OF  GENERATION  78 1 

what  convoluted,  in  the  natural  state,  into  an  ovoid  mass  that  is  firmly 
bound  to  the  vesical  wall.  The  structure  of  the  seminal  vesicles  is  not 
unlike  that  of  the  sacculated  portion  of  the  vasa  deferentia.  They  have 
an  external  fibrous  coat,  a  middle  coat  of  muscular  fibres  and  a  mucous 
lining.  Muscular  fibres  pass  over  these  vesicles  from  the  bladder,  both  in 
a  longitudinal  and  in  a  circular  direction,  and  serve  as  compressors,  by 
the  action  of  which  their  contents  may  be  discharged.  The  mucous  coat 
is  pale,  finely  reticulated,  and  covered  with  cells  of  polygonal  epithelium 
which  are  nucleated  and  contain  brownish  granules.  The  vesicular 
seminales  undoubtedly  serve,  in  part  at  least,  as  receptacles  for  the 
semen,  as  their  contents  often  present  a  greater  or  less  number  of 
spermatozoids.  Although  the  membrane  of  the  vesicles  seems  to 
produce  an  independent  secretion,  the  presence  of  mucous  glands  has 
not  been  demonstrated. 

The  ejaculatory  ducts  are  formed  by  the  union  of  the  vasa  deferentia 
with  the  ducts  of  the  vesiculae  seminales  on  either  side,  and  they  open 
into  the  prostatic  portion  of  the  urethra.  Except  that  their  coats  are 
much  thinner,  they  have  essentially  the  same  structure  as  the  vasa 
deferentia. 

Prostate.  —  Surrounding  the  vesical  extremity  of  the  urethra,  includ- 
ing what  is  known  as  its  prostatic  portion,  is  the  prostate  gland,  or 
body.  This  organ,  except  as  it  secretes  a  liquid  that  forms  a  part  of  the 
ejaculated  semen,  has  chiefly  a  surgical  interest,  so  that  it  is  unnecessary 
to  describe  minutely  its  form  and  relations.  It  is  enveloped  in  a  dense 
fibrous  coat,  contains  many  glandular  structures  opening  into  the 
urethra,  and  presents  a  great  number  of  non-striated,  with  a  few  striated 
muscular  fibres,  some  just  beneath  the  fibrous  coat  and  others  penetra- 
ting its  substance  and  surrounding  the  glands. 

The  glands  of  the  prostate  are  most  distinct  in  that  portion  which 
lies  behind  the  urethra.  In  the  posterior  portion  of  this  canal  are  found 
about  twenty  openings,  which  lead  to  tubes  ramifying  in  the  glandular 
substance.  These  tubes  are  formed  of  a  structureless  membrane  branch- 
ing as  it  penetrates  the  gland.  They  present  hemispherical  diverticula 
in  their  course  and  terminate  in  dilated  extremities  which  are  looped  and 
coiled.  In  the  deeper  portions  of  the  tubes,  the  epithelium  is  columnar 
or  cuboidal,  becoming  tessellated  near  their  openings,  and  sometimes 
laminated. 

The  prostatic  secretion  probably  is  produced  only  at  the  moment  of 
ejaculation.  Its  characters  will  be  considered  in  connection  with  the 
composition  of  the  semen.  According  to  Kraus  it  has  an  important 
office  in  maintaining  the  vitality  of  the  spermatozoids.  "  The  sper- 
matozoa, in  the  absence  of  the  prostatic  fluid,  can  not  live  in  the  mucous 


782  EMBRYOLOGY 

membrane  of  the  uterus  of  mammalia ;  but  with  its  aid  they  may  live 
for  a  long  time  in  the  uterine  mucus,  often  more  than  thirty-six  hours." 

Glands  of  the  Urethra.  —  In  front  of  the  prostate,  opening  into  the 
bulbous  portion  of  the  urethra,  are  two  small  racemose  glands,  called 
the  glands  of  Mery  or  of  Cowper.  These  have  each  a  single  excretory 
duct,  are  lined  throughout  with  cylindrical  epithelium  and  secrete  a 
viscid,  mucus-like  liquid  which  forms  a  part  of  the  ejaculated  semen. 
Sometimes  there  exists  only  a  single  gland,  and  occasionally,  though 
rarely,  both  are  absent.     Their  uses  probably  are  not  very  important. 

The  glands  of  Littre,  found  throughout  the  urethra  and  most  abun- 
dant on  its  anterior  surface,  are  simple  racemose  glands,  extending 
beneath  the  mucous  membrane  into  the  muscular  structure,  present- 
ing here  four  or  five  acini.  As  these  acini  are  surrounded  with  muscu- 
lar fibres,  it  is  easy  to  understand  how  their  secretion  may  be  pressed 
out  during  erection  of  the  penis.  They  are  lined  throughout  with  co- 
lumnar or  conoidal  epithelium,  and  secrete  a  clear  and  somewhat  viscid 
mucus,  which  is  mixed  with  the  ejaculated  semen. 


Male  Elements  of  Generation 

The  spermatozoids  are  the  essential  male  elements  of  generation. 
They  are  produced  in  the  testicle,  by  a  process  analogous  to  that  of  the 
development  of  other  anatomical  elements.  The  testicles  can  not  be  re- 
garded strictly  as  glandular  organs.  They  are  analogous  to  the  ovaries 
and  are  the  only  organs  in  which  spermatozoids  can  be  developed,  as  the 
ovaries  are  the  only  organs  in  which  the  ovum  can  be  formed.  If  the 
testicles  are  absent,  the  power  of  fecundation  is  lost,  none  of  the  secre- 
tions of  the  accessory  organs  of  generation  being  able  to  perform  the 
ofifice  of  the  true  fecundating  elements. 

In  the  healthy  male,  at  the  climax  of  a  normal  venereal  orgasm,  11.6 
to  92.6  grains  (0.75  to  6  grams)  of  semen  are  ejaculated  with  consider- 
able force  from  the  urethra,  by  an  involuntary  muscular  spasm.  This 
liquid  requires  about  four  days  for  its  complete  restoration.  It  is  slightly 
mucilaginous,  grayish  or  whitish,  streaked  with  lines  more  or  less 
opaque,  and  it  evidently  contains  various  kinds  of  mucus.  It  has  a 
faint  and  peculiar  odor,  sui  generis,  which  is  observed  only  in  the 
ejaculated  secretion  and  not  in  any  of  its  constituents  examined 
separately.  It  is  a  little  heavier  than  water  and  does  not  mix  with  it  or 
dissolve.  After  ejaculation  it  becomes  jelly-like  and  dries  into  a  peculiar 
hard  mass,  which  may  be  softened  by  the  application  of  appropriate 
liquids.     The   liquid  is  not  coagulated   by  heat  and   does  not  contain 


MALE    ELEMENTS    OF    GENERATION  783 

albumin.  Its  reaction  is  faintly  alkaline.  It  contains,  in  the  human 
subject,  100  to  120  parts  of  solid  matter  per  1000. 

The  chemical  constitution  of  the  semen  has  not  been  thoroughly  in- 
vestigated and  does  not  present  the  same  physiological  importance  as  do 
its  anatomical  characters.  Aside  from  the  anatomical  elements  derived 
from  the  testicles  and  the  genital  passages,  it  presents  an  organic  sub- 
stance (spermatin),  which  has  nearly  the  same  chemical  characters  as 
ordinary  mucin.  It  contains  also  a  considerable  quantity  of  phosphates. 
During  desiccation,  elongated  rhomboidal  crystals  make  their  appear- 
ance, frequently  arranged  in  groups,  which  are  supposed  to  be  derived 
from  the  prostatic  secretion  and  to  consist  of  phosphoric  acid  combined 
with  an  organic  base,  the  formula  for  which,  united  with  hydrochloric 
acid,  is  C2HgNHCl.     These  are  sometimes  called  spermatic  crystals. 

In  the  dilated  portion  of  the  vasa  deferentia,  the  mucous  glands 
secrete  a  liquid  which  is  the  first  that  is  added  to  the  spermatozoids  as 
they  come  from  the  testicles.  This  is  brownish  or  grayish.  It  contains 
epithelium  and  small  rounded  granules,  which  latter  are  dark  and 
strongly  retractive.  The  liquid  itself  is  very  slightly  viscid.  In  the 
vesiculae  seminales  there  is  a  more  abundant  secretion  of  grayish  liquid, 
with  epithelium,  small  colorless  concretions  of  nitrogenous  matter,  called 
sympexions,  and  a  few  leucocytes.  The  glandular  structures  of  the 
prostate  produce  a  creamy  secretion  wath  fine  granules.  It  is  chiefly 
to  the  admixture  of  this  liquid  that  the  semen  owes  its  whitish  appear- 
ance. Finally,  as  the  semen  is  ejaculated,  it  receives  the  viscid  secretion 
of  the  glands  of  Cowper,  a  certain  quantity  of  stringy  mucus  from  the 
follicles  of  the  urethra,  with  perhaps  a  little  of  the  urethral  epithelium. 

Anatomically  considered,  the  semen  contains  no  important  elements 
except  the  spermatozoids,  the  various  secretions  just  mentioned  serving 
simply  as  a  vehicle  for  the  introduction  of  these  bodies  into  the  gener- 
ative passages  of  the  female. 

Spermatozoids.  —  The  liquid  taken  from  the  vesiculae  seminales  of 
an  adult,  who  has  died  suddenly,  or  the  ejaculated  semen  contains,  in 
addition  to  the  various  accidental  or  unimportant  anatomical  elements 
that  have  been  mentioned,  innumerable  bodies,  resembling  animalcules, 
which  present  a  flattened,  conoidal  head  and  a  long,  tapering,  filamen- 
tous tail.  The  number  of  spermatozoids  in  a  single  ejaculation  has 
been  estimated  at  221,257,900  (Lode).  The  tail  is  in  active  motion,  and 
the  spermatozoids  move  about  the  field  of  view  under  the  microscope  with 
considerable  force,  pushing  aside  little  corpuscles  or  granules  with  which 
they  may  come  in  contact.  Under  favorable  conditions,  particularly  in 
the  generative  passages  of  the  female,  the  movements  may  continue  for 
several  days.     It  is  said,  indeed,  that  they  are  always  present  and  in 


784 


EMBRYOLOGY 


Fig.  213.  —  Spermatozoids,  spermatic  crystals  and  leu- 
cocytes   (Peyer). 


motion  in  the  Fallopian  tubes 
when  sexual  intercourse  is  fre- 
quent (Williams). 

The  head  of  the  spermato- 
zoid  is  about  -50V0  ^^  ^^^  ^'^'^^ 
(5  /i)  long,  80V0  of  an  inch  (3  ix) 
broad,  and  ^sioo  of  an  inch 
(i  /x)  in  thickness.  The  tail 
(flagellum)  is  about  -g^Q-  of  an 
inch  (50  /x)  in  length.  The 
length  of  the  intermediate  seg- 
ment is  about  40V7  of  an  inch 
(6  fi).  At  the  lower  end  of  the 
tail,  is  a  short  and  excessively 
fine  filament,  called  the  terminal 
filament.  The  head  contains  a 
considerable  quantity  of  chromatin.  In  the  intermediate  segment  is 
the  centrosome.  These  play  an  important  part  in  the  process  of  fertili- 
zation of  the  ovum. 

Water  soon  arrests  the  movements  of  the  sperma- 
tozoids, which  may  be  restored  by  the  addition  of 
dense  saline  and  other  solutions.  All  the  alkaline 
animal  liquids  of  moderate  viscidity  favor  the  move- 
ments, while  the  action  of  acid  or  of  very  dilute  solu- 
tions is  unfavorable.  The  movements  are  suspended 
by  extreme  cold,  but  they  return  when  the  ordinary 
temperature  is  restored. 

Before  puberty  the  seminiferous  tubes  are  much 
smaller  than  in  the  adult,  and  they  contain  small 
transparent  cells,  which  in  their  form  and  arrange- 
ment resemble  epithelium.  As  puberty  approaches, 
however,  the  tubes  become  larger,  and  the  contents 
change  their  character. 

In  the  adult  testicle,  the  seminiferous  tubes  are 
lined  with  two  kinds  of  cells:  i.  The  sustentacular 
cells  of  Sertoli,  and  2,  cells  situated  between  the 
sustentacular  cells,  called  spermatogonia.  The  sper- 
matogonia, as  they  undergo  development,  become 
attached  to  the  sustentacular  cells  and  probably  are 
nourished  by  them.  The  spermatogonia  multiply  by 
karyokinesis,  with  intervals  of  rest,  during  which  the 
quantity  of  chromatin  increases.     The  daughter-cells, 


Fig.  214.  —  Human 
spermatozoids  (Retzius 
and     Jensen). 

Left  figure  represents 
a  side  view;  middle 
figure,  flat  view  ;  a,  head  ; 
b,  centrosome;  c,  the 
intermediate  segment  ; 
d,  tail  e,  terminal  fila- 
ment. 


MALE   ELEMENTS    OF    GENERATION 


785 


which  are  the  result  of  the  final  division,  are  called  spermatocytes. 
These  divide  again  to  form  each  two  spermatids,  the  number  of  con- 
tained chromosomes  being  thereby  reduced  one-half,  and  these  sper- 
matids are  developed  into  spermatozoids,  in  fan-shaped  groups  that 
project  into  the  calibre  of  the  seminiferous  tubes. 

The  spermatozoids  are  motionless  while  they  are  within  the  testicle, 
the  epididymis  or  the  vasa  deferentia,  apparently  on  account  of  the 
density  of  the  substance  in  which  they  are  embedded ;  for  movements 
are  sometimes  presented  when  the  contents  of  the  vasa  deferentia  are 
examined  with  the  addition  of  water  or  of  saline  solutions.     Once  in  the 


Fig.  215.  —  Diagrayn  showing  stages  of  spermatogenesis  as  seen  hi  different  sectors  of  a  seminiferous 
tubule  of  a  rat  (McMurrich,  modified  from  von  Lenhossekj . 

J,  Sertoli  cell;  jfi,  spermatocyte  of  the  first  order;  sc'^,  spermatocyte  of  the  second  order  (divided 
into  two)  ;  sg,  spermatogone  ;  sp,  spermatid ;  sz,  spermatozoids. 

In  the  first  section  (to  the  left)  four  different  generations  of  cells  are  shown:  sg,  spermatogones; 
J<:1,  spermatocytes ;  sp,  spermatids ;  js,  spermatozoids.  In  the  second  section  are  spermatocytes, 
spermadds,  and  a  SertoU  cell  increased  in  size.  In  the  third  section  are  spermatocytes,  sc^  undinded 
and  J<;2  divided,  and  a  still  larger  Sertoli  cell,  with  spermatozoids.  In  the  fourth  section  are  the  two 
orders  of  spermatocytes,  spermatids  to  the  right,  and  a  still  larger  Sertoli  cell,  with  spermatozoids.  In 
the  fifth  section  are  four  spermatogones  in  contact  with  the  basement  membrane,  spermatocytes  of 
the  first  and  second  orders,  spermatids  and  a  Sertoli  cell,  with  spermatozoids.  sz,  of  the  first  section, 
shows  spermatozoids  lying  in  the  lumen  of  the  tubule. 

vesiculse  seminales,  and  for  a  certain  time  after  ejaculation,  the  sperma- 
tozoids are  in  active  motion.  When  the  spermatozoids  have  ceased 
their  movements  they  are  incapable  of  fertilizing  the  ovum. 

The  semen,  thus  developed  and  mixed  with  the  various  secretions 
before  mentioned,  is  found  during  adult  Hfe  and  sometimes  even  in 
advanced  age,  and  under  physiological  conditions  it  contains  innumer- 
able spermatozoids  in  active  movement ;  but  if  sexual  intercourse  is 
frequently  repeated  at  short  intervals,  the  ejaculated  liquid  becomes 
more  and  more  transparent,  homogeneous  and  scanty,  and  it  may  con- 
sist of  a  small  quantity  of  secretion  from  the  vesiculse  seminales  and 
the  glands  opening  into  the  urethra,  without  spermatozoids  and  conse- 
quently deprived  of  fertihzing  power. 


786  EMBRYOLOGY 

In  old  men  the  seminal  vesicles  may  not  contain  spermatozoids  ;  but 
this  is  not  always  the  case,  even  in  very  advanced  life.  Instances  are 
constantly  occurring  of  men  who  have  children  in  their  old  age,  in 
which  the  paternity  of  the  offspring  can  hardly  be  doubted.  Duplay, 
in  1852,  examined  the  semen  of  a  number  of  old  men,  and  found,  in 
about  half  the  number,  spermatozoids,  normal  in  appearance  and  num- 
ber, though  in  some  the  vesiculae  seminales  contained  either  none  or 
very  few.  Some  of  the  persons  in  whom  the  spermatozoids  were  nor- 
mal were  between  seventy-three  and  eighty-two  years  of  age.  These 
observations  were  confirmed  by  Dieu,  who  found  spermatozoids  in  a 
man  eighty-six  years  of  age.  The  contents  of  the  seminal  vesicles,  in 
these  cases,  were  examined  twenty-four  hours  after  death.  Some  of 
the  subjects  died  of  acute,  and  others,  of  chronic  diseases ;  but  the  mode 
of  death  did  not  present  any  differences  in  the  cases  classed  with  refer- 
ence to  the  presence  of  spermatozoids.  As  the  result  of  his  own  and 
of  other  recorded  observations,  Dieu  concluded  that  the  power  of  fecun- 
dation often  persists  for  a  considerable  time  after  copulation  has  become 
impossible  on  account  simply  of  loss  of  the  power  of  erection. 


CHAPTER    XXXI 

FERTILIZATION    AND    KARYOKIXESIS    OF    THE    OVUM 

Fecundation  —  Maturation  of  the  ovum — Fertilization  of  the  ovum  —  Mendel's  laws  of  hered- 
ity —  Superfecundation  —  Segmentation   of  the   ovum  —  Gastrulation  —  Primitive   streak 

—  Formation  of  the  membranes  —  Formation  of  the  amnion  —  Amniotic  liquid  —  Forma- 
tion of  the  umbilical  vesicle  (yolk-sac)  —  Formation  of  the  allantois  and  permanent  chorion 

—  Membranse  decidute —  Formation  of  the  placenta  —  Uses  of  the  placenta. 

So  far  as  the  male  is  concerned,  coitus  is  rendered  possible  by  erec- 
tion of  the  penis.  This  may  occur  before  puberty,  but  at  this  time 
intercourse  can  not  be  fruitful.  Coitus  may  be  impossible  in  old  age, 
from  absence  of  the  power  of  erection ;  but  spermatozoids  may  still 
exist  in  the  vesiculas  seminales,  and  fecundation  might  occur  if  the  sem- 
inal fluid  could  be  discharged  into  the  generative  passages  of  the  female. 
Coitus  may  take  place  in  the  female  before  the  age  of  puberty  or  after 
the  final  cessation  of  the  menses,  but  intercourse  can  not  then  be  fruit- 
ful. There  are  many  instances  of  conception  following  what  would  be 
called  imperfect  intercourse,  as  in  cases  of  unruptured  hymen,  deformi- 
ties of  the  male  organs,  etc.,  which  show  that  the  actual  penetration  of 
the  male  organ  is  not  essential,  and  that  fecundation  may  occur  provided 
the  seminal  liquid  find  its  way  into  even  the  lower  part  of  the  vagina. 
Conception  also  has  followed  intercourse  when  the  female  has  been  in- 
sensible or  entirely  passive.  Unlike  certain  of  the  lower  animals,  the 
human  subject  presents  no  distinct  periodicity  in  the  development  of 
the  spermatozoids ;  but  in  reiterated  connection,  an  orgasm  may  occur 
when  the  ejaculated  liquid  has  no  fecundating  power. 

In  regard  to  the  mechanism  of  erection,  little  remains  to  be  said 
after  the  description  that  has  been  given  of  true  erectile  tissue  in  con- 
nection with  the  physiology  of  the  circulation.  The  cavernous  and 
spongy  bodies  of  the  penis  usually  are  taken  as  the  type  of  erectile 
organs.  In  these  parts  the  arteries  are  large,  contorted,  provided  with 
unusually  thick  muscular  coats  and  are  connected  with  the  veins  by 
vessels  considerably  larger  than  the  true  capillaries.  They  are  sup- 
ported by  a  strong  fibrous  network  of  trabeculas,  which  contains  non- 
striated  muscular  fibres ;  so  that  when  the  bloodvessels  are  completely 
filled  the  organ  becomes  enlarged  and  rigid.  Researches  in  regard  to 
the  nerv-es  of  erection  show  that  the  vessels  of  erectile  tissues  are  dis- 

787 


788  EMBRYOLOGY 

tended  by  an  enlargement  of  the  arterioles  of  supply,  and  that  there  is 
not  simply  a  stasis  of  blood  produced  by  constriction  of  the  veins,  ex- 
cept possibly  for  a  short  time  during  the  period  of  greatest  excitement. 
In  experiments  on  dogs,  Eckhard  found  a  nerve  derived  from  the  sacral 
plexus,  stimulation  of  which  produced  an  increase  in  the  flow  of  blood 
through  the  penis,  attended  with  all  the  phenomena  of  erection.  This 
nerve  arises  by  two  roots  at  the  sacral  plexus,  from  the  first  to  the  third 
conte  sacral  nerves,  and  is  connected  with  the  genito-spinal  centre  in  the 
lower  part  of  the  lumbar  region  of  the  spinal  cord.  In  the  experiments 
referred  to,  by  a  comparison  of  the  quantity  of  venous  blood  coming 
from  the  penis  before  and  during  the  stimulation  of  the  nerve,  Eckhard 
found  a  great  increase  during  erection.  It  is  probable  that  in  addition 
to  the  arterial  dilatation,  when  the  penis  attains  its  maximum  of  rigidity, 
there  is  a  certain  degree  of  obstruction  to  the  outflow  of  blood  by  com- 
pression of  the  veins,  and  that  the  rigidity  is  increased  by  contraction  of 
the  trabecular  muscular  fibres  of  the  corpora  cavernosa.  At  the  climax 
of  an  orgasm,  the  semen  is  forcibly  discharged  from  the  urethra  by 
spasmodic  contractions  of  the  vesiculae  seminales  and  the  ejaculatory 
muscles.  Although  this  is  the  physiological  mechanism  of  a  seminal 
discharge,  friction  of  the  parts,  which  usually  precedes  ejaculation,  is 
not  absolutely  necessary,  as  is  shown  by  the  occurrence  of  orgasm  dur- 
ing sleep,  which  is  likely  to  take  place  in  healthy  men  after  prolonged 
continence. 

There  are  some  females  in  whom  the  generative  function  is  per- 
formed, even  to  the  extent  of  bearing  children,  who  have  no  actual 
knowledge  of  a  true  venereal  orgasm  ;  but  there  are  others  who  experi- 
ence an  orgasm  fully  as  intense  as  that  which  accompanies  ejaculation 
in  the  male.  There  is,  therefore,  the  important  difference  in  the  sexes, 
that  preliminary  excitement  and  an  orgasm  are  necessary  to  the  perform- 
ance of  the  generative  act  in  the  male  but  are  not  essential  in  the 
female.  Still,  there  can  be  scarcely  a  doubt  that  venereal  excitement 
in  the  female  facilitates  conception,  other  conditions  being  favorable. 
When  excitement  occurs  in  the  female,  there  is  engorgement  of  the  true 
erectile  tissues  and  possibly  of  the  convoluted  vessels  surrounding  the 
internal  organs.  The  neck  of  the  uterus  becomes  hardened  and  slightly 
elongated ;  and  it  has  been  observed  by  Litzmann  and  others,  that  there 
occurs  a  sudden  opening  and  closing  of  the  os,  which  exerts  more  or 
less  suction  force.  These  conditions,  however,  are  not  essential  to  fe- 
cundation, although  they  may  exert  a  favorable  influence  on  the  pene- 
tration of  spermatozoids  and  may  at  certain  times  determine  the  rupture 
of  a  Graafian  follicle. 

The  spermatozoids,  once  within  the  cervix  uteri,  and  in  contact  with 


FECUNDATION  789 

the  alkaline  mucus,  which  increases  the  activity  of  their  movements, 
may  pass  through  the  uterus  into  the  Fallopian  tubes,  and  even  to  the 
surface  of  the  ovaries.  Precisely  how  their  passage  is  effected,  it  is 
difficult  to  say.  It  can  be  attributed  only  to  the  movements  of  the  sper- 
matozoids  themselves,  to  capillary  action,  and  to  a  possible  peristaltic  con- 
traction of  the  muscular  structures  ;  but  these  points  have  not  as  yet  been 
subjects  of  positive  demonstration.  As  regards  the  human  female,  it  is 
impossible  to  give  a  definite  idea  of  the  time  required  for  the  passage  of 
the  spermatozoids  to  the  ovaries  or  for  the  descent  of  the  ovum  into  the 
uterus  ;  and  it  is  readily  understood  how  these  questions  hardly  admit  of 
experimental  investigation.  It  is  known,  however,  that  spermatozoids 
reach  the  ovaries,  and  they  have  been  seen  in  motion  on  their  surface, 
seven  or  eight  days  after  connection. 

Fecundation 

The  ordinary  situation  at  which  the  ovum  is  fertilized  is  the 
dilated,  or  external  portion  of  the  Fallopian  tube.  All  authorities  are 
agreed  that  fertilization  does  not  take  place  in  the  cavity  of  the  uterus. 
In  rabbits,  when  the  ovum  has  descended  into  the  uterus,  it  is  sur- 
rounded with  a  dense  albuminous  coating  which  the  spermatozoids  can 
not  penetrate.  It  is  possible  that  this  occurs  in  the  human  subject. 
Cases  of  abdominal  pregnancy  show  that  an  ovum  may  be  fertilized 
on  the  ovary  as  soon  as  it  is  discharged  from  the  Graafian  folHcle. 

The  question  of  the  duration  of  vitality  of  the  spermatozoids,  after 
their  passage  into  the  uterus,  has  an  important  bearing  on  the  time  when 
conception  is  most  likely  to  follow  sexual  intercourse.  The  alkaUne 
mucus  of  the  internal  organs  actually  favors  their  movements ;  the 
movements  are  not  arrested  by  contact  with  menstrual  blood ;  and,  in- 
deed, when  the  spermatozoids  are  mixed  with  the  uterine  mucus,  they 
simply  change  their  medium,  and  there  is  no  reason  to  believe  that  they 
may  not  retain  their  vitality  as  well  in  the  uterus  as  in  the  mucus  of  the 
vesiculas  seminales.  It  seems  impossible,  therefore,  to  fix  any  limit  to 
the  vitaHty  of  these  anatomical  elements,  under  physiological  conditions  ; 
and  it  is  not  certain  that  spermatozoids  may  not  remain  either  in  the 
vagina  or  in  the  Fallopian  tubes  and  around  the  ovary,  when  intercourse 
has  taken  place  immediately  after  a  menstrual  period,  until  the  ovulation 
following.  Motile  spermatozoids  have  been  observed  in  the  Fallopian 
tubes  as  long  as  twenty-five  days  after  coitus  (Diihrssen).  The  duration 
of  life  of  an  ovum  has  been  estimated  at  about  sixteen  days  (Issmer). 

Maturation  of  the  Ovum.  —  Before  the  formation  of  the  polar  bodies, 
the  unripe,  or  immature  ovum  is  called  the  resting  cell.     At  this  time, 


790 


EMBRYOLOGY 


the  nucleus,  or  germinal  vesicle,  contains  a  fine  reticulum  of  linin  fibres, 
chromatin  threads,  and  the  nucleolus,  or  germinal  spot.  By  a  process 
of  karyokinesis  confined  to  the  nucleus,  this  divides  in  the  same  way  as 


PB 


PB 


Fig.  216. —  Germ-nuclei  of  the  thread-worm  —  ascaris  megalocephala  (Boveri). 

A,  ovum  immediately  after  the  formation  of  the  second  polar  body  {PB)  ;  E,  egg-nucleus ;  S, 
sperm-nucleus,  derived  from  the  head  of  a  spermatozoid  that  has  entered  the  ovum.  B,  following 
stage,  in  which  E,  the  ego;-nucleus,  and  S,  the  sperm-nucleus,  have  assumed  the  same  size  and  struc- 
ture. C,  each  nucleus  has  been  transformed  into  two  chromosomes,  E,  S\  A,  attraction  sphere 
containing  a  centrosome;  PB,  polar  bodies.  Z>,  karyokinetic  figure;  C,  chromosomes  splitting 
lengthwise;  A,  one  of  the  two  asters;  S,  chromosomes  forming  a  chromatic  spindle. 


the  nucleus  of  an  ordinary  tissue-cell.  After  division  into  two,  one  of 
the  daughter-nuclei  is  extruded  from  the  ovum.  This  is  the  first  polar 
body,  and  it  carries  with  it  a  certain  number  of  chromosomes.    Sometimes 


FERTILIZATION    OF    THE    OVU.M 


791 


the  first  polar  body  itself  divides  into  two.  A  second  polar  body  is 
formed  in  the  same  way  by  karyokinesis  of  the  daughter-nucleus  remain- 
ing in   the  ovum.      These   two   polar    bodies    finally  disappear.      The 


Fig.  217.  —  Karyokinesis  (Boveri). 

A,  two  germ-nuclei  in  the  &'g%  of  the  gastropod  Pterotrachea ;  E,  egg-nucleus ;  S,  sperm-nucleus, 
each  nucleus  containing  sixteen  chromosomes;  PB,  polar  bodies  —  the  centrosome  has  divided  into 
tvvo  to  form  an  amphiaster.     B,  later  stage,  showing  the  fully-developed  amphiaster ;  PB,  polar  bodies. 


process  just  described  is  called  maturation  of  the  ovum,  and  it  occurs  in 
mammals  before  the  ovum  leaves  the  Graafian  follicle. 

Fertilization  of  the  Ovum.  —  The  head  of  a  spermatozoid,  containing 
chromosomes,  penetrates  the  vitelline  membrane  and  comes  in  contact 


792 


EMBRYOLOGY 


with  the  vitellus.  Then  there  forms  on  the  surface,  of  the  vitellus  what 
is  called  the  entrance-cone,  which  receives,  in  a  little  excavation  at  its 
summit,  the  head   of  the  male  element.     The  spermatozoid  afterward 


B 


D 


Fig.  218. —  Cell-division  (Wilson). 


A,  Resting  cell,  showing  A,  double  centrosome;  N,  nucleus;  C,  chromatin;  Z.,  Jinin  netvvork ; 
B,  spongioplasm.  B,  cell  in  process  of  division,  showing  A,  asters;  C,  chromosomes  split  lengthwise 
and  lying  in  the  equator  of  the  achromatic  spindle.  C,  later  stage  of  karyokinesis,  showing  DC, 
daughter-chromosomes  moving  toward  the  two  asters,  with  filaments,  IF,  between  them.  D,  divided 
cell ;  DN,  daughter-nucleus  ;  A,  centrosome. 


penetrates  the  substance  of  the  vitellus,  and  as  it  passes  inward,  it 
rotates  on  its  short  axis  so  that  its  base  looks  toward  the  centre  of  the 
ovum.     The  head  and  the  middle  piece  of  the  spermatozoid  now  form 


MENDEL'S    LAWS    OF    HEREDITY  793 

the  male  pronucleus,  or  sperm-nucleus.  The  tail  of  the  spermatozoid 
disappears. 

Before  the  penetration  of  the  spermatozoid,  the  ovum  has  sent  off 
the  polar  bodies,  and  the  number  of  chromosomes  has  been  reduced 
one-half.  What  remains  of  the  germinal  vesicle,  after  the  separation  of 
the  polar  bodies,  passes  to  the  centre  of  the  ovum  and  forms  the  female 
pronucleus,  or  egg-nucleus.  The  male  pronucleus  now  unites  with  the 
female  pronucleus  to  form  the  cleavage-nucleus,  which  contains  the  same 
number  of  chromosomes  as  the  ordinary  tissue-cells,  the  number  in  each 
pronucleus  having  been  reduced  one-half.  The  centrosome  of  the  ovum 
has  disappeared  and  the  centrosome  of  the  spermatozoid,  which  has  been 
contained  in  the  middle  piece,  divides  into  two,  one  passing  to  either 
side  of  the  cleavage-nucleus.  Under  this  view,  division  of  the  ovum  can 
not  take  place  without  the  introduction  of  a  male  centrosome.  It  is 
thought  that  hereditary  qualities  are  transmitted  in  the  chromosomes. 
The  cleavage-nucleus  thus  contains  chromosomes,  one-half  of  which  are 
from  the  ovum  and  one-half  from  the  spermatozoid. 

MendeVs  Laws  of  Heredity. — About  the  year  i860,  Gregor  Mendel, 
an  Austrian  monk  and  botanist,  in  studying  hybrid  forms  of  certain 
plants,  observed  peculiarities  transmitted  from  parent-stocks  which 
he  formulated  into  what  is  now  known  to  biologists  as  Mendel's  law, 
or,  more  properly,  Mendel's  laws.  He  found  that  hybrids  nearly 
always  presented  the  characters  of  one  parent-stock  only ;  especially 
when  each  parent-stock  was  pure.  The  parent  whose  peculiarities 
were  thus  represented  in  the  offspring  presented  characters  that  he 
called  dominant ;  but  the  characters  of  the  other  parent,  though 
undeveloped  in  the  immediate  offspring,  remained  dormant,  possibly  to 
reappear  later.     These  latter  characters  he  called  recessive. 

This  result  of  cross-breeding,  however,  was  not  constant.  In  some 
offspring,  the  dominant  character  of  one  parent  was  not  only  repeated 
but  became  exaggerated ;  sometimes  the  hybrid  showed  individual 
characters,  not  possessed  by  either  parent  and  differing  from  both, 
possibly  derived  from  an  anterior  ancestral  condition ;  but  the  cross 
always  presented  the  same  characters  in  case  the  germ-cells  from  the 
two  parent-stocks  were  pure.  The  principle  thus  illustrated  in  plants 
was  shown  to  exist  in  crossings  of  animals,  as  white  and  gray  mice.  In 
crossing  pigmented  with  albino  animals,  the  pigment  character  was 
always  dominant  and  the  albinism,  recessive. 

Without  discussing  fully  the  varied  and  frequent  changes  in  char- 
acter produced  by  crossing  hybrids  with  hybrids  and  hybrids  with  either 
one  of  the  pure  parent-stocks,  the  following  may  be  taken  as  the  prin- 
ciples underlying  Mendel's  laws  :  — 


794 


EMBRYOLOGY 


Crossing  of  pure  germ-cells  of  parent-stocks  presenting  different 
characters  produces  a  hybrid  in  which  the  characters  of  one  parent  only 
appear,  this  being  the  dominant. 

Hybrids,  however,  although  presenting  only  the  dominant  char- 
acters of  one  parent,  may  transmit  to  their  offspring,  characters  of  both 
parents,  the  recessive  as  well  as  the  dominant. 

In  cases  in  which  a  hybrid  presents  individual  characters  of  its  own, 
differing  from  those  of  either  parent,  it  is  probable  that  the  distinctive 
characters  are  more  or  less  remotely  ancestral  in  their  origin. 

The  laws  of  Mendel  bid  fair  to  reduce  the  breeding  of  animals  to 
an  almost  exact  science.  It  is  evident,  however,  that  breeding  in  the 
human  subject  can  never  be  conducted  on  scientific  lines,  however  de- 
sirable this  might  appear.  Still,  in  studying  the  fertilization  of  the 
ovum  —  as  will  be  seen  farther  on  —  the  idea  has  occurred  to  embry- 
ologists  that  hereditary  transmission  is  effected  through  the  male  and 
the  female  chromosomes.  It  is  well  known,  also,  that  the  offspring  of 
intermarriages  often  present  intensified  hereditary  characters  derived 
from  one  parent  or  the  other,  as  is  illustrated  in  inherited  predisposi- 
tion to  certain  diseases,  such  as  tuberculosis  and  cancer. 

The  observations  of  Mendel  have  received  but  little  attention  at  the 
hands  of  biologists.  They  are  contemporary  with  what  is  known  as  the 
evolution-theory,  which  was  propounded  by  Darwin  in  1859.  Recent 
discoveries  in  biology  are  more  favorable  to  the  cytologists,  who  adopt 
the  cell-theory  of  inheritance,  than  to  the  evolutionists,  who  knew  little 
of  the  mechanism  of  mitosis,  although  Virchow's  aphorism  "  omnis 
cellula  e  cellula  "  dates  from  1855. 

Hereditary  Transmission,  Snperfccitndation  etc.  —  The  first  question 
that  naturally  arises  relates  to  the  conditions  which  determine  the  sex 
of  offspring.  Statistics  show  the  proportions  between  male  and  female 
births ;  but  nothing  has  ever  been  done  in  the  way  of  procreating  male 
or  female  children  at  will.  According  to  Longet,  the  proportion  of 
male  to  female  births  is  about  104  to  105,  these  figures  presenting  cer- 
tain modifications  under  varying  conditions  of  climate,  season,  nutri- 
tion etc.  It  has  been  shown,  by  observations  on  certain  of  the  inferior 
animals,  that  the  preponderance  of  sex  in  births  bears  a  certain  rela- 
tion to  the  vigor  and  age  of  the  parents ;  and  that  old  and  feeble 
females  fecundated  by  young  and  vigorous  males  produce  a  greater 
number  of  males,  and  vice  versa ;  but  no  exact  laws  of  this  kind  have 
been  found  applicable  to  the  human  subject. 

Reference  has  frequently  been  made  to  the  chromosomes  as  the  parts 
concerned  in  the  transmission  of  inherited  characters.  This  view,  which 
is  now  —  at  least  provisionally  —  adopted  by  most  embryologists,  rests 


HEREDITY  795 

on  certain  positive  and  indisputable  facts  :  The  nuclei  of  the  cells  of 
each  and  every  species  contain  a  definite  number  of  chromosomes 
peculiar  to  such  species  and  always  divisible  by  two.  In  mitosis,  the 
chromosomes  of  the  mother-cells  split  and  one-half  goes  to  each  daugh- 
ter-cell. Maturation  of  the  ovum  involves  the  throwing  off  of  one-half 
the  chromosomes  in  the  polar  bodies.  The  final  phase  of  spermatogenesis 
involves  the  division  of  chromosomes  so  that  the  spermatozoid  has  but 
one-half  the  number  contained  in  ordinary  cells.  When  the  two  cells 
meet,  the  egg  is  fertilized  by  the  union  of  the  egg-nucleus  with  the 
sperm-nucleus,  the  resulting  cleavage-nucleus  containing  the  full  num- 
ber of  chromosomes  ;  but  if  these  two  nuclei  do  not  meet  and  unite,  the 
cells  die.  The  fertilized  egg,  therefore,  contains  chromosomes  derived 
equally  from  the  male  and  from  tbe  female.  These  characters  and 
this  behavior,  being  peculiar  to  and  confined  to  chromatin  and  invariable 
in  all  forms  of  life,  high  or  low,  point  almost  conclusively  to  this  sub- 
stance as  the  medium  of  hereditary  transmission ;  but  they  are  not 
favorable  to  the  theory  of  transmission  of  acquired  qualities.  A  fuller 
discussion,  however,  of  this  subject  would  be  out  of  place  in  this  work. 

A  pecuHar  and,  it  seems  to  be,  an  inexplicable  fact  is  that  previous 
pregnancies  have  an  influence  on  offspring.  This  is  well  known  to 
breeders  of  animals.  If  a  pure-blooded  mare  or  bitch  has  been  once 
covered  by  an  inferior  male,  in  subsequent  fecundations  the  young  are 
likely  to  partake  of  the  character  of  the  first  male,  even  if  bred  afterward 
to  males  of  unimpeachable  pedigree.  The  same  influence  is  sometimes 
■observed  in  the  human  subject.  A  woman  may  have,  by  a  second  hus- 
band, children  who  resemble  a  former  husband,  and  this  is  particularly 
well  marked  in  certain  instances  by  the  color  of  the  hair  and  eyes. 
A  white  woman  who  has  had  children  by  a  negro  may  subsequently  bear 
children  to  a  white  man,  these  children  presenting  some  of  the  peculi- 
arities of  the  negro  race. 

Superfecundation  of  course  does  not  come  in  the  category  of  in- 
fluences just  mentioned.  It  is  not  infrequent  to  observe  twins,  when 
two  males  have  had  access  to  the  female,  that  are  entirely  distinct  from 
each  other  in  their  physical  characters  — •  a  fact  readily  explained  by  the 
assumption  that  two  ova  have  been  separately  fecundated.  This  view 
is  sustained  by  observation  and  experiment,  and  many  illustrative  cases 
are  on  record. 

The  following  communication  was  received  in  January,  1869,  from 
Dr.  John  H.  Janeway,  Assistant  Surgeon,  U.S.A.,  and  it  illustrates 
superfecundation  in  the  human  subject;  or  at  least  that  was  the  view 
taken  by  the  negro  father :  — 

"Frances  Hunt,  a  freedwoman,  aged  thirty-five  years,  gave  birth  to 


796 


EMBRYOLOGY 


twins,  February  4,  1867,  in  New  Kent  County,  Virginia.  One  of  these 
twins  was  black,  the  other  was  white.  Frances  is  a  mulatto.  The  black 
child  is  much  darker  than  she  is.  Previous  to  the  parturition,  she  had 
given  birth  to  seven  children,  ail  single  births.  She  was  living  at  the 
time  of  her  impregnation  in  the  family  of  a  white  man  as  house-servant, 
sleeping  with  a  black  man  at  night.  She  insists,  however,  that  she  never 
had  carnal  intercourse  with  a  white  man.     She  probably  does  this  because 


Fig.  219.  —  Formation  of  the  blastodermic  vesicle  (van  Beneden). 

A,  B,  C,  D,  sections  of  ova  in  successive  stages  of  development  in  the  rabbit;  zp,  zona  pellucida; 
ep,  epiblastic  cells;  hyp,  hypoblastic  cells. 

the  black  man  turned  her  out  of  his  house  when  he  saw  that  one  of  the 
children  was  white.  The  only  negro  feature  in  the  white  child  was  its 
nose.  There,  its  resemblance  to  its  mother  was  perfect.  Its  hair  was 
long,  light,  and  silky.     Complexion  brilliant." 

It  is  a  curious  fact  that  when  a  cow  produces  twins,  one  male  and 
the  other  female,  the  female,  which  is  called  a  free-martin,  is  sterile  and 
presents  an  imperfect  development  of  the  internal  organs  of  generation.' 
This  has  led  to  the  idea  that  possibly  the  same  law  may  apply  to  the 
human  subject,  in  cases  of  twins,  one  male  and  the  other  female;  but 


SEGMENTATION    OF    THE    OVU:\I 


797 


many  observations  are  recorded  in  gynecological  works,  showing   the 
incorrectness  of  this  view. 

It  has  long  been  a  question  whether  strong  impressions  made  on 
the  nervous  system  of  the  mother  can  exert  an  influence  on  the  foetus 
in  utero.  While  many  authors  admit  that  violent  emotions  experienced 
by  the  mother  may  affect  the  nutrition  and  the  general  development  of 
the  foetus,  some  writers  of  authority  deny  that  the  imagination  can  have 
any  influence  in  producing  deformities.  The  remarkable  cases  recorded 
as  instances  of  deformity  due  to  the  influence  of  the  maternal  mind  are 


Fig.  220.  —  Four  stages  in  segmentation  of  the  ovum  of  a  mouse  (Sobotta)  ;  X  ,  polar  globule. 

not  entirely  reliable  ;  and  it  often  happens  that  when  a  child  is  born 
with  a  deformity,  the  mother  imagines  she  can  explain  it  by  some 
impression  received  during  pregnancy,  which  she  recalls  only  after  she 
knows  that  the  child  is  deformed.  There  is,  indeed,  no  satisfactory 
evidence  that  the  maternal  mind  has  anything  to  do  with  the  produc- 
tion of  deformities  in  utero. 

Segmentation  of  the  Ovitin.  —  Soon  after  fertilization  and  the  forma- 
tion of  the  cleavage-nucleus,  a  furrow  appears  at  the  point  of  extrusion 
of  the  polar  globules.  This  is  met  by  a  furrow  upon  the  opposite  side, 
and  the  ovum  is  divided  into  two  globes.  One  of  the  globes  is  slightly 
larger  than  the  other  and  presents  fewer  and  smaller  granules.     The 


798 


EMBRYOLOGY 


larger  sphere  subsequently  forms,  by  its  division,  the  epiblastic  cells, 
and  the  smaller  sphere  forms  the  hypoblastic  cells.  Each  sphere  is 
provided  with  a  distinct  nucleus.  The  two  spheres  resulting  from  the 
first  segmentation  ^  are  divided,  each  one  into  two,  making  four  spheres. 


.^ 


Fig.  221.  —  Later  stages  of  segmentation  of  the  ovum  of  a  bat  (van  Beneden). 
A,  C  and  D  are  sections ;  B,  a  surface  view. 

These  spheres  are  again  divided  into  eight  —  four  epiblastic  and  four 
hypoblastic  spheres  —  each  with  a  nucleus  (van  Beneden).  One  of  the 
four  hypoblastic  spheres  passes  to  the  centre ;  and  the  four  epiblastic 

^  In  the  mammalia,  segmentation,  after  the  first  division  of  the  ovum  into  two,  is  irregular,, 
"three-celled,  four-celled,  five-celled  and  six-celled  stages  having  been  observed  in  various 
instances"  (McMurrich). 


GASTRULATION 


799 


spheres,  which  are  at  the  periphery,  divide,  each  one  into  two,  making 
eight  epiblastic  and  four  hypoblastic  spheres.  When  this  has  occurred, 
the  epiblastic  spheres  are  smaller  and  clearer  than  the  hypoblastic 
spheres.  The  four  hypoblastic  spheres  now  divide  into  eight.  The 
epiblastic  spheres  then  divide  into  sixteen,  the  hypoblastic  spheres  in 
turn  divide,  and  this  goes  on  until  the  process  of  segmentation  is  com- 
pleted. In  the  rabbit,  this  occurs  usually  about  seventy  hours  after 
impregnation.  As  segmentation  progresses,  the  epiblastic  cells  extend 
over  the  hypoblastic  cells,  and  become  irregularly-polygonal  in  form. 
The  hypoblastic  cells  occupy  the  central  portion  of  the  ovum.  At  first 
there  is  a  circular  space  on  the  ovum  where  the  epiblastic  cells  do  not 
cover  the  cells  of  the  hypoblast  (see  Fig.  2ig,  A);  but  this  soon  becomes 
closed  by  an  extension  of  the  cells  of  the  epiblast  (see  Fig.  219,  B).  The 
hypoblastic  cells,  at  the  close  of  segmentation,  are  slightly  larger  than 
the  cells  of  the  epiblast  and  are  darker  and  more  rounded.  The  ovum 
now  consists  of  a  solid  mass  of  cells  and  is  called  the  morula,  on  account 
of  its  fancied  resemblance  to  a  mulberry.  The  cells  of  which  it  is  com- 
posed are  called  collectively  blastodermic  cells.  The  ovum  probably  is 
in  this  condition  when  it  passes  from  the  Fallopian  tube  into  the  uterus. 

Most  of  the  phenomena  of  segmentation  have  been  observed  in  the 
lower  forms  of  animals;  but  there  can  be  no  doubt  that  analogous  pro- 
cesses take  place  in  the  human  ovum.  In  the  rabbit,  forty-five  and  a 
half  hours  after  copulation,  Wiel  observed  an  ovum  with  sixteen  seg- 
mentations, situated  in  the  lower  third  of  the  Fallopian  tube.  He 
observed  an  ovum,  ninety-four  hours  after  copulation,  with  a  delicate 
mosaic  appearance,  presenting  a  small  rounded  eminence  on  its  surface. 
It  is  impossible  to  say  how  long  the  process  of  segmentation  continues 
in  the  human  ovum.  It  is  stated  that  it  is  completed  in  rabbits  in  a  few 
days,  and  in  dogs,  that  it  occupies  more  than  eight  days  (Hermann). 

Gastrulation.  —  After  segmentation  has  been  completed,  a^  cavity 
filled  with  liquid  appears  between  the  hypoblastic  and  epiblastic  cells, 
except  at  that  portion  which  has  last  been  covered  by  the  epiblast.  Here 
the  cells  of  the  hypoblast  are  in  contact  with  the  epiblast.  The  liquid  in 
the  interior  of  the  ovum  gradually  increases  in  quantity,  the  ovum  be- 
comes enlarged  to  the  diamater  of  -^-^  to  2V  of  ^^  \\\z\^  (0.5  to  i  milli- 
meter), and  is  now  called  the  blastula,  or  blastodermic  vesicle.  The 
epiblastic  cells  surround  the  blastodermic  vesicle  completely,  forming  a 
single  layer  over  the  greater  portion  ;  and  the  hypoblastic  cells  form  a 
lenticular  mass  attached  to  the  smaller  portion  of  the  inner  surface  of 
the  layer  of  epiblastic  cells  (see  Fig.  219,  C  and  D).  There  then  occurs 
a  gradual  invagination  of  the  hypoblastic  cells,  forming  a  double-walled 
sac,  called  the  gastrula.    This  is  the  primitive  gut,  or  archenteron.     The 


8oo 


EMBRYOLOGY 


process  of  its  formation  is  called  gastrulation.      It  is  at  this  portion  of 
the  ovum  that  the  embryonic  spot,  or  area,  afterward  appears. 

The  albuminous  covering  which  the  ovum  has  received  in  the  upper 
part  of  the  Fallopian  tube  gradually  liquefies  and  penetrates  the  vitel- 
line membrane,  furnishing,  it  is  thought,  matter  for  the  nourishment  and 
development  of  the  ovum.  In  the  Fallopian  tube,  indeed,  the  adventitious 
albuminous  covering  presents  an  analogy  to  the  albuminous  coverings 
which  the  eggs  of  oviparous  animals  receive  in  the  oviducts  ;  with  the 
difference  that  this  albuminous  matter  is  almost  the  sole  source  of 
nourishment  in  the  latter  and  exists  in  large  quantity,  w^hile  in  viviparous 
animals  the  quantity  is  small,  is  usually  consumed  as  the  ovum  passes 

into  the  uterus,  and  in  the  uterus 
the  ovum  forms  attachments  to 
and  draws  its  nourishment  from 
the  vascular  system  of  the  mother. 
Primitive  Streak.  —  Soon  after 
the  formation  of  the  blastula,  at  a 
certain  point  on  its  surface  there 
appears  a  rounded  elevation  or 
heap  of  smaller  cells,  forming  a 
distinct  spot,  called  the  embryonic 
spot.  As  development  advances, 
this  spot  becomes  elongated  and 
oval  and  is  called  the  embryonic 
shield.  It  is  then  surrounded  by 
a  clear  oval  area,  called  the  area 
pellucida,  and  the  area  pellucida 
is  itself  surrounded  by  a  zone  of 
cells,  more  granular  and  darker 
than  the  rest  of  the  blastoderm, 
called  the  area  opaca.  The  line  thus  formed  and  surrounded  by  the  area 
pellucida  is  called  the  primitive  streak  or  trace.  This  primitive  streak, 
or  groove,  however,  is  a  temporary  structure.  After  the  groove  is 
formed,  there  appears,  in  front  of  but  not  continuous  with  it,  a  new  fold 
and  a  groove  leading  from  it.  This  is  the  "  head-fold,"  and  the  groove 
is  the  true  medullary  groove,  which  afterward  is  developed  into  the 
neural  canal. 

Blastodermic  Layers.  —  The  blastodermic  cells,  resulting  originally 
from  the  segmentation  of  the  vitellus,  are  first  split  apparently  into  tvvo 
layers,  the  external,  or  epiblast,  and  the  internal,  or  hypoblast.  The 
epiblast  is  developed  into  the  epidermis  and  its  appendages  ;  the  glands 
of  the  skin  ;  the  enamel  of  the  teeth ;  the  mucous  lining  of  the  mouth, 


Fig.  222.  —  Embryonic  shield  of  a  rabbit,  show- 
itig  the  primitive  streak  and  the  medullary  groove 
above,  x  28  (Kollmann). 


FORMATION    OF    THE    MEMBRANES  8oi 

nasal  cavities  and  lower  part  of  the  rectum ;  the  brain  and  spinal 
cord;  the  organs  of  special  sense,  and  possibly  some  parts  of  the 
genito-urinary  apparatus.  The  hypoblast  is  developed  into  the  epithe- 
lium Hning  the  mucous  membrane  and  glands  of  the  digestive  tract ;  the 
epithelium  of  the  respiratory  organs;  the  epithelium  of  the  bladder  and 
urethra.  There  is  a  thickening  of  both  these  layers  at  the  line  of  de- 
velopment of  the  cerebro-spinal  system,  with  a  furrow  that  is  iinally 
enclosed  by  an  elevation  of  the  ridges  and  their  union  posteriorly,  form- 
ing the  canal  for  the  spinal  cord. 

As  the  spinal  canal  is  developed,  a  new  layer  of  cells  is  formed  be- 
tween the  epiblast  and  the  hypoblast,  which  is  called  the  mesoblast. 
The  mesoblast  itself  afterward  splits  into  two  layers.  All  the  parts  not 
enumerated  as  developed  from  the  epiblast  or  hypoblast  are  developed 
from  the  two  layers  of  the  mesoblast.     The  outer  layer  of  the  mesoblast, 


»  •> 


Fig.  223.  —  Transverse  section  of  the  embryonic  area  of  a  dog's  ovum  of  about  fifieen  days  (Bonnet). 

This  figure  is  introduced  especially  to  show  the  mesoblast.    The  section  is  through  the 
head-fold  {Ckp.)  ;  A4,  mesoblast. 

or  the  epiblastic  mesoblast,  unites  with  the  epiblast,  and  the  two  mem- 
branes together  form  what  is  sometimes  called  the  somatopleure  ;  from 
which  are  developed  the  bones,  muscles  and  external  parts  generally. 
The  inner  layer  of  the  mesoblast,  the  hypoblastic  mesoblast,  unites  with 
the  hypoblast  to  form  what  is  called  the  splanchnopleure  ;  from  which 
are  developed  the  circulatory  and  glandular  systems  and  the  internal 
parts  generally.  The  cells  lining  the  vessels,  including  the  lymphatics, 
which  exist  in  a  single  layer,  are  called  endothelial  cells.  This  name 
also  is  applied  to  the  cells  lining  the  serous  membranes. 

Formation    of   the    Membranes 

In  the  mammalia  a  portion  of  the  blastoderm  is  developed  into  mem- 
branes by  which  a  communication  and  union  are  established  between 
the  ovum  and  the  mucous  membrane  of  the  uterus.  From  the  ovum  two 
membranes  are  developed ;  one  non-vascular,  the  amnion,  and  another, 


8o2  EMBRYOLOGY 

the  allantois,  which  is  vascular.  The  two  layers  of  decidua  are  formed 
from  the  mucous  membrane  of  the  uterus.  At  a  certain  part  of  the 
uterus,  a  vascular  connection  is  established  between  the  mucous  mem- 
brane and  the  allantois,  and  the  union  of  these  two  structures  forms  the 
placenta.  The  foetal  portion  of  the  placenta  is  connected  with  the  foetus 
by  the  vessels  of  the  umbilical  cord,  and  the  maternal  portion  is  con- 
nected with  the  great  uterine  sinuses. 

The  external  covering  of  the  ovum,  during  the  first  stage  of  its 
development,  is  the  vitelline  membrane.  As  the  ovum  is  received  into 
the  uterus,  the  vitelline  membrane  develops  on  its  surface  little  villosi- 
ties,  which  are  non-vascular  and  formed  of  amorphous  matter  with 
granules.  These  are  the  first  villosities  of  the  ovum,  and  they  assist  in 
fixing  the  egg  in  the  uterine  cavity.  They  are  not  permanent,  they  do 
not  become  developed  into  the  vascular  villosities  of  the  chorion,  and 
they  disappear  as  the  true  membranes  of  the  embryo  are  developed 
from  the  blastodermic  layers.  The  vitelline  membrane  disappears  soon 
after  the  passage  of  the  ovum  into  the  uterus,  when  it  is  replaced  by 
the  amnion. 

Formation  of  the  Amnion.  —  As  the  ovum  advances  in  its  develop- 
ment, it  is  observed  that  a  portion  of  the  blastoderm  becomes  thickened, 
forming  the  epiblast,  the  two  layers  of  the  mesoblast  and  the  hypoblast. 
At  about  the  time  when  this  thickening  begins,  a  fold  of  the  epiblast 
and  of  the  external  layer  of  the  mesoblast  makes  its  appearance,  which 
surrounds  the  thickened  portion  and  is  most  prominent  at  the  cephalic 
and  the  caudal  extremities  of  the  furrow  for  the  neural  canal.  This  fold 
increases  in  extent  as  development  advances,  passes  over  the  dorsal 
surface  of  the  embryo  and  finally  meets  so  as  to  enclose  the  embryo 
completely.  At  a  certain  period  of  the  development  of  the  amnion,  this 
membrane  consists  of  an  external  layer,  formed  of  the  external  layer  of 
the  fold,  and  an  internal  layer ;  and  the  point  of  union  of  the  two 
layers,  or  the  point  of  meeting  of  the  fold,  is  marked  by  a  membra- 
nous septum. 

The  two  amniotic  layers  are  formed  in  the  way  just  described,  and 
a  complete  separation  finally  takes  place,  by  a  disappearance  of  the 
septum  formed  by  the  meeting  of  the  folds  over  the  back  of  the 
embryo.  This  process  occupies  four  or  five  days  in  the  human  ovum. 
The  point  where  the  folds  meet  is  called  the  amniotic  umbilicus.  When 
the  amnion  is  thus  completely  formed,  the  vitelline  membrane  has  been 
encroached  upon  by  the  external  amniotic  layer  and  disappears,  leaving 
this  layer  of  the  amnion  as  the  external  covering  of  the  ovum.  At  this 
time  there  is  a  growth  of  villosities  on  the  surface  of  the  external  amni- 
otic layer,  which,  like  the  villosities  of  the  vitelline  membrane,  are  not 
vascular. 


FORMATION    OF   THE    MEMBRANES 


803 


Fig.  224.  —  Five  diagrammatic  representations  of  the  formation  of  the  membranes  in  mammalia 

(Kolliker). 

i:  a,  a',  epiblast ;  d,  vitelline  membrane;  d' ,  villi  on  the  vitelline  membrane;  i,  hypoblast;  m,  m' , 
mesoblast. 

2:  a',  external  layer  of  the  amnion  ;  ^,  rf',  vitelline  membrane;  ^,  embryo ;  t/j,  umbilical  vesicle;  v  l^ 
k  s,  s  s,  folds  of  the  amnion  ;  d  d,  m' ,  s  t,  hypoblast ;  d  d,  connection  of  the  embryo  with  the  um- 
bilical vesicle. 

3:  d,  d' ,  vitelline  membrane;  v  I,  internal  amniotic  layer;  e,  embryo;  ah,  amniotic  cavity;  s  h,  s  h, 
external  amniotic  layer;  am,  space  between  the  two  layers  of  the  amnion  ;  dd,  hypoblast;  d f,  s t, 
i,  walls  of  the  umbilical  vesicle  ;  d g,  omphalo-mesenteric  canal ;  ds,  cavity  of  the  umbilical  vesicle ; 
a  I,  first  appearance  of  the  allantois. 

4:  s  h,  external  layer  of  the  amnion;  s  z,  villi  of  the  external  layer  of  the  amnion,  which  has  now  be- 
come the  chorion,  the  vitelline  membrane  having  disappeared;  hh,  am,  internal  layer  of  the  am- 
nion ;  e,  embryo  ;  a  h,  amniotic  cavity  ;  dg,  omphalo-mesenteric  canal ;  d s,  cavity  of  the  umbilical 
vesicle;  a  I,  allantois;    r,  space  between  the  two  layers  of  the  amnion.* 

5  :  c  h,  s h,  c  h,  a  I,  allantois  (which  has  now  become  the  chorion,  the  external  amniotic  layer  having  dis- 
appeared) ,  with  its  villi ;  a  ??t,  amnion  ;  a  s,  amniotic  covering  of  the  unibilical  cord  ;  r,  space  between 
the  amnion  and  the  allantois ;  a /%,  amniotic  cavity ;  ^  j,  umbilical  vesicle ;  i^^,  omphalo-mesenteric 
canal. 


804  EMBRYOLOGY 

Soon  after  the  development  of  the  amnion  the  allantois  is  formed. 
This  membrane  is  vascular.  It  encroaches  upon  and  takes  the  place  of 
the  external  amniotic  membrane,  and  is  covered  with  hollow  villi,  which 
take  the  place  of  the  villi  of  the  amnion.  Over  a  certain  portion  of  the 
membrane  the  villi  are  permanent.  The  mode  of  development  of  the 
amnion  is  illustrated  by  the  diagrammatic  Fig.  224.  This  figure 
illustrates  the  formation  of  the  amnion,  the  umbilical  vesicle  and  the 
allantois.  The  last  two  structures  are  derived  from  the  hypoblast  and 
the  internal  layer  of  the  mesoblast. 

When  the  allantois  has  become  the  chorion,  or  the  external  membrane 
of  the  ovum,  having  taken  the  place  of  the  external  layer  of  the  amnion, 
the  structures  of  the  ovum  are  the  following:  i.  The  chorion,  formed 
of  the  two  layers  of  the  allantois  and  penetrated  by  bloodvessels. 
2.  The  umbilical  cord,  which  connects  the  embryo  with  the  placental 
portion  of  the  chorion,  and  the  umbilical  vesicle,  formed  from  the  same 
layers  as  the  allantois.  3.  The  amnion,  which  is  the  internal  layer  of 
the  amniotic  fold,  persisting  throughout  foetal  life.  4.  The  embryo 
itself. 

During  the  early  stages  of  development  of  the  umbilical  vesicle  and 
the  allantois,  the  internal  amniotic  layer,  or  the  true  amniotic  membrane, 
is  closely  applied  to  the  surface  of  the  embryo  and  is  continuous  with 
the  epidermis  at  the  umbilicus.  It  is  then  separated  from  the  allantois 
by  a  layer  of  gelatinous  matter  ;  and  in  this  layer,  between  the  amnion 
and  the  allantois,  is  the  umbilical  vesicle.  At  this  time  the  umbilical 
cord  is  short  and  not  twisted.  As  development  advances,  however,  the 
intermembranous  gelatinous  matter  gradually  disappears ;  the  cavity  of 
the  amnion  is  enlarged  by  the  production  of  liquid  between  its  internal 
surface  and  the  embryo ;  and  at  about  the  end  of  the  fourth  month  the 
amnion  comes  in  contact  with  the  internal  surface  of  the  chorion.  At 
this  time  the  embryo  floats  in  the  liquid  contained  in  the  amniotic 
cavity. 

The  amnion  forms  a  lining  membrane  for  the  chorion.  By  its 
gradual  enlargement  it  has  formed  a  covering  for  the  umbilical  cord  ; 
and  between  it  and  the  cord,  is  the  atrophied  umbilical  vesicle.  The 
amnion  then  resembles  a  serous  membrane,  except  that  it  is  non-vascular. 
It  is  lined  with  a  single  layer  of  pale  delicate  cells  of  pavement-epithe- 
lium, which  contain  a  few  fine  fatty  granules.  At  term  the  amnion 
adheres  to  the  chorion,  although  it  may  be  separated  with  a  little  care 
as  a  distinct  membrane  and  may  be  stripped  from  the  cord.  From  its 
arrangement  and  from  the  absence  of  bloodvessels,  it  is  evident  that  this 
membrane  is  simply  for  the  protection  of  the  foetus  and  is  not  directly 
concerned    in    its    nutrition    and    development  (see    Plate  X,  Fig.  6). 


AMNIOTIC    LIQUID 


805 


The  gelatinous  mass  referred  to  above,  situated,  during  the  early  periods 
of  intra-uterine  life,  between  the  amnion  and  the  chorion,  presents  a  semi- 
liquid  consistence,  with  very  delicate  interlacing  fibres  of  connective 
tissue  and  fine  grayish  granules  scattered  through  its  substance.  These 
fibres  are  gradually  developed  as  the  quantity  of  gelatinous  matter 
diminishes  and  the  amnion  approaches  the  chorion,  until  finally  they 
form  a  rather  soft,  reticulated  layer,  which  is  sometimes  called  the 
membrana  media. 

Aviniotic  Liquid.  —  The  process  of  enlargement  of  the  amnion  shows 
that  the  amniotic  liquid  gradually  increases  in  quantity  as  the  develop- 
ment of  the  foetus  progresses.  At  term  the  quantity  is  variable,  being 
rarely  more  than  two  pints  (about  one  liter)  or  less  than  one  pint  (about 
half  a  liter).  In  the  early  periods  of  utero-gestation  it  is  clear,  slightly 
yellowish  or  greenish,  and  perfectly  liquid.  Toward  the  sixth  month 
its  color  is  more  pronounced  and  it  becomes  slightly  mucilaginous.  Its 
reaction  usually  is  neutral  or  faintly  alkahne,  although  sometimes  it  is 
feebly  acid  in  the  latest  periods.  It  sometimes  contains  a  small  quantity 
of  albumin,  as  determined  by  heat  and  nitric  acid ;  and  there  usually  is 
a  gelatinous  precipitate  on  the  addition  of  acetic  acid.  The  following 
table  gives  its  chemical  composition  (Robin):  — 


COMPOSITION   OF  THE   AMNIOTIC   LIQUID 


Water 

Albumin  and  mucin      .... 
Urea    ....... 

Creatin  and  creatinin  (Scherer,  Robin  and  Verdeil) 

Sodium  lactate  (V^ogt,  Regnauld) 

Fatty  matters  (Rees,  Mack) 

Glucose  (Bernard)        .... 

Sodium  chloride  and  potassium  chloride 

Calcium  chloride  .... 

Sodium  carbonate         .... 

Sodium  sulphate  .... 

Potassium  sulphate  (Rees)  . 

Calcareous  and  magnesian  phosphates  and  sulphates 


991.00  to  975.00 
0.82  to  10.77 
2.00  to  3.50 
not  estimated 

a  trace 
0.13  to      1.25 
not  estimated 
2.40  to      5.95 

a  trace 

a  trace 

a  trace 

a  trace 
1. 14  to       1.72 


The  presence  of  certain  of  the  urinary  constituents  in  the  amniotic 
liquid  has  led  to  the  view  that  the  urine  of  the  foetus  is  discharged  in 
greater  or  less  quantity  into  the  amniotic  cavity.  Bernard,  who  is  cited 
in  the  table  of  composition  of  the  amniotic  fluid  as  having  determined 
the  presence  of  sugar,  has  shown  that  in  animals  with  a  multiple  pla- 
centa, the  amnion  has  'a  glycogenic  action  during  the  early  part  of 
intra-uterine  existence. 

In  regard  to  the  origin  of  the  amniotic  liquid,  it  is  impossible  to  say 


8o6  EMBRYOLOGY 

how  much  of  it  is  derived  from  the  general  surface  of  the  foetus,  how- 
much  from  the  urine,  and  how  much  from  the  amnion  itself,  by  transu- 
dation from  the  vascular  structures  beneath  this  membrane.  The  quan- 
tity apparently  is  too  great,  especially  in  the  early  months,  to  be  derived 
entirely  from  the  urine  of  the  foetus ;  and  there  probably  is  an  exudation 
from  the  general  surface  of  the  foetus  and  from  the  membranes.  After 
the  third  month  the  sebaceous  secretion  from  the  skin  of  the  foetus  pre- 
vents the  absorption  of  any  of  the  liquid.  An  important  property  of 
the  amniotic  liquid  is  that  of  resisting  putrefaction  and  of  preserving 
dead  tissues. 

Formation  of  the  Umbilical  Vesicle  {Yolk-sac).  —  As  the  visceral 
plates,  which  will  be  described  hereafter,  close  over  the  front  of  the 
embryo,  that  portion  of  the  blastoderm  from  which  the  intestinal  canal 
is  developed  presents  a  vesicle,  which  is  cut  off  from  the  abdominal 
cavity  but  which  still  communicates  freely  with  the  intestine.  This  is 
the  umbilical  vesicle.  On  its  surface  is  a  rich  plexus  of  bloodvessels  ; 
and  this  is  an  important  organ  in  birds  and  in  many  of  the  lower  forms 
of  animals.  In  the  human  subject  and  in  mammals,  however,  the  um- 
bilical vesicle  is  not  so  important,  as  nutrition  is  secured  by  means  of 
vascular  connections  between  the  chorion  and  the  uterus.  The  vesicle 
becomes  gradually  removed  farther  and  farther  from  the  embryo,  as 
development  advances,  by  the  elongation  of  its  pedicle ;  and  it  is  com- 
pressed between  the  amnion  and  the  chorion  as  the  former  membrane 
becomes  distended. 

When  the  umbilical  vesicle  is  formed,  it  receives  two  arteries  from 
the  two  aortae,  and  the  blood  is  returned  to  the  embryo  by  two  veins 
which  open  into  the  vestibule  of  the  heart.  These  are  called  the  om- 
phalo-mesenteric  vessels.  At  about  the  fortieth  day  one  artery  and 
one  vein  disappear,  and  soon  after,  all  vascular  connection  with  the 
embryo  is  lost.  At  first  there  is  a  canal  of  communication  with  the 
intestine,  called  the  omphalo-mesenteric  canal.  This  is  gradually  obliter- 
ated, and  it  closes  between  the  thirtieth  and  the  thirty-fifth  day.  The 
point  of  communication  of  the  vesicle  with  the  intestine  is  called  the 
intestinal  umbilicus  ;  and  early  in  the  process  of  development,  there  is 
here  a  hernia  of  a  loop  of  intestine.  The  umbilical  vesicle  remains  as  a 
rather  prominent  structure  as  late  as  the  fourth  or  fifth  month,  but  it  may 
be  discovered  at  the  end  of  pregnancy. 

The  umbilical  vesicle  presents  three  coats  :  an  external  smooth  mem- 
brane, formed  of  connective  tissue,  a  middle  layer  of  transparent  poly- 
hedric  cells,  and  an  internal  layer  of  spheroidal  cells.  The  membrane, 
composed  of  these  layers,  encloses  a  pulpy  mass,  composed  of  a  liquid 
often  containing  cells  and  yellowish  granules. 


FORMATION    OF    THE    MEMBRANES 


807 


Formation  of  the  Allantois  and  the  Pennanerit  Chorion.  —  During 
the  early  stages  of  development  of  the  umbilical  vesicle,  and  as  it  is 
shut  off  from  the  intestine,  there  appears  an  elevation  at  the  posterior 


Fig.  225.  —  Human  embryo  of  twenty  to  twenty-five  days  (Coste) . 

^»?,  amnion;  ZZL,  lower  limb;    i^l^,  umbilical  artery;    6^.;,  umbilical  cord;    671,  upper  limb;    Ys, 
yolk-sac  (umbilical  vesicle). 


portion  of  the  intestine,  which  rapidly  increases  in  extent  until  it  forms 
a  membrane  of  two  layers,  extending  between  the  internal  and  the 
external  layers  of  the  amnion.  This  membrane,  the  allantois,  becomes 
vascular  early  in  its  development,  increases  in  size  quite  rapidly,  and 
finally  it  completely  encloses  the  internal  layer  of  the  amnion  and  the 


8o8 


EMBRYOLOGY 


embryo,  the  gelatinous  mass  already  described  being  situated  between 
it  and  the  internal  amniotic  layer  before  this  layer  becomes  enlarged. 
While  the  formation  of  the  two  layers  of  the  allantois  is  quite  distinct 
in  certain  of  the  lower  forms  of  animals,  in  the  human  subject  and 
in  mammals  it  is  not  so  easily  observed ;  still  there  can  be  no  doubt 
as  to  the  mechanism  of  its  formation,  even  in  the  human  ovum.  Here, 
however,  the  allantois  soon  becomes  a  single  membrane,  the  two  original 
layers  of  which  can  not  be  separated  from  each  other.  The  different 
stages  of  the  development  of  the  allantois  are  shown  in  the  diagram- 
matic Fig.  224(3,  4,  5)- 

It  is  the  vascularity  of  the  allan- 
tois that  causes  the  rapid  develop- 
ment by  which  it  invades  and  finally 
supersedes  the  external  layer  of  the 
amnion,  becoming  the  permanent 
chorion,  or  external  membrane  of  the 
ovum.  At  first  there  are  two  arteries 
extending  into  this  membrane  from 
the  lower  portion  of  the  aorta,  and 
two  veins.  The  tv*'o  arteries  persist 
and  form  the  two  arteries  of  the  um- 
bilical cord,  coming  from  the  internal 
iliac  arteries  of  the  foetus  ;  and  one 
vein,  the  umbilical  vein,  which  returns 
the  blood  from  the  placenta  to  the 
foetus,  is  permanent.  These  vessels 
are  connected  with  the  permanent 
vascular  tufts  of  the  chorion. 

The  development  of  the  allantois 
can  not  be  well  observed  in  human 
ova  before  the  fifteenth  or  the  twenty-fifth  day.  When  the  allantois 
becomes  the  permanent  chorion,  it  presents  a  large  number  of  hollow 
branching  villi  over  its  entire  surface,  which  give  the  ovum  a  shaggy 
appearance.  As  the  ovum  enlarges,  over  a  certain  area  surrounding 
the  point  of  attachment  of  the  pedicle  which  connects  the  chorion  with 
the  embryo,  the  villi  are  developed  more  rapidly  than  over  the  rest 
of  the  surface.  Indeed,  as  the  ovum  becomes  larger  and  larger,  the  villi 
of  the  surface  outside  of  this  area  become  more  and  more  scanty,  lose 
their  vascularity  and  finally  disappear.  That  portion  of  the  allantois 
over  which  the  villi  persist  and  increase  in  length  and  in  the  number  of 
their  branches  is  destined  to  form  connections  with  the  mucous  mem- 
brane of  the  uterus  and  constitutes  the  foetal  portion  of  the  placenta. 


Fig.  226.  —  Human  embryo  of  the  fourth 
to  the  fifth  tueek,  X  2  —  prepared  by  Dr.  C. 
R.  Corson,  of  Savannah,   Ga.  (Gage). 

This  ovum  shows  the  shaggy  chorion, 
which  has  been  spUt  open  and  the  edges  of 
the  opening  drawn  aside  to  show  the  em- 
bryo. The  embryo  is  curved  as  usual,  and 
the  head  rests  on  the  prominent  heart  and  is 
almost  in  contact  with  the  pear-shaped 
umbilical  vesicle.  The  arm-bud  and  the 
branchial  slits  show  clearly.  The  somites 
(protovertebr^)  may  be  seen  on  close  in- 
spection. 


UMBILICAL    CORD  809 

This  change  begins  at  about  the  end  of  the  second  month,  and  the  pla- 
centa becomes  distinctly  limited  at  about  the  end  of  the  third  month. 

It  must  be  remembered  that  as  the  changes  go  on  which  result  in 
the  formation  of  the  permanent  chorion  and  the  limitation  of  the  foetal 
portion  of  the  placenta,  the  formation  of  the  umbilical  vesicle  and  the 
enlargement  of  the  amnion  also  are  progressing.  The  amnion  is  grad- 
ually distended  by  the  increase  in  the  quantity  of  amniotic  liquid.  It 
reaches  the  internal  surface  of  the  chorion  at  about  the  end  of  the  fourth 
month,  extends  over  the  umbilical  cord  to  form  its  external  covering,  in- 
cluding the  cord  of  the  umbilical  vesicle,  and  the  umbilical  vesicle  itself 
lies  in  the  gelatinous  matter  between  the  two  membranes. 

At  about  the  beginning  of  the  fifth  month  the  ovum  is  constituted  as 
follows  :  — 

The  foetus  floats  freely  in  the  amniotic  liquid,  attached  to  the  pla- 
centa by  the  umbilical  cord  ;  the  chorion  presents  a  highly  vascular, 
thickened  and  villous  portion,  the  foetal  portion  of  the  placenta;  the 
rest  of  the  chorion  is  a  simple  membrane,  without  villi  and  without 
bloodvessels ;  the  amnion  lines  the  internal  surface  of  the  chorion  and 
forms,  also,  the  external  covering  of  the  umbilical  cord;  the  umbilical 
vesicle  has  become  atrophied  and  has  lost  its  vascularity ;  the  hernia  at 
the  point  of  connection  of  the  umbilical  vesicle  with  the  intestine  of  the 
foetus  has  closed ;  and  finally  the  foetus  has  undergone  considerable 
development. 

Umbilical  Cord.  —  From  the  description  given  of  the  mode  of  devel- 
opment of  the  chorion  and  the  amnion,  it  is  evident  that  the  umbilical 
cord  is  nothing  more  than  the  pedicle  which  connects  the  embryo  with 
that  portion  of  the  chorion  which  enters  into  the  structure  of  the  placenta. 
It  is,  indeed,  a  process  of  the  allantois,  in  which  the  vessels  have  become 
the  most  important  structures.  The  cord  is  distinct  at  about  the  end  of 
the  first  month ;  and  as  development  advances,  the  vessels  consist  of 
two  arteries  coming  from  the  body  of  the  foetus,  which  are  twisted 
usually  from  left  to  right,  around  the  single  umbilical  vein.  In  addition 
to  the  spiral  turns  of  the  arteries  around  the  vein,  the  entire  cord  may 
be  more  or  less  twisted,  probably  from  the  movements  of  the  foetus. 

The  fully-developed  cord  extends  from  the  umbiHcus  of  the  foetus  to 
the  central  portion  of  the  placenta,  in  which  its  insertion  usually  is 
oblique ;  although  it  may  be  inserted  at  other  points,  and  even  outside 
of  the  border  of  the  placenta,  its  vessels  penetrating  this  organ  from  the 
side.  Its  usual  length,  which  varies  considerably,  is  about  twenty  inches 
(50.8  centimeters).  It  has  been  observed  as  long  as  sixty  (152.4  centime- 
ters), and  as  short  as  seven  inches  (17.8  centimeters).  When  the  cord  is 
very  long,  it  sometimes  presents  knots  or  it  may  be  wound  around  the 


8lO  EMBRYOLOGY 

neck,  the  body  or  any  of  the  members  of  the  foetus ;  and  this  can  be 
accounted  for  only  by  the  movements  of  the  foetus  in  utero. 

The  external  covering  of  the  cord  is  a  process  of  the  amnion  ;  and 
as  it  extends  over  the  vessels,  it  includes  a  gelatinous  substance  (the 
gelatin  of  Wharton)  which  surrounds  the  vessels  and  protects  them  from 
compression.  This  gelatinous  substance  is  identical  with  the  so-called 
membrana  intermedia,  or  the  substance  included  between  the  amnion 
and  the  chorion.  The  entire  cord,  covered  with  the  gelatin  of  Wharton 
and  the  amnion,  usually  is  about  the  size  of  the  little  finger.  According 
to  Robin,  the  umbilical  cord  will  sustain  a  weight  of  about  twelve  pounds 
(5.4  kilos).  As  the  amniotic  liquid  accumulates  and  distends  the  amnion, 
this  membrane  becomes  more  and  more  closely  applied  to  the  cord.  The 
pressure  extends  from  the  placental  attachment  of  the  cord  toward  the 
foetus,  and  it  gradually  forces  into  the  abdomen  of  the  foetus  the  loop 
of  intestine,  which,  in  the  early  periods  of  intra-uterine  life,  forms  an 
umbilical  hernia. 

The  vessels  of  the  cord  —  the  arteries  as  well  as  the  vein  —  are  pro- 
vided with  valves.  These  are  simple  inversions  of  the  walls  of  the  vessels, 
and  they  do  not  exist  in  pairs  nor  do  they  seem  to  influence  the  current 
of  blood.  In  the  arteries  these  folds  are  situated  at  intervals  of  half  an 
inch  to  two  inches  (12.7  to  58. 8. millimeters),  and  they  are  more  abundant 
where  the  vessels  are  very  contorted.  In  the  vein  the  folds  are  most 
abundant  near  the  placenta.  They  are  irregularly  placed,  and  in  a 
length  of  four  inches  (10  centimeters),  fifteen  folds  were  found  (Berger). 
It  is  not  apparent  that  these  valvular  folds  have  any  physiological 
importance. 

As  the  allantois  is  developed,  it  presents,  in  the  early  stages  of  its 
formation,  three  portions :  an  external  portion,  which  becomes  the 
chorion,  an  internal  portion,  enclosed  in  the  body  of  the  embryo,  and 
an  intermediate  portion.  The  intermediate  portion  becomes  the  umbili- 
cal cord.  As  the  umbilicus  of  the  foetus  closes  around  the  cord,  it  shuts 
off  a  portion  of  the  allantois  contained  in  the  abdominal  cavity,  which 
becomes  the  urinary  bladder;  but  there  is  a  temporary  communication 
between  the  internal  portion  and  the  lower  portion  of  the  cord,  called 
the  urachus.  This  usually  is  obhterated  before  birth  and  is  reduced  to 
the  condition  of  an  impervious  cord ;  but  it  may  persist  during  intra- 
uterine life,  in  the  form  of  a  narrow  canal  extending  from  the  bladder  to 
the  umbilicus,  which  is  closed  soon  after  birth. 

At  this  time,  when  the  ovum  measures  one-eighth  to  one-fourth  of  an 
inch  (3  to  6  millimeters)  in  diameter,  the  outer  portion  of  the  villi  is 
covered,  over  either  a  part  of  the  ovum  or  the  entire  surface,  with  a 
special  layer  of  cells  derived  from  the  epiblast.     These  constitute  the 


MEMBRANE    DECIDU^  8ll 

trophoblast.  This  membrane  has  been  studied  in  the  unguiculates  only  ; 
but  probably  it  exists  in  the  human  subject  and  in  all  mammals.  The 
cells  are  fused  into  a  thick  mass  and  are  supposed  to  destroy  the  tissues 
of  the  uterus  with  which  they  come  in  contact  and  secure  implantation 
of  the  ovum  in  the  mucous  membrane.  The  trophoblast  afterward  dis- 
appears, and  the  area  of  implantation  of  the  ovum  finally  becomes  the 
placental  area. 

The  entire  mucous  membrane  of  the  uterus,  however,  has  already 
undergone  certain  changes  by  which  it  is  prepared  for  the  reception 
of  the  ovum. 

Membraiice  Deciduce.  —  In  addition  to  the  two  membranes  connected 
with  the  foetus,  there  are  two  membranes  formed  from  the  mucous 
membrane  of  the  uterus,  which  are  derived  from  the  mother  and  which 
serve  still  further  to  protect  the  ovum.  The  chorion  is  for  the  protec- 
tion of  the  foetus  ;  but  a  portion  of  this  membrane  —  about  one-third  of 
its  surface  —  becomes  closely  united  with  a  corresponding  portion  of  the 
uterine  mucous  membrane,  to  form  the  placenta. 

As  the  fecundated  ovum  descends  into  the  uterus,  it  is  invested  with 
a  villous  covering,  which  is  either  the  permanent  chorion  or  one  of  the 
membranes  that  invests  the  ovum  previous  to  the  complete  development 
of  the  allantois.  The  changes  incident  to  menstruation  have  already 
been  described.  It  has  been  seen  that  during  an  ordinary  menstrual 
period,  the  membrane  is  increased  three 'or  four  times  in  thickness  and 
becomes  more  or  less  rugous.  If  a  fertilized  ovum  descends  into  the 
uterus,  the  changes  in  the  mucous  membrane  progress.  The  glands 
enlarge  and  the  membrane  becomes  thicker,  so  that  at  the  end  of  the 
first  month  it  measures  about  two-fifths  of  an  inch  (lo  millimeters).  This 
thickening  is  due  chiefly  to  development  of  tissue  between  the  glands, 
and  the  membrane  becomes  soft  and  pulpy.  In  the  meantime  the  ovum 
has  effected  its  lodgement  between  the  folds,  usually  near  the  fundus  and 
near  the  opening  of  one  of  the  Fallopian  tubes ;  and  the  adjacent  parts 
of  the  mucous  membrane  extend  over  the  ovum  so  that  it  is  at  last  com- 
pletely enclosed.  This  occurs  at  the  twelfth  or  thirteenth  day.  The 
extension  of  the  mucous  membrane  which  covers  the  ovum  becomes  the 
decidua  reflexa ;  the  changed  mucous  membrane  which  lines  the  uterus 
becomes  the  decidua  vera  ;  and  the  portion  of  the  mucous  membrane 
that  remains  at  the  site  of  the  placenta  becomes  the  decidua  serotina. 
The  vascular  villosities  of  the  chorion  probably  do  not,  as  was  once 
thought,  penetrate  the  uterine  tubules,  but  they  become  surrounded  with 
tissues  developed  between  the  tubules. 

As  development  advances,  the  decidua  vera  becomes  extended, 
loses  its  vessels  and  glands  and  is  reduced  to  the  condition  of  a  simple 


8l2 


EMBRYOLOGY 


membrane.  The  cylindrical  epithelium  of  the  mucous  membrane  of  the 
body  of  the  uterus,  soon  after  fecundation,  becomes  exfoliated,  and  its 
place  is  supplied  with  flattened  cells.  This  change  is  effected  at  the 
sixth  or  the  eighth  week.     The  epithelium  of  the  cervix  retains  its  cylin- 


Fig.  227.  —  Seventeeft-days'  gravid  uterus,  x   I.  —  From  the  Anatomical  Museum  of  Johns  Hopkins 
University.  —  Embryo  drawn  relatively  too  large  (Williams). 

D.R.,  decidua  reflexa;  D.S.,  decidua  serotifla;  D.V.,  decidua  vera;  E,  embryo;    O.L.,  ovarian 
ligament;  A'.Z..,  round  ligament. 

drical  character,  but  most  of  the  cells  lose  their  cilia.  The  decidua 
reflexa,  which  is  thinner  than  the  decidua  vera,  has  neither  bloodvessels, 
glands  nor  epithelium. 

During  the  first  periods  of  utero-gestation,  the  two  layers  of  decidua 
are  separated  by  a  small  quantity  of  an  albuminous  and  sometimes  a 


FORMATION    OF    THE    PLACENTA  813 

sanguinolent  liquid ;  but  this  disappears  at  about  the  end  of  the  fourth 
month,  and  the  membranes  then  come  in  contact  with  each  other.  They 
soon  become  so  closely  adherent  as  to  form  a  single  membrane,  which 
is  in  contact  with  the  chorion.  Sometimes,  at  full  term,  the  membranes 
of  the  foetus  can  be  separated  from  the  decidua ;  but  frequently  the  dif- 
ferent layers  are  closely  adherent  to  each  other. 

The  changes  just  described  are  not  participated  in  by  the  mucous 
membrane  of  the  neck  of  the  uterus.  The  glands  in  this  situation 
secrete  a  semisolid,  transparent,  viscid  mucus,  which  closes  the  os  and 
is  sometimes  called  the  uterine  plug. 

Toward  the  fourth  month  a  very  delicate,  soft,  homogeneous  layer 
appears  over  the  muscular  fibres  of  the  uterus  beneath  the  decidua  vera, 
which  is  the  beginning  of  a  new  mucous  membrane.  This  is  developed 
very  gradually,  and  the  membrane  is  completely  restored  about  two 
months  after  parturition. 

Formation  of  the  Placenta.  —  At  about  the  end  of  the  second  month 
the  villi  of  the  chorion  become  enlarged  and  arborescent  over  that  part 
which  eventually  forms  the  foetal  portion  of  the  placenta.  They  are 
then  highly  vascular  and  are  embedded  in  the  soft  substance  of  the 
hypertrophied  mucous  membrane.  This  portion  of  the  chorion  is  called 
the  chorion  frondosum.  At  the  same  time  the  villi  over  the  rest  of  the 
chorion  (chorion  leve)  are  arrested  in  their  growth,  and  they  finally  dis- 
appear during  the  third  month.  The  bloodvessels  penetrate  the  villi  in 
the  form  of  loops  at  about  the  fourth  week ;  and  the  placenta  is  dis- 
tinctly marked  at  about  the  end  of  the  third  month.  The  placenta  then 
rapidly  assumes  the  anatomical  characters  observed  after  it  may  be  said 
to  be  fully  developed  (see  Plate  X,  Fig.  6). 

The  fully-formed  placenta  occupies  about  one-third  of  the  uterine 
mucous  membrane,  and  usually  is  rounded  or  ovoid  in  form,  with  a  dis- 
tinct border  connected  with  the  decidua  and  the  chorion.  It  is  seven  to 
nine  inches  (18  to  23  centimeters)  in  diameter,  a  little  more  than  an  inch 
{2.5  centimeters)  in  thickness  at  the  point  of  penetration  of  the  um- 
bilical cord,  slightly  attenuated  toward  the  border,  and  weighs  fifteen 
to  thirty  ounces  (425  to  850  grams).  Its  foetal  surface  is  covered  with 
the  smooth  amniotic  membrane,  and  its  uterine  surface,  when  detached, 
is  rough,  and  divided  into  irregular  lobes,  or  cotyledons,  half  an  inch  to 
an  inch  and  a  half  (12.7  to  38.1  millimeters)  in  diameter.  Between  these 
lobes  are  membranes,  called  dissepiments,  which  penetrate  into  the 
substance  of  the  placenta  and  at  its  border  extend  as  far  as  the  foetal 
surface. 

On  the  uterine  surface  of  the  placenta,  is  a  thin  soft  membrane,  the 
decidua   serotina.     This    is    composed    of   amorphous   matter,  a    large 


8 14  EMBRYOLOGY 

number  of  granules,  and  colossal  cells  with  enlarged  and  multiple  nuclei. 
A  portion  of  this  membrane  is  not  thrown  off  with  the  placenta  in  par- 
turition, but  processes  extend  into  the  placenta  and  closely  surround 
the  foetal  tufts. 

The  two  arteries  of  the  umbilical  cord  branch  on  the  foetal  surface 
beneath  the  amnion  and  finally  penetrate  the  substance  of  the  placenta. 
The  branches  of  the  veins,  which  are  about  sixteen  in  number,  converge 
toward  the  cord  and  unite  to  form  the  umbilical  vein.  On  the  uterine 
surface  of  the  placenta  are  oblique  openings  of  a  large  number  of  veins 
which  return  the  maternal  blood  to  the  uterine  sinuses.  There  are,  also, 
the  small  spiral  arteries,  which  pass  into  the  substance  of  the  placenta 
to  supply  blood  to  the  maternal  portion.  These  are  the  "  curling 
arteries,"  described  by  John  Hunter.  If  the  umbilical  arteries  are 
injected,  the  liquid  is  returned  by  the  umbilical  vein,  having  passed 
through  the  vascular  tufts  of  the  foetal  portion  of  the  placenta. 

According  to  Winkler,  there  are  three  kinds  of  foetal  villi :  i.  Those 
which  terminate  just  beneath  the  chorion,  without  penetrating  the  vascu- 
lar lacunae.  2.  Longer  villi,  which  hang  free  in  the  lacunae.  3.  Long, 
branching  villi,  which  penetrate  more  deeply  into  the  placenta,  some 
extending  as  far  as  its  uterine  surface. 

The  great  vascular  spaces,  or  lacunae  of  the  maternal  portion  of  the 
placenta,  present  a  number  of  trabeculae,  which  extend  from  the  uterine 
to  the  foetal  surface ;  and  between  these  trabeculae,  are  exceedingly 
delicate  transverse  and  oblique  secondary  trabecular  processes.  The 
bloodvessels  of  the  foetal  tufts  are  surrounded  with  a  gelatinous  con- 
nective-tissue structure,  and  as  late  as  the  sixth  month  are  covered  with 
a  layer  of  chorionic  cells. 

The  mode  of  formation  of  the  vascular  spaces  in  the  placenta  has 
been  a  subject  of  much  discussion.  The  following,  however,  seems  to 
be  the  most  reasonable  view  in  regard  to  this  question  :  That  portion  of 
the  uterine  mucous  membrane  which  becomes  the  maternal  portion  of 
the  placenta  extends  from  the  decidua  serotina  and  surrounds  the  villi, 
which  are  embedded  in  its  substance.  As  the  arborescent  villi  extend, 
they  encroach  on  the  bloodvessels  of  the  prolongations  from  the 
serotina,  which  latter  become  much  enlarged  and  finally  form  the  great 
vascular  spaces  traversed  by  the  trabeculae  mentioned  above.  At  term, 
however,  according  to  Heinz  (1888),  the  foetal  vessels  have  lost  their 
covering  of  epithelium  that  is  observed  in  the  earlier  months  of  preg- 
nancy. Thus  the  most  important  parts  of  the  placenta  are  formed  by  an 
interlacement  of  the  villi  of  the  chorion  with  the  altered  structures  of  the 
mucous  membrane  of  the  uterus. 

In  the  human  subject  the  maternal  and  foetal  portions  of  the  pla- 


USES    OF    THE   PLACENTA  815 

centa  are  so  closely  united  that  they  cannot  be  separated  from  each 
other.  In  parturition  the  curling  arteries  and  the  veins  on  the  uterine 
surface  of  the  placenta  are  torn  off,  and  the  placenta  then  consists  of 
the  parts  just  described;  the  torn  ends  of  the  vessels  attached  to  the 
uterus  are  closed  by  the  contractions  of  the  surrounding  muscular  fibres  ; 
and  the  blood  that  is  discharged  is  derived  mainly  from  the  placenta 
itself. 

Uses  of  the  Placenta.  —  The  placenta  is  the  respiratory,  excretory  and 
nutritive  organ  of  the  foetus.  Its  action  as  a  respiratory  organ  has  already 
been  mentioned  in  connection  with  the  physiology  of  respiration.  It  cer- 
tainly serves  as  an  organ  for  the  elimination  of  carbon  dioxide,  and 
probably  for  other  products  of  excretion.  It  is  the  only  source  of 
materials  for  the  development  and  nutrition  of  the  foetus.  It  is  thought 
that  cells  derived  from  the  serotina  elaborate  a  liquid  called  uterine  milk, 
which  is  absorbed  by  the  foetal  tufts.  This  Hquid  has  been  collected 
from  between  the  foetal  tufts  of  the  placenta  of  the  cow  and  has  been 
found  to  contain  fatty  matters,  albuminous  matters  and  certain  salts,  but 
no  sugar  or  casein.  It  is  not  probable,  however,  that  such  a  liquid  exists 
in  the  human  placenta ;  although  "  uterine  milk  "  of  the  ruminants  was 
mentioned  by  Haller  and  has  been  alluded  to  by  even  earlier  writers. 


CHAPTER   XXXII 

DEVELOPMENT   OF    THE    OVUM 

Development  of  the  cavities  and  layers  of  the  trunk  in  the  chick  —  Development  of  the  skeleton, 
muscular  system  and  skin  —  Notochord  —  Vertebral  column  etc.  —  Development  of  the 
nervous  system  —  Development  of  the  digestive  system — Development  of  the  respiratory 
system  —  Development  of  the  face  —  Development  of  the  teeth  —  Development  of  the 
genito-urinary  apparatus  —  Development  of  the  urinary  system  —  Development  of  the 
external  organs  of  generation'' — Development  of  the  circulatory  system — The  first,  or  vitelline 
circulation  —  The  second,  or  placental  circulation  —  Development  of  the  heart  —  Peculiari- 
ties of  the  foetal  circulation  —  The  third,  or  adult  circulation. 

The  product  of  generation  retains  the  name  of  ovum  until  the  form 
of  the  body  begins  to  be  apparent,  when  it  is  called  the  embryo.  At 
the  fourth  month,  about  the  time  of  quickening,  it  is  called  the  foetus, 
a  name  retained  during  the  rest  of  intra-uterine  life.  The  membranes 
are  appendages  formed  for  the  purposes  of  protection  and  nutrition ; 
and  the  embryo  itself,  in  the  mammalia,  is  developed  from  a  restricted 
portion  of  the  layers  of  cells  resulting  from  the  segmentation  of  the 
ovum. 

The  formation  of  the  blastodermic  cells  and  the  appearance  of  the 
groove  which  is  subsequently  developed  into  the  neural  canal  have 
already  been  described.  At  this  portion  of  the  ovum,  there  is  a 
thickening  of  the  blastoderm,  which  then  presents  three  layers,  the 
mesoblast  —  the  thickest  and  most  important  —  being  developed  between 
the  epiblast  and  the  hypoblast.  The  earliest  stages  of  development  have 
been  studied  most  successfully  in  the  chick  ;  and  it  is  probable  that  the 
appearances  here  observed  nearly  represent  the  earlier  processes  of 
development  in  the  human  subject. 

Development  of  the  Cavities  and  Layers  of  the  Trunk  in  the 

Chick 

As  an  introduction  to  a  description  of  the  development  of  special 
organs  in  the  human  subject  and  in  mammals,  it  will  be  found  useful  to 
study  the  first  stages  of  development  in  the  chick,  which  will  give  an 
idea  of  the  arrangement  of  the  different  blastodermic  layers  and  the  way 
in  which  they  are  developed  into  the  different  parts  of  the  trunk,  with 
the  mode  of  formation  of  the  great  cavities.     The  figures  by  which  this 

8i6 


DEVELOPMENT    OF   THE    OVUM 


817 


description  is  illustrated  in  the  text  are  those  of  Briicke,  which  were 
photographed  on  wood  from  drawings  made  by  Seboth.  The  Plates 
in  the  atlas  are  photographic  representations  in  color,  of  stained  sections. 
Figure  228  shows  an  early  stage  of  development  of  the  chick,  in  a 
transverse  section  near  the  caudal  extremity.  In  this  figure,  the  upper 
layer  of  dark  cells  {B,  B)  represents  the  epiblast.  The  lower  layer  of 
dark  cells  {D,  D)  represents  the  hypoblast.  The  middle  layer  of  lighter 
cells  is  the  mesoblast,  which,  toward  the  periphery,  is  split  into  two 


Fig.  228.  —  Early  stage  of  development  of  the  chick  —  about  twetity-four  hours  (Seboth  and  Briicke). 

layers.  This  figure  represents  a  transverse  section.  At  A,  is  a  trans- 
verse section  of  the  groove  that  afterward  is  developed  into  the  neural 
canal.  Beneath  this  groove  is  a  section  of  a  rounded  cord  {E),  the 
notochord.  The  openings  {G,  G)  represent  the  situation  of  the  two 
aortas.  The  other  cavities  are  as  yet  indistinct  in  this  figure  (see 
Plate  XV,  Fig.  3). 

Figure  229  shows  the  structures  in  a  transverse  section  near  the  head. 
The  dorsal,  or  vertebral  plates,  which  bound  the  furrow  (A)  in  Fig. 
228,  are  closed  above,  and  include  {A)  the  neural  canal.  The  noto- 
chord {E)  is  separated  from  the  cells  surrounding  it  in  Fig.  228.     The 


Fig.  229. —  Tra?isverse  section  near  the  head  (Seboth  and  Briicke). 

epiblast  {B,  B)  and  the  hypoblast  {D,  D)  present  certain  curves  that 
follow  the  arrangement  of  the  cells  of  the  mesoblast.  By  the  sides 
of  the  boundaries  of  the  neural  canal,  are  two  distinct  masses  of  cells 
(C,  C),  which  are  the  primitive  somites.  Outside  of  these  masses  of 
cells,  are  two  smaller  collections  of  cells,  afterward  developed  into  the 
Wolffian  bodies.  Beneath  these  two  masses,  are  two  large  cavities 
{G,  G),  the  largest  cavities  shown  in  Fig.  229,  presenting  an  irregular 
form,  which  are  sections  of  the  two  primitive  aortas.  The  two  openings 
{H,  H)  afterward  become  the  celom,  or  body-cavity  (see  Plate  XV, 
Figs.  4  and  5). 


8l8  EMBRYOLOGY 

In  Fig.  230  the  parts  are  still  further  developed.  The  neural  canal 
is  represented  (A)  nearly  the  same  as  in  Fig.  229,  with  the  notochord 
(E)  just  beneath  it.  A  groove,  or  gutter  (D)  has  been  formed  in  front, 
which  is  the  groove  of  the  intestinal  canal,  which  remains  open  at  this 
time  and  is  lined  with  the  hypoblast.  Just  above  Z>  is  a  single  opening 
(G),  which  is  formed  by  the  union  of  the  two  openings  (G,  G)  in  Figs. 
228  and  229;  and  this  is  the  abdominal  aorta,  which  has  here  become 
single.  The  two  openings  (//,  H)  represent  a  section  of  the  body-cavity. 
The  outer  wall  of  this  cavity  is  the  outer  visceral  plate,  which  is  devel- 
oped into  the  muscular  walls  of  the  abdomen.  The  lower  and  inner 
wall  is  the  inner  visceral  plate,  which  forms  the  main  portion  of  the 
intestinal  wall.  The  outer  wall  is  the  outer  layer  of  the  mesoblast,  and 
the  inner  wall  is  the  inner  layer  of  the  same  membrane.  The  two 
round  openings  (1,1)  are  sections  of  the  Wolffian  ducts  (see  Plate  XV, 

Fig.  6). 

The  figures  just  described,  it  must  be  borne 
in  mind,  represent  transverse  sections  of  the 
body  of  the  chick,  made  through  the  middle 
portion  of  the  abdomen.  The  dorsal  parts,  it 
is  seen,  are  developed  first,  the  situation  of 
the  vertebral  column  being  marked  soon  after 
the  enclosure  of  the  neural  canal  by  the  verte- 
bral plates  ;  and  at  about  the  same  time,  the 
"Fig.  2^0.  — Later  stage  0/  de-  two  aortae  make  their  appearance,  with  the 
veiopme»toftAeckick(s^bo\h^nd  fij-gt  traccs  of   the  body-cavity  (celom).     The 

enclosure  of  the  neural  canal  takes  place 
from  before  backward,  beginning  at  the  cephalic  end.  The  canal  re- 
mains open  at  the  caudal  end  for  some  time  after  it  has  been  enclosed 
above,  as  is  shown  in  Figs.  228  and  229.  The  next  organs  in  the 
order  of  development,  after  the  vascular  system,  are  the  Wolffian  bodies. 
The  intestinal  canal  is  then  a  simple  groove,  and  the  embryo  is  open  in 
front.  In  the  further  processes  of  development,  the  visceral,  or 
abdominal  plates  advance  and  close  over  the  abdominal  cavity,  in 
the  same  way  as  the  medullary  plates  have  closed  over  the  neural 
canal.  Thus  there  is  formed  a  closed  tube,  the  intestine,  which  is  lined 
with  the  hypoblast,  the  walls  of  the  intestine  being  formed  of  the 
inner  layer  of  the  mesoblast.  This  brings  the  external  layer  of  the 
mesoblast  around  the  intestine,  to  form  the  muscular  walls  of  the  ab- 
domen, the  external  covering  being  the  epiblast.  At  this  time  the 
Wolffian  bodies  lie  next  the  spinal  column,  between  the  intestine  and 
the  abdominal  walls,  with  the  single  abdominal  aorta  situated  behind 
the  intestine. 


SKELETON,    MUSCULAR    SYSTEM    AND    SKIN 


;i9 


Development  of  the  Skeleton,  Muscular  System  and    Skin 

Notochord.  —  One  of  the  earliest  structures  observed  in  the  develop- 
ing embryo  is  the  chorda  dorsalis,  or  notochord.  This  is  situated  be- 
neath the  neural  canal  and  extends  the  entire  length  of  the  body.  It  is 
formed  of  a  cord  of  simple  cells  and  marks  the  situation  of  the  ver- 
tebral column,  though  it  is  not  itself  developed  into  the  vertebrae, 
which  grow  around  it  and  encroach 
on  its  substance  until  it  finally  dis- 
appears. In  many  mammals,  the 
notochord  presents  a  slight  en- 
largement at  the  cephalic  extrem- 
ity, which  extends  to  the  auditory 
vesicles  ;  and  it  is  somewhat  dimin- 
ished in  size  at  the  caudal  ex- 
tremity. By  the  sides  of  this  cord 
are  masses  of  cells  (mesoblastic 
somites),  which  unite  in  front  of 
the  neural  canal  and  were  formerly 
thought  to  be  developed  into  the 
vertebrae. 1  These  are  the  so-called 
protovertebrae  (or  somites)  and  are 
shown  in  Fig.  233  {C,m  A  and  B). 
Twelve  pairs  of  somites  are  shown 
in  Fig.  233,  C.  In  the  chick  two 
pairs  are  first  formed  in  the  upper 
cervical  region  on  the  second  day. 
They  rapidly  increase  in  number 
from  above  downward,  until  at  the 
fourth  day  there  are  twenty-one 
or  twenty-two  pairs.  They  are  not 
formed  in  the  region  of  the  head 
or  at  the  lowest  part  of  the  verte- 
bral column.  The  vertebrae,  as  they  are  developed,  are  formed  of 
temporary  cartilaginous  structure,  gradually  extending  around  the  noto- 
chord, which  then  occupies  the  axis  of  the  spinal  column.     These  carti- 


Fig.  231. —  The  first  six  cervical  vertebrcB  of  the 
embryo  of  a  rabbit  (Robin). 

a,  (5,  cephalic  portion  of  the  notochord,  exposed 
by  the  removal  of  the  cartilage ;  b,  portion  of 
the  notochord  slightly  enlarged,  which,  in  this 
embryo,  was  situated  between  the  atlas  and 
the  occipital  bone  ;  c,  odontoid  process  ;  d,  base 
of  the  odontoid  process ;  e,  inferior,  or  second 
part  of  the  body  of  the  axis ;  f  k,  enlarge- 
ments of  the  notochord,  between  the  vertebrje; 
£■,  cartilage  of  the  lateral  portion  of  the  atlas; 
h,  lateral  portion  of  the  axis ;  i,  i,  transverse 
apophyses  of  vertebrse. 


^  The  mesoblastic  somites  (protovertebrs)  are  sometimes  called  muscle-plates,  or  myotomes. 
It  is  thought  that  cells  from  their  inner  walls  are  concerned  in  the  development  of  the  vertebrae 
and  that  the  other  cells  are  developed,  some  into  muscular  structure  and  some  into  the  true 
skin  ;  but  their  destination  is  somewhat  obscure.  The  outer  cells  —  developed  into  cutis  —  are 
called  the  skin-plates,  or  dermatomes. 


820  EMBRYOLOGY 

lages  are  not  divided  at  the  lines  of  separation  of  the  somites,  but  the 
somites  fuse  together  and  the  cartilages  which  are  to  be  developed  into 
the  bodies  of  the  vertebras  are  so  divided  off  that  one  cartilage  occupies 
the  place  of  the  adjacent  halves  of  two  somites.  Between  the  bodies 
of  the  vertebrae,  the  notochord  presents  regular  enlargements  sur- 
rounded by  a  delicate  membrane.  As  ossification  of  the  spinal  column 
advances,  that  portion  of  the  notochord  which  is  surrounded  by  the 
bodies  of  the  vertebrae  disappears,  leaving  the  enlargements  between 
the  vertebrae  distinct.  These  enlargements,  w^hich  are  not  permanent, 
are  gradually  invaded  by  fibrous  tissue,  their  gelatinous  contents  disap- 
pear, and  the  intervertebral  disks,  composed  of  fibro-cartilaginous  struc- 
ture, remain.      These  disks   are  permanent  between  the  cervical,  the 

dorsal  and  the  lumbar  vertebrae ;  but  they 
eventually  disappear  from  between  the  differ- 
ent parts  of  the  sacrum  and  coccyx,  as  these  are 
consolidated,  this  occurring,  in  the  human  sub- 
ject, between  the  ninth  and  the  twelfth  years. 

Vertebral  Column,  etc.  —  In  Figs.  229  and 

230  (C,  C),  are  seen  the  two  masses  of  cells 

(somites)  situated  by  the  sides  of  the  neural 

canal.     Cells   of   the    inner   borders  of   these 

„  ,  bodies  extend    around   and    encroach    on    the 

Fig.  232.  —  Human  embryo, 

about  07te  month  old, shoxuuig  the     notochord  and  form  the  bodies  of  the  verte- 

larpe  size  of  the  head  and  upper        ,  ^^i  i  ^        i  ^l  i  i 

paftsofthebodyjhetwtstedform  ^ras.  They  also  extend  over  the  neural  canal, 
of  the  spinal  column,  the  rudi-      closiug  abovc,  and  their   proccsscs  are  called 

■mentary  condition  of  the  upper  ,  _,  , 

and  lower  extremities  and  the  the  medullarv,  or  dorsal  platcs.  Jbrom  the 
rudimentary  tail  at  the  end  of     gjjgg  ^f  ^|^g  bodics  of  the  Vertebrae,  the  various 

the  spinal  column  (Dalton). 

processes  of  these  bones  are  formed.  As  the 
spinal  column  is  developed,  its  lower  portion  presents  a  projection 
beyond  the  pelvis,  which  constitutes  a  temporary  caudal  appendage, 
curved  toward  the  abdomen  ;  but  this  no  longer  projects  after  the  bones 
of  the  pelvis  are  fully  developed.  At  the  same  time  the  entire  vertebral 
column  is  curved  toward  the  abdomen,  and  it  is  twisted  on  its  axis  from 
left  to  right,  so  that  the  anterior  face  of  the  pelvis  presents  a  right  angle 
to  the  upper  part  of  the  body  ;  but  as  the  inferior  extremities  and  the 
pelvis  are  developed,  the  spine  becomes  straight.  The  vertebrae  make 
their  appearance  first  in  the  middle  of  the  dorsal  region,  from  which 
point  they  rapidly  extend  upward  and  downward  until  the  spinal  column 
is  complete. 

At  the  base  of  the  skull,  on  either  side  of  the  superior  prolongation 
of  the  notochord,  are  two  cartilaginous  processes  that  are  developed 
into  the  so-called  cranial  vertebras.      In  this  cartilaginous  mass,  three 


k 


SKELETON,  MUSCULAR   SYSTEM   AND    SKIN  82 1 

ossific  points  appear,  one  behind  another.  The  posterior  point  of 
ossification  is  for  the  basilar  portion  of  the  occipital  bone,  which  is 
developed  in  the  same  way  as  one  of  the  vertebrae  ;  the  middle  point  is 
for  the  posterior  portion  of  the  sphenoid  ;  and  the  anterior  point  is  for 
the  anterior  portion  of  the  sphenoid.  The  frontal  bone,  the  parietal 
bone,  the  temporal  bone  and  a  portion  of  the  occipital  bone  are  devel- 
oped from  the  connective  tissue  without  the  intervention  of  preexisting 
cartilaginous  structure.  At  the  time  when  the  vertebrae  are  developed, 
with  their  laminae  and  their  spinous  and  transverse  processes,  the  ribs 
extend  over  the  thorax,  and  the  clavicle,  scapula  and  sternum  make 
their  appearance. 

At  about  the  beginning  of  the  second  month,  four  papillary  promi- 
nences, the  first  traces  of  arms  and  legs,  appear  on  the  body  of  the 
embryo.  These  progressively  increase  in  length,  the  arms  appearing 
near  the  middle  of  the  embryo,  and  the  legs,  at  the  lower  portion. 
Each  extremity  is  divided  into  three  portions,  the  arm,  forearm,  and 
hand,  for  the  upper  extremities,  and  the  thigh,  leg  and  foot,  for  the 
lower  extremities.  At  the  end  of  each  extremity,  there  are,  finally, 
divisions  into  the  fingers  and  toes,  with  the  various  cartilages  and  bones 
of  all  these  parts,  and  their  articulations. 

Early  in  intra-uterine  life  the  skeleton  begins  to  ossify  from  bony 
points  in  the  cartilaginous  structure.  The  first  points  appear  at  nearly 
the  same  timo — about  the  beginning  of  the  second  month  —  in  the 
clavicle  and  the  upper  and  the  lower  jaw.  Similar  ossific  points,  which 
gradually  extend,  are  seen  also  in  the  other  parts,  the  head,  ribs,  pelvis, 
scapula,  metacarpus  and  metatarsus,  and  the  phalanges  of  the  fingers 
and  toes.  At  birth  the  carpus  is  entirely  cartilaginous,  and  it  does  not 
begin  to  ossify  until  the  second  year.  The  same  is  true  of  the  tarsus, 
except  the  calcaneum  and  astragalus,  which  ossify  just  before  birth. 
The  pisiform  bone  of  the  carpus  is  the  last  to  take  on  osseous  transfor- 
mation, this  occurring  between  the  twelfth  and  the  fifteenth  years.  As 
ossification  progresses,  the  deposits  in  the  various  ossific  points  grad- 
ually extend  until  they  reach  the  joints,  which  remain  incrusted  with 
the  permanent  articular  cartilage  (see  Plate  X,  Fig.  3). 

While  the  skeleton  is  thus  developing,  the  muscles  are  formed  from 
the  outer  layer  of  the  mesoblast,  and  the  visceral  plates  close  over  the 
thorax  and  abdomen  in  front,  leaving  an  opening  for  the  umbilical  cord. 
The  various  tissues  of  the  external  parts,  particularly  the  muscles,  begin 
to  be  distinct  at  the  end  of  the  second  month.  The  deep  layers  of  the 
dorsal  muscles  are  the  first  to  be  distinguished  ;  then  successively,  the 
long  muscles  of  the  neck,  the  anterior  straight  muscles  of  the  head, 
the  straight  and  transverse  muscles  of  the  abdomen,  the  muscles  of  the 


822  EMBRYOLOGY 

extremities,  the  superficial  muscles  of  the  back,  the  oblique  muscles  of 
the  abdomen  and  the  muscles  of  the  face. 

The  skin  appears  at  about  the  beginning  of  the  second  month,  when 
it  is  thin  and  transparent.  At  the  end  of  the  second  month  the  epi- 
dermis may  be  distinguished.  The  sebaceous  follicles  are  developed  at 
the  third  month  ;  and  at  about  the  fifth  month  the  surface  is  covered 
with  their  secretion  mixed  with  desquamated  epithelium.  This  cheesy 
substance  is  the  vernix  caseosa.  At  the  third  month  the  nails  make 
their  appearance,  and  the  hairs  begin  to  grow  at  about  the  fifth  month. 
The  sudoriparous  glands  first  appear  at  about  the  fifth  month,  by  the 
formation  of  flask-like  processes  of  the  true  skin,  which  are  gradually 
elongated  and  convoluted  until  they  are  fully  developed  only  a  short 
time  before  birth. 


Development  of  the  Nervous  System 

It  has  been  seen,  in  studying  the  development  of  the  spinal  column, 
how  the  dorsal,  or  medullary  plates  close  over  the  groove  for  the  neural 
canal.  In  the  interior  of  this  canal,  the  cerebro-spinal  axis  is  devel- 
oped, by  cells  which  gradually  encroach  on  its  calibre,  until  there 
remains  only  the  small  central  canal  of  the  spinal  cord,  communicating 
with  the  ventricles  of  the  brain.  As  the  nervous  tissue  is  developed  in 
the  interior  of  the  neural  canal,  there  is  a  separation  of  the  histological 
elements  at  the  surface  to  form  the  membranes.  The  dura  mater  and 
the  pia  mater  are  formed  first,  appearing  at  about  the  end  of  the  second 
month  ;  while  the  arachnoid  is  not  distinct  until  the  fifth  month.  The 
nerves  are  not  produced  as  prolongations  from  the  cord  into  the  various 
tissues  nor  do  they  extend  from  the  tissues  to  the  cord ;  but  they  are 
developed  in  each  tissue  by  a  separation  of  histological  elements  from 
the  cells  of  which  the  parts  are  originally  constituted.  The  nerves  of 
the  sympathetic  system  are  developed  in  the  same  way. 

The  mode  of  development  of  the  spinal  cord  is  thus  sufficiently 
simple ;  but  with  the  growth  of  the  embryo,  dilatations  are  observed  at 
the  superior  and  the  inferior  extremities  of  the  neural  canal.  The  cord 
is  nearly  uniform  in  size  in  the  dorsal  region,  marked  only  by  the 
regular  enlargements  at  the  sites  of  origin  of  the  spinal  nerves ;  but 
there  soon  appears  an  ovoid  dilatation  below,  which  forms  the  lumbar 
enlargement,  from  which  the  nerves  are  given  off  to  the  inferior  ex- 
tremities, and  the  brachial  enlargement  above,  where  the  nerves  of  the 
superior  extremities  take  their  origin.  At  the  same  time  there  is  a 
more  marked  dilatation  of  the  canal  at  its  cephalic  extremity.  Here 
a  single  enlargement  appears,  which  is  soon  divided  into  three  vesicles. 


DEVELOPMENT   OF    THE    NERVOUS    SYSTEM 


823 


called  the  anterior,  middle  and  posterior  cerebral  vesicles.  These  be- 
come more  and  more  distinct  as  development  advances.  The  formation 
of  these  parts  is  shown  in  Fig.  233.  This  figure,  in  C,  shows  the  pro- 
jections, on  either  side,  of  the  vesicles  that  are  eventually  developed 
{o,  Fig.  233,  C)  into  the  nervous  portions  of  the  organ  of  vision. 

The  three  cerebral  vesicles  now  undergo  further  changes.  The 
superior,  or  the  first  primitive  vesicle,  is  soon  divided  into  two  secondary 
vesicles,  the  anterior  of  which  becomes  the  cerebral  hemispheres,  and 
the  posterior,  the  diencephalon,  including  the  optic  thalami  and  the 
third  ventricle,  which  are  eventually  covered  by  the  greater  relative 
development    of    the    hemi-  a  b  c 

spheres.  The  middle,  or  sec- 
ond primitive  vesicle,  does 
not  undergo  division  and  is 
developed  into  the  tubercula 
quadrigemina.  The  poste- 
rior, or  third  primitive  vesicle, 
is  divided  into  two  secondary 
vesicles,  the  anterior  of  which 
becomes  the  cerebellum,  and 
the  posterior,  which  is  cov- 
ered by  the  anterior,  the  bulb 
and  the  pons  Varolii.  While 
this  division  of  the  primitive 
cerebral  vesicles  is  going 
on,  the  entire  chain  of  en- 
cephalic ganglia  becomes 
curved  from  behind  forward, 
forming  three  prominent 
angles.  The  first  of  these  angles  or  prominences  {c,  Fig.  234,  A,  B,  C), 
counting  from  before  backward,  is  formed  by  a  projection  of  the  tuber- 
cu!a  quadrigemina,  which  at  this  time  constitute  the  most  projecting 
portion  of  the  encephalic  mass;  the  second  prominence  {c,  Fig.  234), 
situated  behind  the  tubercula  quadrigemina,  is  formed  by  the  projection 
of  the  cerebellum  ;  the  third  {d,  Fig.  234,  A,  B,  C)  is  the  bend  of  the 
superior  portion  of  the  spinal  cord.  These  projections  and  the  early 
formation  of  certain  parts  of  the  encephalon  in  the  human  subject  are 
illustrated  in' Fig.  234  (see  also  Plate  XVI,  Figs.  5  and  6). 

The  cerebrum  is  developed  from  the  anterior  division  of  the  first 
primitive  cerebral  vesicle.  The  development  of  this  part  is  more  rapid 
in  its  lateral  portions  than  in  the  median  line,  which  divides  the  cerebrum 
imperfectly  into  two  lateral  halves,  forming  in  this  way  the  great  longi- 


ng. 233.  —  Development  of  the  -nervous  syste?n  of  the  chick 
(Wagner). 

A,  the  two  primitive  halves  of  the  nervous  system, 
twenty-four  hours  after  incubation  ;  B,  the  same,  thirty-six 
hours  after ;  C,  the  same,  at  a  more  advanced  stage.  C,  the 
somites  ;  b,  posterior  dilatation  (the  lumbar  enlargement)  ; 
d,  anterior  dilatation  of  the  neural  canal ;  i,  2,  3,  anterior, 
middle  and  inferior  cerebral  vesicles ;  a,  slight  flattening 
of  the  anterior  cerebral  vesicle ;  0,  formation  of  the  ocular 
vesicles. 


824 


EMBRYOLOGY 


tudinal  fissure.  At  the  same  time,  by  the  rapid  development  of  the 
posterior  portion,  it  extends  over  the  optic  thalami,  the  corpora  quad- 
rigemina  and  the  cerebellum.  Until  the  end  of  the  fourth  month,  the 
hemispheres  are  smooth  on  their  surface  ;  but  they  then  begin  to  present 
large  depressions,  following  folds  of  the  pia  mater,  which  are  the  first 
convolutions,  these  increasing  rapidly  in  number  and  complexity, 
especially  after  the  seventh  month.  The  septum  lucidum  is  then  formed 
by  an  elevation  of  nervous  matter  from  the  base,  which  divides  the  lower 
portion  of  the  space  left  between  the  hemispheres  as  they  ascend,  and 
forms  the  two  lateral  ventricles.     At  the  base  of  these  are  developed 

the  corpora  striata.  The 
septum  lucidum  is  formed 
of  two  laminae,  with  a  small 
space  between  them,  which 
is  the  cavity  of  the  fifth 
ventricle.  The  posterior  di- 
vision of  this  first  primitive 
vesicle  forms  the  optic  thai- 
ami.  These  become  sepa- 
rated in  front  into  two 
lateral  halves,  but  they 
remain  connected  together 
at  their  posterior  portion, 
which  becomes  the  posterior 
commissure.  The  central 
canal  of  the  cord  is  pro- 
longed upward  between  the 
optic  thalami  and  forms  the 
third  ventricle,  which  is  cov- 
ered by  the  hemispheres. 
The  second,  or  middle 
cerebral  vesicle,  becomes  filled  with  medullary  substance,  extends  ftp- 
ward  and  forms  the  peduncles  of  the  cerebrum,  the  upper  portion  being 
divided  to  form  the  tubercula  quadrigemina. 

The  anterior  portion  of  the  third  primitive  vesicle  is  developed  into 
the  cerebellum,  the  convolutions  of  which  appear  at  about  the  fifth 
month.  Its  posterior  portion  forms  the  bulb,  in  the  substance  of  which 
is  the  fourth  ventricle,  communicating  with  the  third  ventricle  by  the 
aqueduct  of  Sylvius,  which  is  left  in  the  development  of  the  middle 
vesicle.  At  about  the  fourth  month  there  is  a  deposition  of  nervous 
matter  in  front  and  above,  forming  the  pons  Varolii. 

In  Fig.  234  {C,  0),  it  is  seen  that  the  vesicles  for  the  organs  of  vision 


Fig.  234.  —  Development  of  the  spinal  cord  and  brain  of 
the  human  subject  (Longet,  after  Tiedemann). 

A,  brain  and  spinal  cord  of  an  embryo  of  seven  weeks, 
lateral  view. 

B,  the  same,  from  an  embryo  further  advanced  in  develop- 
ment; b,  spinal  cord;  d,  enlargement  of  the  spinal  cord, 
with  its  anterior  curvature ;  c,  cerebellum  ;  c,  tubercula 
quadrigemina;  f,  optic  thalamus;  g,  cerebral  hemi- 
spheres. 

C,  brain  and  spinal  cord  of  an  embryo  of  eleven  weeks; 
b,  spinal  cord;  d,  enlargement  of  the  spinal  cord,  with 
its  anterior  curvature  ;  c,  cerebellum  ;  e,  tubercula  quad- 
rigemina; g,  cerebral  hemispheres;  <?,  optic  nerve  of  the 
left  side. 

C ,  the  same  parts  in  a  vertical  section  in  the  median  line, 
from  before  backward;  b,  membrane  of  the  spinal  cord, 
turned  backward;  d,  second  curvature  of  the  upper 
portion  of  the  spinal  cord,  which  has  become  thickened 
and  constitutes  the  peduncles  of  the  cerebrum  ;  e,  tuber- 
cula quadrigemina ;  f,  optic  thalami,  covered  by  the 
hemispheres. 


DEVELOPMENT    OF   THE   NERVOUS    SYSTEM  825 

appear  very  early,  as  lateral  offshoots  of  the  anterior  cerebral  vesicle. 
These  gradually  increase  in  size  and  advance  anteriorly  as  development 
of  the  other  parts  progresses.  The  eyes  are  situated  at  first  at  the  sides 
of  the  head,  gradually  approaching  the  anterior  portion.  At  the  ex- 
tremity of  each  of  these  lateral  prolongations,  a  rounded  mass  appears, 
which  becomes  the  globe  of  the  eye.  The  superficial  portions  of  the 
globe  are  developed  into  the  sclerotic  and  the  cornea,  which  seem  to 
be  formed  of  a  process  from  the  dura  mater.  The  pedicle  attached  to 
the  globe  becomes  the  optic  nerve.  The  iris  is  developed  at  about 
the  seventh  week  and  is  at  first  a  simple  membrane  without  a  central 
opening.  As  the  pupil  appears,  it  is  closed  by  a  vascular  membrane  — 
which  probably  belongs  to  the  capsule  of  the  crystalline  lens  —  called 
the  pupillary  membrane.  This  membrane  gradually  disappears  by  an 
atrophy  extending  from  the  centre  to  the  periphery.  It  attains  its 
maximum  of  development  at  the  sixth  month  and  disappears  at  the 
seventh  month.  The  vitreous  humor  is  formed  of  the  liquid  contents 
of  the  optic  vesicle.  The  crystalline  lens  is  regarded  as  a  product  of 
the  epiblast.  At  the  tenth  week  there  is  the  beginning  of  the  formation 
of  the  eyelids.  These  meet  at  about  the  fourth  month  and  adhere  to- 
gether by  their  edges.  In  many  mammals  the  eyelids  remain  closed 
for  a  few  days  after  birth  ;  but  they  become  separated  in  the  human 
subject  in  the  later  periods  of  foetal  life. 

It  is  probable  that  the  vesicle  which  is  developed  into  the  internal 
ear  is  formed  independently  ;  and  cases  have  been  observed  in  which 
there  was  congenital  absence  of  the  auditory  nerves,  the  parts  of  the  in- 
ternal ear  being  perfect.  Soon  after  the  formation  of  the  auditory  vesi- 
cle, however,  it  communicates  with  the  third  primitive  cerebral  vesicle, 
the  filament  of  communication  being  developed  into  the  auditory  nerve. 

The  auditory  vesicle,  which  appears  later  than  the  organ  of  vision, 
is  eventually  developed  into  the  vestibule.  The  next  formations  are 
the  arches,  or  diverticula,  which  constitute  the  semicircular  canals. 
The  membranous  labyrinth  appears  long  before  the  osseous  labyrinth  ; 
and  it  has  been  found  perfectly  developed  at  three  months.  The  bones 
of  the  middle  ear,  which  have  no  connection,  in  their  development,  with 
the  nervous  system,  but  which  it  is  convenient  to  mention  here,  are 
remarkable  for  their  early  appearance.  They  appear  at  the  beginning 
of  the  third  month  and  are  as  large  in  the  foetus  at  term  as  in  the  adult. 
A  remarkable  anatomical  point  in  relation  to  these  structures  is  the 
existence  of  a  cartilage  attached  to  the  malleus  on  either  side  and  ex- 
tending from  this  bone  along  the  inner  surface  of  the  lower  jaw,  the 
two  cartilages  meeting  and  uniting  in  the  median  line  to  form  a  single 
cord.     "  This  cartilage  now  ossifies,  although,  in  the  commencement,  it 


826  EMBRYOLOGY 

forms  most  of  the  mass  of  the  bone  ;  it  disappears  at  the  eighth  month  " 
(Meckel).     This  structure  is  known  as  the  cartilage  of  Meckel. 

There  are  no  special  points  for  description  in  the  development  of  the 
olfactory  lobes,  which  is  very  simple.  These  are  offshoots  from  the 
first  cerebral  vesicle,  appearing  at  the  inferior  and  anterior  part  of 
the  cerebral  hemispheres,  a  little  later  than  the  parts  connected  with 
vision  and  audition.  The  vesicles  themselves  become  filled  with  gan- 
glionic matter  and  constitute  the  olfactory  bulbs,  their  pedicles  being  the 
so-called  olfactory  nerves,  or  olfactory  commissures. 

So  far  as  the  action  of  the  nervous  system  of  the  foetus  is  concerned, 
it  is  probable  that  it  is  restricted  mainly  to  reflex  phenomena  depending 
on  the  spinal  cord,  and  that  perception  and  volition  hardly  exist.  It 
is  probable  that  many  reflex  movements  take  place  in  utero.  When 
a  fcEtus  is  removed  from  the  uterus  of  an  animal,  even  during  the  early 
months  of  pregnancy,  movements  of  respiration  occur;  and  it  is  well 
known  that  efforts  of  respiration  sometimes  take  place  within  the  uterus. 
These  are  due  to  the  want  of  oxygen-carrying  blood  in  the  bulb  when 
the  placental  circulation  is  interrupted. 

Development  of  the  Digestive  System 

The  intestinal  canal  is  the  first  formation  of  the  digestive  system. 
This  is  at  first  open  in  the  greatest  part  of  its  extent,  presenting,  at 
either  extremity  of  the  longitudinal  gutter  in  front  of  the  spinal  column, 
a  rounded  blind  extremity,  which  is  closed  over  in  front  for  a  short 
distance.  The  closure  of  the  visceral  plate  then  extends  laterally  and 
from  the  two  extremities  of  the  intestine,  until  only  the  opening  remains 
for  the  passage  of  the  umbilical  cord  and  the  pedicle  of  the  umbilical 
vesicle.  There  is  at  first  an  open  communication  between  the  lower 
part  of  the  intestinal  tube  and  the  allantois,  which  forms  the  canal 
known  as  the  urachus ;  but  that  portion  of  this  communication  which 
remains  enclosed  in  the  abdominal  cavity  becomes  separated  from  the 
urachus,  is  dilated  and  eventually  forms  the  urinary  bladder.  When 
the  bladder  is  shut  off,  it  communicates  with  the  lower  portion  of  the 
intestine,  which  is  called  the  cloaca ;  but  it  finally  loses  this  connection 
and  presents  a  special  opening,  the  urethra. 

As  development  advances,  the  intestine  grows  rapidly  in  length  and 
becomes  convoluted.  It  is  held  loosely  to  the  spinal  column  by  the 
mesentery,  a  fold  of  the  peritoneum,  this  membrane  being  reflected 
along  the  walls  of  the  abdominal  cavity.  In  the  early  stages  of  develop- 
ment, a  portion  of  the  intestine  protrudes  at  the  umbilicus,  where  the 


DEVELOPMENT    OF    THE   DIGESTIVE    SYSTEM  827 

first  intestinal  convolution  appears ;  and  sometimes  there  is  a  congenital 
hernia  of  this  kind  at  birth,  which  usually  disappears  under  the  influence 
of  gentle  and  continued  pressure.  An  illustration  of  this  is  given  in 
Fig.  235.  This  protrusion,  in  the  normal  process  of  development,  is 
gradually  returned  into  the  abdomen,  as  the  cavity  of  the  pedicle  of  the 
umbilical  vesicle  is  obHterated,  at  about  the  tenth  week. 

At  the  upper  part  of  the  abdominal  cavity,  the  ahmentary  canal 
presents  two  lateral  projections,,  or  pouches.  The  one  on  the  left  side, 
as  it  increases  in  size,  becomes  the  greater  pouch  of  the  stomach,  and 
the  one  on  the  right  side,  the  lesser  pouch  (see  Plate  XVI,  Fig.  3). 

At  a  short  distance  below  the  attachment  of  the  pedicle  of  the 
umbilical  vesicle  to  the  intestine,  there  appears  a  rounded  diverticulum, 
which  is  eventually  developed  into  the  caecum. 
The  cascum  gradually  recedes  from  the  neighbor- 
hood of  the  umbilicus,  which  is  its  original  situa- 
tion, and  finally  becomes  fixed,  by  a  shortening 
of  the  mesentery,  in  the  right  iliac  region.  As 
the  cascum  is  developed  it  presents  a  conical 
appendage,  which  is  at  first  as  large  as  the  small 
intestine  and  is  relatively  longer  than  in  the 
adult.  During  the  fourth  week  this  appendage 
becomes  relatively  smaller  and  more  or  less 
twisted,  forming  the  appendix  vermiformis.     At       ^Jg-    235.  —  FcBtai  pig, 

.  ,  ,       ,  .  ,  1  -T  showing    a    loop    of   intestine 

the  second  month  the  caecum  is  at  the  umbihcus,  forming  an  umbilical  hemia 

and  the  large  intestine  extends  in  a  straight  line   (Daiton). 

toward  the  anus  ;  at  the  third  month  it  is  situated       ^^°'^  *^«  convexity  of  the 

.  .      loop,  a  thin   filament    is   seen 

at  about  the  middle  of  the  abdomen ;  and  it  passing  to  the  umbilical  vesi- 
gradually  descends,  until  it  reaches  the  right  iliac  ^'^'  '"^''^'V.'f  ^/'^  flattened 

,  into   a  leaf-like  form. 

region  at  about  the  seventh  month.      Thus  at  the 

second  month,  there  is  only  a  descending  colon  ;  the  transverse  colon  is 
formed  at  the  third  month ;  and  the  ascending  colon,  at  the  fifth  month. 
The  ileo-caecal  valve  appears  at  the  third  month ;  the  rectum,  at  the 
fourth  month  ;  and  the  sigmoid  flexure  of  the  colon,  at  the  fifth  month. 
During  this  time  the  large  intestine  increases  more  rapidly  in  its  diame- 
ter than  the  small  intestine,  while  the  latter  develops  more  rapidly  in 
its  length. 

In  the  early  stages  of  development  the  internal  surface  of  the  intes- 
tines is  smooth  ;  but  villi  appear  on  its  mucous  membrane  during  the 
latter  half  of  intra-uterine  existence.  These  are  found  at  first  both  in  the 
large  and  the  small  intestine.  At  the  fourth  month  they  become  shorter 
and  less  abundant  in  the  large  intestine,  and  they  are  lost  at  about  the 
eighth  month,  when  the  projections  which  bound  the   sacculi   of  this 


828  EMBRYOLOGY 

portion  of  the  intestinal  canal  make  their  appearance.  The  valvulae 
conniventes  appear  in  the  form  of  slightly  elevated  transverse  folds  in 
the  upper  portion  of  the  small  intestine.  The  vilU  of  the  small  intes- 
tine are  permanent. 

The  mesentery  is  first  formed  of  two  perpendicular  folds  attached  to 
the  sides  of  the  spinal  column.  As  the  intestine  undergoes  develop- 
ment, a  portion  of  the  peritoneal  membrane  extends  in  a  quadruple  fold 
from  the  stomach  to  the  colon,  to  form  the  great  omentum,  which  covers 
the  small  intestine  in  front. 

As  the  head  undergoes  development  a  large  cavity  appears,  which 
finally  is  bounded  by  the  arches  that  are  destined  to  form  the  different 
parts  of  the  face.  This  is  the  pharynx.  It  is  entirely  independent,  in 
its  formation,  of  the  intestinal  canal,  the  latter  terminating  in  a  blind 
extremity  at  the  stomach  ;  and  between  the  pharynx  and  the  stomach, 
there  is  at  first  no  channel  of  communication.  The  anterior  portion  of 
the  pharynx  presents,  during  the  sixth  week,  a  large  opening,  which  is 
afterward  partially  closed  in  the  formation  of  the  face.  The  rest  of  the 
cavity  remains  closed  until  a  communication  is  effected  with  the 
oesophagus.  The  oesophagus  appears  in  the  form  of  a  tube,  which 
finally  opens  into  the  pharynx  above  and  into  the  stomach  below.  At 
this  time  there  is  really  no  thoracic  cavity,  the  upper  part  of  the 
stomach  is  very  near  the  pharynx,  the  oesophagus  is  short,  the  rudi- 
mentary lungs  appear  by  its  sides  and  the  heart  lies  just  in  front.  As 
the  thorax  is  developed,  however,  the  oesophagus  becomes  longer,  the 
lungs  increase  in  size,  and  finally  the  diaphragm  shuts  off  its  cavity 
from  the  cavity  of  the  abdomen.  The  growth  of  the  diaphragm  is  from 
its  periphery  to  the  central  portion,  which  latter  gives  passage  to  the 
vessels  and  the  oesophagus. 

The  development  of  the  anus  is  very  simple.  At  first  the  intestine 
terminates  below  in  a  blind  extremity ;  but  at  about  the  seventh  week 
a  longitudinal  slit  appears  below  the  external  organs  of  generation,  by 
which  the  rectum  opens.  This  is  the  anus.  The  opening  of  the  anus 
appears  about  a  week  after  the  opening  of  the  mouth,  at  or  about  the 
seventh  week. 

The  rudiments  of  the  liver  appear  very  early,  and,  indeed,  at  the 
end  of  the  first  month  this  organ  has  attained  a  large  size.  Two  pro- 
jections, or  buds,  appear  on  either  side  of  the  intestine,  which  form  the 
two  principal  lobes  of  the  liver.  This  organ  is  at  first  symmetrical,  the 
two  lobes  being  of  nearly  the  same  size,  with  a  median  fissure.  One  of 
these  prolongations  from  the  intestine  becomes  perforated  and  forms 
the  excretory  duct,  of  which  the  gall-bladder,  with  its  duct,  is  an  append- 
age.    During  the  early  part  of  foetal  life  the  liver  occupies  the  greatest 


1 


DEVELOPMENT   OF   THE    RESPIRATORY    SYSTEM  829 

part  of  abdominal  cavity.  Its  weight,  in  proportion  to  the  weight  of 
the  body  at  different  ages,  is  as  follows  :  At  the  end  of  the  first  month, 
I  to  3;  at  term,  i  to  18;  in  the  adult,  i  to  36.  Its  structure  is  soft  dur- 
ing the  first  months.  As  development  advances  and  as  the  relative 
size  of  the  liver  diminishes,  its  tissue  becomes  more  solid. 

The  pancreas  appears  at  the  left  side  of  the  duodenum,  by  the 
formation  of  two  ducts  leading  from  the  intestine,  which  branch  and 
develop  glandular  structure  at  their  extremities.  The  spleen  is  devel- 
oped, about  the  same  time,  at  the  greater  curvature  of  the  stomach  and 
becomes  distinct  during  the  second  month. 

The  figures  in  Plate  XVI  show  very  clearly  several  of  the  important 
stages  in  the  development  of  the  nervous  system,  the  vertebrae,  the  ali- 
mentary canal,  liver  and  pancreas. 

Development  of   the  Respiratory  System 

On  the  anterior  surface  of  the  membranous  tube  which  becomes  the 
oesophagus,  an  elevation  appears,  which  soon  presents  an  opening  into 
the  oesophagus,  the  projection 
forming  at  this  time  a  single, 
hollow  cul-de-sac.  This  opening 
becomes  the  rima  glottidis,  and 
the  single  tube  with  which  it  is 
connected  is  developed  into  the 
trachea.  At  the  lower  extrem- 
ity of  this  tube,  a  bifurcation  ap- 
pears, terminating  first  in  one        _.        ^      „       ,.       .  ^,    ,       ,■  ,        -^ 

^            '                              ^  Fig.   230.  —  Formation    of  the  bronchial   raviijica- 

and    afterward    in    several  CjUs-  tions  and  of  the  pulmonary  cells.  — a,  B,  development 

7                     T-'i          1-T            i.     1  j_    1  of  the  lun-s^s,  after  Rathke ;    C.D,  histolos'ical  develop- 

de-sac.         The      bifurcated  tube  Lu  of  the  lungs,  after  J.  MulleriX.or.i^X.). 

constitutes,  after  the  lungs  are 

developed,  the  primitive  bronchia,  at  the  extremities  of  which  are  the 
branches  of  the  bronchial  tree.  As  the  bronchia  branch  and  subdivide, 
they  extend  downward  into  what  becomes  afterward  the  cavity  of  the 
thorax.  The  pulmonary  vesicles  are  developed  before  the  trachea. 
The  lungs  contain  no  air  during  intra-uterine  life  and  receive  but  a  small 
quantity  of  blood ;  but  at  birth  they  become  distended  with  air,  are  in- 
creased thereby  in  volume  and  receive  all  the  blood  from  the  right  ven- 
tricle. This  process  of  development  is  illustrated  in  Fig.  236.  The 
lungs  appear,  in  the  human  embryo,  during  the  sixth  week.  The  two 
portions  into  which  the  original  bud  is  bifurcated  constitute  the  true 
pulmonary  structure ;  and  the  formation  of  the  trachea  and  bronchial 
tubes  occurs  afterward  and  is  secondary  (see  Plate  XVI,  Figs,  i  and  2). 


830 


EMBRYOLOGY 


Development  of  the  Face 

The  anterior  portion  of  the  embryo  remains  open  in  front  long  after 

the  medullary  plates  have  met  at  the  back  and  enclosed  the  neural  canal. 

The  common  cavity  of  the  thorax  and  abdomen  is  closed  by  the  growth 

of  the  visceral  plates,  which  meet  in  front.     At  the  time  that  the  vis- 

^  _ — ,=™^^  ceral    plates    are    closing    over    the 

:^  thorax    and    abdomen,    four    distinct 

tongue-like    projections    appear,    one 

above  the  other,  by  the  sides  of  the 

-^         neck.     These  are    called  the  visceral 

\      arches,  and   the   slits  between  them 

]     are  called  the  visceral  clefts.      The 

ilfr  ,-^  J      first  three  arches,  enumerating  them 

loBft: '',r^-'  ,;._/         ^J'-      from    above    downward,    correspond, 

5Mi£:.  ::— .:    ^    jm^^      J         in  their  origin,  to  the  three  primitive 

-,—,--  ,  t^        cerebral  vesicles.      The  fourth  arch 

'**•'• ■Bffe :*  :>      5  corresponds  to  the  superior  cervical 

vertebrae.     Of  these  four  arches,  the 
ii-,u      ;■  .  S^  ^^^s^^^  first  is  the  most  important,  as  its  de- 

'*-^  ^^'-^''^'^  velopment,  in  connection  with  that  of 

94^E-  "^^        j\  the  frontal  process,   forms  the    face 

^«r. .  '^  and   the   malleus   and   incus    of   the 

Fig-  -izi-  — Mouth  of  a  human  embryo  of    middle  ear.      The  second  arch  forms 

t^enfy-five  to  twenty-e.ght  days,  x  15  (Coste).         ^^^   ^^^^^^  ^^^^^^  ^^    ^^^    j^^^.^  ^^^^^^ 
I,  median,  or  frontal  process,  the  inferior     ,,  ,  j    ,^1.         ^    1    -j    t  ,. 

portion  of  which  is  considerably  enlarged;    the  stapcs  and  the  Styloid  ligament. 
2,  ri.?ht  nostril;  3,  left  nostril;  4,4,  inferior    The   third  arch  forms  the  body  and 

maxillary    processes,    already    united    in    the  ^     ,        ,         .  ,  _,, 

median    line;    5,    5,    superior    maxillary  pro-  the  greater  COmua  of  the  hyOld.  The 

cesses,  which   have  become   quite  prominent  fourth    arch    fomiS    the    laryUX.  The 
and  have  descended  to  the  level  of  the  slope                                     _                                      -^ 

of  the  frontal  process;   6,  mouth;  7,  first  vis-  first    clcft,    situated    between    the  firSt 

ceral  arch ;   8.  second  visceral   arch;  9.  third  ^^^  ^j^^   SCCOnd   arch,  is   finally   cloScd 
visceral  arch ;    10,  eye ;   11,  ear.  '  •' 

in  front ;  but  an  opening  remains  by 
the  side,  which  forms,  externally,  the  external  auditory  meatus,  and  in- 
ternally, the  tympanic  cavity  and  the  Eustachian  tube.  The  other  clefts 
become  obliterated  as  the  arches  advance  in  their  development. 

From  the  above  sketch  it  is  seen  that  the  face  and  the  neck  are 
formed  by  the  advance  and  closure  in  front  of  projections  from  behind, 
in  the  same  way  as  the  cavities  of  the  thorax  and  abdomen  are  closed ; 
but  the  closure  of  the  first  visceral  arch  is  complicated  by  the  projec- 
tion, from  above  downward,  of  the  frontal,  or  intermaxillary  process, 
and  by  the  formation  of  several  secondary  projections,  which  leave  cer- 
tain permanent  openings,  forming  the  mouth,  nose  etc. 


DEVELOPMENT    OF   THE    FACE 


831 


In  the  very  first  stages  of  development  of  the  head,  there  is  no 
appearance  of  the  face.  The  cephalic  extremity  consists  simply  of  the 
cerebral  vesicles,  the  surface  of  this  enlarged  portion  of  the  embryo 
being  covered,  in  front  as  well  as  behind,  by  the  epiblast.  During  the 
sixth  week,  after  the  cavity  of  the  pharynx  has  appeared,  the  membrane 
gives  way  in  front,  forming  a  large  opening,  which  may  be  called  the 
■  first  opening  of  the  mouth.     At  this  time,  however,  the  face  is  open  in 


Fig.  238.  —  Mouth  of  a  human  einbryo  of  thirty- 
Jive  days  (Coste) . 

I,  frontal  process,  widely  sloped  at  its  inferior 
portion  ;  2,  2,  incisor  processes  produced  by  this 
sloping;  3,3,  nostrils;  4,  lower  lip  and  maxilla, 
formed  by  the  union  of  the  inferior  maxillary 
processes;  5,  5,  superior  maxillary  processes, 
contiguous  to  the  incisor  process ;  6,  mouth,  still 
confounded  with  the  nasal  fossae ;  7,  first  appear- 
ance of  the  closure  of  the  nasal  fossse;  8,  8,  first 
appearance  of  the  two  halves  of  the  palatine 
arch;  9,  tongue;  10,  10,  eyes;  11,  12,  13,  visceral 
arches. 


Fig.  239. — Mouth  of  an  embryo  of  forty  days 
(Coste). 

I,  first  appearance  of  the  nose;  2,  2,  first  ap- 
pearance of  the  alse  of  the  nose  ;  3,  appearance  of 
the  closure  beneath  the  nose  ;  4,  middle,  or  median 
portion  of  the  upper  lip,  formed  by  the  approach 
and  union  of  the  two  incisor  processes,  a  little 
notch  in  the  median  line  still  indicating  the  primi- 
tive separation  of  the  two  processes  ;  5,  5,  superior 
maxillary  processes,  forming  the  lateral  portions 
of  the  upper  lip ;  6,  6,  groove  for  the  develop- 
ment of  the  lachrymal  sac  and  the  nasal  canal ; 
7,  lower  lip  ;  8,  mouth  ;  9,  9,  the  two  lateral  halves 
of  the  palatine  arch,  already  nearly  approximated 
to  each  other  in  front,  but  still  widely  separated 
behind. 


front  as  far  back  as  the  ears.  The  first,  or  superior  visceral  arch, 
now  appears  as  a  projection  of  the  mesoblast,  extending  forward.  This 
is  soon  marked  by  two  secondary  projections,  the  upper  projection 
forming  the  superior  maxillary  portion  of  the  face,  and  the  lower,  the 
inferior  maxilla.  The  two  projections  that  form  the  lower  jaw  soon 
meet  in  the  median  line,  and  their  superior  margin  is  the  lower  lip.  At 
the  same  time  there  is  a  projection  from  above,  extending  between  the 


832  EMBRYOLOGY 

two  superior  projections,  which  is  called  the  frontal,  or  intermaxillary 
process.  This  extends  from  the  forehead  —  that  portion  which  covers 
the  front  of  the  cerebrum  —  downward.  The  superior  maxillary  pro- 
jections then  advance  forward,  gradually  passing  to  meet  the  frontal 
process,  but  leaving  two  small  openings  on  either  side  of  the  median 
line,  which  are  the  openings  of  the  nostrils.  The  upper  portion  of  the 
frontal  process  thus  forms  the  nose ;  but  below,  is  the  lower  end  of  this 
process,  which  is  at  first  split  in  the  median  line,  projects  below  the 
nose,  and  forms  the  incisor  process,  at  the  lower  border  of  which  are 
finally  developed  the  incisor  teeth.  As  the'superior  maxillary  processes 
advance  forward,  the  eyes  are  moved,  as  it  were,  from  the  sides  of  the 
head  and  present  anteriorly,  until  finally  their  axes  become  parallel. 
These  processes  advance  frorn  the  two  sides,  come  to  the  sides  of  the 
incisor  process,  beneath  the  nose,  unite  with  the  incisor  process  on 
either  side,  and  their  lower  margin,  with  the  lower  margin  of  the  incisor 
process,  forms  the  upper  lip ;  but  before  this,  the  two  lateral  halves  of 
the  incisor  process  have  united  in  the  median  line.  At  the  bottom  of 
the  cavity  of  the  mouth,  a  small  papilla  makes  its  appearance,  which 
gradually  elongates  and  forms  the  tongue  (see  Plate  XVI,  Fig.  5). 

While  this  process  of  development  of  the  anterior  portion  of  the  first 
visceral  arch  is  going  on,  at  its  posterior  portion  the  malleus  and  incus 
are  developing,  the  former  being  at  first  connected  with  the  cartilage  of 
Meckel,  which  extends  along  the  inner  surface  of  the  inferior  maxilla, 
the  cartilages  from  either  side  meeting  at  the  chin.  The  cleft  between 
the  first  and  the  second  visceral  arch  has  closed,  except  at  its  posterior 
portion,  where  an  opening  is  left  for  the  external  auditory  meatus,  the 
cavity  of  the  tympanum  and  the  Eustachian  tube. 

At  the  same  time  the  second  visceral  arch  advances  and  forms  the 
stapes,  the  styloid  ligament  and  the  lesser  cornua  of  the  hyoid  bone. 
The  third  arch  advances  in  the  same  way  ;  and  the  arches  from  the  two 
sides  meet,  become  united  in  the  median  line  and  form  the  body  and 
the  greater  cornua  of  the  hyoid  bone.  The  clefts  between  the  second 
and  the  third  and  between  the  third  and  fourth  arches  finally  are 
obliterated. 

The  fourth  arch  forms  the  sides  of  the  neck  and  the  larynx,  the 
arytenoid  cartilages  being  developed  first.  In  front  of  the  larynx  and 
just  behind  the  tongue,  is  a  little  elevation  that  is  developed  into  the 
epiglottis.  The  openings  of  the  nostrils  appear  during  the  second  half 
of  the  second  month.  A  little  elevation,  the  nose,  appears  between  these 
openings,  and  the  nasal  cavity  begins  to  be  separated  from  the  mouth. 
The  lips  are  distinct  during  the  third  month,  and  the  tongue  first 
appears  in  the  course  of  the  seventh  week. 


DEVELOPMENT    OF    THE    TEETH  833 

The  palatine  arch  is  developed  by  two  processes,  which  arise  on 
either  side,  from  the  incisor  process,  pass  backward  and  upward  and 
finally  meet  and  unite  in  the  median  line.  The  union  of  these  forms  the 
plane  of  separation  between  the  mouth  and  the  nares.  At  the  same 
time  a  vertical  process  forms  in  the  median  line,  between  the  palatine 
arch  and  the  roof  of  the  nasal  cavity,  which  separates  the  two  nares. 

Develop7nent  of  the  Teeth.  —  The  first  appearance  of  the  organs  for 
the  development  of  the  teeth  is  marked  by  the  formation  of  a  cellular 
projection  extending  the  entire  length  of  the  border  of  either  jaw,  which 
forms  a  rounded  band  above  and  dips  down  somewhat  into  the  subjacent 
structure.  This  band  is  readily  separated  by  maceration,  and  the  re- 
moval of  the  portion  that  dips  into  the  maxilla  leaves  a  groove.  It 
extends  the  entire  length  of  the  jaws  without  interruption.  Its  superior 
surface  is  rounded,  and  that  portion  which  dips  into  the  subjacent 
mucous  structure  is  wedge-shaped,  so  that  its  section  has  the  form  of  a  V. 

So  soon  as  this  primitive  band  is  formed  —  which  occurs  at  the  sixth 
or  seventh  week — a  flat  band  projects  from  its  internal  surface,  near  the 
mucous  structure,  which  is  called  the  epithelial  band.  This  also  extends 
over  the  entire  length  of  the  jaw.  It  is  thin,  flattened,  with  its  free 
edge  curved  inward  and  toward  the  jaw,  and  is  composed  at  first  of  a 
central  layer  of  polygonal  cells  covered  with  a  layer  of  columnar 
epithelium. 

At  certain  points  —  these  points  corresponding  to  the  situation  of  the 
true  dental  bulbs  —  there  appear  rounded  enlargements  at  the  free  mar- 
gin of  the  epithehal  band  just  described.  Each  one  of  these  is  developed 
into  one  of  the  structures  of  the  perfect  tooth.  The  mechanism  of  the 
formation  of  this,  which  is  called  the  enamel-organ,  and  of  the  dental 
bulb  is  the  following  :  — 

A  rounded  enlargement  appears  at  the  margin  of  the  epithehal  band. 
This  soon  becomes  directed  downward  —  adapting  the  description  to  the 
lower  jaw  —  and  dips  into  the  mucous  structure,  being  at  first  connected 
with  the  epithelial  band  by  a  narrow  pedicle  which  soon  disappears, 
lea\'ing  the  enlargements  enclosed  completely  in  a  follicle.  This  is  the 
dental  folhcle,  and  it  has  no  connection  with  the  wedge-shaped  band 
described  first.  While  this  process  is  going  on,  a  conical  bulb  appears 
at  the  bottom  of  the  follicle.  The  enamel-organ,  formed  from  the 
epithelial  band,  becomes  excavated,  or  cup-shaped,  at  its  under  surface, 
and  fits  over  the  dental  bulb,  becoming  united  to  it. 

The  tooth  at  this  time  consists  of  the  dental  bulb,  with  the  enamel- 
organ  closely  fitted  to  its  projecting  surface.  The  enamel-organ  is 
developed  into  the  enamel ;  the  dental  bulb,  which  is  pro\-ided  with 
vessels    and    nerves,    becomes    the    tooth-pulp ;    and    on    the    surface 


834 


EMBRYOLOGY 


of  the  dental  bulb,  the  dentin  is  developed  in  successive  layers.  The 
cement  is  developed  by  successive  layers  upon  that  portion  of  the  den- 
tin which  forms  the  root  of  the  tooth.  As  these  processes  go  on,  the 
tooth  projects  more  and  more,  the  upper  part  of  the  wall  of  the  follicle 
gives  way,  and  the  tooth  finally  appears  at  the  surface. 

The  permanent  teeth  are  developed  beneath  the  follicles  of  the  tem- 
porary, or  milk-teeth.     The  first  appearance  is  a  prolongation,  or  diver- 


Fig.  240. —  Temporary  and  permanent  teeth  (Sappey). 

I,  I,  temporary  central  incisors;  2,  2,  temporary  lateral  incisors;  3,  3,  temporary  canines;  4,4,  tem- 
porary anterior  molars;  5,  5,  temporary  posterior  molars;  6,  6,  permanent  central  incisors;  7,  7,  per- 
manent lateral  incisors;  8,  8,  permanent  canines;  9,  9,  permanent  first  bicuspids;  10,  10,  permanent 
second  bicuspids;  11,  11,  first  molars. 


ticulum,  from  the  enamel-organ  of  the  temporary  tooth,  which  dips  more 
deeply  into  the  mucous  structure.  This  becomes  the  enamel-organ  of 
the  permanent  tooth ;  and  the  successive  stages  of  development  of  the 
dental  follicles  and  the  dental  pulp  progress  in  the  same  way  as  in  the 
temporary  teeth.  As  the  permanent  teeth  increase  in  size,  they  gradu- 
ally encroach  on  the  roots  of  the  temporary  teeth.  The  roots  of  the 
latter  are  absorbed,  the  permanent  teeth  advance  more  and  more 
toward  the  surface,  and  the  crown  of  each  temporary  tooth  finally  is 
pushed  out.  The  number  of  the  temporary  teeth  is  twenty,  and  there 
are  thirty-two  permanent  teeth.     Thus  there  are  three  permanent  teeth 


DEVELOPMENT    OF    THE    GENITO-URINARY    SYSTEM  835 

on  either  side  of  both  jaws,  which  are  developed  de  novo  and  are  not 
preceded  by  temporary  structures. 

The  first  dental  follicles  appear  usually  in  regular  succession.  The 
folhcles  for  the  internal  incisors  of  the  lower  jaw  appear  first,  this 
occurring  at  about  the  ninth  week.  All  the  follicles  for  the  temporary 
teeth  are  completely  formed  at  about  the  eleventh  or  twelfth  week. 

The  temporary  teeth  appear  successively,  the  corresponding  teeth 
appearing  a  Httle  earher  in  the  lower  jaw.  The  usual  order,  subject  to 
certain  exceptional  variations,  is  as  follows  :  — • 

The  four  central  incisors  appear  six  to  eight  months  after  birth. 

The  four  lateral  incisors  appear  seven  to  twelve  months  after  birth. 

The  four  anterior  molars  appear  twelve  to  eighteen  months  after  birth. 

The  four  canines  appear  sixteen  to  twenty-four  months  after  birth. 

The  four  posterior  molars  appear  twenty-four  to  thirty -six  months  after  birth. 

The  order  of  eruption  of  the  permanent  teeth  is  as  follows  :  — 

The  two  central  incisors  of  the  lower  jaw  appear  between  the  sixth  and  the  eighth 
years. 

The  two  central  incisors  of  the  upper  jaw  appear  between  the  seventh  and  the  eighth 
years . 

The  four  lateral  incisors  appear  between  the  eighth  and  the  ninth  years. 

The  four  first  bicuspids  appear  between  the  ninth  and  the  tenth  vears. 

The  four  canines  appear  between  the  tenth  and  the  eleventh  years. 

The  four  second  bicuspids  appear  between  the  twelfth  and  the  thirteenth  years. 

The  above  are  the  permanent  teeth  which  replace  the  temporary 
teeth.  •  The  permanent  teeth  which  are  developed  de  novo  appear  as 
follows  :  — 

The  first  molars  appear  between  the  sixth  and  the  seventh  vears. 

The  second  molars  appear  between  the  twelfth  and  the  thirteenth  years. 

The  third  molars  appear  between  the  seventeenth  and  the  twenty-first  years. 

Development  of  the  Genito-Urinary  System 

The  genital  and  the  urinary  organs  are  developed  together,  and  both 
are  preceded  by  the  appearance  of  two  large  symmetrical  structures, 
known  as  the  Wolffian  bodies,  or  the  bodies  of  Oken.  These  are  some- 
times called  the  false,  or  primordial  kidneys.  They  appear  at  about  the 
thirtieth  day,  develop  very  rapidly  on  either  side  of  the  spinal  column 
and  are  so  large  as  almost  to  fill  the  cavity  of  the  abdomen.  Figure  241 
shows  how  large  these  bodies  are  in  the  early  life  of  the  embryo,  at 
which  time  their  office  undoubtedly  is  important. 

Soon  after  the  Wolffian  bodies  have  made  their  appearance,  there 
appear  at  their  inner  borders,  two  ovoid  bodies,  which  finally  are  devel- 


836  EMBRYOLOGY 

oped  into  the  testicles  for  the  male,  or  the  ovaries  for  the  female.  At 
their  external  borders  are  two  ducts  on  either  side,  one  of  which,  the 
internal,  is  called  the  duct  of  the  Wolffian  body.  This  finally  disap- 
pears in  the  female,  but  it  is  developed  into  the  vas  deferens  in  the 
male.  The  other  duct,  which  is  external  to  the  duct  of  the  Wolffian 
body,  disappears  in  the  male,  but  it  becomes  the  Fallopian  tube  in  the 
female.  This  is  known  as  the  duct  of  Miiller.  Behind  the  Wolffian 
bodies,  are  developed  the  kidneys  and  the  suprarenal  capsules. 

As  the  development  of  the  Wolffian  bodies  attains  its  maximum  their 

structure  becomes  somewhat  complex.      From  their  proper  ducts,  which 

are  applied  directly  to  their  outer  borders,  tubes  make  their  appearance 

at  right  angles,   which  extend  into    the    substance    of    the    bodies  and 

become  somewhat  convoluted  at  their  extremities. 

These  tubes  communicate  directly  with  the  ducts, 

and  the  ducts  themselves   open   into   the    lower 

part  of  the  intestinal  canal  opposite  the  point  of 

its  communication  with  the  allantois.     The  tubes 

of  the  Wolffian  bodies  are  simple,  terminating  in 

single,  somewhat   dilated,  blind   extremities,  are 

lined  with  epithelium,  and  are  penetrated  at  their 

extremities  by  bloodvessels  which  form  coils  or 

Fig.  241. — Fxtal  pig  \  of  ^ 

an  inch  {\b  millimeters)  long,    convolutious  in  their  interior.     These  undoubtedly 

From^a  specimen  prepared  by   ^^^  organs  of  dcpuratiou  for  the  cmbryo  and  take 

on    the  office  to  be  afterward    assumed    by  the 

I,   heart;    2,   anterior    ex-  ■' 

tremity;     3,    posterior    ex-  kiducys  ;  but  in  the  female  they  are  temporary 

''' Ti'Te'atd^t^fwaSave  structurcs,  disappearing  as  development  advances 

been  cut  away  in  order  to  and  having  nothing  whatever  to  do  with  the  de- 
show    the    position     of     the  ,  ,       r    ,  1        .  •  /  -ni    , 

Wolffian  bodies  velopment  of  the  true  urmary  organs  (see  rlate 

XV,  Fig.  6). 

The  testicles  or  ovaries  are  developed  at  the  internal  and  anterior 
surface  of  the  Wolffian  bodies,  first  appearing  in  the  form  of  small  ovoid 
masses.  Beginning  just  above  and  passing  along  the  external  borders 
of  the  Wolffian  bodies,  are  the  tubes  called  the  ducts  of  Miiller.  These 
at  first  open  into  the  intestine  near  the  point  of  entrance  of  the  Wolffian 
ducts.  In  the  female  their  upper  extremities  remain  free,  except  the 
single  fimbria  which  is  connected  with  the  ovary.  Their  inferior 
extremities  unite  with  each  other,  and  at  their  point  of  union  they  form 
the  uterus.  The  Wolffian  bodies  and  their  ducts  disappear  in  the  female 
at  about  the  fiftieth  day.  A  portion  of  their  structure,  however,  persists 
in  the  form  of  a  collection  of  closed  tubes  constituting  the  parovarium, 
or  organ  of  Rosenmiiller. 

In  the  female  the  ovaries  pass  down  no  farther  than  the  pelvic  cavity  ; 


DEVELOPMENT    OF   THE    GENITO-URINARY    SYSTEM  837 

but  the  testicles,  which  are  at  first  in  the  abdomen  of  the  male,  finally 
descend  into  the  scrotum.  As  the  testicles  descend  they  carry  with 
them  the  Wolffian  duct,  that  portion  of  the  Wolffian  body  which  is  per- 
manent constituting  the  head  of  the  epididymis.  At  the  same  time  a 
cord  appears,  attached  to  the  lower  extremity  of  the  testicle  and  extend- 
ing to  the  symphysis  pubis.  This  is  the  gubernaculum  testis.  It  is  at 
first  muscular,  but  the  muscular  fibres  disappear  during  the  later  periods 
of  utero-gestation.  It  is  not  known  that  its  muscular  structure  takes  any 
part,  by  contractile  action,  in  the  descent  of  the  testicle  in  the  human 
subject.  The  epididymis  and  the  vas  deferens  are  formed  from  the 
Wolffian  duct. 

At  about  the  end  of  the  seventh  month  the  testicle  has  reached  the 
internal  abdominal  ring  ;  and  at  this  time  a  double  tubular  process  of 
peritoneum,  covered  with  a  few  fibres  from  the  lower  portion  of  the 
internal  oblique  muscle  of  the  abdomen,  gradually  extends  into  the 
scrotum.  The  testicle  descends,  following  this  process  of  peritoneum, 
which  latter  becomes  eventually  the  visceral  and  parietal  portions  of  the 
tunica  vaginalis.  The  canal  of  communication  between  the  abdominal 
cavity  and  the  cavity  of  the  scrotum  is  finally  closed  and  the  tunica 
vaginalis  is  separated  from  the  peritoneum.  The  fibres  derived  from 
the  internal  oblique  constitute  the  cremaster  muscle. 

At  the  eighth  or  the  ninth  month  the  testicles  have  reached  the  exter- 
nal abdominal  ring  and  soon  after  descend  into  the  scrotum.  The  vas 
deferens  passes  from  the  testicle,  along  the  base  of  the  bladder,  to  open 
into  the  prostatic  portion  of  the  urethra ;  and  as  development  advances, 
two  sacculated  diverticula  from  these  tubes  make  their  appearance, 
which  are  attached  to  the  bladder  and  constitute  the  vesiculae  seminales. 

As  the  ovaries  descend  to  their  permanent  situation  in  the  pelvic 
cavity,  there  appears,  attached  to  the  inner  extremity  of  each,  a  rounded 
cord,  analogous  to  the  gubernaculum  testis.  A  portion  of  this,  connect- 
ing the  ovary  with  the  uterus,  constitutes  the  ligament  of  the  ovary ; 
and  the  inferior  portion  forms  the  round  ligament  of  the  uterus,  which 
passes  through  the  inguinal  canal  and  is  attached  to  the  symphysis 
pubis. 

Development  of  the  Urinary  Apparatus.  —  Behind  the  Wolffian  bodies, 
and  developed  independently  of  them,  the  kidneys,  suprarenal  capsules 
and  ureters  make  their  appearance.  The  kidneys  are  developed  in  the 
form  of  small  rounded  bodies,  composed  of  short  blind  tubes,  all  con- 
verging toward  a  single  point,  which  is  the  hilum.  These  tubes  increase 
in  length,  branch,  become  convoluted  in  a  certain  portion  of  their  extent, 
and  they  finally  assume  the  structure  and  arrangement  of  the  renal 
tubules,  with  their  Malpighian  bodies,  bloodvessels  etc.     They  all  open 


838 


EMBRYOLOGY 


into  the  hilum.  At  the  time  that  the  kidneys  are  undergoing  develop- 
ment, the  suprarenal  capsules  are  formed  at  their  superior  extremities. 
These  bodies  are  relatively  so  much  larger  in    the  foetus  than  in  the 


Fig.  242.  —  Diagrammatic  representation  of  the  genito-urinary  system   (Henle'). 

I,  embryonic  condition,  in  which  there  is  no  distinction  of  sex;  II,  female  form  ;  III,  male  form.  The 
dotted  lines  in  II  and  III  represent  the  situations  which  the  male  and  female  genital  organs  assume 
after  the  descent  of  the  ovaries  and  testicles.  The  small  letters  in  II  and  III  correspond  to  the 
capital  letters  in  I. 

Fig.  242,  I.  —  A,  kidney;  B,  ureter;  C,  bladder;  D,  urachus,  developed  into  the  median  ligament  of 
the  bladder;  E,  constriction  which  becomes  the  urethra;  /',  Wolffian  body;  G,  Wolffian  duct, 
with  its  opening  below,  G' ;  //,  duct  of  Miiller,  united  below,  from  the  two  sides,  into  a  single  tube, 
/,  which  presents  a  single  opening,/',  between  the  openings  of  the  Wolffian  ducts;  K,  ovary  or 
testicle;  L,  gubernaculum  testis  or  round  ligament  of  the  uterus  ;  M,  genito-urinary  sinus;  jV,  O, 
external  genitalia. 

Fig.  242,  II  (female).  —  a,  kidney;  b,  ureter;  c,  bladder;  d,  urachus;  e,  urethra;  f,  remains  of  the 
Wolffian  body  (parovarium);  g,  remnant  of  the  Wolffian  duct;  h.  Fallopian  tube;  /,  uterus; 
/',  vagina;  k,  ovary;  /,  round  ligament  of  the  uterus;  w,  extremity  of  the  urethra;  «,  clitoris; 
n' ,  corpus  cavernosum  of  the  clitoris;  «",bulb  of  the  vestibule;  o,  external  genital  opening;  /,  ex- 
cretory duct  of  the  gland  of  Bartholinus. 

Fig.  242,  III  (male).  —  a,  kidney;  i^,  ureter;  ^r,  bladder;  </,  urachus;  e,  ni,  urethra;  /,  epididymis; 
^,  vas  deferens;  g' ,  seminal  vesicle;  _^",  ejaculatory  duct;  /z, /,  remains  of  the  duct  of  Miiller; 
k,  testicle;  /,  gubernaculum  testis;  »,  «',  «",  urethra  and  penis;  0,  scrotum;  /,  gland  of  Cowper; 
q,  prostate. 


DEVELOPMENT    OF   THE   CIRCULATORY    SYSTEM  839 

adult  that  they  have  been  supposed  to  be  peculiarly  important  in  intra- 
uterine life,  although  nothing  definite  is  known  on  this  point  (see  Plate 
XVI,  Fig.  3).  The  kidneys  are  relatively  very  large  in  the  foetus. 
Their  proportion  to  the  weight  of  the  body,  in  the  foetus,  is  i  to  80,  and 
in  the  adult,  i  to  240.  The  ureters  are  developed  as  tubular  processes 
from  the  kidneys,  which  finally  extend  to  open  into  the  bladder.  The 
development  of  the  genito-urinary  apparatus  can  be  readily  understood, 
after  the  description  just  given,  by  a  study  of  Fig.  312. 

Development  of  the  External  Organs  of  Generation.  —  The  external 
organs  of  generation  begin  to  be  developed  at  about  the  fifth  week.  At 
the  inferior  extremity  of  the  body  of  the  embryo,  a  small  ovoid  eminence 
appears  in  the  median  line,  at  the  lower  portion  of  which  there  is  a 
longitudinal  slit  which  forms  the  common  opening  of  the  anus  and  the 
genital  and  urinary  passages.  This  is  the  cloaca.  There  is  soon  devel- 
oped internally  a  septum,  which  separates  the  rectum  from  the  vagina, 
the  urethra  of  the  female  opening  above.  In  the  male  this,  septum  is 
developed  between  the  rectum  and  the  urethra,  the  generative  and  the 
uninary  passages  opening  together.  From  this  median  prominence  two 
lateral  rounded  bodies  make  their  appearance.  These  are  developed, 
with  the  median  elevation,  into  the  glans  penis  and  corpora  cavernosa 
of  the  male  or  into  the  clitoris  and  the  labia  minora  of  the  female.  In 
the  male  these  two  lateral  prominences  unite  in  the  median  line  and 
enclose  the  spongy  portion  of  the  urethra.  In  the  female  there  is  no 
union  in  the  median  line,  and  an  opening  remains  between  the  two 
labia  minora.  The  scrotum  in  the  male  is  analogous  to  the  labia  majora 
of  the  female ;  the  distinction  being  that  the  two  sides  of  the  scrotum 
unite  in  the  median  line,  while  the  labia  majora  remain  permanently 
separated.  This  analogy  is  further  illustrated  by  the  anatomy  of 
inguinal  hernia,  in  which  the  intestine  descends  into  the  labium  in  the 
female  or  into  the  scrotum  in  the  male.  It  sometimes  occurs,  also, 
that  the  ovaries  descend,  much  as  the  testicles  pass  down  in  the  male, 
and  pass  through  the  external  abdominal  ring. 

Development  of  the  Circulatory  System 

The  blood  and  the  bloodvessels  are  developed  very  early  in  the  life 
of  the  ovum  and  make  their  appearance  nearly  as  soon  as  the  primitive 
streak.  The  mode  of  development  of  the  first  vessels  differs  from  that 
of  vessels  formed  later,  as  they  appear  de  nozw  in  the  blastodermic 
layers,  while  afterward,  vessels  are  formed  as  prolongations  of  preexist- 
ing tubes.  Soon  after  the  epiblast  and  the  hypoblast  have  become 
separated  from  each  other,  and  the  mesoblast  has  been  formed  at  the 


840 


EMBRYOLOGY 


thickened  portion  of  the  ovum,  which  is  destined  to  be  developed  into 
the  embryo,  certain  of  the  blastodermic  cel|s  undergo  a  transformation 
into  blood-corpuscles.  These  are  larger  than  the  blood-corpuscles  of 
the  adult  and  usually  are  nucleated.     At  about  the  same  time  certain  of 


Fig.  243.  —  Area  vasculosa  of  a  rabbit  of  ten  days  (van  Beneden  and  Julin) . 

In  this  figure  the  arteries,  the  arterial  capillaries  and  the  sinus  ferminalis  (arterial)  are  in  red,  and 
the  veins  and  venous  capillaries  are  in  blue. 


the  blastodermic  cells  fuse  with  each  other  and  arrange  themselves  so 
as  to  form  vessels.  Leucocytes  probably  are  developed  in  the  same  way 
as  the  red  corpuscles.  The  vessels  thus  formed  constitute  the  area  vas- 
culosa, which  is  the  beginning  of  what  is  known  as  the  first  circulation. 
The  cells  of  the  mesoblast  do  not  take  part  in  the  formation  of  the 
blood  and  bloodvessels,  as  indicated  above,  but  cells  penetrate  at  the 


DEVELOPMENT    OF    THE    CIRCULATORY    SYSTEM  84 1 

edges,  between  the  epiblast  and  the  hypoblast,  and  these,  which  are 
called  parablastic  cells,  are  developed  into  bloodvessels  and  blood-cor- 
puscles. The  connective  tissue  also  is  supposed  to  be  developed  from 
parablastic  cells.  According  to  this  view — which,  however,  is  not  gen- 
erally adopted  —  the  parablastic  cells  are  to  be  distinguished  from  the 


Fig.  244. — Area  vasculosa  of  a  rabbit  of  eleven  days  (van  Beneden  and  Julin). 
The  capillaries  are  not  shown  in  this  figure. 

cells  of  the  mesoblast,  which  latter  are  called  archiblastic  cells.  Ac- 
cording to  Rindfieisch,  the  so-called  parablastic  cells  are  derived  from 
the  area  opaca. 

The  First,  or  Vitelline  Circulation.  —  In  the  development  of  ovipa- 
rous animals,  the  first,  or  vitelline  circulation  is  very  important ;  for  by 
these  vessels  the  contents  of  the  nutritive  yolk  are  taken  up  and  carried 
to  the  embryo,   constituting  the  only  source  of   material  for  its  nutri- 


842  EMBRYOLOGY 

tion  and  growth.  In  mammals,  however,  nutritive  matter  is  absorbed 
almost  exclusively  from  the  mother,  by  simple  imbibition,  before  the  pla- 
cental circulation  is  established,  and  by  the  placental  vessels  at  a  later 
period.  The  vitelline  circulation  is  therefore  not  important,  and  the 
vessels  disappear  with  the  atrophy  of  the  umbilical  vesicle. 

The  area  vasculosa  in  mammals  consists  of  vessels  coming  from  the 
body  of  the  embryo,  forming  a  nearly  circular  plexus  in  the  substance 
of  the  vitellus.  The  vessels  of  this  plexus  open  into  a  sinus  at  the 
border  of  the  area,  called  the  sinus  terminalis  (see  Figs.  243  and  244). 

In  examining  the  ovum  when  the  area  vasculosa  is  first  formed,  the 
embryo  is  seen  lying  in  the  direction  of  the  diameter  of  the  nearly  cir- 
cular plexus  of  bloodvessels.  The  plexus  surrounds  the  embryo,  except 
at  the  cephalic  extremity,  where  the  terminal  sinuses  of  the  two  sides 
curve  downward  toward  the  head  to  empty  into  the  omphalo-mesenteric 
veins.  As  the  umbilical  vesicle  is  separated  from  the  body  of  the  em- 
bryo, it  carries  the  plexus  of  vessels  of  the  area  vasculosa  with  it,  the 
vessels  of  communication  with  the  embryo  being  the  omphalo-mesen- 
teric arteries  and  veins.  As  these  processes  are  going  on,  the  great 
central  vessel  of  the  embryo  becomes  enlarged  and  twisted  on  itself 
at  a  point  just  below  the  cephalic  enlargement  of  the  embryo,  between 
the  inferior  extremity  of  the  pharynx  and  the  superior  cul-dc-sac  of  the 
intestinal  canal.  The  excavation  which  receives  this  vessel  is  called  the 
fovea  cardiaca.  Simple  undulatory  movements  take  place  in  the  heart 
of  the  chick  at  about  the  middle  of  the  second  day ;  but  there  is  not  at 
that  time  a  regular  circulation.  At  the  end  of  the  second  day  or  the 
beginning  of  the  third,  the  currents  of  the  circulation  are  established. 
The  time  of  the  first  appearance  of  the  circulation  in  the  human  embryo 
has  not  been  accurately  determined. 

In  the  arrangement  of  the  vessels  for  the  first  circulation  in  the 
embryo,  the  heart  is  in  the  median  line  and  gives  off  two  arches  which 
curve  to  either  side  and  unite  into  a  single  central  trunk  at  the  spinal 
column  below.  These  are  the  two  aortae,  and  the  single  trunk  formed 
by  their  union  becomes  the  abdominal  aorta.  The  two  aortic  arches  — 
only  one  of  which  is  permanent  —  are  sometimes  called  the  inferior 
vertebral  arteries.  These  vessels  give  off  a  number  of  branches  which 
pass  into  the  area  vasculosa.  Two  of  these  branches,  however,  are 
larger  than  the  others,  pass  to  the  umbilical  vesicle  and  are  called  the 
omphalo-mesenteric  arteries.  In  the  embryo  of  mammals,  there  are  at 
first  four  omphalo-mesenteric  veins,  two  superior,  which  are  the  larger, 
and  two  inferior ;  but  as  development  advances,  the  two  inferior  veins 
are  closed,  and  there  are  then  two  omphalo-mesenteric  arteries  and  two 
omphalo-mesenteric  veins.     At  about  the  fortieth  day,  one  artery  and 


DEVELOPMENT    OF    THE    CIRCULATORY    SYSTE.M  843 

one  vein  disappear,  leaving  one  omphalo-mesenteric  artery  and  one  vein. 
Soon  after,  as  the  circulation  becomes  established  in  the  allantois,  the 
vessels  of  the  umbilical  vesicle  and  the  omphalo-mesenteric  vessels  are 
obliterated  and  the  first  circulation  is  superseded  by  the  second. 

As  the  septum  between  the  two  ventricles  makes  its  appearance, 
that  division  of  the  right  aortic  arch  which  constitutes  the  vascular 
portion  of  one  of  the  branchial  arches  disappears  and  loses  its  connec- 
tion with  the  abdominal  aorta ;  a  branch,  however,  persists  during  the 
whole  of  intra-uterine  life  and  constitutes  the  ductus  arteriosus,  and 
another  branch  is  permanent,  forming  the  pulmonary  artery. 

TJie  Second,  or  Placental  Circulatioji.  —  As  the  omphalo-mesenteric 
vessels  disappear,  and  as  the  allantois  is  developed  to  form  the  chorion, 
two  vessels — the  hypogastric  arteries  —  are  given  off,  first  from  the 
abdominal  aorta ;  but  afterward,  as  the  vessels  going  to  the  lower 
extremities  are  developed,  the  branching  of  the  abdominal  aorta  is  such 
that  the  vessels  become  connected  with  the  internal  iliac  arteries.  The 
hypogastric  arteries  pass  to  the  chorion  through  the  umbilical  cord  and 
constitute  the  two  umbilical  arteries.  At  first  there  are  two  umbilical 
veins ;  but  one  of  them  afterward  disappears,  and  there  is  finally 
but  one  vein  in  the  umbilical  cord.  It  is  in  this  way  —  the  umbilical 
arteries  carrying  the  blood  to  the  tufts  of  the  foetal  placenta,  which  is 
returned  by  the  umbilical'  vein  —  that  the  placental  circulation  is 
estabUshed. 

Corresponding  to  the  four  visceral  arches,  which  have  been 
described  in  connection  with  the  development  of  the  face,  are  four 
pairs  of  vascular  arches.  These,  with  the  two  aortas,  constitute  the 
five  branchial  or  arterial  arches,  not  counting  an  unimportant  rudimen- 
tary branch  connected  with  the  fourth  arch,  described  by  Zimmermann. 
These  arches  are  numbered  from  above  downward. 

In  the  development  of  the  arteries  distributed  to  the  head  and  upper 
extremities,  the  first  change  observed  is  the  disappearance  of  the  first 
arch,  its  stem  being  continued  forward  as  the  temporal  artery,  giving 
off  the  internal  maxillary  and  perhaps  the  facial  (His).  The  second 
arch  afterward  disappears  and  is  replaced  with  what  is  thought  to  form 
the  lingual  artery.  The  third  arch  remains  and,  with  the  upper  part  of 
the  posterior  aortic  root,  forms  the  internal  carotid.  The  common 
carotid  and  the  external  carotid  are  formed  from  the  anterior  aortic 
root,  the  posterior  and  the  anterior  aortic  roots  coming  from  the  same 
primitive  vessel.  The  fourth  arch  on  the  right  side  becomes  the  sub- 
clavian artery.  It  joins  also  with  the  anterior  aortic  root  to  form  the 
innominate  artery.  The  fourth  arch  on  the  left  side  remains  as  the 
arch  of  the  aorta.     The  fifth  arch  on  the  left  side  becomes  the  pulmo- 


844 


EMBRYOLOGY 


nary  artery  and  the  ductus  arteriosus.  The  fifth  arch  on  the  right 
side  disappears.  These  changes  occur  in  man  and  in  some  mammals ; 
but  in  fishes  the  five  arches  are  permanent,  giving  off  branches  that 
are  distributed  to  the  gills.  In  following  the  metamorphoses  of  the 
arches  in  man,  it  is  seen  that  the  symmetrical  vascular  system  that 
exists  in  early  embryonic  life  is  developed  gradually  into  an  unsym- 
metrical  system,  and  that  two  arches  —  the  fourth  and  fifth  — soon 
far  exceed  the  others  in  size  and  importance.  The  destination  of 
the  five  arches  is  well  illustrated  diagrammatically  in  Fig.  245,  modi- 
fied from  Rathke.      The  aortic  bulb  and  the  five  arches  are  represented 


LEFT 
SUBCLAVIAN 


DUCTUS 
ARTLRI0SU8 


DESCENDING  AORTA 


Fig.  2^<).— Arterial  arches  in  man  and  mammals  (modified  from  Rathke). 

in  outline  and  the  permanent  vessels  in  colors.  The  vessels  belonging 
to  the  aortic  system  are  in  red  and  the  pulmonary  vessels  are  in  blue. 

At  the  same  time  that  the  arteries  going  to  the  head  and  upper 
extremities  are  undergoing  development,  the  vessels  of  the  trunk  and 
lower  extremities  are  branching  from  the  descending  aorta  and  its  exten- 
sions. These  processes,  however,  are  not  complex  and  do  not  call  for 
extended  description  in  this  work. 

Two  venous  trunks  make  their  appearance  by  the  sides  of  the  spinal 
column,  called  the  cardinal  veins.  These  run  parallel  with  the  superior 
vertebral  arteries,  or  the  two  aortae,  emptying  finally  into  the  auricular 
portion  of  the  heart  by  two  canals,  called  the  ducts  of  Cuvier.  These 
veins  change  their  relations  and  connections  as  the  first  circulation  is 
replaced  by  the  second.     The  omphalo-mesenteric  vein  opens  between 


DEVELOPMENT    OF    THE   CIRCULATORY    SYSTEM  845 

the  two  ducts  of  Cuvier  into  the  heart.  As  development  advances,  the 
liver  is  formed  in  the  course  of  this  vessel  a  short  distance  below  the 
heart,  and  the  vein  ramifies  in  its  substance;  so  that  the  blood  of 
the  omphalo-mesenteric  vein  passes  through  the  liver  before  it  goes  to 
the  heart.  The  omphalo-mesenteric  vein  is  obliterated  as  the  umbilical 
vein  makes  its  appearance.  The  blood  from  the  umbilical  vein  is  at 
first  emptied  directly  into  the  heart ;  but  this  vessel  soon  establishes  the 
same  relations  with  the  liver  as  the  omphalo-mesenteric  vein,  and 
its  blood  passes  through  the  liver  before  it  reaches  the  heart.  As 
the  omphalo-mesenteric  vein  atrophies,  the  mesenteric  vein,  bringing 
the  blood  from  the  intestinal  canal,  is  developed,  and  this  penetrates  the 
liver,  finally  becoming  the  portal  vein. 

As  the  lower  extremities  are  developed,  the  inferior  vena  cava  makes 
its  appearance  between  the  two  inferior  cardinal  veins.  This  vessel 
receives  an  anastomosing  branch  from  the  umbilical  vein  before  it  pene- 
trates the  liver,  and  this  branch  is  the  ductus  venosus.  As  the  inferior 
vena  cava  increases  in  size,  it  communicates  below  with  the  two  inferior 
cardinal  veins ;  and  the  portions  of  the  two  inferior  cardinal  veins  which 
remain  constitute  the  two  iliac  veins.  The  inferior  cardinal  veins, 
between  that  portion  which  forms  the  iliac  veins  and  the  heart,  finally 
become  the  right  and  the  left  azygos  veins. 

The  right  duct  of  Cuvier,  as  the  upper  extremities  are  developed, 
enlarges  and  becomes  the  vena  cava  descendens,  finally  receiving  the 
blood  from  the  head  and  the  superior  extremities.  The  left  duct  of 
Cuvier  diminishes  in  size  and  remains  as  the  coronary  sinus.  The 
upper  portions  of  the  superior  cardinal  veins  are  developed  into  the 
jugulars  and  subclavians  on  the  two  sides.  As  the  lower  portion  of 
the  left  cardinal  vein  and  the  left  canal  of  Cuvier  atrophy,  a  venous 
trunk  appears,  connecting  the  left  subclavian  with  the  right  canal  of 
Cuvier.  This  increases  in  size  and  becomes  the  left  vena  innominata, 
which  connects  the  left  subclavian  and  internal  jugular  with  the  vena 
cava  descendens. 

Development  of  the  Heart.  — The  central  enlargement  of  the  vascular 
system  in  the  first  circulation,  which  becomes  the  heart,  is  twisted  on 
itself  by  a  single  turn.  The  portion  connected  with  the  cephalic  ex- 
tremity of  the  embryo  gives  origin  to  the  arterial  system,  and  the 
portion  connected  with  the  caudal  extremity  receives  the  blood  from 
the  venous  system.  The  walls  of  the  arterial  portion  of  the  heart  soon 
become  thickened,  while  the  walls  of  the  venous  portion  remain  com- 
paratively thin.  There  then  appears  a  constriction,  which  partly  sepa- 
rates the  auricular  from  the  ventricular  portion.  At  a  certain  period  of 
development  the  heart  presents  a  single  auricle  and  a  single  ventricle. 


846  •  EMBRYOLOGY 

The  division  of  the  heart  into  two  ventricles  appears  before  the  two 
auricles  are  separated.  This  is  effected  by  a  septum,  which  gradually 
extends  from  the  apex  of  the  heart  upward  toward  the  auricular  portion. 
At  the  seventh  week  there  is  a  large  opening  between  the  two  ventricles. 
This  gradually  closes  from  below  upward,  the  heart  becomes  more 
pointed  and  the  separation  of  the  two  ventricles  is  complete  at  about  the 
end  of  the  second  month. 

At  about  the  end  of  the  second  month,  a  septum  begins  to  be  formed 
between  the  auricles.  This  extends  from  the  base  of  the  heart  toward 
the  ventricles;  but  it  leaves  an  opening  between  the  two  sides  —  the 
foramen  ovale,  or  the  foramen  of  Botal  —  which  persists  during  foetal 
life.  At  the  anterior  edge  of  the  opening  of  the  vena  cava  ascendens 
into  the  right  auricle,  there  is  a  membranous  fold  which  projects  into 
the  auricle.  This  is  the  valve  of  Eustachius,  and  it  divides  the  right 
auricle  incompletely  into  two  portions. 

During  the  sixth  week  the  heart  is  vertical  and  is  situated  in  the 
median  line,  with  the  aorta  arising  from  the  centre  of  its  base.  At  the 
end  of  the  second  month  it  is  raised  up  by  the  development  of  the  liver, 
and  its  point  presents  forward.  During  the  fourth  month,  it  is  twisted 
slightly  on  its  axis,  and  the  point  presents  to  the  left.  At  this  time 
the  auricular  portion  is  larger  than  the  ventricles ;  but  the  auricles 
diminish  in  their  relative  capacity  during  the  latter  half  of  intra-uterine 
life.     The  pericardium  makes  its  appearance  during  the  ninth  week. 

Early  in  intra-uterine  life  the  relative  size  of  the  heart  is  very  great. 
At  the  second  month  its  weight,  in  proportion  to  the  weight  of  the  body, 
is  as  I  to  50.  This  proportion,  however,  gradually  diminishes,  until  at 
birth  the  ratio  is  as  i  to  120.  The  weight  in  the  adult  is  about  as  i  to 
160.  During  about  the  first  half  of  intra-uterine  life  the  thickness  of 
the  two  ventricles  is  nearly  the  same ;  but  after  that  time  the  relative 
thickness  of  the  left  ventricle  gradually  increases. 

Peculiarities  of  the  Fcetal  Circulation.  —  Beginning  at  the  abdominal 
aorta,  the  blood  passes  into  the  two  primitive  iliacs,  and  thence  into  the 
internal  iliacs.  From  the  two  internal  iliacs  the  two  hypogastric  arteries 
arise,  which  ascend  along  the  sides  of  the  bladder,  to  its  fundus,  pass  to 
the  umbilicus  and  go  to  the  placenta,  forming  the  two  umbilical  arteries. 
In  this  way  the  blood  of  the  foetus  goes  to  the  placenta. 

The  umbilical  vein  enters  the  body  of  the  foetus  at  the  umbilicus ;  it 
passes  along  the  margin  of  the  suspensory  ligament  to  the  under  surface 
of  the  liver ;  it  gives  off  one  branch  of  large  size  and  one  or  two  smaller 
branches  to  the  left  lobe ;  it  sends  a  branch  each  to  the  lobus  quadratus 
and  the  lobus  Spigelii,  and  the  vessel  reaches  the  transverse  fissure. 
At   the  transverse  fissure  it    divides  into  two  branches,  the  larger  of 


DEVELOPMENT    OF    THE    CIRCULATORY    SYSTEM 


847 


which  joins  the  portal  vein  and  enters  the  Uver ;  and  the  smaller,  which 
is  the  ductus  venosus,  passes  to  the  vena  cava  ascendens,  at  the  point 
where  it  receives  the  left  hepatic  vein.  Thus  the  greater  part  of  the 
blood  returned  to  the  foetus  from  the  placenta  passes  through  the  liver, 
a  relatively  small  quantity  being  emptied  into  the  vena  cava,  by  the 
ductus  venosus. 

The  vena  cava  ascendens  —  containing  the  placental  blood  which  has 
passed  through  the  liver,  the  blood  conveyed  directly  from  the  umbilical 


Supevior  vena  cava  — 


Ductus  venosus 


Hepatic  vein 


Umbilical  vein 


Portal  vein  — 


Umbilical  vein 


Ductus  arteriosus 

Pulmonary  artery 
Pulmonary  vein 


Inferior  vena  cava 


— Aorta 


inferior  vena  cava 


Intestine 


-   -    Umbilical  artery 


Fig.  246.  —  Diagram  of  the  f(etal  circulation  (Kollmann). 

vein  by  the  ductus  venosus  and  the  blood  from  the  lower  extremities  — 
passes  to  the  right  auricle.  As  the  blood  enters  the  right  auricle  it  is 
directed  by  the  Eustachian  valve,  passing  behind  the  valve,  through  the 
foramen  ovale,  into  the  left  auricle.  At  the  same  time  the  blood  from 
the  head  and  the  superior  extremities  passes  down,  by  the  vena  cava 
descendens,  in  front  of  the  Eustachian  valve,  through  the  right  auricle, 
into  the  right  ventricle.  The  arrangement  of  the  Eustachian  valve  is 
such  that  the  right  auricle  simply  affords  a  passage  for  the  two  currents 


848  EMBRYOLOGY 

of  blood  ;  the  one,  from  the  vena  cava  ascendens,  through  the  foramen 
ovale,  passes  into  the  left  auricle  and  the  left  ventricle ;  and  the  other, 
from  the  vena  cava  descendens,  passes  through  the  right  auriculo- 
ventricular  opening,  into  the  right  ventricle.  It  is  probable,  indeed, 
that  there  is  very  little  admixture  of  these  two  currents  of  blood  in  the 
natural  course  of  the  foetal  circulation. 

The  blood  poured  into  the  left  auricle,  from  the  vena  cava  ascendens, 
through  the  foramen  ovale,  passes  from  the  left  auricle  into  the  left 
ventricle.  The  left  auricle  and  the  left  ventricle  also  receive  a  small 
quantity  of  blood  from  the  lungs,  by  the  pulmonary  veins.  Thus  the 
left  ventricle  is  filled.  At  the  same  time  the  right  ventricle  is  filled  with 
blood  which  has  passed  through  the  right  auricle,  in  front  of  the 
Eustachian  valve.  The  two  ventricles,  thus  distended,  then  contract 
simultaneously.  The  blood  from  the  right  ventricle  passes  in  small 
quantity  to  the  lungs,  the  greater  part  passing  through  the  ductus 
arteriosus,  or  ductus  Botalli,  into  the  descending  portion  of  the  arch  of 
the  aorta.  This  duct  is  half  an  inch  (12.7  miUimeters)  in  length  and 
about  the  size  of  a  goose-quill.  The  blood  from  the  left  ventricle  passes 
into  the  aorta  and  goes  to  the  system.  The  vessels  of  the  head  and 
superior  extremities  being  given  off  from  the  aorta  before  it  receives  the 
blood  from  the  ductus  arteriosus,  these  parts  receive  almost  exclusively 
the  pure  blood  from  the  vena  cava  ascendens,  the  only  mixture  with  the 
placental  blood  being  the  blood  from  the  lower  extremities,  the  blood 
from  the  portal  system  and  the  small  quantity  of  blood  received  from 
the  lungs.  After  the  aorta  has  received  the  blood  from  the  ductus 
arteriosus,  however,  it  is  mixed  blood  ;  and  it  is  this  which  supplies 
the  trunk  and  lower  extremities. 

The  Third,  or  Adult  Circulation.  —  When  the  child  is  born  the  pla- 
cental circulation  is  suddenly  arrested.  After  a  short  time  the  sense  of 
want  of  air  becomes  sufficiently  intense  to  give  rise  to  an  inspiratory 
effort,  and  the  first  inspiration  is  made.  The  pulmonary  organs  are 
then  for  the  first  time  distended  with  air,  the  pulmonary  arteries  carry 
the  greatest  part  of  the  blood  from  the  right  ventricle  to  the  lungs  and  a 
new  circulation  is  established.  During  the  later  periods  of  foetal  life, 
the  heart  is  gradually  prepared  for  the  new  currents  of  blood.  The 
foramen  ovale,  which  is  largest  at  the  sixth  month,  after  that  time  is 
partly  occluded  by  the  gradual  growth  of  a  valve  which  extends  from 
below  upward  and  from  behind  forward  on  the  side  of  the  left  auricle. 
The  Eustachian  valve,  which  is  also  largest  at  the  sixth  month,  gradually 
atrophies  after  this  time,  and  at  full  term  it  has  nearly  disappeared. 
At  birth,  then,  the  Eustachian  valve  is  practically  absent ;  and  after 
pulmonary  respiration  becomes  established,  the  foraman  ovale  has  nearly 


DEVELOPMENT    OF   THE   CIRCULATORY   SYSTEM  849 

closed.  The  arrangement  of  the  valve  of  the  foramen  ovale  is  such  that 
at  birth  a  small  quantity  of  blood  may  pass  from  the  right  to  the  left 
auricle,  but  none  can  pass  in  the  opposite  direction.  The  situation  of 
the  Eustachian  valve  on  the  right  side  of  the  interauricular  septum  is 
marked  by  an  oval  depression,  called  the  fossa  ovalis. 

When  the  placental  circulation  is  arrested  at  birth,  the  hypogastric 
arteries,  the  umbilical  vein  and  the  ductus  venosus  contract,  and  they 
become  impervious  between  the  second  and  the  fourth  days.  The  hypo- 
gastric arteries  remain  pervious  at  their  lower  portion  and  constitute  the 
superior  vesical  arteries.  A  rounded  cord,  which  is  the  remnant  of  the 
umbilical  vein,  forms  the  round  ligament  of  the  liver.  A  slender  cord, 
the  remnant  of  the  ductus  venosus,  is  lodged  in  a  fissure  of  the  Hver, 
called  the  fissure  of  the  ductus  venosus. 


31 


CHAPTER   XXXIII 

FCETAL    LIFE  — DEVELOPMENT   AFTER    BIRTH  — DEATH 

Duration  of  pregnancy  —  Size,  weight  and  position  of  the  fcetus —  Multiple  pregnancy  —  Cause 
of  the  first  contractions  of  the  uterus  in  normal  parturition  —  Involution  of  the  uterus  — 
Meconium  —  Dextral  preeminence  —  Development  after  birth  — Ages —  Death. 

As  the  development  of  the  ovum  advances,  the  uterus  becomes  en- 
larged and  its  walls  are  thickened.  The  form  of  the  organ,  also,  gradu- 
ally changes,  as  well  as  its  position.  Immediately  after  birth  its  weight 
is  about  a  pound  and  a  half  (680  grams),  while  the  virgin  uterus  weighs 
less  than  two  ounces  (56.7  grams).  The  neck  of  the  uterus,  while  it  be- 
comes softer  and  more  patulous  during  pregnancy,  does  not  change  its 
length,  even  in  the  latest  periods  of  utero-gestation.  The  changes  in  the 
walls  of  the  uterus  during  pregnancy  are  important.  The  bloodvessels 
become  much  enlarged,  and  the  muscular  fibres  increase  immensely  in 
size,  so  that  their  contractions  are  very  powerful  when  the  foetus  is 
expelled. 

It  is  evident  that  on  account  of  the  progressive  increase  in  the  size 
of  the  uterus  during  pregnancy,  it  can  not  remain  in  the  cavity  of  the 
pelvis  during  the  later  months.  During  the  first  three  months,  however, 
when  it  is  not  too  large  for  the  pelvis,  it  sinks  back  into  the  hollow  of 
the  sacrum,  the  fundus  being  directed  somewhat  backward,  with  the  neck 
presenting  downward,  forward  and  a  little  to  the  left.  After  this  time 
the  increased  size  of  the  organ  causes  it  to  extend  into  the  abdominal 
cavity,  so  that  its  fundus  eventually  reaches  the  epigastric  region.  Its 
axis  then  has  the  general  direction  of  the  axis  of  the  superior  strait  of 
the  pelvis. 

The  enlargement  of  the  uterus  and  the  necessity  of  carrying  on  a 
greatly-increased  circulation  in  its  walls  during  pregnancy  are  attended 
with  a  temporary  hypertrophy  of  the  heart.  It  is  mainly  the  left  ven- 
tricle that  is  thickened  during  utero-gestation,  and  the  increase  in  the 
weight  of  the  heart  at  full  term  amounts  to  more  than  one-fifth.  After 
delivery,  the  weight  of  the  heart  soon  returns  nearly  to  the  normal 
standard. 

Duration  of  Pregnancy. — The  duration  of  pregnancy,  dating  from  a 
fruitful  intercourse,  is  variable  within  certain  Hmits.     The   method   of 

850 


FCETAL    LIFE  85  I 

calculation  most  in  use  by  obstetricians  is  to  date  from  the  end  of  the 

last  menstrual  period.  Taking  into  account,  however,  the  various  cases 
quoted  by  authors,  in  which  conception  has  been  supposed  to  follow  a 
single  coitus,  there  appears  to  be  a  range  of  variation  in  the  duration  of 
pregnancy  of  not  less  than  forty  days,  the  extremes  being  two  hundred 
and  sixty  and  three  hundred  days.  As  regards  the  practical  applica- 
tions of  calculations  of  the  probable  duration  of  pregnancy  in  individual 
cases,  the  fact  must  be  recognized  that  the  period  is  variable.  Dating 
from  the  end  of  the  last  menstrual  flow,  an  average  of  two  hundred  and 
seventy-eight  days,  or  a  little  more  than  nine  calendar  months,  may  be 
adopted. 

Size,  Weight  aiid  Position  of  the  Fcetus.  — Estimates  in  regard  to  the 
size  and  weight  of  the  embryo  and  fcetus  at  different  stages  of  intra- 
uterine life  present  wide  variations ;  still,  it  is  important  to  have  at  least 
an  approximate  idea  as  to  these  points,  and  the  estimates  by  Scanzoni 
are  given,  as  presenting  fair  averages. 

At  the  third  week  the  embryo  is  two  to  three  lines  (4.2  to  6.4 
millimeters)  in  length.  This  is  about  the  earliest  period  at  Avhich 
measurements  have  been  taken  in  the  normal  state. 

At  the  seventh  week  the  embryo  measures  about  nine  lines  ("19.1 
milUraeters).  Points  of  ossification  have  appeared  in  the  clavicle  and 
the  lower  jaw;  the  Wolffian  bodies  are  large  ;  the  pedicle  of  the  umbili- 
cal vesicle  is  much  reduced  in  size  ;  the  internal  organs  of  generation 
have  just  appeared ;  the  liver  is  of  large  size ;  the  lungs  present  several 
lobules. 

At  the  eighth  week  the  embryo  is  ten  to  fifteen  hnes  ^21.2  to  31.8 
millimeters)  in  length.  The  lungs  begin  to  receive  a  small  quantity  of 
blood  from  the  pulmonary  arteries ;  the  external  organs  of  generation 
have  appeared,  but  it  is  difficult  to  determine  the  sex  ;  the  abdominal 
walls  have  closed  over  in  front. 

At  the  third  month  the  embryo  is  two  to  two  and  a  half  inches 
(50.8  to  63.5  millimeters)  long  and  weighs  about  one  ounce  (28.3  grams). 
The  amniotic  liquid  is  then  more  abundant  in  proportion  to  the  size  of 
the  embryo  than  at  any  other  period ;  the  umbilical  cord  begins  to  be 
twisted ;  the  abdominal  glandular  organs  appear ;  the  pupillary  mem- 
brane is  formed ;  the  limitation  of  the  placenta  has  become  distinct. 
At  this  time  the  upper  part  of  the  embryo  is  relatively  much  larger  than 
the  lower  portion. 

At  the  end  of  the  fourth  month  the  embryo  is  called  the  foetus.^     It 

^  The  periods  of  evolution  are  divided  differently  by  authors.  His  distinguishes  the  three 
periods,  as  follows :  First  two  weeks,  the  product  is  called  the  ovum  ;  from  the  third  to  the  fifth 
week,  the  embrj'o  ;   and  after  the  fifth  week  it  is  called  the  fcetus. 


852  EMBRYOLOGY 

is  then  four  to  five  inches  (lo. i  to  12.7  centimeters)  long  and  weighs 
about  five  ounces  (141. 7  grams).  The  muscles  show  contractility;  the 
eyes,  mouth  and  nose  are  closed;  the  gall-bladder  is  just  developed; 
the  fontanelles  and  sutures  are  wide ;  the  sex  is  distinguishable. 

At  the  fifth  month  the  foetus  is  nine  to  twelve  inches  (22.8  to  30.5 
centimeters)  long  and  weighs  five  to  nine  ounces  (141. 7  to  255.1  grams). 
The  hairs  begin  to  appear  on  the  head ;  the  liver  begins  to  secrete  bile, 
and  the  meconium  appears  in  the  intestinal  canal;  the  amnion  is  in 
contact  with  the  chorion. 

At  the  sixth  month  the  foetus  is  eleven  to  fourteen  inches  (27.9  to 
35.5  centimeters)  long  and  weighs  one  and  a  half  to  two  pounds  (680 
to  907  grams).  If  the  foetus  is  delivered  at  this  time,  life  may  continue 
for  a  few  moments ;  the  bones  of  the  head  are  ossified,  but  the  fonta- 
nelles and  sutures  are  still  wide  ;  the  prepuce  has  appeared  ;  the  testicles 
have  not  descended. 

At  the  seventh  month  the  foetus  is  fourteen  to  fifteen  inches  (35.5  to 
38.1  centimeters)  long  and  weighs  two  to  three  pounds  (907  to  1361 
grams).  The  hairs  are  longer  and  darker  ;  the  pupillary  membrane 
disappears,  undergoing  atrophy  from  the  centre  to  the  periphery  ;  the 
relative  quantity  of  the  amniotic  fluid  is  diminished,  and  the  foetus  is 
not  so  free  in  the  cavity  of  the  uterus  ;  the  foetus  is  now  viable. 

At  the  eighth  month,  the  foetus  is  fifteen  to  sixteen  inches  (38.1  to 
40.9  centimeters)  long  and  weighs  three  to  four  pounds  (1361  to  1814 
grams).  The  eyelids  are  opened  and  the  cornea  is  transparent ;  the 
pupillary  membrane  has  disappeared;  the  left  testicle  has  descended; 
the  umbilicus  is  at  about  the  middle  of  the  body,  the  relative  size  of  the 
lower  extremities  having  increased. 

At  the  ninth  month  the  foetus  is  about  seventeen  inches  (43.2  centi- 
meters long  and  weighs  five  to  six  pounds  (2.27  to  2.72  kilograms).  Both 
testicles  usually  have  descended,  but  the  tunica  vaginalis  still  communi- 
cates with  the  peritoneal  cavity. 

At  birth  the  infant  weighs  a  little  more  than  seven  pounds  (3.17 
kilograms),  the  usual  range  being  four  and  ten  pounds  (1.81  and  4.53 
kilograms),  although  these  limits  are  sometimes  exceeded. 

The  position  of  the  foetus  in  the  great  majority  of  cases,  excluding 
abnormal  presentations,  is  with  the  head  downward.  In  the  early 
months  of  pregnancy  the  foetus  floats  quite  freely  in  the  amniotic 
liquid  ;  and  it  is  probable  that  the  natural  gravitation  of  the  head  and 
of  the  upper  part  of  the  foetus  is  the  determining  cause  of  the  ordinary 
position  in  utero. 

The  shape  of  the  uterus  at  full  term  is  ovoid,  the  lower  portion  being 
the  narrower.    The  foetus  has  the  head  slightly  flexed  upon  the  sternum, 


MULTIPLE    PREGNANCY  853 

the  arms  flexed  upon  the  chest  and  crossed,  the  spinal  column  curved 
forward,  the  thighs  flexed  upon  the  abdomen,  the  legs  slightly  flexed  and 
usually  crossed  in  front,  and  the  feet  flexed  upon  the  legs,  with  their 
inner  margin  drawn  toward  the  tibia.  This  is  the  position  in  which  the 
foetus  is  best  adapted  to  the  size  of  the  uterine  cavity,  and  in  which  the 
expulsive  force  of  the  uterus  can  be  most  favorably  exerted,  both  as 
regards  the  foetus  and  the  generative  passages  of  the  mother. 

Multiple  Pregnancy.  —  It  is  not  rare  to  observe  two  infants  at  a 
birth,  and  cases  are  on  record  where  there  have  been  four  or  even  five, 
though  in  these  latter  instances  they  survive  usually  but  a  short  time, 
or  as  is  more  common,  abortion  takes  place  during  the  first  months. 
Examples  of  three  at  a  birth  have  been  often  observed. 

In  cases  of  twins  it  is  an  interesting  question  to  determine  whether 
the  development  always  takes  place  from  two  ova  or  whether  a  single 
ovum  may  be  developed  into  two  beings.  In  the  majority  of  cases, 
twins  are  of  the  same  sex,  though  sometimes  the  sexes  are  different. 
In  some  cases  there  are  two  full  sets  of  membranes,  each  foetus  having 
its  distinct  decidua,  placenta  and  chorion ;  in  others  there  is  a  single 
chorion  and  a  double  amnion ;  but  in  some,  both  foetuses  are  enclosed  in 
the  same  amnion.  As  a  rule  the  two  placentae  are  distinct ;  but  some- 
times there  is  a  vascular  communication  between  them,  or  what  appears 
to  be  a  single  placenta  may  give  origin  to  two  urabihcal  cords.  If  there 
is  but  a  single  chorion  and  amnion  and  a  single  placenta,  it  has  been 
thought  that  the  two  beings  are  developed  from  a  single  ovum  ;  other- 
wise it  would  be  necessary  to  assume  that  there  were  originally  two  sets 
of  membranes  which  had  become  fused  into  one.  The  instances  on 
record  of  twins,  one  white  and  the  other  black,  show  conclusively  that 
two  ova  may  be  developed  in  the  uterus  at  the  same  time.  While  there 
can  be  no  doubt  of  this,  the  question  of  the  possibility  of  the  develop- 
ment of  two  beings  from  a  single  ovum  remains  unsettled. 

As  pathological  conditions,  extra-uterine  pregnancies  occur,  in  which 
the  fecundated  ovum,  forming  its  attachments  in  the  Fallopian  tube 
(Fallopian  pregnancy)  or  within  the  abdominal  cavity  (abdominal  preg- 
nancy), undergoes  a  certain  degree  of  development.  The  uterus  usually 
enlarges  in  these  instances  and  forms  an  imperfect  decidua. 

Cause  of  the  First  Cofitractions  of  the  Uterus  in  Normal  Parturition.  — 
The  first  contraction  of  the  uterus  in  normal  parturition  is  undoubtedly 
referable  to  some  change  in  the  attachment  of  its  contents,  which  causes 
the  foetus  and  its  membranes  to  act  as  a  foreign  body.  When  for  any 
reason  it  is  advisable  to  empty  the  uterus  before  the  full  term  of 
pregnancy,  the  physiological  method  of  bringing  on  the  contractions 
of  this  organ  is  to  separate  cautiously  a  portion  of  the  membranes,  as  is 


854  EMBRYOLOGY 

often  done  by  introducing  an  elastic  catheter  between  the  ovum  and  the 
uterine  wall.  A  certain  time  after  this  operation,  the  uterus  contracts 
to  expel  the  ovum,  which  then  acts  as  a  foreign  body. 

In  the  normal  state,  toward  the  end  of  pregnancy,  the  cells  of  the 
decidua  vera  and  of  that  portion  of  the  placenta  attached  to  the  uterus 
undergo  fatty  degeneration,  and  in  this  way  there  is  a  progressive  separa- 
tion of  the  outer  membrane,  so  that  the  contents  of  the  uterus  gradually 
lose  their  anatomical  connection  with  the  mother.  When  this  change 
has  advanced  to  a  certain  extent,  the  uterus  begins  to  contract ;  each  con- 
traction then  separates  the  membranes  more  and  more,  the  most  depend- 
ent part  pressing  on  the  os  internum  ;  and  the  subsequent  contractions 
are  due  to  reflex  action.  The  first  "  pain  "  is  induced  by  the  presence 
of  the  foetus  and  its  membranes  as  a  foreign  body,  a  mechanism  similar 
to  that  which  obtains  when  premature  labor  has  been  brought  on  by 
separation  of  the  membranes. 

According  to  Korner,  there  exists  in  the  spinal  cord,  at  the  site  of 
the  first  and  second  lumbar  vertebrae,  a  reflex  centre  for  parturition. 
This,  like  other  centres  in  the  cord,  is  subordinate  to  a  centre  situated  in 
the  bulb. 

The  mechanism  of  parturition,  although  this  is  entirely  a  physiologi- 
cal process,  is  considered  elaborately  in  works  on  obstetrics.  The  first 
contractions  of  the  uterus,  by  pressing  the  bag  of  waters  against  the  os 
internum,  gradually  dilate  the  cervix ;  the  membranes  usually  rupture 
when  the  os  is  pretty  fully  dilated,  and  the  amniotic  fluid  is  discharged; 
the  head  then  presses  on  the  outlet ;  and  the  uterine  contractions  be- 
coming more  and  more  vigorous  and  efficient,  the  child  is  brought  into 
the  world,  this  being  followed  by  the  expulsion  of.  the  membranes  and 
placenta.  There  then  follows  a  tonic  contraction  of  the  muscular  walls 
of  the  uterus,  which  becomes  a  hard  globular  mass,  easily  felt  through 
the  flaccid  abdominal  walls.  The  very  contractions  of  the  muscular 
fibres  of  the  uterus  which  expel  the  foetus  close  the  vessels  ruptured  by 
the  separation  of  the  placenta  and  arrest  haemorrhage  from  the  mother. 
The  changes  which  then  take  place  in  the  respiration  and  circulation  of 
the  infant  have  been  considered  in  connection  with  the  development  of 
the  circulatory  system. 

Involution  of  tlie  Uterus.  —  At  four  to  six  days,  and  seldom  later  than 
eight  days  after  parturition,  the  uterus  has  sensibly  advanced  in  the 
process  of  involution ;  and  it  is  then  gradually  reduced  to  the  size  and 
structure  which  it  presents  during  the  non-pregnant  condition,  though 
it  never  becomes  quite  so  small  as  in  the  virgin  state.  The  new  mucous 
membrane,  which  has  been  developing  during  the  latest  periods  of  preg- 
nancy, becomes  perfect  at   about  the  end  of  the  second  month  after 


NORMAL   PARTURITION 


855 


delivery.  It  has  then  united,  at  the  os  internum,  with  the  mucous  mem- 
brane of  the  neck,  which  has  not  participated  in  the  formation  of  the 
decidua.  The  muscular  fibres,  after  parturition,  present  granules  and 
globules  of  fat  in  their  substance,  and  are  gradually  reduced  in  size  as 
the  uterus  becomes  smaller.  Their  involution  is  complete  at  about  the 
end  of  the  second  month.  During  the  first  month,  and  particularly 
within  the  first  two  weeks  after  delivery,  there  is  a  sero-sanguinolent 
discharge  from  the  uterus,  which  is  due  to  disintegration  of  the  blood 
and  of  the  remains  of  the  membranes  in  its  cavity,  this  debris  being 
mixed  with  a  certain  quantity  of  sero-mucous  secretion.  This  discharge 
constitutes  the  lochia.  It  is  at 
first  red  but  becomes  paler  as  it 
is  reduced  in  quantity. 

Meconiitin.  —  At  about  the 
fifth  month  there  is  a  certain 
quantity  of  secretion  in  the 
intestinal  canal,  which  becomes 
more  abundant,  particularly  in 
the  large  intestine,  as  develop- 
ment advances.  This  is  rather 
light  colored  or  grayish  in  the 
upper  portion  of  the  small  in- 
testine, becoming  yellowish  in 
the  lower  portion,  and  it  is  of  a 
dark  greenish  color  in  the  colon. 
The  dark,  pasty,  adhesive  mat- 
ter, which  is  discharged  from  the  rectum  soon  after  birth,  is  called 
meconium. 

The  meconium  appears  to  consist  of  a  thick  mucous  secretion,  with 
abundant  grayish  granules,  a  few  fatty  granules,  intestinal  epithelium, 
and  frequently  crystals  of  cholesterin.  The  color  seems  to  be  due  to 
granules  of  the  coloring  matter  of  the  bile ;  but  the  bihary  salts  can 
not  be  detected  in  the  meconium  by  Pettenkofer's  test.  The  constituent 
of  meconium  that  possesses  the  greatest  physiological  importance,  is 
cholesterin.  Although  but  few  crystals  of  cholesterin  are  found  on 
microscopical  examination,  the  simplest  processes  for  its  extraction  will 
reveal  the  presence  of  this  substance  in  large  quantity.  In  a  specimen 
of  meconium  in  which  a  quantitative  examination  was  made,  the  pro- 
portion of  cholesterin  was  6.245  parts  per  1000  (Flint).  The  meconium 
contains  cholesterin  and  no  stercorin ;  stercorin  in  the  adult  resulting 
from  a  transformation  of  cholesterin  by  the  digestive  Hquids,  which  are 
not  secreted  durins;  intra-uterine  life. 


Fig.  247.  —  Cholesteriii  extracted  from  meconium. 


856  EMBRYOLOGY 

None  of  the  secretions  concerned  in  digestion  appear  to  be  produced 
in  utero,  and  it  is  also  probable  that  the  true  biliary  salts  are  not  formed 
at  that  time ;  but  the  katabolic  processes  and  excretion  are  then  active, 
and  the  cholesterin  of  the  meconium  is  the  product  of  the  excretory 
action  of  the  liver.  The  relations  of  cholesterin  as  a  product  of  katabo- 
lism  have  already  been  very  fully  discussed,  in  connection  with  the  bile 
and  with  excretion. 

Dexti'al  Pjrcminence.  —  Most  persons  use  the  right  arm,  leg,  eye, 
etc.,  in  preference  to  the  left ;  but  exceptionally  some  use  the  left  instead 
of  the  right.  Exceptions,  however,  in  regard  to  the  eye,  are  not  infre- 
quent. There  can  be  no  doubt  of  the  fact  of  a  natural  dextral  pre- 
eminence, and  also  that  left-handedness  is  congenital,  difficult  if  not 
impossible  to  correct  entirely,  and  not  due  simply  to  habit.  It  would 
appear  that  there  must  be  some  condition  of  organization,  which  pro- 
duces dextral  preeminence  in  the  great  majority  of  persons,  and  left- 
handedness,  as  an  exception ;  but  what  this  condition  is,  it  is  very 
difficult  to  determine.  An  explanation  offered  by  some  anatomists  is 
that  the  right  subclavian  artery  arises  nearer  the  heart  than  the  left, 
that  the  right  arm  is  therefore  better  supplied  with  arterial  blood, 
develops  more  fully,  and  consequently  is  commonly  used  in  preference 
to  the  left ;  but  exceptional  predominance  of  the  left  hand  can  not  be 
explained  in  this  way. 

The  most  important  anatomical  and  pathological  facts  bearing  on 
the  question  under  consideration  are  the  following  :  Boyd  has  shown 
that  the  left  side  of  the  brain  almost  invariably  exceeds  the  right  in 
weight,  by  about  one-eighth  of  an  ounce  (3.5  grams).  In  aphasia  the 
lesion  is  almost  always  on  the  left  side  of  the  brain.  These  facts  point 
to  a  predominance  of  the  left  side  of  the  brain,  which  presides  over  the 
movements  of  the  right  side  of  the  body.  Again,  a  few  cases  of  aphasia 
with  left  hemiplegia,  the  lesion  being  on  the  right  side  of  the  brain,  have 
been  reported  as  occurring  in  left-handed  persons.  Ogle  gives  several 
such  instances,  in  which  the  brain-lesion  was  on  the  right  side.  In  two 
left-handed  individuals,  the  brain  was  examined  and  compared  with  the 
brain  of  right-handed  persons.  It  was  found  that  the  brain  was  more 
complex  on  the  left  side  in  the  right-handed,  and  on  the  right  side,  in 
the  left-handed.  Bastian  found  the  gray  matter  of  the  brain  ordinarily 
to  be  heavier  on  the  left  than  on  the  right  side.  In  regard  to  the  cause 
of  the  superior  development  of  the  left  side  of  the  brain,  the  only  ex- 
planation offered  is  the  fact  that  the  arteries  going  to  the  left  side  usually 
are  larger  than  those  on  the  right.  There  are  no  observations  respect- 
ing the  comparative  size  of  the  arteries  on  the  two  sides  in  left-handed 
persons. 


DEXTRAL   PREilMIXEXCE  857 

Reasoning  from  the  facts  just  stated,  Ogle  has  assumed  that  dextral 
preeminence  depends  on  a  natural  predominance  of  the  left  side  of  the 
brain,  the  reverse  obtaining  in  the  left-handed.  Ordinarily  it  is  true  that 
the  members  of  the  right  side  are  stronger  than  the  left,  particularly  the 
arm  ;  but  this  is  not  always  the  case,  even  in  the  right-handed,  although 
the  right  hand  is  more  conveniently  and  easily  used  than  the  left.  In 
many  feats  of  strength,  the  left  arm  appears  less  powerful  than  the  right, 
because  there  is  less  command  over  the  muscles.  As  regards  the  cause 
of  the  superior  development  of  the  left  side  of  the  brain,  it  must  be 
admitted  that  the  anatomical  explanation  is  not  entirely  satisfactory. 
It  is  a  fact,  however,  that  the  two  sides  of  the  brain  usually  are  not 
exactly  equal  in  their  development,  the  left  side  being  superior  to  the 
right,  and  that  the  muscles  of  the  right  side  of  the  body  are  used  habitu- 
ally in  preference  to  those  of  the  left  side. 

While  it  is  not  yet  possible  to  explain  why  the  left  side  of  the  brain 
has  peculiar  psychic  functions  not  possessed  by  the  right  side,  it  is  never- 
theless true  that  intellectual  processes  take  their  origin  mainly  —  and  in 
some  instances  entirely  —  in  the  left  half  of  the  cerebrum.  In  man,  sight, 
hearing  and  speech  are  closely  connected  with  mental  operations,  at 
least  in  so  far  as  they  give  rise  to  or  express  ideas.  The  two  eyes  are 
necessary  to  perfect  vision  ;  but  the  psychic  visual  centre,  which  receives 
ideas  or  meaning  conveyed  by  objects  seen,  is  on  the  left  side  of  the 
cerebrum,  except  in  the  left-handed.  The  same  may  be  said  of  the 
sense  of  hearing,  the  psychic  auditory  centre  being  on  the  left 
side,  except  in  the  left-handed.  The  location  of  the  speech-centre  on 
the  left  side  was  made  in  1836  (Marc  Dax);  and  a  case  of  aphasia  with 
right  hemiplegia  was  fully  reported  by  Pourfour  du  Petit,  in  1766. 
Agraphia,  or  inability  to  express  ideas  in  written  language,  is  due  to 
lesion  of  the  left  side  of  the  brain.  All  these  conditions  are  reversed, 
however,  in  the  left-handed.  When  one  eye  is  used  as  a  means  of  form- 
ing a  judgment  or  opinion,  it  usually  is  the  right  eye  for  the  right-handed 
and  the  left  eye  for  the  left-handed.  Curiously  enough,  it  has  lately 
been  observed  that  deaf-mutes  may  have  an  aphasia  that  prevents  the 
use  of  the  right  hand  in  the  sign-language.  It  seems,  indeed,  that 
movements,  more  or  less  automatic,  may  be  executed  by  the  muscles  of 
either  side,  remembering,  always,  that  muscles  of  the  left  as  well  as 
of  the  right  side  may  be  educated  ;  but  in  movements  that  involve  men- 
tal operations  and  attention  at  the  time  they  are  made,  the  right  side 
usually  predominates.  Apart  from  the  question  of  education  of  muscles, 
it  appears  that  the  more  automatic  acts  are  performed  indifferently  bv 
either  the  right  or  the  left  side ;  but  movements  more  closely  connected 
with  direct  mental  operations  are  made  preferably  by  right  muscles  in 


858  EMBRYOLOGY 

the  right-handed  and  by  left  muscles  in  the  left-handed.  Still,  while 
this  may  satisfactorily  explain  dextral  preeminence,  it  does  not  explain 
the  preeminence  of  the  left  side  of  the  brain. 

Development  after  Birth  —  Ages  and  Death 

When  the  infant  is  born,  the  organs  of  special  sense  and  the  intelli- 
gence are  dull ;  there  is  then  very  little  muscular  power ;  and  the  new 
being  for  several  weeks  does  little  more  than  eat  and  sleep.  The  natural 
food  at  this  time  is  the  milk  of  the  mother ;  and  the  digestive  secretions 
do  not  for  some  time  possess  the  varied  solvent  properties  that  are  found 
in  the  adult,  though  observations  on  the  secretions  of  the  infant  are  few 
and  rather  unsatisfactory.  The  full  activity  of  pulmonary  respiration  is 
gradually  and  slowly  established.  Young  animals  appropriate  a  compara- 
tively small  quantity  of  oxygen,  and  just  after  birth  they  present  a  much 
greater  power  of  resistance  to  asphyxia  than  the  adult.  The  power  of 
maintaining  the  animal  temperature  also  is  much  less  in  the  newly-born. 
The  processes  of  ossification,  development  of  the  teeth  etc.,  have  already 
been  described.  The  hairs  are  shed  and  replaced  by  a  new  growth  a 
short  time  after  birth.  The  fontanelles  gradually  diminish  in  size  after 
birth  and  are  completely  closed  at  the  age  of  about  four  years. 

The  period  of  life  which  dates  from  birth  to  the  age  of  two  years  is 
called  infancy.  At  the  age  of  two  years  the  transition  takes  place  from 
infancy  to  childhood.  The  child  is  then  able  to  walk  without  assistance, 
the  food  is  more  varied  and  the  digestiv^e  operations  are  more  complex. 
The  special  senses  and  the  intelligence  become  more  acute,  and  the  being 
begins  to  learn  to  express  ideas  in  language.  The  child  gradually  develops, 
and  the  milk-teeth  are  replaced  by  the  permanent  teeth.  At  puberty, 
which  begins  between  the  fourteenth  and  the  seventeenth  years  —  a 
little  earlier  in  the  female  —  the  development  of  the  generative  organs 
is  attended  with  important  physical  and  moral  changes. 

The  different  ages  recognized  by  physiologists  are  the  following : 
Infancy,  from  birth  to  the  age  of  two  years  ;  childhood,  to  the  time  of 
puberty  ;  adolescence,  or  youth,  to  the  twenty-fifth  year  ;  adult  age,  to  the 
thirty-fifth  year ;  middle  Hfe,  to  the  fiftieth  year ;  old  age,  to  the  sixtieth 
year ;  and  then,  extreme  old  age.  A  man  mav  be  regarded  at  his  maxi- 
mum of  intellectual  and  physical  development  at  about  the  age  of  thirty- 
five,  and  he  begins  to  decline  after  the  sixtieth  year,  although  as  regards 
intellectual  vigor,  this  has  many  exceptions. 

As  regards  nutrition,  it  may  be  stated  in  general  terms  that  the  appro- 
priation of  new  matter  (anabolism)  is  a  little  superior  to  katabolism,  up 
to  about  the  age  of  twenty-five  years  ;  between  twenty-five  and  forty-five, 


DEVELOP-AIEXT    AFTER    BIRTH  — AGES    AND    DEATH  859 

these  two  processes  are  nearly  equal;  and  at  a  later  period  the  nutrition 
does  not  completely  supply  the  physiological  waste  of  the  tissues,  the 
proportion  of  organic  to  inorganic  matter  gradually  diminishes,  and 
death  follows  as  an  inevitable  consequence  of  life.  In  old  age  the  mus- 
cular movements  gradually  become  feeble ;  the  bones  contain  an  excess 
of  inorganic  matter;  the  ligaments  become  stiff;  the  special  senses 
are  usually  somewhat  obtuse  ;  and  there  is  a  diminished  capacity  for 
mental  labor,  with  more  or  less  loss  of  memory  and  of  intellectual  \-igor. 
It  is  a  curious  fact  that  remote  events  are  more  clearly  and  easily  recalled 
to  the  mind  in  old  age  than  those  of  recent  occurrence ;  and,  indeed,  early 
impressions  and  prejudices  then  appear  to  be  unusually  strong. 

It  frequently  happens  in  old  age  that  some  organ  essential  to  life 
gives  way,  and  that  this  is  the  immediate  cause  of  death,  or  that  an  old 
person  is  stricken  down  by  some  disease  to  which  his  age  renders  him 
peculiarly  liable.  It  is  so  infrequent  to  obsen,'e  a  perfectly  physiological 
life  continuing  throughout  the  successive  ages  of  man,  that  it  is  difficult 
to  present  a  picture  of  physiological  death  ;  but  it  sometimes  occurs  that 
there  is  a  gradual  fading  away  of  vitality  in  old  persons,  who  die  without 
being  affected  with  any  special  disease.  It  also  is  difficult  to  fix  the 
natural  period  of  human  life.  Some  persons  die,  apparently  of  old  age, 
at  seventy,  and  it  is  rare  that  life  is  preserved  beyond  one  hundred  years. 
The  tissues  usually  die  successively  and  not  simultaneously,  nearly  all 
being  dependent  on  the  circulating,  oxygen-carrying  blood  for  the  main- 
tenance of  their  physiological  properties.  It  has  been  demonstrated, 
indeed,  that  the  properties  of  tissues  may  be  restored  for  a  time,  after 
apparent  death,  by  the  injection  of  blood  into  their  vessels. 

After  death  there  often  is  a  discharge  of  the  contents  of  the  rectum 
and  bladder ;  and  parturition,  even,  has  been  known  to  take  place.  The 
appearance  which  indicates  growth  of  the  beard  after  death  is  probably 
due  to  shrinking  of  the  skin  and,  perhaps,  contraction  of  the  smooth  mus- 
cular fibres  attached  to  the  hair-follicles.  The  most  important  phenom- 
enon, however,  observed  before  putrefaction  begins,  is  a  general  rigidity 
of  the  muscular  system,  or  rigor  mortis,  which  has  already  been  de- 
scribed. 


ATLAS 


INTRODUCTION    TO    THE    ATLAS 


As  has  been  stated  in  the  Preface,  the  original  figures  in  the  Atlas  are  reproductions  of 
actual  objects  by  the  three-color  photographic  process,  without  retouching  of  the  process-plates. 
Figures  and  letters  are  not  used  to  designate  the  special  histological  structures.  I  have  indi- 
cated, however,  as  clearly  as  I  could  without  such  aid,  what  I  specially  desire  to  illustrate  in 
each  picture.  Most  of  the  figures  it  has  been  easy  to  describe;  but  others  will  be  found  to 
require  careful  and  patient  study,  particularly  those  relating  to  embryology.  In  the  study 
of  these  pictures,  it  will  be  of  advantage  to  consult  first  the  descriptions  and  illustrations  —  which 
latter  are  more  or  less  diagrammatic — given  in  the  text.  It  should  then  be  easy  to  recognize  the 
structures  as  they  are  shown  in  the  Atlas.  Indeed,  I  have  endeavored  to  supplement  the  text 
with  what  approaches  actual  laboratory  study.  The  hours  spent  in  such  work,  although  without 
the  advantage  of  a  microscope  and  personal  demonstration,  can  hardly  fail  of  practical  value. 

It  will  be  e^adent  to  histologists  that  I  have  been  peculiarly  fortunate  in  certain  objects  for 
reproduction.  The  section  of  the  stomach,  showing  peptic  cells  and  acid-cells,  I  believe  to  be 
unique  ;  the  platelets  from  human  blood  are  seldom  so  clearly  shown  ;  the  same  may  be  said 
of  branching  heart-muscle  ;  serous  and  mucous  cells  and  demilunes  of  the  submaxillary ;  intes- 
tinal glands  ;  islands  of  Langerhans ;  solitary  glands  ;  structure  of  adrenals,  spleen,  thyroid, 
and  thymus ;  bone-canaliculi  and  elastic  cartilage.  The  sections  of  the  human  embr}-o  are 
seldom  seen  and  will  repay  careful  examination. 

As  a  matter  that  can  not  fail  to  be  of  interest,  I  add  to  this  introduction  a  note  on  tech- 
nique, by  Dr.  Learning  :  — 


NOTE   ON   THE   TECHNIQUE   OF   PHOTOMICROGRAPHY   IN   COLORS 

As  at  the  present  time  photomicrography  finds  one  of  its  most  useful  applications  in 
medicine,  it  seems  but  natural  to  expect  that  the  future  photomicrographer  should  be  found 
among  medical  students.  Bearing  this  in  mind,  a  few  words  on  the  photomicrographs  in  color 
in  the  Atlas  may  prove  of  interest.  The  apparatus  need  not  be  discussed  ;  any  first-class  instal- 
lation will  be  quite  equal  to  the  demands  upon  it ;  but  it  is  essential  that  the  operator  should 
be  thoroughly  familiar  with  his  apparatus  and  its  peculiarities.  The  most  important  of  the 
accessories  will  be  the  color-filters,  or  screens,  whereby  the  rays  not  needed  are  absorbed  before 
they  reach  the  object,  and  only  those  desired  for  each  particular  negative  are  allowed  to  pass 
through.  It  must  be  remembered  that  for  our  purposes  the  visible  spectrum  is  divided  arbi- 
trarily into  three  zones ;  one  near  the  red  end,  one  near  the  blue  end  and  one  near  the  middle. 
From  each  of  these  zones  one  color  is  taken,  and  these  three  colors  form  the  primary-,  or  print- 
ing colors;  they  are  a  particular  pinkish  or  madder-red,  a  canary-yellow,  and  a  brilliant  greenish 
blue.  If  we  combine  the  above  in  pairs,  we  obtain  an  entirely  new  set  of  colors,  and  these  form 
our  taking  screens,  or  color-filters.  These  new  colors  are  termed  the  secondary  colors.  Thus, 
primary  red  plus  primary  yellow  makes  secondary  red  —  an  orange-red  screen  which  the 
spectroscope  will  show  to  admit  the  red  end  of  the  spectrum  only  ;  primary  red  plus  primary 
blue  equals  secondary  violet  —  blue  end  only ;  and  finally,  primary  blue  plus  primar\'  yellow 
makes  secondary  green  —  middle  only.  It  will  be  seen  from  the  above,  that  these  secondary 
colors  are  complementary  to  the  primary'.  For  example,  an  object  taken  through  the  green 
screen  (blue  and  yellow)  is  printed  in  red  ;   the  violet  screen  (blue   and  red)  is  printed  in 

863 


864  ATLAS 

yellow ;  the  orange  screen  (red  and  yellow)  is  printed  in  blue.  Having  such  screens,  we  find 
that  they  are  valuable  for  ordinary  photomicrography  where  the  results  are  to  be  viewed  in 
monocrome,  as  we  are  enabled  to  emphasize  certain  points  much  better  than  when  dependent 
on  the  orthochromatic  yellow  screen  alone.  Now,  the  study  of  stained  sections  through  the 
microscope  will  impress  the  fact  upon  our  minds  that  the  great  majority  are  stained  with  two 
colors  at  most;  and  as  the  section  before  staining  was  white,  or  nearly  transparent,  the  need  of 
usino'  three  colors  for  its  reproduction  does  not  exist.  It  will  suffice  in  many  cases,  therefore, 
to  use  but  two  screens  —  taking  a  negative  with  each  —  and  leave  the  reproducer  to  mix  his 
printing  inks  so  that  two  impressions  will  give  a  satisfactory  result.  Most  of  the  photomicro- 
graphs in  this  Atlas  were  taken  in  this  manner,  only  a  few  in  three  colors,  and  the  remainder  in 
one  or  two,  as  the  subject  seemed  to  demand.  By  eliminating  one  process  in  this  way  through 
all  steps  of  the  work,  there  is  a  great  gain  in  every  direction,  —  less  liability  to  error  in  the 
original  negatives,  sharper  impressions  in  the  reproduction,  and  a  saving  in  time  and  cost 
throughout. 

An  isochromatic  plate  was  used  with  all  colored  sections,  but  not  one  specially  dyed  for 
each  particular  region  of  the  spectrum  that  the  screens  allowed  to  pass  through.  Development 
was  with  glycin,  the  plates  being  allowed  to  stay  undisturbed  in  the  tray  until  developed,  with- 
out rocking.  Two  negatives  were  taken  on  the  same  plate,  usually  the  red  and  blue  printing 
negatives,  by  means  of  a  sliding  plate-holder,  and  thus,  as  they  were  afterward  developed 
together,  each  exposure  had  to  be  carefully  timed  to  the  ratio  of  its  respective  screen.  The 
screens  had  the  following  ratio  to  each  other,  —  green,  3  ;  red,  5  ;  violet,  9,  the  electric  arc 
being  the  illuminant.  The  exposure  varied  according  to  the  objective,  density  of  object,  magni- 
fication, position  of  substage  condenser,  and  length  of  camera  draw,  between  J^  of  a  second  and 
five  minutes,  the  usual  time  being  three  to  ten  seconds.  As  for  illustrative  purposes,  flatness 
of  field  and  depth  of  focus  were  important  points,  use  was  made  of  an  objective  of  low  power 
combined  with  a  high  eyepiece  and  sufficient  camera  length  to  obtain  the  desired  magnification. 

—  Edward  Leaming. 

March,  1905. 


ATLAS 

LIST   OF    PLATES 

PLATE    I 

Blood  and  Bone-marrow 

(Sobotta) 

PLATE  II 
By  Three-color  Photographic  Process 

Fig.  I  Fig.  4 

Human  blood  Trachea 

Fig.  2  Fig.  5 

Hemin  crystab  Lung,  injected 

Fig.  3  Fig.  6 

Heart-muscle  Lung,  stained 

PLATE    III 

Sections  of  Blood\'essels 
(Sobotta) 

PLATE    IV 
By  Three-color  Photographic  Process 
Fig.  I  Fig.  4 

Submaxillar}-  gland  Duodenum  —  glands  of  Brunner 

Fig.  2  Fig.  5 

CEsophagus  Small  intestine  —  %-illi  and  goblet-cells 

Fig.  3  Fig.  6 

Human  stomach  Small  intestine  —  \illi,  etc. 

PLATE  V 
By  Three-color  Photographic  Process 

Fig.  i  Fig.  4 

Duodenum  of  cat,  injected  Human  pancreas 

Fig.  2  Fig.  5 

Small  intestine  of  rat,  injected  Solitary  gland 

Fig.  3  Fig.  6 

Bloodvessels  of  pancreas  Human  breast 

K  865 


866  ATLAS 

PLATE  VI 

Section  of  the  Human  Scalp 
(Sohotta) 

PLATE  VII 

By  Three-color  Photographic  Process 

Fig.  I  Fig.  4 

Sebaceous  glands  Kidney,  injected 

Fig.  2  Fig.  5 

Sweat-glands  Liver,  injected  and  stained 

Fig.  3  Fig.  6 

Kidney,  injected  and  stained  Liver,  stained 

PLATE   VIII 

Lymph-gland  —  Spleen 

(Sobotta) 


PLATE  IX 

By  Three-color  Photographic  Process 

Fig.  I  Fig.  4 

Adrenal  Thyroid 

Fig.  2  Fig.  5 

Spleen,  injected  Thymus 

Fig.  3  Fig.  6 

Spleen,  stained  Human  muscle 


PLATE  X 

By  Three-color  Photographic  Process 

Fig.  I  Fig.  4 

Muscle  of  pig,  injected  Elastic  cartilage 

Fig.  2  Fig.  5 

Bone,  injected  Fallopian  tube 

Fig.  3  Fig.  6 

Bone-development  Placenta  and  membranes 

PLATE   XI 

Nerve-cells 
(Sobotta) 

PLATE   XII 

Spinal  Cord 
(Sobotta) 


ATLAS 

PLATE  XIII 

Two  Early  Stages  of  Cleavage  of  the  Egg 
(Wilson) 

PLATE   XIV 

Two  Later  Stages  of  Cleavage  of  the  Egg 

(Wilson) 

PLATE   XV 
By  Three-color  Photographic  Process 

^'^-  '  Fig.  4 

Section  of  the  ovary  Section  of  the  chick 

^^^°:  2  Fig.  5 

^^^^'^^^  Section  of  the  chick 
,          ^^^-  3  Fig.  6 

Section  of  the  chick  Section  of  the  chick 

PLATE   XVI 

By  Three-color  Photographic  Process 

Fig.  I 

High  section  through  thorax  of  human  embryo 

Fig.  2 

Low  section  through  thorax  of  human  embryo 

Fig.  3 

High  section  through  abdomen  of  human  embryo 

Fig.  4 

Low  section  through  abdomen  of  human  embryo 

Fig.  5 

Sagittal  section  of  a  pig-embryo 

Fig.  6 
Sagittal  section  of  a  pig-embryo 


86/ 


PLATE   I 

Human  Blood,  x  700  (Sobotta) 

(Dry  preparation.     Ether-alcohol.     Hematoxylin-eosin.     In   i,  3,  and  4,  Ehrlich's  triacid 
solution.) 

6  to  12,  inclusive,  erythrocytes,  or  red  corpuscles  (9,  nucleated  corpuscle). 

1,  small  lymphocyte. 

2,  3,  polynuclear  leucocytes,  with  neutrophile  granulation. 
4,  5,  14,  16,  18,  ordinary  polynuclear  leucocytes. 

15,  19,  21,  leucocytes,  with  eosinophile  granulation. 
13,  20,  large  lymphocytes. 
17,  mononuclear  leucocyte. 

From  the  Bone-marrow  of  a  Mouse,  x  700 

22,  polynuclear  giant-cell. 

23,  28,  marrow-cells. 
25,  26,  eosinophile  cells. 

27,  28,  cells  with  beginning  karyokinesis. 

29,  erythrocyte. 

30,  31,  nucleated  erythrocytes. 

These  figures  can  be  studied  to  best  advantage  in  connection  with  the  text  relating  to  the 
development  of  blood-corpuscles  and  leucocytes. 


PLATE  I 


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PLATE    II 

Fig.  I.    Human  blood  (Xocht- Romano wsky  stain),  X  335.  —  Ewing. 

This  figure  shows  the  red  blood-corpuscles  (erythrocytes),  two  clumps  of  platelets  near  the 
centre  of  the  field  and  to  the  right  and  one  large  mononuclear  leucocyte.  The  outlines  of  the 
leucocyte  are  faint  and  the  nucleus  is  stained  a  dark  purple. 

Fig.  2.    Hemin  crystals,  X  500.  —  Schultze. 

This  specimen  was  prepared  from  a  human  blood-stain  on  muslin,  4S  hours  old.  The  spot 
was  extracted  with  a  1-2000  sali-solution. 

Fig.  3.    Human  heart-muscle  (hematein  and  eosin),  x  125.  —  Ferguson. 

This  figure  shows  the  branching  and  inosculation  of  the  fibres  of  the  heart-muscle. 

Fig.  4.  Cross-section  of  the  trachea  of  the  dog  (hematoxylin-eosin),  x  20. — Author's 
collection. 

At  the  top  of  this  section  is  the  layer  of  epithelium,  darkly  stained,  covering  the  mucosa ; 
below  is  the  submucosa,  with  three  mucous  glands  ;  below,  stained  blue,  is  the  cartilage,  with 
the  perichondrium  next  the  submucosa ;    beneath  the  cartilage  is  the  outer  fibrous  coat. 

Fig.  5.    Section  of  the  lung  of  a  sheep,  injected,  x  75.  —  Author's  collection. 

This  figure  shows  the  bloodvessels,  especially  the  capillaries.  The  large  vessel  at  the  lower 
part  is  a  branch  of  the  pulmonary  artery ;  the  large  vessels  near  the  upper  border  and  to  the 
right  are  branches  of  the  pulmonary  veins  ;  some  of  the  rounded  or  ovoid  spaces,  each  bounded 
by  a  ring  of  capillaries  seen  vertically,  are  alveoli,  one  of  these  being  nearly  in  the  centre  of  the 
field. 

Fig.  6.    Section  of  the  lung  of  a  child  (hematoxylin-eosin),  X  125.  —  Ewing. 

The  larger  spaces  shown  in  this  section  are  the  infundibula  ;  the  smaller  spaces  are 
alveoH,  some  opening  into  infundibula  and  some  surrounded  by  the  pulmonary  tissue  ;  at  the 
top  of  the  figure,  part  of  a  bronchiole,  lined  with  epithelium,  is  seen. 


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PLATE   III 
Sections  of  Bloodvessels  (Sobotta) 

Fig.  I.  Section  of  vein  —  from  an  executed  criminal  (Zenker's  solution;  Weigert's  elastic- 
tissue  stain  ;    alum-carmin),  x  50.     The  elastic  tissue  is  stained  dark  violet. 

A,  adventitia  ;  /,  intima  ;  Jll,  media  ;  /;«,  longitudinal  muscle  of  the  adventitia  ;  vz',  vasa 
vasorum. 

Fig.  2.    Section  of  a  large  branch  of  the  internal  spermatic  artery,  x  80. 

A,  adventitia  ;   ei,  elastic  lamella  of  the  intima  ;    en,  endothelium  ;  /,  intima  ;  J/,  media. 

Fig.  3.    Section  of  a  small  artery,  x  220. 

A,  adventitia  ;  3/,  media  ;  en,  endothelium  ;  ei,  elastic  lamella  of  the  intima  ;  ee,  elastic 
lamella  of  the  media. 

Fig.  4.    Section  of  a  very  small  artery. 

Lettering  as  in  Fig.  3. 


PLATE  III 


Fig.l. 


Fig.  4-. 


PLATE   IV 

Fig.  I.    Section  of  the  submaxillary  gland  of  the  human  adult  (hematoxylin-eosin,  x  125). 

—  Ewing. 

This  figure  shows  the  so-called  serous  acini,  in  which  the  cells  are  deeply  stained  ;  those 
with  the  cells  relatively  clear  are  mucous  acini ;  a  number  of  demilunes  are  distinctly  shown  ; 
near  the  left  lower  border  of  the  figure  is  a  cross-section  of  a  small  duct,  lined  with  epithelium. 

Fig.  2.  Section  of  the  oesophagus  of  the  dog  (hematoxylin-eosin),  x  10.  —  Author's 
collection. 

This  section  shows,  at  the  upper  border,  the  layer  of  epithelium,  deeply  stained,  resting  on 
a  thick  corium  ;  beneath  the  corium  is  a  layer  of  mucous  glands  ;  just  beneath  the  glands,  the 
fibrous  tissue  is  plainly  shown  ;  beneath  the  fibrous  tissue  is  the  inner  layer  of  the  muscular 
coat,  composed  of  striated  and  non-striated  fibres,  with  the  outer  layer  below,  deeply  stained  ; 
beneath  this  is  the  outer  layer  of  fibrous  tissue. 

Fig.  3.    Section  of  the  stomach  (hematoxylin-eosin),  x  125. — Author's  collection. 

This  section  is  from  the  greater  curvature,  near  the  pylorus.  The  subject  was  executed  by 
electricity  at  6.01  A.M.,  April,  1905,  and  the  specimen  was  put  into  Zenker's  solution  two  min- 
utes after  death.  He  was  twenty-eight  years  of  age,  in  perfect  health  and  had  not  taken  food 
for  about  twelve  hours.  The  negatives  for  two  colors,  blue  and  red,  were  taken  a  few  days 
after  the  section  had  been  cut  and  stained. 

The  figure  shows  the  tubules  of  the  mucous  membrane,  the  acid-cells  stained  red  and  the 
peptic  cells,  blue  ;  it  should  be  studied  in  connection  with  the  text  in  the  body  of  the  book 
(see  page  188). 

It  will  be  observed  that  although  the  section  is  near  the  pylorus,  there  are  many  red  acid- 
cells  mixed  with  the  blue  peptic  cells.  There  are  no  tubes  shown  in  this  figure  that  contain 
peptic  cells  only,  although  such  tubes  existed  in  other  parts  of  the  specimen,  as  well  as  some 
tubes  nearly  filled  with  acid-cells. 

Fig.  4.    Vertical    transverse    section    of  the    duodenum    of   the  cat   (picro-carmin),  X  35. 

—  Author's  collection. 

This  figure  shows  above,  the  csecal  ends  of  the  follicles  of  Lieberkiihn  ;  below,  are  Brun- 
ner's  glands  and  connective  tissue ;  beneath  the  connective  tissue  is  a  small  portion  of  the 
muscular  coat. 

Fig.  5.    Section  of  the  small  intestine  of  an  infant  (hematoxylin-eosin),  x  125.  —  Ewing. 

This  figure  shows  sections  of  the  villi  and  of  the  tubes  ;  the  cells  are  red  and  the  nuclei 
are  blue  ;  the  great  number  of  circular  vacuoles,  that  are  unstained,  are  the  empty  portions  of 
goblet-cells. 

Fig.  6.  Lower  portion  of  the  duodenum  of  the  dog  (picro-carmin),  x  30.  —  Author's 
collection. 

This  figure  shows  above,  the  villi,  with  the  epithelium  deeply  stained ;  below,  are  the 
follicles  of  Lieberkiihn,  also  deeply  stained  ;  in  the  submucous  tissue,  are  several  glands  of 
Brunner ;  the  lowest  part  of  the  figure  shows  the  muscular  coat.  The  magnification  is  too  low 
to  show  the  cells  distinctly. 


PLATE  IV 


PLATE   V 

Fig.  I.    Section  of  the  duodenum  of  the  cat,  injected,  x  20.  —  Author's  collection. 

The  upper  part  of  this  section  shows  the  distribution  of  the  bloodvessels  in  the  villi  ;  im- 
mediately belowf  the  villi  are  the  follicles  of  Lieberkiihn,  not  defined  by  reason  of  the  low- 
magnification  ;  beneath  these  are  glands  of  Brunner  (not  well  defined),  surrounded  with  plex- 
uses of  capillaries  ;  the  bottom  of  the  figure  shows  the  peculiar  distribution  of  bloodvessels  in 
the  muscular  coat. 

Fig.  2.    Section  of  the  small  intestine  of  the  rat,  injected,  x  20.  —  Author's  collection. 

This  figure  shows  the  distribution  of  bloodvessels  in  the  villi  of  the  rat,  the  form  of  the 
villi  being  quite  different  from  the  form  of  these  structures  in  the  cat. 

Fig.   3.    Bloodvessels  of  the  pancreas  of  the  cat,  injected,  X  30.  —  Author's  collection. 

This  figure  shows  arterioles  breaking  up  into  several  plexuses  of  capillaries  surrounding 
lobules  of  the  pancreas. 

Fig.  4.    Section  of  the  human  pancreas  (hematoxylin-eosin),  x  125.  —  Ewing. 

Just  above  the  centre  of  this  figure,  is  a  collection  of  centro-acinar  cells  forming  an  island  of 
Langerhans ;  the  rest  of  the  figure  is  filled  with  the  ordinary  secreting  cells  of  the  pancreas  ; 
the  outer  and  inner  zones  of  the  cells  are  shown,  but  not  very  distinctly,  on  account  of  the 
low  magnification. 

Fig.  5.  Section  of  the  large  intestine  of  the  dog  (hematoxylin-eosin),  x  20.  —  Author's 
collection. 

This  figure  shows  the  follicles  of  Lieberkiihn  —  which  are  larger  than  in  the  small  intestine 
—  both  in  long  section  and  in  cross-section  ;  a  solitary  gland  is  in  the  centre  of  the  figure,  lying 
in  the  submucous  connective  tissue  ;  the  lowest  part  of  the  figure  shows  a  section  of  the  muscular 
coat,  deeply  stained  ;   the  connective  tissue  is  stained  red. 

Fig.  6.    Section  of  an  active  human  breast  (hematoxylin-eosin),  x  125.  —  Ewing. 

This  figure  shows  a  portion  of  a  lobule,  the  secreting  cells  presenting  nuclei  deeply 
stained  ;  a  portion  of  a  duct  is  shown  at  the  lower  part  of  the  figure. 


PLATE  V 


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PLATE   VI 

Sechon  of  the  Human  Scalp,  x  15.  —  (Sobotta.)  (From  an  executed  criminal.  Miil- 
ler's  liquid ;   hematoxylin-eosin.) 

Ap,  erector  muscle  ;  c,  corium  ;  ep,  epidermis  ;  fp,  hair-follicle  ;  KH,  "  club-hairs  " ;  //, 
papilla ;  Re,  cutis  ;  Kp,  root  of  hair ;  Sp,  shaft  of  hair  ;  ts,  subcutaneous  layer ;  x,  new 
formation  of  hair. 


PLATE  VI 


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PLATE   VII 

Fig.   I.    Section  of  the  scalp  of  an  infant  (hematoxylin-eosin),  x  35. —  Ewing. 

This  figure  shows  a  collection  of  sebaceous  glands  near  its  upper  portion  ;  below  the  hori- 
zontal diameter  is  adipose  tissue ;  a  few  sections  of  hairs  are  rather  imperfectly  shown  at  the 
left  border. 

Fig.  2.  Section  of  the  skin  of  the  sole  of  the  foot  (hematoxylin-eosin),  x  20. — Author's 
collection. 

This  figure  shows,  with  great  distinctness,  the  two  layers  of  the  epidermis,  with  spiral 
sudoriferous  ducts  in  the  horny  layer;  the  ducts  take  a  nearly  straight  course  through  the 
corium,  which  is  stained  pink  ;  the  sudoriparous  glands  He  in  the  panniculus  adiposus,  just 
beneath  the  corium. 

Fig.  3.  Section  of  the  cortical  substances  of  the  kidney  of  the  dog,  injected  and  stained 
(hematoxyhn-eosin),   x  125. —  Author's  collection. 

This  figure  shows  three  Malpighian  bodies  and  part  of  fourth,  each  enclosed  in  its  capsule. 
It  also  shows  the  general  arrangement  of  the  convoluted  tubes.  The  magnification  is  too  low 
to  show  distinctly  the  cells  lining  the  tubes. 

Fig.  4.    Section  of  the  kidney  of  the  cat,  injected,  x  125. — Author's  collection. 

This  figure  shows  only  the  glomeruli  and  the  distribution  of  capillaries  in  the  cortical 
substance. 

Fig.  5.  Cross-section  of  the  liver  of  the  pig,  injected  and  stained  (hematoxylin-eosin), 
X  125.  —  Author's  collection. 

This  figure  is  from  a  liver  injected  with  blue  through  the  portal  vein,  with  the  cells  stained. 
The  lobular  vessels  are  purple  ;  the  staining  shows  the  cells  arranged  in  radiating  columns  ;  the 
central  (intralobular)  veins  are  empty.  A  section  of  a  small  artery  appears  at  the  lower  part  of 
the  figure. 

Fig.  6.    Cross-section  of  a  lobule  of  a  pig's  liver  (hematein  and  eosin),  X  50.  —  Ferguson. 

In  this  figure  the  empty  intralobular  vein  is  shown  in  the  centre  of  the  polygonal  section 
of  the  lobule,  three  sides  of  which  are  shown  to  the  left  and  above  ;  the  hepatic  cells  are  shown 
in  slightly  wavy  columns  radiating  from  the  centre  toward  the  periphery. 


PLATE    VII 


« 


PLATE   VIII 

Lymph-gland  —  Spleen  (Sobotta) 

Fig.  I.  Transverse  section  of  a  human  cervical  lymph-gland  from  an  executed  criminal 
(sublimate;    hematoxylin-eosin),  X  i8. 

The  figure  shows  the  general  structure  of  a  lymph-gland. 

bg,  bloodvessels  ;  cf,  fibrous  capsule  ;  H,  hiluni  ;  Kz,  germ-centre  ;  nl,  lymph-nodules  ; 
sCy  cortical  substance  ;  sin,  medullary  substance  ;  tr,  trabeculse ;  via,  afferent  lymph-vessels ; 
vie,  efferent  lymph- vessels. 

Fig.  2.    Portion  of  an  injected  spleen  of  a  rabbit,  x  28. 

This  preparation  was  taken  from  the  material  of  the  Institute  for  Comparative'  Anatomy, 
Wiirzburg. 

The  arterial  trunks  of  the  lymph-nodules  (Malpighian  corpuscles)  are  injected  red,  the 
veins  and  spleen-sinuses,  blue. 

a,  artery  of  a  Malpighian  corpuscle  ;   Mkn,  Malpighian  corpuscle  ;  p,  spleen-pulp. 


PLATE  VIII 


Fig.£. 


Lah.AristE RudUi old^  Muachen : 


PLATE   IX 

Frc.  I.    Section  of  the  adrenal  body  of  the  rabbit  (picro-carmin),  x  20.  —  Author's  collection. 

This  figure  is  from  a  section  of  the  adrenal  body  taken  under  a  magnification  too  low  to 
show  the  cells.  It  shows  the  fibrous  capsule  and  the  cortical  and  medullar  substances.  The 
cortical  substance  has  a  radiated  appearance,  due  to  the  arrangement  of  the  cells  in  columns. 

Fig.  2.    Section  of  the  spleen  of  the  cat,  injected,  X  125.  —  Collection  of  Dr.  A.  W.  Baird. 

This  figure  shows  Malpighian  bodies,  which  are  gray.  The  spleenic  veins  and  sinuses  are 
filled  with  a  red  injection. 

Fig.  3.    Section  of  the  spleen  of  the  dog  (hematoxylin-eosin),  x  30.  —  Author's  collection. 

This  figure  shows  Malpighian  bodies  embedded  in  the  spleen-pulp. 

Fig.  4.    Section  of  the  thyroid  of  the  dog  (hematoxylin-eosin),  X  125.  —  Author's  collection. 

This  figure  shows  several  alveoli  lined  with  epithelial  cells  and  filled  with  colloid  substance. 
The  nuclei  are  distinct,  but  the  magnification  is  too  low  to  bring  out  the  contour  of  the  cells. 

Fig.  5.    Section  of  the  thymus  of  a  human  foetus  (hematoxyhn-eosin),  x  20.  —  Ewing. 

This  section  shows  parts  of  several  lobules,  each  surrounded  by  the  connective  tissue  of  the 
trabeculse ;  the  cortex  is  more  deeply  stained  than  the  medullary  substance  ;  in  the  medullary 
substance  are  sections  of  small  bloodvessels  and  a  few  concentric  corpuscles  of  Hassall,  but 
these  are  very  indistinct  on  account  of  the  low  magnification. 

Fig.  6.    Striated  human  muscle,  unstained,   X  125.  —  Author's  collection. 

This  figure  shows  the  structure  of  striated  muscle  ;  the  transverse  stria;  are  apparent 
on  close  examination,  especially  in  the  fibres  to  the  left,  although  the  magnification  is  low. 


PLATE   IX 


PLATE   X 

Fig.   I.    Muscular  tissue  of  the  pig,  injected,  x  125. — Author's  collection. 

This  figure  shows  the  arrangement  of  the  small  arteries  and  capillaries.  The  magnification 
is  too  low  to  show  the  structure  of  the  muscular  fibres. 

Fig.  2.  Cross-section  of  the  human  radius  from  a  young  adult,  injected,  x  125.  —  Author's 
collection. 

Nearly  in  the  centre  of  this  figure  is  an  Haversian  canal  surrounded  with  lacunae  and  cana- 
liculi,  all  filled  with  red  material. 

Fig.  3.    Section  of  the  finger  of  a  child  (hematoxylin-eosin),  x  10.  —  Author's  collection. 

This  section  shows  bone-development.  To  the  left,  deeply  stained,  is  the  forming  bony 
structure  invading  the  cartilage  ;  to  the  right  are  the  cartilaginous  articulating  surfaces  of  the 
phalanges  ;  next  the  sides  of  the  developing  bone  is  periosteum  ;  the  epidermis  and  corium 
are  shown  at  the  top  of  the  figure  ;    the  magnification  is  too  low  to  show  the  cartilage-cells. 

Fig.   4.    Section  of  the  ear  of  a  bullock  (hematoxylin-eosin),  X  125.  —  Author's  collection. 

This  section  shows  cartilage-cells,  the  nuclei  rather  deeply  stained,  surrounded  with  a  retic- 
ulum of  very  fine  elastic  fibres.     These  fibres  are  most  distinct  at  the  upper  part  of  the  figure. 

Fig.  5.  Transverse  section  of  the  Fallopian  tube  of  the  rabbit  (hematoxylin-eosin),  X  lO. 
—  Author's  collection. 

The  folds  of  the  mucosa  are  shown  about  the  horizontal  diameter  of  the  figure,  the  cells 
being  rather  more  deeply  stained  than  the  submucosa,  which  is  not  sharply  differentiated  ;  the 
magnification  is  much  too  low  to  show  the  structure  of  the  cells ;  the  muscular  layers  are 
stained  red. 

Fig.  6.  Section  through  the  thorax  of  the  fcetus  of  the  Guinea  pig,  showing  especially  the 
placenta  and  membranes  (hematoxylin-eosin),  X  4.  — Author's  collection. 

The  placenta  is  to  the  right  of  the  figure  and  occupies  about  one-third  of  the  circumference 
of  the  section  ;  internal  to  the  lower  half  of  the  placenta  is  a  portion  of  detached  chorion, 
showing,  under  higher  magnification,  chorionic  villi  ;  the  inner  membrane,  lining  that  portion 
of  the  ovum  not  occupied  by  the  placenta,  is  the  amnion  ;  the  outer  layer  of  the  section  is  the 
uterine  wall ;   between  the  placenta  and  the  uterine  wall,  slightly  separated,  is  the  decidua. 

The  section  of  the  foetus  shows  the  body  of  a  vertebra  and  the  spinal  canal  at  the  top  of 
the  figure  ;  below  this  is  the  single  aorta  ;  below  the  aorta  and  between  the  lungs  is  the  oesoph- 
agus ;  by  the  sides  of  the  aorta  and  oesophagus  are  the  lungs,  with  the  primitive  bronchia, 
the  one  to  the  left  more  clearly  shown  ;  a  portion  of  the  liver  lies  below  the  lungs,  but  the 
liver  has  been  broken  in  the  section  and  a  great  part  is  lost ;  tJie  process  on  the  left  of  the 
fretus  is  the  forearm. 

The  parts  of  the  foetus  are  shown  more  clearly  in  the  human  sections,  in  Plate  XVI. 


PLATE    X 


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PLATE   XI 

■Nerve-cells  (Sobotta) 

Fig.  I.  Two  isolated  multipolar  cells  from  the  human  spinal  cord  (isolation  in  weak 
chromic  acid  ;   carmin),  x  i6o  ;   x,  neurite  torn  away. 

Fig.  2.  Two  multipolar  cells  from  the  lumbar  enlargement  of  the  spinal  cord  of  a  stillborn 
child  (absolute  alcohol ;   methyline-blue,  according  to  Nissl),  x  480. 

This  figure  shows  the  cell-bodies  and  roots  of  dendrites,  with  Nissl's  granules  intensely 
stained. 

D,  dendrites  ;   A",  nucleus ;   i,  Nissl's  granules. 

Figs.  3,  4,  5.  Three  cells  from  a  human  spinal  ganglion  from  an  executed  criminal  (Zen- 
ker's solution  ;   hematoxylin-eosin),  X  420. 

These  figures  show  three  spherical  cells  with  their  nucleated  capsules  of  connective  tissue. 

i>//,  connective-tissue  capsule  ;  /,  pigment. 


PLATE   XT 


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Fig.  4.. 


Fig.S 


PLATE   XII 

Spinal  Cord  (Sobotta) 

Fig.  I.  Cross-section  of  the  human  spinal  cord  at  the  cervical  enlargement  (from  an 
adult  and  fixed  two  and  one-half  hours  after  death  —  Miiller's  liquid  ;   sodium  carminate)'  X  8. 

bg,  sections  of  bloodvessels ;  x,  region  of  the  obliterated  central  canal ;  cp,  posterior 
cornua  ;  fa,  column  of  Tiirck  and  anterior  ground  column  ;  cma,  anterior  median  fissure  ; 
fe,  column  of  Burdach  ;  fg,  column  of  Golt;  fl,  lateral  column  ;  /;;/,  pia  mater ;  ra,  anterior 
nerve-root ;  rp,  posterior  nerve-root ;  sg,  substantia  gelatinosa  ;  sp,  posterior  median  fissure  ; 
fr,  formatio  reticularis. 

This  section  shows  quite  distinctly  several  of  the  columns  indicatetl  in  diagrammatic  figures 
in  the  text. 

Fig.  2.  Cross-section  of  the  human  spinal  cord  at  the  lumbar  enlargement  —  two-thirds  of 
the  section  shown  —  fixed  two  and  one-half  hours  after  death  (pia  mater  in  red;  medullated 
fibres  in  blue;  nuclei  in  red  ;  Miiller's  liquid;  Weigert- Pal's  stain  for  medullary  sheaths;  alum- 
carmin),  X  15. 

caa,  anterior  white  commissure ;  Cc,  remains  of  the  central  canal ;  pna,  anterior  median 
fissure;  gl,  external  glia  sheath  (neuroglia);  Gz,  cells  of  the  anterior  horn;  nd,  dorsal  nucleus; 
pm,  pia  mater  ;  Ra,  anterior  nerve-roots  ;  Rp,  posterior  nerve-roots  ;  sg,  gelatinous  substance 
of  Rolando  ;   snip,  posterior  median  fissure. 


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TLATE   XIII 
Two  Early  Stages  of  Cleavage  of  the  Egg  of  the  Sea-urchin,  x  iooo  (Wilson) 

Fig.  I .  "  The  section  passes  horizontally  through  the  egg  at  the  moment  of  division.  In 
the  centre  lies  the  mid-body,  darker  and  somewhat  ill-detined.  On  either  side  of  this  is  a  group 
of  2-3  nuclear  vesicles  formed  by  the  fusion  of  the  chromosomal  vesicles  of  the  preceding  stage. 
The  remains  of  the  centrosphere,  scarcely  defined,  surround  the  nuclear  vesicles." 

Fig.  2.    "  Two-cell  stage  preparing  for  the  second  cleavage. 

"A  typical  karyokinetic  figure  is  forming  in  each  cell  at  right  angles  to  that  of  the  first 
cleavage." 


PLATE  XIII 


PLATE   XIV 

Two  Later  Stages  of  Cleavage  of  the  Egg  of  the  Sea-urchin,  x  iooo  (Wilson) 

Fig.  1.  "The  embryo  is  here  shown  in  vertical  section  at  the  moment  preceding  the  divi- 
sion from  8  to  1 6  cells.  The  two  lower  cells  are  dividing  equally  and  vertically,  one  of  the 
amphiasters  being  seen  endwise,  the  other  en  face.  The  two  upper  cells  are  about  to  divide 
unequally  to  form  two  smaller  cells  or  micromeres." 

Fig.  2.   "The  blastula.     Sixteen-celled  stage. 

"  This  section  shows  the  blastomeres  arranged  in  a  hollow  sphere  surrounding  a  central 
blastocoel  or  cleavage-cavity.  The  nucleus  is  visible  in  each  cell,  and  some  of  them  show  also 
the  attraction-spheres  (asters)." 

The  figures  in  Plates  XIII  and  XIV  are  reproduced  from  the  original  negatives  made  for 
Wilson's  Atlas.  The  eggs  were  fixed  with  sublimate-acetic,  afterward  preserved  in  alcohol, 
embedded  in  paraffin,  sectioned  and  stained  on  the  slide  with  Heidenhain's  iron-hematoxylin 
for  twenty-four  hours,  and  "  differentiated  in  a  one  per  cent  solution  of  iron-alum  to  a  bright 
but  delicate  blue."  The  figures  were  printed  in  the  Atlas  in  black.  They  are  printed  here 
in  blue,  but  without  an  attempt  to  reproduce  the  exact  shade  of  the  objects. 


PLATE  XIV 


PLATE   XV 

Fig.  I.  Section  of  the  ovan-  of  a  kitten,  injected  and  stained  (hematoxylin-eosin),  x  335. 
—  Author's  collection. 

This  figure  shows  the  ovum,  ^^'ith  the  vitelline  membrane,  the  protoplasm  of  the  vitellus 
stained  rose-color,  the  germinal  vesicle  and  the  germinal  spot,  surrounded  with  the  cells  of  the 
corona  radiata.     The  ovum  nearly  fills  the  Graafian  follicle. 

Fig.  2.    Section  of  the  testicle  of  the  rabbit  (hematoxylin-eosin),  x  35.  —  Ferguson. 

This  figure  shows  simply  the  tortuous  arrangement  of  the  seminiferous  tubes  and  the  inter- 
stitial tissue.     The  magnification  is  not  sufficient  to  show  the  structures  within  the  tubes. 

Fig.  3.  Transverse  section  of  a  chick  of  about  24  hours,  near  the  caudal  end,  x  50  (picro- 
carmin) .  —  Strauss. 

In  the  centre  above,  bounded  by  the  vertebral  plates,  is  the  neural  groove.  The  outer, 
delicate  layer  is  the  epiblast.  The  innermost  layer  is  the  h>-poblast.  The  large  cavity  below  is 
the  enteron,  finally  to  be  closed  over  by  the  abdominal  plates.  The  round  body  below  the 
neural  groove  is  a  section  of  the  notochord.  The  masses  of  cells  by  the  sides  of  the  notochord 
are  the  primitive  somites.  The  thick  layer  extending  from  the  somites  between  the  epiblast 
and  the  hypoblast  is  the  mesoblast. 

Fig.  4.  Transverse  section  of  same  chick  at  about  the  middle  of  the  abdomen  (same  tech- 
nique and  magnification).  — Strauss. 

The  neural  canal  is  nearly  closed.  The  epiblast,  hvpoblast,  and  somites  are  as  in  Fig.  3. 
The  mesoblast  has  split  into  the  somatopleure  above  and  the  splanchnopleure  below,  enclosing 
a  large  cavity,  the  celom. 

Fig.  5.  Transverse  section  of  a  chick  of  about  24  hours,  near  the  head,  x  50  (hema- 
toxylin) .  —  Strauss. 

The  neural  canal  is  closed  over.  The  epiblast  and  hypoblast  are  as  in  Figs.  3  and  4. 
By  the  side  of  the  primitive  somite  is  a  smaller  mass  of  cells,  the  Wolffian  duct.  The  celom  is 
as  in  Fig.  4.     Between  the  splanchnopleure  and  the  h%-poblast  is  the  omphalo-mesenteric  vein. 

Fig.  6.  Trans^-erse  section  of  a  chick  of  about  48  hours  (same  technique  and  magnification 
as  Figs.  3  and  4).  —  Strauss. 

The  uppermost  layer  of  cells  is  the  external  (false)  amnion.  The  next  layer  below  is  the 
true  amnion.  The  primitive  somites  have  given  off  externally  the  muscle-plates.  The  two  aortae 
lie  below  the  notochord.  The  Wolffian  ducts  are  external  to  the  aort^e  and  in  the  same  plane. 
The  somatopleure  is  thickened  and  curxed  and  gives  off  the  true  amnion.  The  celom  lies 
between  the  somatopleure  and  the  splanchnopleure.  The  omphalo-mesenteric  veins  are  better 
defined  than  in  Fig.  5,  especially  the  vein  on  the  right  side  of  the  figure. 


PLATE    XV 


^^^r-^' 


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PLATE   XVI 

Fig.  I.  Section  through  the  upper  part  of  the  thorax  of  a  human  embryo  (hematoxylin 
and  orange  G),  X  4.  —  Author's  collection. 

At  the  lop  of  this  figure  is  the  spinal  cord,  with  the  body  and  the  laminte  of  a  vertebra; 
by  the  side  of  the  lamina  on  the  left  is  a  rib,  and  *;ctions  of  ribs  are  seen  in  the  walls  of  the 
thorax;  on  either  side  of  the  lower  portion  of  the  section  is  the  arm;  occupying  the  middle 
of  the  thorax,  on  either  side,  are  the  lungs;  the  opening  to  the  right,  just  below  the  vertebra, 
is  the  oesophagus,  on  the  right  of  what  probably  is  the  aorta;  below  the  aorta  and  oesophagus 
are  the  two  primary  bronchia;  below  and  between  the  lungs  are  the  auricles  of  the  heart; 
at  the  lowest  part  of  the  figure,  in  the  median  line,  is  a  section  of  the  sternum. 

Fig.  2.  Section  through  the  lower  part  of  the  thorax  of  the  same  embryo  (same  technique 
and  magnification).  —  Author's  collection. 

The  left  side  of  the  figure  is  the  right  side  of  the  embryo. 

The  spinal  cord,  vertebra,  sections  of  ribs,  lungs  and  sections  of  the  arms  are  as  in 
Fig.  I.  The  round  opening  below  the  vertebra  is  the  aorta;  below  the  aorta  and  between  the 
lungs  is  the  oesophagus;  below  the  lung  on  the  left  side  of  the  figure  are  the  ventricles  of  the 
heart,  the  right  ventricle  above  the  left;  the  large  oval  cavity  below  the  lung  on  the  right  side 
of  the  figure  is  the  abdominal  cavity;  between  the  right  ventricle,  the  lung  and  the  abdominal 
cavity  is  the  ductus  venosus. 

Fig.  3.  Section  through  the  upper  part  of  the  abdomen  of  the  same  embryo  (same  tech- 
nique and  magnification).  —  Author's  collection. 

The  right  side  of  the  figure  is  the  right  side  of  the  embryo. 

The  spinal  cord  and  vertebra  as  are  in  Figs,  i  and  2;  immediately  at  the  sides  of  the  cord 
are  the  ganglia  of  the  spinal  nerves;  in  the  centre  of  the  body  of  the  vertebra  is  a  small  spot, 
not  seen  in  the  other  figures,  which  is  a  section  of  the  notochord;  by  the  sides  of  the  body 
of  the  vertebra  are  the  kidneys,  with  the  adrenal  bodies  below,  which  are  larger;  the  immense 
liver  nearly  fills  the  abdomen;  below  the  vertebra  is  the  aorta;  between  the  left  adrenal  and 
the  stomach,  on  the  left  side,  is  the  pancreas,  extending  to  the  median  line;  the  opening,  be- 
tween the  pancreas  and  the  liver  on  the  left  side,  is  the  stomach;  to  the  right  of  the  stomach 
and  below  the  pancreas  is  intestine. 

FiG.  4.  Section  through  the  lower  part  of  the  abdomen  of  the  same  embryo  (same  tech- 
nique and  magnification).  —  Author's  collection. 

The  left  side  of  the  figure  is  the  right  side  of  the  embryo. 

The  cord,  vertebra,  kidneys  and  aorta  are  as  in  Fig.  3;  the  section  of  the  liver,  being 
lower  down,  is  not  so  large  as  in  Fig.  3;  the  intestines  lie  between  the  aorta  and  kidneys  above 
and  the  liver  below. 

Fig.  5.    Sagittal  section  of  a  pig-embryo  of  f  inch  (20  mm.),  X  4  (picro-carmin).  —  Strauss. 

In  the  description  of  this  figure,  only  those  parts  mentioned  in  the  text  are  noted,  although 
the  section  shows  very  distinctly  many  other  structures. 

At  the  convex  border  of  the  figure  is  the  spinal  cord,  deeply  stained,  with  the  bulb  at  the 
first  bend  above ;  in  front  of  the  chord  is  the  notochord,  with  the  forming  intervertebral  disks 
deeply  stained ;  the  uppermost  part  of  the  figure  is  the  head-cavity ;  the  midbrain  is  in  the 
central  part  of  the  head-cavity,  above  the  nearly  vertical  projection  continuous  with  the  bulb, 
which  forms  its  floor  ;  the  hindbrain  and  the  cerebellum  lie  behind  the  midbrain  ;  the  dien- 
cephalon  is  in  front  ;  beneath  the  snout  is  the  tongue,  with  the  heart  below  ;  the  liver  is 
below  the  heart,  separated  from  it  by  the  diaphragm  ;  the  bronchia  and  lungs  lie  behind  the 
heart  and  liver  ;  the  stomach  and  intestines  lie  below  the  liver,  and  a  loop  of  small  intestine 
extends  into  the  umbilical  cord,  which  lies  in  front  of  the  intestines  ;  the  testis  lies  behind  the 
intestines,  close  to  the  notochord. 

Fig.  6.    Sagittal  section  of  a  pig-embryo  of  J  inch  (12  mm.),  x  5  (picro-carmin).  —  Strauss. 

This  figure  shows  an  earlier  stage  of  development  than  is  shown  in  Fig.  5.  Below  the 
head-cavity  is  the  mandible  —  the  tongue  has  not  appeared  ;  the  diaphragm  has  not  appeared, 
and  the  thorax  and  abdomen  form  a  single  cavity. 


PLATE    XVI 


:rv 


Sfe'^' 


INDEX 


Abdominal  nerves 542 

Absorption 240 

by  closed  cavities,  reservoirs  of  glands, 

etc 254 

by  lacteals 252 

by  the  respiratory  surface 253 

by  the  skin 253 

influence  of  circulation 255 

influence  of  nervous  system 255 

of  fats 254 

Accommodation  of  the  eye 686 

Acid-albumin 199 

Acromegaly 390 

Addison's  disease 378 

Adolescence 858 

Adrenalin  378 

Adrenals 376 

development  of 838 

Adult  age 858 

After-images 696 

Ages 858 

Agglutins 13 

Air,  composition  of 116 

Alcohol 150 

formation  of,  from  carbohydrates 393 

heat-value  of 404 

influence  of,  on  milk 294 

Alexins 11 

Alimentation 143 

Allantois 804,  807 

Amboceptors 12 

Ameba  proteus i 

Ameboid  movements 412 

Amitosis 8 

Amnion 802 

Amniotic  liquid 805 

Arnphiaster 4 

Amputated  members,  sensation  in 479 

Amylopsin 218 

Amyloses 145 

Anabolism 392 

Anaphase 5 

Anelectrotonus 489 

Angle  alpha 667 

Antibodies 12 

Anticomplement 12 

Anti-immune  body 12 

Antitoxins 10 

Antrum  pylori 187 

Aorta,  development  of 842 

Aphasia 591 

Aqueous  humor 663 


Arachnoid r  .g 

Archenteron ygn 

Archiblastic  cells 841 

Archoplasm . 

Area  vasculosa 840,  842 

appearance  of  blood-corpuscles  in 21 

Arms,  development  of 821 

Arterial  pressure rg 

Arteries,  anatomy  of rj 

classification  of 1-2 

development  of 843 

rapidity  of  blood-current  in 61 

Asphyxia 135 

Associated  movements ^yy 

Astigmatism gSi 

Attraction  sphere 2 

Audition jn 

Auditory  centres 7-2 

Auditory  nerve 711 

Auricular  nerves ^36 

Axillary  glands 317 

Beats,  a  cause  of  discord 732 

Bile,  action  of,  in  digestion 221 

composition  of 365 

quantity  of 364 

secretion  of 364 

tests  for 368 

Biliary  fistula 222 

Biliary  salts 222 

Bilirubin 368 

Binocular  vision 691 

"  Black  hole  "  of  Calcutta 137 

Bladder 333 

Blastoderm 800 

Blastodermic  layers  in  the  chick 817 

"  Bleeders  " 29 

Blood 14 

coagulation  of 26 

color  in  veins  of  glands   16 

gases  of 132 

general  characters  of 16 

laking  of u,  17 

— — -  precipitin-test  for 21 

quantity  of 15 

table  of  composition  of 25 

test  for  hemalin 20 

transfusion  of 15 

Blood-corpuscles 18 

chemistry  of 20 

development  of 21 

relations  of  spleen  to 384 


869 


870 


INDEX 


Blood-corpuscles,  structure  of 20 

Blood-plasma 24 

Blood-platelets 23 

Blood-serum 27 

Bone-formation  821 

Bones,  anatomy  of 428 

Botal,  foramen  of 846 

Brain 565 

development  of 823 

Bread 160 

Bronchia 91 

Brunner,  glands  of 209 

Bulb 598 

nerve  centres  in 601 

Butter 299 

Cadaveric  rigidity 428,  859 ' 

Caicum 225 

Calcium  oxalate ■ 346 

Calcium  phosphate 149 

Calories 396 

Calorimeter 396 

Capillaries,  anatomy  of 63 

pressure  of  blood  in 67 

Capillary  circulation 63 

causes  of 68 

influence  of  temperature  on 68 

relations  of,  to  respiration 67 

Carbamid 340 

Cardiac  nerves 539 

Cardiometer 57 

Cartilage,  anatomy  of 432 

Caruncula  lacrymalis    707 

Casein 298 

Catelectrotonus 489 

Cell,  typical  animal 2 

Cells,  death  of,  from  old  age 8 

number  of,  in  human  adult 3 

reproductive  power  of 753 

Cellulose 146 

Centro-acinar  cells 217 

Centrosomes ....  2 

Cephalo-rachidian  liquid 547 

Cerebellar  ataxia 597 

Cerebellum 593 

connections  of,  with  cerebrum 579 

extirpation  of 597 

histology  of 594 

Cerebral  convolutions 570 

Cerebral  localization 581 

Cerebrin ■ 473 

Cerebro-spinal  axis 565 

Cerebrum 567 

comparative  anatomy  of 587 

connections  of,  with  cerebellum 570 

extirpation  of 586 

fibres  of 579 

general  uses  of 585 

histology  of 568 

in  different  races 588 

pathology  of 589 

Cerumen 288 

Ceruminous  glands 285 

Chick,  development  of 816 


Childhood 858 

Chocolate 155 

Cholesteremia 371 

Cholesterin 147,  367,  369 

Chondrin 432 

Chorda-tympani  nerve 505,  507,  638 

Chorion 804,  807 

Chorion  frondosum  813 

Chorion  leve 813 

Choroid 651 

Chromatic  aberration 673 

Chromatin 2 

Chromatolysis 470 

Chromosomes 5 

number  of,  in  different  animals 5 

Chyle,  properties  and  composition  of 262 

Ciliary  movements 413 

Ciliary  muscle 653 

Ciliary  processes 652 

Circulation 30 

derivative 83 

in  erectile  tissues 82 

in  the  arteries 51 

in  the  capillaries 63 

in  the  cranial  cavity 81 

in  the  heart-walls 84 

in  the  veins 69 

rapidity  of 85 

Circulatory  system,  conditions  in,  after  death  88 

Climacteric 771 

Cloaca 839 

Cochlea,  bony 720 

distribution  of  nerves  in 747 

membranous 743 

scalse  of 745 

uses  of  diiferent  parts  of 750 

Coffee 153 

Coitus 787 

Colon 226 

Color-blindness 705 

Color-perception 704 

Colors 669 

Colostrum 301 

Complemental  air 113 

Complements 11 

Condiments 155 

Conjunctiva 707 

Connective  tissue 420 

Consonants 453 

Contact,  sense  of 628 

Contraction,  law  of 486 

Coordination  centre 597 

Corium 306 

Cornea 650 

Corpora  striata 573 

Corpus  luteum .  773 

Correlation  and  conservation  of  forces 408 

Corresponding  points  in  the  retina 692 

Corti,  ganglion  and  organ  of 747 

Coughing 1 10 

Cowper,  glands  of 782 

Cranial  nerves 494 

Cream 296 

Creatin  and  Creatinin 345 


INDEX 


871 


Cresol 230,  235 

Cretinism 386 

Crura  cerebri 577 

Crystalline  lens 661 

Current  of  rest  and  current  of  action 427 

Cuvier,  duct  of  ... 844 

Cytoplasm 2 

Dacryolin 710 

Death 859 

phenomena  in   the  circulatory  system 

after 88 

Deciduas 811 

Decidua  serotina 813 

Defecation 236 

Deglutition 176 

duration  of 184 

influence  of  the  spinal  accessory  on. . . .  516 

mechanism  of 180 

of  air 184 

protection  of  air-passages  during 181 

Demilunes 170 

Depressor  nerves 539 

Derivative  circulation 83 

Dermatomes 819 

Deuteroalbumose 199 

Dextral  preeminence 856 

Dextrose 145 

Diapedesis 85 

Diaphragm 97 

Diaster 5 

Dicrotic  pulse 55 

Diencephalon 823 

Digestion,  duration  of,  in  the  stomach 201 

gastric .  .  185 

influence  of  various  conditions  on 202 

in  the  small  intestine 206 

Dilator  tubas 719 

Discords  and  dissonance 731 

Dispirem 6 

Dreams 619 

Ductless  glands 375 

Duodenum 206 

Dura  mater 546 

Ear,  development  of 825 

external 713,  734 

internal 720,  742 

middle 715,  734 

muscles  of 717 

ossicles  of 716,  740 

Eggs 161 

Ehriich's  side-chain  hypothesis 9 

Eighth  nerve 711 

Elastic  cartilage 433 

Elastic  tissue 415 

Electrodes,  non-polarizable 485 

Electrotonus 489 

P21eventh  nerve 513 

Encephalon 565 

connections  of,  with  spinal  cord 580 

weights  of •.  . .   566 

End-bulbs 466 

Endosmosis  and  exosmosis 2^6 


Enterokinase 215 

Epiblast 800 

Epidermis 308 

Epididymis 778 

Epiglottis 91 

in  deglutition 91,  182 

Epinephrin 378 

Erectile  tissues,  circulation  in 82 

Erection,  mechanism  of 787 

Erepsin 215 

Eructation 205 

Erythroblasts 21,  431 

Erythrocytes 18 

Esophagus  {see  Oesophagus) 179 

Esthesiometer 628 

Estivation 395 

Eustachian  tube 718 

Eustachian  valve 846 

Excretin  and  excretoleic  acid 232 

Excretion,  mechanism  of 273 

Expiration 102 

muscles  of 104 

Expression,  nerve  of 505 

Eye,  binocular  vision 691 

blind  spot  in 676 

chambers  of 663 

development  of 824 

erect  impressions  of  inverted  images. . .   690 

refraction  in 679 

simple  schematic 68i 

summary  of  anatomy  of 665 

Eyeball,  anatomy  of 649 

muscles  of  ...  - 698 

Eyelids 705 

muscles  of 706 

Face,  development  of 830 

Facial  angle 589 

Facial  nerve 505 

Fallopian  tubes 764 

Falsetto  voice 446 

Fatigue  of  muscle 426 

Fatigue-products 623 

Fats 146 

Fauces -. 178 

Feces 231 

Fecundation 789 

Fermentation  in  the  intestines 230 

Fertilization  of  the  ovum 791 

Fibrin 28 

Fibrin-globulin 28 

Fibrinogen 24,  28 

Fibro-cartilage 433 

Fifth  nerve,  large  root  of 521 

small  root  of 502 

First  nerve 632 

Flavors 637 

Foetal  circulation 846 

Foetus,  respiration  by 135 

weights  of 851 

Foods 143 

digestibility  of 201 

heat-value  of 404,  411 

necessary  quantity  and  variety  of 155 


8/2 


INDEX 


Forced  movements 604 

Forces,  correlation  and  conservation  of 408 

Fossa  ovalis 849 

Fourth  nerve 499 

Fovea  cardiaca 842 

Fovea  centralis 656 

Free-martin 772,  796 

Fromann,  striations  ot 459 

Galactose 145 

Gall-bladder 362 

Gallon's  whistle 724 

Gases  in  the  alimentary  canal 237 

partial  pressure  of 134 

tension  of 134 

Gasser,  ganglion  of 522 

Gastric  digestion 185 

Gastric  fistula 191 

Gastric  juice 190 

digestive  action  of 195 

Gastrulation 799 

Gelatin,  as  food 161 

Generation,  female  organs  ot 754 

development  of  female  organs  of 839 

male  organs  of 775 

development  of  male  organs  of 839 

Geniculate  ganglion 507 

Genito-spinal  centre 336, 780 

Genito-urinary  system,  development  of 835 

Giannuzzi's  crescents 170 

Giantism  39° 

Giraldes,  organ  of 780 

Ghosts  of  the  blood-corpuscles 17,  20 

Glands,  classification  of 275 

ductless 276 

motor  nerves  of 274 

terminations  of  nerves  in 463 

Globin 20 

Glosso-pharyngeal  nerve 639 

Glottis 90.  435 

respiratory  movements  of 91 

vocal  movements  of 439 

Glucoses 14s 

Glycerin i47 

Glycogen 146,  372 

Goblet-cells 210,  212 

Graafian  follicles 757 

Gums 146 

Gustation 637 

Gustatory  nerves 638 

Hairs 31° 

sudden  blanching  of 314 

Harmony 73° 

Hassall,  concentric  corpuscles  of 388 

Hauser,  Kaspar,  case  of 693 

Heart 33 

accelerator  nerves  of 46 

capacity  of  cavities  of 35 

cause  of  contractions  of 45 

development  of 845 

first  appearance  of 842 

frequency  of  action  of 41 

ganglia  of 45 


Heart,  influence  of  respiration  on 

" influence  of  spinal  accessory  on 

inhibition  of 

revolution,  or  cycle  of 

Stannius  experiment 

valves  ot  

work  of 

Heart-muscle 

Heart-sounds 

Heart-walls,  circulation  in 

Heat,  animal 

mechanism  of  production  of 

— —  estimation  of  body-heat 

relations  of,  to  force 

Heat-centres 

Heat-units 

Heat-value  of  foods  404, 

Hematin   

Hematoidin 

Hematophorin 

Hemianopsia  

Hemin 

Hemochromogen 

Hemodrometer 

Hemodynamometer 

Hemoglobin 

compounds  of,  with  oxygen,  carbon  mo- 
noxide, and  nitrous  oxide 

Hemolysis 

Hemophilia 

Hernia  at  the  umbilicus  of  the  foetus 

806,  809,  810, 

Heteroalbumose 

Hibernation 

respiration  in 

Hiccough 

Hippuric  acid,  etc 

Histohematins 

Horner,  muscle  of 706, 

Horopter 

Hunger 

Hyaloplasm 

Hydrobilirubin 

Hypermetropia 

Hypoblast 

Hypophysis  

Hypoxanthin 


43 

516 

47 

39 

46 

38 

49 

37 

40 

84 

395 

403 

396 

408 

403 

395 

411 

20 

20 

20 

703 


28 

827 
199 

395 
119 
no 
344 
135 
709 
692 

139 
2 

231 
671 
801 
389 
346 


Ileo-cascal  valve 227 

Ileum  208 

Immune  bodies 12 

Immunity 9 

hacti^riolytic u 

Inanition  ^39 

Indol 230,  235 

Induced  muscular  contraction 488 

Infancy 858 

Inosite 146 

Inspiration 93 

muscles  of 96 

Intercostal  muscles 99 

Internal  capsule 573 

Internal  secretion  375 

Intestinal  digestion 20fc 


INDEX 


>7l 


Intestinal  digestion,  duration  of 225 

Intestinal  fistula 215 

Intestinal  juice 215 

Intestinal  movements 224 

Intestinal  villi 211 

Intestine,  large 225 

movements  of 235 

Intestine,  small 206 

Intestines,  development  of 826 

Invert-sugar  145 

Involution  of  the  uterus 854 

lodothyrin 386 

Iris 654 

movements  of 683 

action  of,  in  accommodation 689 

Iron 149 

Irradiation   696 

Isodynamic  values  of  foods 394 

Jejunum    207 

Jercorin    363,  382 

Karyokinesis 3 

duration  of,  in  cells 8 

Karyokinetic  figure 5 

Karyoplasm  2 

Karyosome 2 

Kidneys 322 

development  of 837 

extirpntion  of 331 

internal  secretion  by 353 

work  of 354 

Kinase 219,  384 

Kinetoplasm 470 

Krause,  end-bulbs  of 466 

Kymograph 58 

Labyrinth,  bony 720 

distribution  of  nerves  in 746 

liquids  of 746 

membranous 742 

Lachr\'mal  apparatus 708 

Lachrymin 710 

Lacteals 241,  247 

absorption  by 254 

Lactose 145,  299 

Laking  of  blood 11,  17 

Langerhans,  islands  of 217 

Laryngeal  nerves 537 

Laryngoscope 439 

Larynx 90,  436 

action  of,  in  phonation 442 

development  of 832 

respiratory  movements  of 91 

Laughing no 

Lecithin 147,  473 

Leech-drawn  blood 28 

Legs,  development  of 821 

Leucin 346 

Leucocytes 22 

migration  of 84 

Levulose 145 

Lieberkiihn,  follicles  of 209 

Lienin 382 


Light 669 

Linin 2 

Lipochrome 297 

Littre,  glands  of 782 

Liver 355 

chemistry  of 363 

development  of 82b 

excretory  action  of 368 

formation  of  glycogen  in 372 

Locomotor  ataxia 557 

Lungs 94 

capacity  of in 

development  of 829 

Luxus-consumption 394 

Lymph  and  chyle 258 

movements  of 265 

Lymph,  origin  and  uses  of 261 

corpuscles 260 

glands  (nodes) 243,  246,  250 

Lymphatic  duct 246 

Lymphatics 241,  248 

valves  of 243,  249 

Lymphocytes 261 

Macula  acustica 742 

Macula  lutea 656 

Maltose 146 

Mammary  glands 289 

secretion 289 

Marrow  of  the  bones 430 

Mastication 162 

muscles  of 167 

nerve  of 502 

Mastoid  cells 718 

Meats 156 

Meckel,  cartilage  of 826 

Meconium 855 

Meibomian  glands 285 

secretion 289 

Meissner,  corpuscles  of 465 

Membrana  tympani 734 

Membranes  of  the  embryo 801 

Mendel's  laws  of  heredity 793 

Menstruation 771 

Mery,  glands  of 782 

Mesenteric  glands 247 

Mesentery,  development  of 828 

Mesoblast 801 

Metabolism 392 

Metakinesis 5 

Metaphase 5 

Metaplasm 2 

Methyl  mercaptan 235 

Microsomes 2 

Midbody  5 

Middle  age 858 

Migration  of  leucocytes 23,  84 

Milk 160 

composition  of 296 

globules 297 

influence  of  alcohol  on 294 

in  the  newly-born 304 

quantity  of 295 

secretion  of 292 


8/4 


INDEX 


Milk,  uterine 815 

Mitosis 3 

Monaster S 

Morula 799 

Motor  cortical  zone 582 

Motor  oculi  communis 495 

influence  of,  on  tlie  iris 448 

Motor  oculi  externus 501 

Mouth,  development  of 831 

Movements 412 

ameboid 412 

Mucous  glands 279 

Mucous  membranes 279 

Mucus 280 

Miiller,  duct  of 836 

Muscle,  chemistry  of 421 

fatigue  of 426 

involuntary 417 

properties  of 422 

voluntary 418 

Muscle-currents 427 

Muscle-nerve  preparation 425 

Muscle-plates 819 

Muscle-spindles 463,  626 

Muscles,  development  of 821 

Muscular  contraction 424 

Muscular  movements 417 

Muscular  sense 626 

Musical  scale 725 

Myelocytes,  of  bone 431 

of  nerve-centres 473 

Myeloplaxes 431 

Myo-albumin 422 

Myoglobulin 422 

Myohematin 135 

Myopia 67 1 

Myosin 421 

Myotomes 819 

Myxoedema 386 

Nails 309 

Negative  variation  of  muscle-current 427 

of  nerve-current 491 

Nerve-cells 468 

Nerve-centres 468 

accessory  anatomical  elements  of 472 

Nerve-currents 489,  491 

Nerve,  dying  of 487 

Nerve-fibres 457 

Nerve-muscle  preparation 425 

Nerves,  accessory  anatomical  elements  of.  .  461 

action  of  electricity  on 483 

action  of  motor 476 

action  of  sensory 478 

cranial 494 

degeneration  and  regeneration  of 474 

end-plates  of 462 

motor  and  sensory 473 

negative  variation  in 491 

sensory,  terminations  of 463,  467 

• — —  spinal 492 

Nervous  conduction,  rapidity  of 480 

Nervous  excitability  and  conductivity 479 

Nervous  matter,  composition  of 473 


Nervous  system,  development  of 822 

divisions  of 455 

Neurilemma 457 

Neuroglia 473 

Neuro-muscular  spindles 463,  626 

Neuron 471 

Neutral  point 490 

Ninth  nerve 639 

Nissl's  granules 470 

Nitrogen,  elimination  of 340 

Nose,  development  of 832 

Notochord 819 

N  utrition 394 

Odors 635 

CEsophageal  nerves 541 

CEsophagus 179 

development  of 828 

Oken,  bodies  of 835 

Old  age 858 

Olfaction 631 

Olfactory  cells 634 

Olfactory  centre 636 

Olfactory  lobes,  development  of 826 

Olfactory  nerve 632 

Omphalo-mesenteric  vessels 842 

Optic  nerve 646 

Optic  thalami 573 

Orgasm,  venereal 788 

Osmosis 256 

Osmotic  pressure 257 

Ossicles  of  the  ear 716 

Otoliths 743 

Ovaries 755 

development  of 836 

internal  secretion  by 391 

Overtones 727 

Ovum 766 

development  of 816 

—  discharge  of 769 

fertilization  of 791 

maturation  of 789 

segmentation  of 797 

Oxidation  in  the  body 405 

Pacini,  corpuscles  of 464 

Palate 177 

Pancreas 216 

development  of 829 

Pancreatic  fistula 219 

Pancreatic  juice 217 

Parablastic  cells 841 

Paramyosinogen  421 

Parapeptones 199 

Parathyroids 385 

Parotid 170 

Parovarium 759,  836 

Parturition 853 

centre 854 

Patheticus 499 

Pawlow's  pouch 192 

Penis,  development  of 839 

Peptones 198 

Perimeter 691 


INDEX 


875 


Periosteum  431 

Perivascular  canals 242 

Personal  equation 482 

Perspiration 315 

Pettenkofer's  chamber 118 

Peyer's  patches 213 

Pfliiger's  law  of  contraction 486 

Pharyngeal  nerves 536 

Pharyngeal  secretion 172 

Pharynx 177 

development  of 828 

Phenol , 230,  235 

Phonograph 454 

Pia  mater 546 

Pinna 713 

Pituitary  body 389 

Placenta 813 

Plastids 2 

Pleura 94 

Pneumogastric 530 

branches  of 532 

branches  of,  to  abdominal  viscera 542 

general  properties  of 536 

Polar  bodies 3,  790 

Pons  Varolii 577 

Potatoes 160 

Precipitins 13.  21 

Precipitin-test  for  blood 21 

Pregnancy,  duration  of 850 

multiple 853 

Presbyopia 672 

Primitive  streak 800 

Propeptone 199 

Prophases  of  karyokinesis 3 

Prostate 781 

Protagon 473 

Prothrombin 28 

Protoalbumose 199 

Protoplasm 2 

Protovertebras 819 

Pseudopods 2 

Puberty 771,  858 

Pulmonary  circulation 183 

Pulmonary  nerves 539 

Pulse 53 

— —  dicrotic 55 

form  of 54 

Pupil 654 

Pupillary  membrane 655,  825 

Purkinje  cells 596 

Purposive  movements 561 

Pyloric  muscle 187 

Ranvier,  nodes  of 458 

Ration,  daily 156 

Reaction-time 590 

Receptaculum  chyli 247 

Receptors 9,  10 

Rectum 229 

Reflex  movements 559 

Refraction  in  the  eye 667,  679 

Remak,  fibres  of 459 

Renin 354 

Rennin 198 


Reserve  air 112 

Residual  air 112 

Respiration 89 

changes  of  the  blood  in 132 

consumption  of  oxygen  in 117 

cutaneous 136 

diffusion  of  air  in  the  lungs 115 

exhalation  of  ammonia,  organic  matters 

and  nitrogen  in 131 

exhalation  of  carbon  dioxide  in 121 

inhalation  of  irrespirable  or  poisonous 

gases 117 

in  hibernation 119 

of  pure  oxygen 117 

in  the  foetus 135 

in  the  newly-born 119 

in  the  tissues 135 

movements  of 95,  107 

organs  of 89 

relations  between  oxygen  consumed  and 

carbon  dioxide  exhaled 127 

sources  of  carbon  dioxide  in 129 

temperature  of  expired  air  . .  .    120 

types  of 106 

under  different  degrees  of  atmospheric 

pressure 116 

volumes  of  inspired  and  of  expired  air     114 

Respiratory  centres 602 

Respiratory  quotient    129 

Respiratory  sounds 108 

Retina   656 

corresponding  points  in 692 

Rhodopsin    677 

Rigor  mortis 428,  859 

Rodded  cells 327 

Rolandic  area 582 

Rosenmiiller,  organ  of 759,  836 

Saccharoses 145 

St.  Martin,  case  of 191 

Saliva 169 

action  of,  on  starch .  < 174 

mechanical  action  of 176 

Sarcolactic  acid 428 

Savors    637 

Schwann,  sheath  of 458 

Sclerotic    650 

Scorbutus 159 

Sebaceous  glands 282 

Sebaceous  matter 286 

Sebum 286 

Second  nerve 646 

Secretion 268 

changes  in  the  circulation  in  the  glands 

during 271 

influence  of  the  blood  on 273 

mechanism  of 270 

paralytic 275 

Secretions,  classification  of 269 

Secretions  and  excretions 277 

Semen 782 

Semicircular  canals,  bony 720 

membranous 743 

uses  of 750 


?,76 


INDEX 


Serum-albumin 24 

Serum-globulin 24 

Seventh  nerve 505 

Shadows  ot  the  retinal  vessels 675 

Sighing no 

Sixth  nerve 501 

Skatol 230,  235 

Skeleton,  development  of 819 

Skin  305 

absorption  by 253 

development  of 822 

effects  of  covering  with  an  impermeable 

coating 315 

Skin-plates 819 

Sleep 618 

Smegma  of  the  prepuce  and  of  the  labia  mi- 
nora    287 

Smell  (see  Olfaction)  631 

Sneezing no 

Sobbing no 

Sodium  chloride 149 

Solitary  glands 212 

Somatopleure    801 

Somites 819 

Sound,  physics  of 721 

vibrations  of 722 

Sounds,  musical 723 

Speech,  mechanism  of 450 

Speech-centre 590 

Spermatin 783 

Spermatogenesis 784 

Spermatozoids 783 

Spherical  aberration 672 

Sphygmograph 54 

Sphygmomanometer   60 

Spinal  accessory 513 

Spinal  cord 545 

columns  of 55° 

connections  of,  with  the  encephalon  .  . .   580 

direction  of  fibres  in 553 

general  properties  of 554 

• motor  and  sensory  paths  in 555 

nerve-centres  in 558,  564 

relations  of,  to  muscular  coordination. .  557 

Spinal  nerves 492 

Spindle  in  karyokinesis 4 

Spirem 5 

Splanchnopleure 801 

Spleen 378 

chemistry  of 382 

development  of 829 

extirpation  of 3^2 

relations  of,  to  blood-corpuscles 384 

rhythmical  contractions  of 382 

Spongioplasm 2 

Slannius  experiment 46 

Stapedius 717 

Starch 146 

Starvation 139 

Steapsin 218 

Stercobilin 231 

Stercorin 147,  233,  370 

Stomach 185 

closed  follicles  of 190 


Stomach,  development  of 827 

gases  of 205 

glands  of 188 

movements  of 203 

regurgitation  from 205 

Stomata  in  lymphatics 250 

Sublingual  gland 171 

Sublingual  nerve 518 

Submaxillary  gland 171 

Sudoriparous  glands 316 

Sugars 144 

Sulphocyanate  in  saliva 171,  173,  174 

Superfecundation 795 

Suprarenal  capsules 376 

development  of 838 

Sweat 315 

colored 321 

in  special  parts 321 

properties  and  composition  of 320 

Sweat-centres 318 

Sympathetic  system  of  nerves 606 

direct  experiments  on 612 

Synapses 556 

Synovia 277 

Syntonin 199 

Tactile  centre 629 

Tactile  corpuscles 465 

Taste  (see  Gustation) 637 

Taste-buds 644 

Taste-centre 645 

Taurin 346 

Tea 154 

Tears 709 

Teeth 162 

development  of 833 

Telephone 454 

Telophases,  in  karyokinesis 6 

Temperature  of  the  body 397 

equalization  of 407 

sense  of 630 

variations  of,  under  different  conditions 

and  influences 397 

Tenon's  capsule 649 

Tensor  tympani 717 

Tenth  nerve 530 

Testicles 775 

development  of 836 

internal  secretion  by 390 

interstitial  gland  of 391,  778 

Tetanus 427 

Theobromin IS5 

Third  nerve 495 

Thirst 140 

Thoracic  duct 247 

Thorax 95 

Thra?nin 71° 

Thrombin 28 

Thymus 387 

Thyroids 3^4 

accessory 3^5 

extirpation  of 3^6 

Tidal  air "3 

Tigroid  granules 47° 


INDEX 


^77 


Tones  by  influence 733 

Tongue 642 

development  of 832 

Tonsils 172 

Touch 625,  627 

Toxic  molecules 10 

Trachea 91 

Trifacial  nerve 521 

Triolein 147 

Tripalmitin  147 

Tristearin 147 

Trochlearis  nerve 499 

Trophic  centres  and  nerves 617 

Trophoblast 811 

Trypsin 218 

Tubercula  quadrigemina 576 

Tw^elfth  nerve 518 

Tyrosin 346 

Umbilical  cord 809 

Umbilical  vesicle 806 

Urachus 810,  826 

Urea 339 

elimination  of 340 

Ureters 332 

Urethra 334 

glands  of 782 

Uric  acid,  etc 343 

Urinary  bladder 333 

Urinary  passages 332 

Urine 336 

discharge  of 335 

gases  of 350 

inorganic  salts  of 347 

modifications  of 340 

production  of 330 

variations  in 352 

Urochrome 350 

Uterine  plug 813 

Uterus 754,  759 

involution  of 854 

Vagina 754,  766 

Vagus  nerve 530 

Vagus  pneumonia 540 

Valvules  conniventes 208 

Vas  aberrans 778 

Vascular  arches 843 

Vas  deferens 779 

Vaso-inhibitory  nerves 616 

Vasomotor  centres  and  nerves 614 

Vater,  corpuscles  of 464 

Veins 69,  70 

capacity  of 69 

conditions  that  impede  circulation  in  .  .  80 

development  of 844 


Veins,  number  of 69 

pressure  of  blood  in 74 

strength  of 71 

valves  of 72,  79 

Vernix  caseosa 287,  822 

Vertebral  column,  development  of 820 

Vesiculas  seminales 780 

Vestibule,  bony 720 

membranous 742 

Villi  of  the  small  intestine 211 

Visceral  arches  and  visceral  clefts 830 

Vision  (see  Eye)  644 

binocular 691 

duration  of  impressions  in 695 

field  of 675,  690 

perception  of  colors  in 704 

Visual  centres 703 

Visual  purple 677 

Vital  capacity 113 

Vital  point 603 

Vitreous  humor 664 

Vocal  chords  90,  435 

Voice,  anatomy  of  organs  of 435 

action  of  accessory  pans  in 443 

after  castration  in  the  male 441 

different  kinds  of 441 

different  registers  of 445 

in  children 441 

■ mechanism  of  production  of 439 

nerve  of 515 

range  of 441 

Voltaic  alternation 488 

Vomiting 205 

Vowels 451 

Wagner,  corpuscles  of 465 

Wallerian  method 474 

Wandering  cells 23 

Water 148 

as  an  excretion 351 

production  of,  in  the  body, 351,  406 

Wharton,  gelatin  of 810 

Whispering 453 

Wolffian  bodies 818,  835 

Word-blindness   703 

Word-deafness 752 

Wrisberg,  nerve  of 505 

Xanthin 346 

Yawning no 

Yolk-sac 806 

Youth 858 

Zone  of  Zinn 663 


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APT  5      ™9 

DATE    BORROWED 

DATE    DUE 

U  V  1    "^            *^ ' 

C28(955)100MEE 

F64? 


,':i! 


